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4 The epidemiological approach to sports injury: the case for rugby league

A Thesis Submitted for the Degree of Doctor of Philosophy

By

Conor Gissane Department of Health and Social Care, Brunel University

May 2003 11

Abstract

In any sporting activity it is important to know how many injuries players might receive and also what type of injuries will be received, so that efforts can be made to reduce the risk of injury. This thesis examines the injury incidence associated with playing professional rugby league, and examines some of the risks associated with injury whilst playing the game.

The first paper describes the pattern of injury incidence in professional rugby league and noted that it is higher than in other popular team sports.

The second paper examines the different exposures of forward and back players and observes that forwards experience higher rates of injury.

The third and fourth papers examine the effect of moving the playing calendar to summer rugby. The risk of injury has increased 67%, and it is also shown that 13% of players experience a 2-3% body mass loss in 14 of 16 games played in excess of 19°C ambient temperature.

The next two papers look specifically at the number of collisions experienced by players during the course of a game. Forwards are involved in more collisions (55) than backs (29) during the course of each game. Also, backs have a significantly higher injury rate per 10,000 physical collisions compared to forwards.

The next paper proposes a cyclical operational model to examine the inter- relationship of a number of factors that are involved in sports injury epidemiology. The application of this proposed cyclical model may lead to greater success in understanding the multi-faceted nature of sports injuries.

The final study in the series summarise the injury rates in professional rugby league football from previously published studies. The overall injury rate is 40.3 injuries per 1,000 hours (95% CI 36.9 to 43.8). The majority of injuries are to the lower half of the body (20.7 per 1,000 hours, 17.7 to 24), with the trunk receiving the least (6.7 per 1,000 hours, 5 to 8.6). 111

Acknowledgements

When carrying out research of this size and this length, it is necessary to recognize to part played by other parties. Throughout the course of these investigations several others have been involved.

I would like to thank and acknowledge the assistance of my good friend

John White, and also to Kate Kerr who were involved in large parts of this research. I would also like to acknowledge the role played by my two supervisors Alex Farrow and David Marsland, without them it would not have been possible to put this work into thesis format. Thank you to you both.

Periodically, it has also been necessary to involve other persons when specialist areas of expertise were needed to take the investigations into new areas. For this I would like to acknowledge and thank Angela

Cumine, Sarah Stephenson and Susie Robertson, and Paul Standing.

As I am neither a medical nor a therapeutic practitioner, I have, throughout this research, been dependent upon the clinical diagnosis provided by others. None of this would have been possible without the clinical and record keeping skills of the medical officers of the London

Broncos Rugby League team, De Jennings and Simon Jennings. I would like to offer my sincerest thanks to my good friend De Jennings whom I iv have known for 13 years, and with whom we began our injury register in

July 1990.

Lastly, I want to thank every player who has played for the

Fulham/London Crusaders/London Broncos team. Without those guys being prepared to put their bodies on the line, there would be very little to write about.

r- V

Contents

Page Abstract ii Acknowledgements iii Contents v

Chapter 1: Introduction - The importance of epidemiological methods in sports injury research.

Chapter 2: Injury in rugby league: a four year prospective survey 40

Chapter 3: Differences in the incidence of injury between rugby 58 league forwards and backs

Chapter 4: Injury in summer rugby league football - the 74 experiences of one club

Chapter 5: Body mass loss as an indicator of dehydration in 88 summer rugby

Chapter 6: Physical collisions in professional super league rugby, 98 the demands on different player positions

Chapter 7: Physical collisions and injury rates in professional 113 super league rugby

Chapter 8: An operational model to investigate contact sports 127 injuries 147 Chapter 9: A pooled data analysis of injury incidence in rugby league football

Chapter 10: Discussion and recommendations 163

References 171

Appendix: Papers associated with this thesis 1

The importance of epidemiological methods in sports injury research

Introduction

Epidemiology is the branch of medicine that deals with the occurrence, causes and prevention of disease (Schootman et al., 1994b). It is based on the assumptions that diseases do not occur at random, and that diseases do have causal and preventative factors that can be identified through the systematic investigation of populations (Henekens and Buring, 1987). The overall aim of epidemiologist is to identify factors that are associated with the onset of the disease, and then make recommendations for control and prevention (Schootman et al., 1994b). Although the origins of epidemiology are rooted in human disease and public health medicine, the methods employed have a wider applicability, and the outcomes need not be restricted to disease (McNeil, 1996). Epidemiological methods have been used to investigate areas such as, occupational health and disease (Harber et al., 1994, Schilling and Walford, 1981) accidents (Gordon, 1949), injury control (Berger and Mohan, 1996), and sports traumatology or sports injury (Caine et al., 1996, Schootman et al., 1994b, Walter and Hart,

1990).

Indeed, it has long been recognised that injuries do have a number of similarities to diseases. They obey certain biological laws, and they can, 2 therefore, be studied using basic epidemiological principles (Gordon,

1949). However, while there are similarities between diseases and accidents, there are also a number of differences. Many diseases have long latency periods, for example cancer, whereas injuries can take place in an instant, for example a fracture (Schootman et al., 1994b). Also, a specific disease can result from exposure to an unknown causative agent, which may or may not be present under a number of different circumstances.

Injuries, however, only occur under specific circumstances, when an individual is exposed to that situation (Schootman et al., 1994b).

Sports injury epidemiology

Sporting injury has been described as one of the unwelcome by products of

participating in sport (Lower, 1995). But the magnitude and type of injury

depend upon the sport and the way it is practised (Tweller et al., 1996).

For example, at the community level sports injuries have been reported to

be responsible for 17% of all medically treated injuries (deLoes, 1990).

While in professional sports, it has been reported that injuries in soccer

cost clubs a 17% loss of all game hours in a season (Neilsen and Yde,

1989). In both situations, such injuries represent substantial economic

costs either directly in terms of medical treatment expenses, and

indirectly in the form of absence from work. 3

The study of sports injuries represents a unique case in terms of injury

(Schootman et al., 1994b). They occur under specific conditions when individuals are participating or practising for sport. Sports people are also often willing to play in spite of the playing conditions, and players are also

quite willing to challenge the healing process by wanting to return to competition before they have completely recovered from injury (Schootman

et al., 1994b). Because of its peculiarities, it has been argued that sports

medicine research needs to consider dimensions that other clinical

research does not (Noyes, 1988).

Although some of the methodologies may be transferable from disease or

injury epidemiology (Powell, 1994), there is some disagreement as to

which techniques can be successfully applied to sports injury research

(Schootman et al., 1994b). But, if sports injuries are to be reduced, a

comprehensive approach needs to be taken to define the nature and

magnitude of the problem (Waller et at, 1994).

Caine et al. (1996), has stated that every one involved in sports, whether

they be players, parents or sports medicine practitioners need to have

answers to certain questions such as the following: -

i. Is the risk of injury greater in some sporting activities than others? ii. What types of injuries are most common in a given sport? iii. What is the average time lost from injury, and what is the risk of permanent impairment? iv. Are some athletes more injury prone than others? v. Are particular physical and psychological characteristics associated with a greater risk of injury? 4 vi. How can injury be predicted or prevented? vii. How effective are the preventative measures that are implemented?

In an attempt to provide answers to these questions an epidemiological

approach can be employed, and to function efficiently in the field of sports

medicine epidemiologists need to become better acquainted with the

correct employment of these study designs and their inherent limitations

(Schootman et al., 1994b). Until this has taken place, and the numerous

messages contained in sports medicine literature have been examined, no

one can claim to know very much about sports injuries (Caine et al., 1996).

Hunter and Levy (1988) stated that injury patterns from sports activities

should be considered for all those who care for athletes. They added that,

the objective of an epidemiological investigation is firstly to describe those

deleterious patterns and, ultimately to relate them to causative factors, in

the hope that strategies can be developed to influence the future pattern.

For epidemiologists to be in a position to influence future patterns of

morbidity by controlling and/or preventing injury, they need to be able to

quantify the occurrence of injury, identify who would be affected by certain

injuries, and distinguish where and which method is to be used to study

the injury outcome.

Previously the ability to perform these tasks has been limited because

investigations involving sports injuries have traditionally used clinical

case series data (Walter et al., 1985, Walter and Hart, 1990). These are 5 able to document unusual medical events, and often can represent the initial clues of adverse effects of exposures (Henekens and Buring, 1987).

However, this provides no information as to how to identify and examine sports persons at risk of injury, or any risk factors associated with specific injury.

Descriptive epidemiology

Several authors have suggested that the role of descriptive epidemiology is to quantify the occurrence of the human condition under investigation

(Henekens and Buring, 1987, Bonita et al., 1993). The initial investigative step in epidemiological investigation before searching for risk factors is to collect descriptive data with regard to the frequency, type and severity of injuries in specific populations (Schootman et al., 1994b). Descriptive studies are observational in design, allowing nature to take its course without regard to causal or other hypotheses (Last, 1995).

To investigate whether an exposure is a potential risk factor and is related to the frequency of a condition, these frequencies are compared among people with varying levels of exposure to the risk factor (Wickham, 1989).

When attempting to describe the distribution of injuries it is necessary to relate this to the population at risk (Caine et al., 1996). To do this, the size of the source population must be known or, injury must be related to exposure time. 6

A number of descriptors have been used in the sports medicine literature to describe the occurrence of injury. Typically, they are attempting to describe incidence rates, which pertain to the number of new injuries that occur in the observation period, or prevalence, which refers to the total number of injuries both new and old in the study population at risk in a

given time (Henekens and Buring, 1987, Schootman et al., 1994b, Caine et

al., 1996, Last, 1995). Previous research has sought to generalise exposure into participant years, and injuries per 100 or 1000 participants (Mendryk

and Kramer, 1978). But it has been suggested that this can lead to

questionable conclusions, particularly when comparisons across sports are

made (Caine et al., 1996). In rugby, there has been a trend to standardise

rates per 1000 hours (equation 1), where exposure time can be either

playing time or, practice time plus playing time (Gibbs, 1993a, Seward et

al., 1993, Garraway and MacLeod, 1995, Estell et al., 1995). This has

allowed comparison across sports (Edgar, 1995), and across age groups

(Estell et al., 1995).

Number of injuries Injuries per 1000 hours = x 1000 (1) Total hours exposure

A major limitation of descriptive sports injury research is the lack of a

common operational definition of what constitutes a sports injury (Caine

et al., 1996). Powell (1994) reported that the two most popular procedures

for developing a definition are the criteria of an accurate medical 7 diagnoses and time lost from participation. The two have often been used in conjunction, but can still result in different overall definitions. For example, in rugby league injury research one operational definition that has been used defined a sports injury as an injury that required a player to miss a subsequent game or, required specific medical attention (Seward et al., 1993). Another interpretation has defined an injury specifically as an injury that occurred during match play and resulted in a player missing a subsequent game (Gibbs, 1993a). Both definitions require accurate medical diagnosis, but slightly different time determinations.

By using descriptive studies, an epidemiologist can observe statistical associations between a population characteristic and the occurrence of a disease or a condition. This information can then be used to generate hypotheses. However, it is not possible to determine the importance of specific characteristics until athletes or players with or without specific symptoms have been followed (Walter et al., 1985).

Analytical epidemiology

Once the injury or injuries have been described, the search for risk factors that affect the occurrence of injury can be investigated (Schootman et al.,

1994b). The epidemiological approach is rooted in the assumption that injuries do not happen purely by chance, so an important part of sports injury epidemiology is in the identification of factors that contribute to the occurrence of athletic injury (Caine et al., 1996) Last (1995), suggested 8 that analytical epidemiology is about investigating which subsets of a defined population who are, have been, or in future may be either exposed or unexposed, or exposed in a different degrees, to a factor(s) hypothesised to influence the probability of occurrence of a given disease or other outcome.

In public health epidemiology it has been suggested that analytical investigations fall into three broad categories; case-control studies, cohort studies, and intervention studies (Lilienfield and Stolley, 1994), while some include a fourth, cross-sectional studies (McNeil, 1996, Schootman et al., 1994b). Each of these designs seeks to investigate an explicit comparison between exposure and disease status (Henekens and Buring,

1987). It has been recognised by a number of investigators that intervention studies, specifically randomised clinical trials, are the strongest research design available in epidemiology (Caine et al., 1996), and they also provide the most reliable evidence (Henekens and Buring,

1987). They are followed in order of strength by cohort studies and case control studies (Caine et al., 1996, Wade, 1988a). However, depending upon the specific exposure, the condition under investigation and the availability of resources, each type of study design has its own merits.

Case-control studies

Case-control studies are particularly efficient for investigating relatively rare conditions, they are both relatively simple and economical to carryout 9

(Bonita et al., 1993). All case-controls studies are carried out retrospectively, with the subjects' exposure history being assessed for a period in the past (Lilienfield and Stolley, 1994). This study commences at the end rather than the beginning of the causal pathway (Wade, 1988b).

This form of study seeks to compare a group of cases, for example injured players, with one or more control groups, uninjured players, with respect to one, or more preceding exposures (Schootman et al., 1994a). An example of this type of study sought to compare the level of flexibility and the musculoskeletal systems of female gymnasts with normal values obtained from non-athlete age-matched controls (Kirby et al., 1981).

The condition under investigation may be a specific injury (Wade, 1988b).

After the condition has been clearly defined, subjects who have the condition must be identified to form the case group. It has been suggested that often the best source of cases for sports medicine will be persons who have sought specific medical care for an injury. Or, alternatively, injured players can be identified through medical surveillance systems

(Schootman et al., 1994a).

When selecting the cases, medical epidemiologists have suggested that they should represent as homogenous a disease entity as possible

(Henekens and Buring, 1987). This needs to be ensured by the use of strict diagnostic criteria. For example, Rovere and Bowden (1986) suggested that including players with medial collateral ligament (MCL) injuries and 10 players with anterior cruciate ligament (ACL) injuries in the same control group to study the effects of preventive knee braces would be inappropriate. This was because knee braces were not expected to protect against ACL injuries. Similarly, there needs to be strict exclusion criteria for subjects. All cases and controls need to have the same potential for exposure, which will in part depend upon the risk factor under investigation (Schootman et al., 1994a). For example, not all rugby players will have a similar potential exposure, and therefore risk, for injury in scrum situations.

With all case-control studies recall bias is a very frequent problem

(Sackett, 1979). Frequently studies are hindered by inaccurate or biased recall of exposure, (Walter et al., 1985) which should be determined in the same manner for both cases and controls (Bonita et al., 1993). There is also the potential for cases, because they are injured, to be more motivated to provide a more detailed exposure history than the controls (Walter and

Hart, 1990). So, when the subjects, both cases and controls, are either interviewed or questioned, the interviewer should be blind as to their subject status, so that there is not a conscious or unconscious attempt to question cases in more detail. This can be difficult in certain instances such as a broken leg, or when a case is wearing a neck brace.

The case-control study design has great potential in sports medicine epidemiology (Schootman et al., 1994a). However, they do require careful 11 planning before initiation, not least because of the very high potential for biased information on the past.

Cohort studies

A cohort is a designated group of persons who are followed over a period of time (Last, 1995). They provide the best information about the causal factors of a condition, and also the most direct measurement of the risk of acquiring a condition (Bonita et al., 1993). They also reduce recall bias, which is so common in case-control studies. Exposure information in a prospective cohort is ascertained either prior to or at the time of the adverse event.

Some authors have suggested that cohort designs are prospective, beginning with a disease free group of people and following them overtime

(Schootman et al., 1994b, Bonita et al., 1993, Lilienfield and Stolley, 1994).

While others have suggested that they can be either prospective or retrospective (Henekens and Buring, 1987, Rudicel, 1988), with the distinguishing feature being whether the outcome of interest has occurred at the point in time when the investigator(s) initiate(s) the study

(Henekens and Buring, 1987). Furthermore, cohorts can be subdivided into fixed or closed cohorts, membership of which is restricted to a specific time period (Last, 1995, Checkoway et al., 1989), and open cohorts that can add to membership through the course of the follow-up (Checkoway et al., 1989). 12

A further variation in the design of cohort analysis is the use of non- concurrent cohorts (Lilienfield and Stolley, 1994). In this type of study it is not possible to compare two groups where data has been collected concurrently. So, data on a previous cohort is compared with that of a current cohort. This design is often used when industrial processes alter, and it is unfeasible to follow two cohorts simultaneously (Lilienfield and

Stolley, 1994). In sports medicine epidemiology this is sometimes the only feasible method. For example, when comparing injury rates before and after the advent of professionalism in rugby union (Garraway et al., 2000).

In sports medicine cohorts have often been used to provide descriptive data with regard to the incidence and prevalence of injury over a period of one to several seasons (Gibbs, 1993a, Seward et al., 1993, Garraway and

MacLeod, 1995, Estell et al., 1995, Gerrard et al., 1994, Hughes and

Fricker, 1994). While some studies have used sub-cohort analysis, such as different playing levels (Lee and Garroway, 1996) or players' physiques

(Lee et al., 1997) to assess risk factors for injury.

Intervention studies

Intervention studies, specifically randomised controlled trials, are widely regarded as the strongest level of information available in epidemiological research (Caine et al., 1996, Henekens and Buring, 1987, Wade, 1988a,

Rudicel, 1988). They have been referred to as the 'gold standard' (Wade, 13

1988a), and are the criterion against which other study designs are contrasted (Rudicel, 1988). The primary advantage of this type of study is that the treatments to be investigated are allocated at random to subjects in a sample of sufficiently large size (Henekens and Buring, 1987).

Because subjects are allocated to treatment groups randomly many of the effects of bias and confounding that could be associated with non randomised studies are controlled for (Walter and Hart, 1990). This is because the process of randomisation should ensure that the comparison groups are balanced, both in terms of known determinants for a condition and all possible risk factors (McNeil, 1996). This approach is most comparable to that of laboratory experiments in basic sciences (Lilienfield and Stolley, 1994, Henekens and Buring, 1987).

These studies can be sub classified by various factors including the types of subjects involved and the size of the study (McNeil, 1996). Several types of intervention study have been defined in the literature: therapeutic trials in which a therapeutic agent or procedure is given in an attempt to cure, relieve the symptoms, or prolong the survival of those with the condition being investigated; intervention trials in which the investigator intervenes prior to a condition developing in individuals with characteristics that increase their risk of developing the disease; preventive trials in which an attempt is made to determine the efficacy of a preventive agent or procedure among those without the condition. For example, adding fluoride to the water supply to prevent dental caries 14

(Kunzel and Fischer, 1997). These are also referred to as prophylactic trials (Lilienfield and Stolley, 1994).

It has been suggested that randomised control type of investigative design offers an effective method for evaluating acute therapeutic modalities

(Wade, 1988a), and it has been used to investigate the effectiveness of operative versus non-operative treatment for knee injuries (Sandberg et al., 1987). But in spite of this, and the acknowledgement that this is the strongest available evidence, they have been relatively little used for evaluation of a proposed means of injury prevention, or hypothesised causes of injury (Caine et al., 1996). This may be because there are a number of practical reasons why the design cannot be utilised (Hart,

1996). Indeed, some texts on epidemiological methods in occupational epidemiology do not cover the design strategy (Checkoway et al., 1989,

Hernberg, 1992).

There are four main components to a randomised controlled trial; the selection of subjects; the random allocation of treatments to subjects; the treatment period; and the statistical analysis (Tygstrup et al., 1982). To design a trial effectively, careful attention must be paid to each stage in turn. One problem associated with such studies in sports injury research may be the identification of a large enough population from which patients can be recruited. For example, Wade (1988a), has suggested that if the objective was to evaluate knee braces in the prevention of knee injuries, 15 the incidence is relatively small so assembling a study group may not be feasible.

Often an essential feature of clinical trials is the blinding that is carried out. The purpose of blinding is to reduce the effect that knowledge of treatment may have on the outcome measures. Altman (1991), suggests that this can be done at three levels. Single blinding is where the patient is unaware of the treatment they have been given. A double-blind experiment is when neither the patient, nor the person evaluating the treatment knows which treatment was administered. A further extension to the double-blind study is to carry out the statistical analysis unaware of the treatment allocation, which is known as triple-blind (Last, 1995).

However, while such strict terminology is relatively easily applied to drug and surgical trials, when other forms of therapeutic treatment are evaluated, the situation is not quite so easy to define. The term 'clinical trial' can be applied to any planned experiment, which has been designed to elucidate the most appropriate treatment, and this may be conducted successfully with or without blinding (Pocock, 1983). For example, a trial to evaluate the treatments for low back pain was randomised, but not blinded (Meade et al., 1990). While a trial comparing treatments of shoulder complaints was referred to as single-blind (Winters et al., 1997).

However, the masking in each of these studies was only to the physiotherapist carrying-out the follow-up examination. In the final 16 analysis, the treatments were not allocated blindly, only the follow-up evaluation was carried out blindly.

In sports medicine epidemiology, the intervention study or clinical trial is primarily designed to evaluate the efficacy and safety of new treatments

(Pocock, 1983), for example whether they are surgical or therapeutic. But to evaluate protective equipment, such as prophylactic strapping and gum shields, it is unlikely that subjects could be randomly allocated to groups, and it may be unethical to attempt it. Certainly, blinding of the subjects will be almost impossible, a gum shield wearer would know if it was in his or her mouth. Therefore, studies involving protective equipment could, at best, be prospective cohort studies, with a blind evaluative stage and a

'blind' analysis.

Nevertheless, authors have argued that they do have their place in sports medicine research (van Mechelen, 1998, Eston and Rowland, 2000).

However, debate remains as to the extent and precise location of the blinding (Gissane, 2000, Gissane, 1999). But the small number that have been carried out are single blind, with the practitioner carrying out the evaluation, blinded to the subjects' treatment allocation (Pope et al., 2000).

The epidemiological evaluation of sports injuries is a valid investigative tool and although there has been some disagreement over the best methods to use (Caine et al., 1996), it appears clear that traditional 17 methods often need to be adapted only slightly. This can be seen with the use of non-concurrent cohorts (Garraway et al., 2000), and single blind randomised controlled trials (Pope et al., 2000) in sports medicine epidemiology.

Descriptive statistics are always the first stage of a research process in

order to identify whether there is a problem or trend. The methodology

used in the first paper (Stephenson et at, 1996) (see pages 40 to 57)

presented in the thesis lays the basis for describing injury incidence, and

identifying trends in a sample of rugby league players over four seasons.

All injuries that were reported by players during the four seasons between

July 1990 and May 1994 were recorded. A season ran from the beginning

of pre-season training, to the last competitive match in either April or

May. An injury was taken to be the onset of pain or a disability that

occurred while playing Rugby League football (Gissane et al., 1993). The

diagnosis and classification of injury was carried out by the club doctor

and the physiotherapist... ' The site and injuries were categorised as

described (Alexander The following details previously et -al., 1980). were

recorded about each injury:

" The position of the player " The site of the injury " The nature of injury " Whether the injury occurred in playing or training " The team played for (first or `A' team) " Activity at the time of injury " Time off as a result of injury 18

The total number of games played during the four seasons were recorded.

In total, there were 249 games played (138 first team, 111 `A' team), this included all competitions and friendlies. Playing hours at risk were

calculated as the number of matches played x 1.33 (each match lasting 80

minutes). Thirteen players in a side constitute 17.29 playing hours at risk

during a game. Training sessions took place at the rate of two or three per

week, involving approximately 5 hours work on game skills, with minimal

body contact.

Statistical analysis consisted of the calculation of rates per 1000 hours of

play, percentages, and where appropriate rates were compared using the

normal approximation as described by Clarke (1994). Significance was set

at the P<0.05 level.

The methods in the second publication (Gissane et al., 1997a) (see pages

58 to 73) presented as part of this thesis, seek to describe the differences

in the incidence of injury between rugby league forwards and backs: For

this paper the exposure under investigation was whether players were

playing in either the forwards or the backs.

The data used in this investigation have been described previously

(Stephenson et al., 1996). All injuries that were reported by players during

the four seasons between July 1990 and May 1994, at one professional 19

Rugby League club were recorded. A season ran from the beginning of pre- season training, to the last competitive match in either April or May. An injury was taken to be the onset of pain or a disability that occurred while playing Rugby League Football and resulted in the player missing either matches or training for a period of seven days. The diagnosis and

classification of injury was carried out by the club doctor and the physiotherapist. The following details were recorded about each injury:

The position of the player (forward or back), the site of the injury, the

nature of injury, the team played for (first or `A' team), activity at the time

of injury, time off as a result of injury

During the time of the injury survey a total of 249 games were played,

which included all pre-season, league, cup and post-season games. This

represented a total of 4305.21 player hours at risk (13 players x 1.33 hours

x 249 games), each game lasting 80 minutes. Since a team of 13 is

comprised of six forwards and seven backs, forwards were at risk for a

total of 1987.02 playing hours, and backs for 2318.19 hours.

The statistical analysis consisted of the calculation of injury rates per

1000 hours of play as a standardised rate of exposure, for both forwards

and backs. The relative risk (RR) was calculated using the person time

cohort method as described by Hennekens and Buring (1987):

no of forward injuries/exposure time (hrs) RR = no of back injuries/exposure time (hrs) 20

The injury rates for the different playing units were compared using the normal approximation as described by Clarke (1994)

Y t2 where ri and r2 are the two rates being examined and tl and t2 are the respective time periods.

The methodology for the third paper(Gissane et al., 1998) (see pages 74 to

87) allowed the comparison of two non-current cohorts, with regard to their exposure to summer and winter rugby league.

During the initial European Super League season all injuries that were reported for the first team at one professional rugby league club were recorded. The injury data were compared with first team data from a previous study on the same club over a period of four seasons reported previously (Stephenson et al., 1996). An injury was defined as a physical impairment received during a competitive match which prevented a player being available for selection for the next competitive game (Gibbs, 1993a).

The games were 7(1.09) [Mean(SD)] days apart. The diagnosis and classification of injury was carried out by the club doctor and physiotherapist. The information recorded about each injury has been 21 reported previously (Gissane et al., 1993, Gissane et al., 1997a,

Stephenson et al., 1996).

The population at risk was defined as the players who were selected to play for the first team in a given match, and the defined time at risk for calculating injury rates was the duration of the games multiplied by the number of players (1.33 hrs. x 13 players), multiplied by the number of games played. The average number of games played during the winter seasons was 34.5 (596.5 player hours), with each player averaging 12.1 appearances per season, and during the summer season, 23 games (397.67 player hours) were played in the Super League of 1996, with each player averaging 8.3 appearances.

Statistical analyses consisted of the calculation of injury rate per 1000 hours of play as a standardised rate of exposure (Edgar, 1995). To calculate the relative risk (RR) of injury between winter and summer rugby league the method using the incidence density ratio (IDR) for the two cohorts was used as described by Hennekens and Boring (1987).

no. of summer injuries/exposure time (hrs) (IDR) = . no. of winter injuries/exposure time (hrs)

Confidence intervals (95%) were calculated using the method as described by McNeil (1996). Where the confidence interval did not contain the null 22 value (RR = 1.0) the RR was taken as being significant at the P<0.05 level

(Henekens and Buring, 1987).

The methodology for the fourth paper (Jennings et al., 1998) (see pages 88 to 97) is descriptive and investigates body mass loss during a competitive match. Simple correlations were used to determine associations between variables. The subjects for this study were the members of the playing squad at one Super League Club, whose physical characteristics are displayed in table 1.

Table 1. Physical characteristics of players [mean±SD].

Age (yrs) Mass (kg) Height (cm) All players (n=28) 24.7±4.0 90.9±11.8 181.8±7.2 Backs (n=15) 25.1±4.3 84.6±7.5 178.4±2.1 Forwards (n=13) 24.3±3.8 98.1±12.1 185.4±7.7

The members of the squad who were selected for a given game took part in the assessment procedure on that occasion. Players' body mass was determined in the standard position before starting each game in underwear only, after they were towel dried. Each measurement was recorded to the nearest 100 g using a calibrated Seca 770 model scales. A similar procedure was completed on the players' completion of the game with minimal time delay. During the game the mean ambient temperature

(°C) and mean relative humidity (%) was recorded using a Casella polymeter (Model M 112050: Reliability; humidity f5% between 30% and

90% RH, Temperature fl%). 23

For each game played, each player that played was treated as an independent event making a total of 268 player appearances. Therefore, all data were collected with body mass being determined as the difference between pre-game mass and post-game mass. Players were allowed to drink water ad libitum after pre-game body mass determination, during the game and at half time. For the purposes of analysis, only players who completed each full game of 80 minutes were included in the analysis

(n=120).

The methodology used in the fifth publication (Gissane et al., 2001c) (see pages 98 to 112) makes use of video to examine the number and type of physical collisions experienced by players during competitive matches.

Using video recordings provides the researcher with a detailed observation of what takes place during a game. Players representing one professional rugby league comprised subjects for the present study (N=35, forwards n=

15, backs n= 20). In order to assess the number and type of physical collisions in which players were involved while playing, video recordings of all 22 regular season games played during the 1996 Super League season were analysed. This represents a total of 29.3 hours of match play or 380.4 player hours (13 players x 1.33 hrs x 22 games). The video tapes used were master copies of recordings produced by two T. V. media broadcasting companies (British Sky Broadcasting, Isleworth and Micron Video, 24

Wigan), and permission to use the material was granted by the Rugby

Football League.

Each video was a standard VHS (25 frames. sec-1)and was analysed by the principal investigator. Each physical collision that took place was classified into one of the following categories:

Defence (defending collisions)

1. Tackles - where the defending player(s) halted the progress of the ball carrier, and as a result the ball carrier had to play the ball.

2. Incomplete tackles - where the defending player(s) made contact with the ball carrier, but failed to prevent forward progress, or were unable to stop the passing of the ball.

Attack (attacking collisions)

3. "Tackled in possession" - where the ball carrier was tackled whilst in possession of the ball, forward progress was halted and the ball carrier had to play the ball.

4. "Broken tackles" - where the ball carrier was able to break through the tackle and continue forward progress.

5. Passes out of the tackle - where the ball carrier was tackled but was able to pass the ball.

Following this analysis it was possible to calculate each player's total defensive involvement (the sum of tackles and incomplete tackles), total attacking involvement (the sum of "tackled in possession", "broken tackles" and passes out of the tackle), and total physical involvement (in defence and attack) in each game analysed. 25

In order to determine the reliability of the physical collision analysis, three videos were analysed twice (each one week apart) by the principal author and the 95% limits of agreement were calculated using previously recommended methods (Nevill and Atkinson, 1997, Bland and Altman,

1986). Because the differences between readings did not vary in a systematic way across the all values, it was necessary to log transform the original data (Bland and Altman, 1986). Descriptive statistics (mean and

95% CI) for each physical collision category were computed for each playing position. To determine differences in the number and type of physical collision between forwards and backs, and between attacking involvement and defensive involvement, further analysis was undertaken using a proportion test (Altman, 1991).

The sixth publication (Gissane et al., 2001a) (see pages 113 to 126) presented in this thesis sought to make use of data collected from an injury register and combine this with the detailed observations regarding collisions from video analysis.

All injuries that were reported for the first team of one professional super league rugby club were recorded over one season. An injury was defined as a physical impairment received during a competitive match, which prevented a player being available for selection for the next competitive game (Gibbs, 1993a). The position of the player; the site of the injury; the nature of injury; the activity at the time of injury and the time off as a 26 result of injury were recorded for each game played over the full season.

The details of each category have been described previously (Gissane et al., 1993, Gissane et al., 1998, Gissane et al., 1997a).

The population at risk was defined as the players who were selected to play for the first team in a given match, and the defined time at risk for calculating injury rates was the duration of the games multiplied by the number of players (1.33 hrs. x 13 players), multiplied by the number of games played. A total of 23 games (22 regular season plus one play-off game) were played during one season (397.7 player hours).

In order to assess the number and type of collisions that players were involved in while playing, video recordings of 22 regular season games played during the 1996 Super League season were analysed (29.3 hours of match-play, 380.4 player hours). The video tapes used for analysis were master copies of recordings produced by two TV media broadcasting companies (British Sky Broadcasting, Isleworth and Micron Video,

Wigan), and permission to use the material was granted through the

Rugby Football League. The categorisation of physical collisions was carried out as outlined previously (Gissane et al., 2001c).

Following the analysis of physical collision categories, it was possible to calculate the following; 1) each player's total defensive involvement (the sum of tackles and incomplete tackles), 2) total attacking involvement (the 27 sum of "tackled in possession", "broken tackle" and passes out of the tackle), 3) total physical involvement (defensive plus attack) in each game analysed, and 4) the differences in physical collisions incurred by backs and forwards.

Statistical analyses consisted of the calculation of injury rate per 10,000 physical collisions as standardised rates of exposure, and descriptive statistics for physical collisions (mean and 95% CI). In order to compare differences between the proportions of physical collisions a single proportion test was used (Altman, 1991), while a test for differences between injury rates used the method of Clarke (Clarke, 1994), and the relative risk (RR and 95% CI) was computed. In order to analyse the differences between forwards and backs in the number of games missed by injured players, the Mann Whitney U and Kruskal Wallis tests were employed since the data were not normally distributed

The seventh publication (Gissane et al., 2001b) (see pages 127 to 146) develops an operational model to investigate contact sports injuries.

Traditional approaches to the epidemiological investigation of sports injuries have tended to focus on the incidence and prevalence of injury, applied both to individual sports, and to overall national statistics. The model developed in the work reported in the thesis aims to expand this 28 traditional approach to take into consideration the multitude of factors which may predispose to injury, and which may determine the ultimate

outcome of the injury for the contact sport athlete.

The cyclical model consists of five linked stages. First the ostensibly

healthy/fit athlete may be at risk of injury from a number of

predisposing factors. These may, with or without the additional exposure

to external risk factors, in the presence of a potential injury event,

result in injury incidence. The duration of time that the injury persists,

during treatment and rehabilitation, contribute to the prevalence of the

injury, and the ultimate outcome may be a return to sport at the original

level, thus completing the cycle, or a return at a different level, or even

premature retirement (figure 2). Each of the elements of the model are

now described in greater detail.

The healthy fit player

Inherent within the ostensibly healthy/fit player, exist a myriad of

intrinsic risk factors that have been suggested by the literature

(Meeuwisse, 1994). For example, it has been reported that field hockey,

soccer and lacrosse players exhibited an increased risk for ankle sprain

when they displayed an increased eversion: inversion strength ratio

(Barker et al., 1997). 29

Figure 2. A cyclical operational model for the investigation of contact sports injuries. Intrinsic Risk Primary Prevention Return Factors of Healthy/Fit Medics/Physios/ Healthy/Fit Player Coaches Player

Exposure to External No Injury Risk Factors Event Potential Outcomes Injury Event _ Injury A, Recurrence

Injury injury Injury 14 reva] Incidence

Premature Retirement/ Factors in the Lower Playing Level Treatment and Rehabilitation Mechanisms of Injury

At this stage in the cycle the strategies for intervention may be termed

`primary prevention' (Lysens et al., 1991), with the aim of preventing injuries from occurring in the first instance (Fletcher et al., 1996).

Knowledge of the individual's risk factors may be of benefit in primary prevention. These strategies amongst others, might include such measures as appropriate warm up, adequate hydration, prophylactic taping. They might also include the wearing protective equipment such as gum shields in rugby (Jennings, 1990), hurling (Crowley et al., 1995) and ice hockey

(Rampton et al., 1997), or head guards in hurling (Crowley et al., 1995) and ice hockey (Kujala et al., 1995, Rampton et al., 1997). Such strategies would also include the coaching of proper technique in contact sports when 30 either making or receiving a tackle (Corcoran, 1979), and teaching correct falling technique in judo (Kujala et al., 1995). Coaches and sports medicine practitioners seek to prevent injury, and it is the most logical and least costly method of health care (Meeuwisse, 1994). Additionally, prevention screening could take place to assess intrinsic risk factors that could lead to sports injury problems (McKeag, 1985). For example, it has been shown that postural and mechanical factors can predispose female basketball players (Garraway and MacLeod, 1995), rugby and soccer (Watson, 1995) players to injury, while screening has been advocated for groin injury prevention in rugby league football (O'Connor, 1995b).

Potential Injury Event

In addition to the intrinsic factors, extrinsic factors will play an important part in the potential for injury. The exposure to extrinsic risk factors will undoubtedly vary across sports and may vary within positions in

certain sports, as well as the conditions under which sport is played. For

example, both field hockey (Jamison and Lee, 1989) and American football

(Skovron et al., 1990) have reported increased injury rates when games

are played on astroturf. In American Football, both the risk of knee (RR =

1.18) and ankle (RR = 1.39) injuries are increased when the game is played on artificial compared with real grass (Powell and Schootman,

1992). 31

The event that initiates an injury is one of the most identifiable parts of the injury process and has been the focus of much research (Meeuwisse,

1994). In contact team sports these events are likely to be highly game specific, and indeed position specific. It has been suggested there are a high number of thigh injuries in professional soccer (Inklaar, 1994), and that are commonly result from physical contact with an opponent

(Ekstrand and Gillquist, 1983). It has also been suggested that with the exception of goalkeepers, there are few upper body injuries that prevent soccer players from playing (McKeag, 1985).

At this stage in the cycle, a player that is not injured can continue to play whilst still exhibiting the same intrinsic risk factors, whereas if he/she becomes injured the player progresses to the next stage of the model.

Injury Incidence

In descriptive sports medicine epidemiological terminology incidence has been defined by the number of new events or cases of injury that develop in a population of individuals at risk during a specified time interval

(Henekens and Buring, 1987). The incidence of injury in specific sports is an area that has received much attention (Garraway and MacLeod, 1995,

Hickey et al., 1997, Kujala et al., 1995). However, the comparison across studies is often difficult due to the varying definitions of injury that have been employed (van Mechelen et al., 1996). Nevertheless, where 32 comparisons can be made, there is a range of injury incidence rates among contact sports as demonstrated in table 2.

Table 2. Injury incidence rates across team sports.

Sport Injuries per 1000 Reference player hours

Rugby League 34* Stephenson et al., 1996 Rugby Union 20* Hughes and Fricker, 1994 Australian 35 Seward et al., 1993 Rules

Soccer 22.6 Inklaar et al., 1996

*Injuries requiring a player to be unable to play for more than one week

Injury Prevalence

In descriptive sports epidemiology, injury prevalence has been quantified by the proportion of individuals in a population who have an injury at a specific instant. It provides an estimate of the probability or risk that an individual will be injured at some point in time (Henekens and Buring,

1987). Injury prevalence depends upon both the incidence rate of an injury, and the period of time between the initiating event to the return to full fitness. In sporting terms the prevalence of an injury is an important consideration, since the treatment and rehabilitation of injuries takes time, and this is often a major factor in injury prevalence. It has been 33 suggested that because professional sport is a business, it is often desirable on the part of both the team and the player to keep time lost from playing to a minimum (Lewin, 1989). Prevalence can also be influenced by game regulations, for example in rugby union football a player who is concussed is required not to either play or train for a period of 21 days (International Rugby Football Board resolution 5.7), whereas in rugby league football there is a sliding scale of required abstinence for the severity of injury based on the symptom severity of concussion. Therefore, concussions that are considered relatively minor in rugby league football, would have a far higher prevalence in rugby union football, which could contribute to a distortion in specific injury prevalence among similar sports.

The type and duration of treatment of the athlete is dependent upon each specific injury which the player is has sustained. For example it has been reported that 44% of rugby injuries only require treatment with RICE

(rest, ice, compression and elevation) (Hughes and Fricker, 1994), while others may require surgical intervention (Thomas and Thomas, 1999).

During the rehabilitation process, both secondary and tertiary prevention can take place. The aim of secondary prevention is to restore health when it is impaired (Last, 1995). In sports medicine it is defined as the process of preventing or delaying the development of irreversible structural damage, by therapeutic intervention (Lysens et al., 1991). These measures can influence the prevalence of injury by reducing the amount of time that 34 a person remains injured, but not the incidence. Appropriate and early management of soft tissue injury in particular, has been shown to promote early recovery (MacLeod, 1993).

Therapy that seeks to limit the injury process from becoming either chronic or persistent has been termed tertiary prevention (Lysens et al.,

1991). The aim of tertiary prevention is to reduce both the incidence and prevalence of long term disability (Lysens et al., 1991). Sound treatment and rehabilitation have been suggested to be one of the most adequate preventive measures for secondary and tertiary prevention (Lysens et al.,

1984).

Event Outcomes

In the proposed cyclical operational model for the investigation of sports injuries (figure 2), an injury has three possible event outcomes. A player can return to a healthy/fit state, the injury can recur, and either, the player can retire from competition at that level, or continue participating at a lower level The obvious ideal is to return to playing at the pre-injury level of performance. In order for an athlete to be regarded as healthy they must be able to take part fully in both training and playing. (Lysens et al.,

1991) However, professional athletes are unlike a number of other occupational groups in that they are often quite willing to train and play in spite of injury, compared with others, who normally return to work only when they are completely recovered (Schootman et al., 1994b). 35

Recurrent injuries are also a major problem in sport and have been reported to account for 16.5% of all injuries in rugby union football

(Garraway and MacLeod, 1995). Recurrent injuries increase the

incidence rate and the amount of time lost for an injured player, thus

also increasing the prevalence rate of injury. Furthermore, one of the

greatest risk factors for injury is the history of previous injury (Watson,

1997).

In extreme circumstances professional sport players are sometimes forced

into premature retirement because of injury. In such cases, it has been

reported that rugby league football players who suffered long term

consequences of injury after their playing careers, experienced difficulties,

which included job limitations, reduced income earning potential and

increased personal medical costs (Meir et al., 1997).

In certain situations players will be unable to return to playing and the

management of such an injury may. seek to maximise the quality of life

rather than fully remediate the injury (Lysens et al., 1984). Previous work

has described cervical spine injuries of two rugby union football players

who could no longer return to play (Secin et al., 1999). These players are

now members of the Rugby Amistat Foundation, which is dedicated to the

well being of players who have suffered physical and mental trauma

following disabling injury (Secin et al., 1999). 36

The overall design of the proposed operational model is cyclical because even if a player returns to health/fitness, the sports injury itself may constitute an intrinsic risk factor for the predisposition of future injury.

Even if a player is fortunate enough to avoid an injury, the individual's intrinsic risk factors are unlikely to remain the same over time. For example, at the beginning of every season a player has another year of experience and is another year older, both of which have been described as potential sports injury risk factors (Lysens et al., 1991, Watson, 1997).

This will serve to alter the nature of intrinsic risk factors present. In addition to this, coaches in contact sports often emphasise increasing muscle bulk during the closed season (Meir, 1993), which may also serve to alter an individual's intrinsic risk factors.

The eighth publication (Gissane et al., 2002) (see pages 148 to 162) uses pooled data analysis of injury incidence in rugby league football. To carry out a pooled data analysis of injury in rugby league football methods included the development of a search strategy to locate relevant papers investigating injury in the game. Inclusionlexclusion criteria were developed to ensure compatibility of the data, and finally the combined analysis was performed. Databases identified for searching included

Medline, Sports Discus and Web of Science databases, covering the period from 1985 to 2000 and 18 studies were identified. The terms used were, rugby with league and injury. 37

Inclusion criteria for the present analysis were Studies published later than 1990; data collection carried out prospectively on professional players; a definition of a recordable injury being one that required an injured player to miss the subsequent game; and finally a count of the number of games studied to allow the calculation of person time injury rates.

A total of 18 articles were identified that reported prospective data collection of rugby league injury, and details of these studies are shown in table 1. Of these, only ten satisfied the inclusion criteria, (Gissane et al.,

1993, Seward et al., 1993, Estell et al., 1995, Gibbs, 1993a, Gissane et al.,

1997a, Gissane et al., 1998, Hodgson-Phillips et al., 1998, Stephenson et al., 1996) two of these studies were excluded (Hodgson-Phillips, 1998,

Hodgson-Phillips et al., 1997) because of reporting the same source data as in a previous paper. (Hodgson-Phillips et al., 1998) A further two studies were also excluded as the same common baseline data set had been used to highlight further trends. For example, Stephenson et al. (Stephenson et

al., 1996) and Gissane et al. (Gissane et al., 1997a) used the same baseline

data, only the former reported the overall incidence of injury in rugby

league (Stephenson et al., 1996), while the latter sought to highlight the

differences in injury rates between forwards and backs (Gissane et al.,

1997a). Therefore a total of six studies were included in the final pooled

analysis which are highlighted in table 1, three of which reported both 38 first team and reserve grade information (Stephenson et at, 1996, Estell et al., 1995, Gibbs, 1993a).

Since many studies did not include all areas of interest for analysis, it was

necessary to extract specific information from individual studies at

different stages of the analytical process.

The data from individual studies were combined using the method

described by Breslow and Day (Breslow and Day, 1987). Person-time

incidence rates and 95% confidence intervals were calculated using

Confidence Interval Analysis Software (Altman et al., 2000). To test for

significant differences, proportion tests (z), chi-squared (x2) goodness of fit

tests were used, along with relative risk (RR) where appropriate. 39

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Injury in rugby league: a four year prospective survey

Abstract

injury in English Objective - To investigate the incidence of professional

Rugby League over a period of four playing seasons.

by during Methods - All injuries that were received players match play

were recorded. Each injury was classified according to site, type, player

position, team playing for, activity at the time of injury, and time off as a

result of injury.

(95% CI Results - The overall injury rate was 114 105 - 124) per 1000

playing hours, the most frequent type of injury were muscular injuries (34

hours), frequently injured [29 - 40] per 1000 playing while the most site hours). was the head and neck region (38 [16 - 25] per 1000 playing

Players received the largest percentage of injuries when being tackled

injuries less from (46.3% [41.9 - 50.7]), most required than one week away forwards had higher injury playing and training (70.1% [66.1 - 74.2]) and a

rate than backs (139 vs. 93 injuries per 1000 hours).

high injury in Rugby League Conclusions - The rates of are undoubtedly

due to the high amount of bodily contact in the game. Being tackled has

the highest risk of injury, because of being hit forcibly by other players.

Forwards suffer higher injury rates than backs probably because they are

involved in a greater number of physical collisions.

Key words: rugby league, injury, injury rate, prospective study 41

Introduction

Rugby League is a physical game in which players are required to demonstrate speed, stamina, strength and agility (Gibbs, 1993a). It has been suggested that injury rates in Rugby League are higher than in other main body contact sports such as, Rugby Union (Seward et al., 1993,

Gissane et al., 1993), Australian rules football and soccer (Seward et al.,

1993). The possible reasons for the high injury rate are that players are involved in 20 to 40 physical `confrontations' per game, and that players wear minimal protective equipment (Gibbs, 1994), such as padding, which is designed to protect the soft tissues but not the bones and joints (Doran and Dunn, 1987), or padded supports and sleeves for which, it has been suggested, there is no evidence of protection for injured muscles (MacLeod,

1993).

However, it is acknowledged that research into many aspects of Rugby

League is extremely limited (Brewer and Davis, 1995), not least the incidence of injury. Previous investigations have reported on short time periods (Alexander et al., 1980, Gissane et al., 1993), and the only longitudinal investigations have been carried out in the Australian game

(Gibbs, 1993a, Gibbs, 1994). These studies also report widely differing findings, which could be due to the playing conditions, the skill level of players, the design of the studies, or the definition of what constitutes an injury. Therefore, the purpose of this study was to describe the incidence 42 of injury in one professional Rugby League club over a period of four seasons.

Methodology

All injuries that were reported by players during the four seasons between

July 1990 and May 1994 were recorded. A season ran from the beginning of pre-season training, to the last competitive match in either April or

May. An injury was taken to be the onset of pain or a disability that occurred while playing Rugby League football (Gissane et al., 1993). The diagnosis and classification of injury was carried out by the club doctor and the physiotherapist. The site and injuries were categorised as described previously (Alexander et al., 1980). The following details were recorded about each injury:

" The position of the player " The site of the injury., " The nature of 'injury " Whether the injury occurred in playing or training " The team played for (first or `A' team) " Activity at the time of injury " Time off as a result of injury

The total number of games played during the four seasons were recorded.

In total, there were 249 games played (138 first team, 111 `A' team), this included all competitions and friendlies. Playing hours at risk were calculated as the number of matches played x 1.33 (each match lasting 80 43 minutes). Thirteen players in a side constitute 17.29 playing hours at risk during a game. Training sessions took place at the rate of two or three per week, involving approximately five hours work on game skills, with minimal body contact.

Statistical analysis consisted of the calculation of rates per 1000 hours of play, percentages, and where appropriate rates were compared using the normal approximation as described by Clarke (Clarke, 1994). Significance was set at the P<0.05 level.

Results

During the four seasons under investigation a total of 599 medical conditions that prevented a player from either playing or taking part in club training for Rugby League were recorded. Of these, 27 were illnesses and conditions such as sickness, and were excluded from the analysis.

This left a total of 572 sports injuries, 492 (82.1%) of which were received during match play and 80 (13.9%) during training.

Of the 492 match injuries, 297 (60.4%) were to first team players and 195

(39.6%) to Alliance (`A' team) players. This equates to an overall incidence rate of 114 injuries per 1000 hours of match play (first team, 124; A team,

102; z=2.2, P<0.05). 44

The type of injuries sustained during match play are displayed in table 1, which indicated that the highest injury rates are for muscular injuries

(haematomas and strains) (34 per 1000 hours). When examining the first and A teams separately the same type of injury was the most common

(first team 37, A team 31 per 1000 hours; z=4.7, P<0.05). The types of injuries that were least common were abrasions & skin infections and

`others' (both 2 per 1000 hours)

The site of injuries sustained by players are displayed in table 2, which indicated that the region of the body that suffers the highest injury rates is the head and neck (38 per 1000 hours). The same site was also the most injured when comparing the first and A teams, although the two rates are markedly different (47 vs. 28 per 1000 hours; first team vs. A team; z=

3.2, P<0.05). The next most commonly injured site in the body was the thigh and calf, but the injury rate was less than half that of the head and neck (20 per 1000 hours). The least injured sites of the body were the arm and the `others' category, which included such areas as fingers and toes

(both 7 per 1000 hours). 45

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The figures for the first and 'A' teams are displayed in table 3 and tended to be quite similar. Of all the playing injuries the largest percentage were received when a player was being tackled (46.3%), while a tackler was injured in 21.3% of the injury events. The remaining 32.3% were classified as others, which included injuries during such activities as running and scrummaging.

The amount of time off taken by players as a result of injury is shown in table 4. It can be seen that more than two-thirds of all injuries sustained required a player to take less than one week away from playing and training, a relatively small proportion of injuries (7.5%) required a player to be away from training for more than four weeks.

The incidence of injury for forwards and backs is shown in table 5. From this it can be seen that forwards are injured more frequently than backs in absolute terms (56.3 vs. 43.7%, both first and A teams). When the rate is standardised for the number of players (six forwards and seven backs), the injury rate differences are even larger (forwards 139 vs. backs 93 per 1000 hours; z=4.5, P<0.05). 48

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Discussion

The study found an overall injury incidence rate in Rugby League of 114 injuries per 1000 man hours of play. It has been suggested that the high injury rate is due to repeated hard body contact (Gibbs, 1994). The injury rate in the current study is higher than the rate of 14 that has been reported for Rugby Union (Garraway and MacLeod, 1995), and also higher than the rate of 45 per 1000 hours that has been reported for Australian

Rugby League (Gibbs, 1993a). One probable reason for the differing rates between Australian and English Rugby League, and League and Union was the decision of previous studies (Gibbs, 1993a, Garraway and

MacLeod, 1995) to only include injuries that required a player to miss a subsequent game, the games being played on a weekly basis. If in the present study injuries requiring less than one week to recover from are excluded the overall rate is reduced to 34 per 1000 hours (first team 30, A team 39 per 1000 hours). However, this may not strictly be comparable, as situations such as whether conditions in England may result in more than a week between games. Then postponed games, which must be played later in the season could result in a fixture backlog requiring more than one game a week to be played.

Muscular injuries accounted for 29.9% of all injury types. This is similar to values that have previously been reported (Walker, 1985, Alexander et al.,

1979). Injuries of this type to the quadriceps have been reported to be 52 common as this is the first point of contact in the tackle (Gibbs, 1994). It could be argued that a game that has been likened to being mugged 30 times in 80 minutes (O'Hare, 1995), which involves a player in 20 to 40 physical `confrontations' per game (Larder, 1992) predisposes players to this type of injury.

The site of the body to which most injuries took place was the head and neck region with 33.3% of all injuries. This is higher than has been previously reported, with studies quoting values ranging from 5.8%

(Gibbs, 1993a) to 28.8% (Alexander et al., 1980) of all injuries. Again, the decision to include minor injuries may account for part of the difference.

But at least one other study chose to include minor injuries (MacLeod,

1993), and commented that head and neck injuries were on the increase.

While another reported that head lacerations were very common although they did not require players to miss games (Gibbs, 1994).

The observation that a majority of injuries are caused in the tackle is common to both rugby codes (Gissane et al., 1993, Garraway and

MacLeod, 1995, Addley and Farren, 1988, Inglis and Stewart, 1981, Lythe and Norton, 1992). The findings of the present study also showed that the player being tackled was more likely to be injured (46.3%), this is also in agreement with previous research (Lythe and Norton, 1992, Gissane et al.,

1993). In Rugby League, the tackle is a very prominent part of the game, 53 which carries inherent dangers such as, being knocked over backwards, whiplash and the clashing of heads (Larder, 1992).

This study also reported that 32.3% of players were injured in situations classified as `others', this must be considered to be a limitation of this study. With almost one third of injuries falling into this category, it is clear that it is too large as a general classification, and that future research should attempt to break this down into more component parts.

For example, some injuries may have occurred as a result of foul play but were not recorded as such. Nevertheless, the sport is concerned about such incidents, which was emphasised by the Rugby League issuing a directive in January 1995 specifically making lifting a player and `spear tackling' him a sending off offence under Law 15.1d regarding illegal throws.

The vast majority of injuries recorded in this study (70.1%) required that a player be absent from training and playing for less than a week. Part of the reason for this high figure was the decision to include all injures received while playing. Gibbs (1993a), who defined an injury as an event that required a player to miss the next week's game, reported that the largest proportion (38%) of injuries required players to miss the next game. If the injuries requiring less than one week are excluded from the current analysis, the largest proportion required 1-2 weeks absence (46%).

However, classifying injuries in this way can be shown to miss a lot of minor injuries (Inklaar, 1994). Also, it should be pointed out that 17% of 54 the injuries recorded in this study were lacerations. The majority of these would have involved the `blood-bin', which began in the 1991-2 season after concern over such injuries. Furthermore, one investigation reported that such injuries rarely cause a player to miss a game, but counted 101 over five seasons (Gibbs, 1994). If they were counted, they would add considerably to both the numbers of, and the injury rates.

A possible explanation for differences between the League and Union codes might be the specific regulations regarding concussions. The

International Rugby Football Board resolution (5.7) requires a concussed player to refrain from playing and training for a period of at least three weeks from the injury, and subject to being cleared by a proper examination (MacLeod, 1993). However, in Rugby League concussion is graded by severity as shown in table six. This could result in injuries being recorded but players requiring less time away from playing and training.

Finding that backs are injured much more frequently than forwards, has been observed by others (Gibbs, 1993b, Garraway and MacLeod, 1995,

Seward et al., 1993). It has also been reported that forwards received a higher than expected number of injuries, based on the number of player positions (Gibbs, 1993b). As backs run the ball more and forwards tend to be involved in more collisions (Larder, 1992), then perhaps they should be more susceptible to injuries. It has also been suggested that the pattern of 55 injury between forwards and backs might change with an alteration in the style of play (Garraway and MacLeod, 1995).

Table 6. Classification of concussions

Severity of concussion Action Mild: no loss of consciousness (L. O.C. ) i. Full memory of event can usually continue playing (after being checked) ii. Memory deficit of event must cease playing: no training or playing for 48 hours, and only after medical check by the club doctor. Moderate: (L. O. C.) of up to 2 must cease playing: no playing or minutes training for 15 days and only after a medical check by the club doctor. Severe: i. L. O. C. of up to 3 minutes must cease playing: no playing or training for 22 days and only after a medical check by the club doctor. ii. L. O. C. of over 3 minutes must cease playing: and be admitted to hospital for observation: no playing or training for 29 days and only after a medical check by the club doctor. All cases of SEVERE concussion should have X-rays of the skull and cervical spine.

Source: Rugby Football League (1993).

The results from the present study show that Rugby League has very high injury rates. This is undoubtedly due to the large amount of physical body contact between players. Injury rates were shown to be higher at the highest standards of play. Forwards experience greater rates of injury than backs, which is probably due to them being involved in more repetitive body contact than backs. Perhaps future research should examine the differing injury rates between forwards and backs in relation 56 to their game specific workloads, and also to analyse what types of injury these respective groups receive during the course of a game.

Acknowledgements

The authors would like to thank Dr JA White, Dr L Rushton, Dr JCG

Pearson and Ms CAC Coupland for their assistance while writing this paper.

Postscript

During the peer review of this paper, the reviewers made some extremely useful and helpful comments. With some of the points, the authors had the necessary information available and could address the issues. While, unfortunately, for others we could not.

One of these points was the incidence of foul play, which was not collected.

The reason for this was that when the register was begun back in 1990, we collected what we thought was relevant at the time. At that time, there were almost no studies available on Rugby League and an overall picture of the injury situation was needed. This is not to say that foul play is not an extremely important issue, but with the advent of the Super League concern has shifted. The Rugby League Medical Association is currently more concerned with the effect playing on hard ground will have on 57 overall injury rates, and, also, what is the potential for heat stress injuries? 58

Differences in the incidence of injury between rugby league forwards and backs

Abstract

Evidence with regard to the incidence of injury to forwards and backs in the game of rugby league is extremely limited. A four year prospective study of all the injuries from one professional Rugby League club was conducted. All injuries that were received during match play were recorded, and those for forwards and backs compared. Forwards had a higher overall rate of injury than backs (139.4 [124.2 - 154.6] vs. 92.7 [80.9

hours, P<0.00006). Forwards - 104.6] per 1000 player had a higher rate of injuries to all body sites with the exception of the ankle and the `others' category of injury. They had significantly higher rates for the arm (11.6

[1.4 hours, [6.9 - 16.3] vs. 3.9 - 6.4] per 1000 player P=0.005) and, the head and neck (53.9 [43.9 - 63.8] vs. 25.0 [18.7 - 31.4] injuries per 1000 player hours, P<0.00006). Forwards had significantly more injuries than backs for contusions (17.1 vs. 7.3 per 1000 player hours, z=2.85, P=

0.0044), lacerations (26.7 13.8 1000 hours, P= . vs. per player z=2.92,

0.0035) and haematomas (20.6 vs. 11.6 per 1000 player hours, z=2.29, P=

0.02). Forwards were also more likely to be injured when in possession of the ball (70.5 [59.2 - 81.7] vs. 38.0 [30.2 - 45.7]), and also when tackling

(33.2 [25.3 - 41.1] vs. 16.8 [11.6 - 22.1]). The higher rates of injury experienced by forwards were most likely as a result of their greater physical involvement in the game, both in attack and in defence. 59

Introduction

In many team sports, different demands are made on different player positions. Within Rugby League there has been a trend to reduce specialisation, so that the work carried out by players varies less from position to position (Larder, 1992) and it has been suggested that fitness training is uniform for all positions (O'Connor, 1995a). Nevertheless, match analysis has demonstrated that backs cover greater distances in a game than forwards (7336 vs. 6647m (heir et al., 1993)), and also that forwards are involved in a larger number of physical collisions than backs

(36.3 vs. 19.14) (Larder, 1992). It can be said that the forwards' main role in possession is to gain ground quickly and to put the opposition on the back foot, while backs attempt to move the ball wide and exploit space.

Similarly when defending, forwards do the majority of the tackling, attempting to stop the opposition gaining ground, and so denying them space in which to operate.

With these variations in physical effort demanded of the two playing units within a team it was hypothesised that there is a differing risk of injury, and that the injuries received by members of these playing units might also differ. It has been demonstrated that forwards do experience higher rates of injury than backs (Gibbs, 1993a, Gissane et al., 1993, Norton and

Wilson, 1995) while in Rugby Union, it has been reported that 80% of injuries to backs took place whilst players were involved in the tackle 60 situation (Garraway and MacLeod, 1995). But to date, the specific question of whether, and how, differing roles in game situations alters the risk of injury has not been addressed.

The purpose of this study was to describe the differences in the incidence of injury to forwards and backs, and to determine if there is a greater risk of injury when playing as a forward or a back in a professional Rugby

League club over a period of four seasons.

Methods and procedures

The data to be used in this investigation have been described previously

(Stephenson et al., 1996). All injuries that were reported by players during the four seasons between July 1990 and May 1994, at one professional

Rugby League club were recorded. A season ran from the beginning of pre- season training, to the last competitive match in either April or May. An injury was taken to be the onset of pain or a disability that occurred while playing Rugby League Football (Gissane et al., 1993), which has been reported to best correspond with daily reality (Tweller et al., 1996). The diagnosis and classification of injury were carried out by the club doctor and the physiotherapist. The site and type of injuries were categorised as described previously (Alexander et al., 1980). The following details were recorded about each injury: The position of the player (forward or back), the site of the injury, the nature of injury, the team played for (first or `A' 61 team), activity at the time of injury, time off from playing and training as a result of injury.

During the time of the injury survey a total of 249 games were played, which included all pre-season, league, cup and post-season games. This represented a total of 4305.21 player hours at risk (13 players x 1.33 hours x 249 games), each game lasting 80 minutes. Since a team of 13 is comprised of six forwards and seven backs, forwards were at risk for a total of 1987.02 playing hours, and backs for 2318.19 hours. The age of a player was taken as the age at the beginning of the season (1st

September). Based on this, the mean age (±SE) was 24.3±0.27 yrs.

The statistical analysis consisted of the calculation of injury rates per

1000 hours of play as a standardised rate of exposure, for both forwards and backs. The injury rates for the different playing units were compared using the normal approximation as described by Clarke (1994):

(7 r2) 0 z_ F+ r7t2

where ri and r2 are the two rates being examined and tl and t2 are the respective time periods. 62

Results

During the four years of the study a total of 492 injuries were recorded,

277 to forwards and 215 to backs. The overall injury rate for all players was 114.3 injuries per 1000 player hours (95% CI 104.8 to 123.8). The rates for forwards and backs were 139.4 (124.2 to 154.6) and 92.7 (80.9 to

104.6) per 1000 player hours (z = 4.45, P<0.0006). The relative risk of injury when comparing forwards and backs was 1.50 (1.32 to 1.68).

Injuries to different sites of the body are displayed in Figure 1. Forwards had higher rates of injury in all categories than backs, with the exception of the ankle and the `others' category of injury. Forwards also demonstrated higher injury rates in six of the eight site category classifications, and had significantly higher injury rates for head and neck injuries (53.9 vs. 25.0 injuries per 1000 player hours, z=9.32, P<0.00006), and arm injuries (11.6 vs. 3.9 per 1000 player hours, z=2.81, P=0.005).

The two categories in which backs recorded higher injury rates were ankle

(9.9 vs. 8.6 per 1000 player hours, z=0.46, P=0.65) and `others' (7.3 vs.

7.1 per 1000 player hours, z=0.11, P=0.91), although these were not statistically significant.

Analysis of the types of injuries sustained (Table 1), demonstrated that forwards and backs had significantly different rates of injury for contusions (17.1 vs. 7.3 per 1000 player hours, z=2.85, P=0.0044), 63 lacerations (26.7 vs. 13.8 per 1000 player hours, z=2.92, P=0.0035) and haematomas (20.6 vs. 11.6 per 1000 player hours, z=2.29, P=0.02). It was observed that forwards exhibited higher injury rates for each type of injury with the exception of the dislocations and the others category.

However, in both cases the observed rates were small and the differences non-significant (dislocations z=0.05, P=0.96; others z=0.18, P=0.86).

Activity at the time of receiving an injury is shown in Table 2. From this it can be seen that the tackle is the phase of play associated with most injury. The results indicated that forwards had significantly higher rates of injury than backs when they were the tackler, i. e. defending (33.2 vs.

16.8 per 1000 player hours, z=3.35, P=0.00082), and when they were being tackled i. e. attacking (70.5 vs. 38.0 per 1000 player hours, z =4.52,

P<0.0006). It was also found that when incidence rates for being tackled and tackling were compared directly, both forwards (tackler 33.2, tackled

70.5 per 1000 player hours, z=5.16, P<0.0006) and backs (tackler 16.8, tackled 38.0 per 1000 player hours, z=4.35, P<0.0006), were significantly more likely to be injured when being tackled.

Finally, when the rates for time off as a result of injury (Figure 2) were analysed, the only category in which there were significant differences between forwards and backs was the rate of injury requiring less than one 64

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Discussion

The major finding of this study was the differing injury rates of forwards and backs per 1000 player hours at risk. The RR of 1.50 indicates that forwards had a 50% greater risk of injury than backs. Overall, forwards received 56.3% of all injuries and backs 43.7%. While other studies have reported that the number of injuries to forwards are more numerous than injuries to backs (Gissane et al., 1993, Gibbs, 1993b, Norton and Wilson,

1995, Stephenson et al., 1996) injury rates do need to be standardised relative to exposure, and consideration needs to be given to the fact that forwards have a lower overall game time exposure, as there are fewer forwards, six, in a side than backs, seven. When these factors are taken into account, the differences between the two playing units are much larger than raw numbers would convey. It has been suggested that forwards experiencing a higher injury rate, may be due to their involvement in more physical body contact than backs (Gibbs, 1993a). This is supported by match analysis at international level, which has shown that each player in a side is involved in an average of 27 physical confrontations (tackles and being tackled) per game, forwards average

36.3 physical confrontations and backs only 19.1 (Larder, 1992). While at club level Robinson (1996), reported that forwards and backs were 69 involved in 32.4±1.2 and 19.0±0.8 (mean±SE) physical confrontations per game respectively.

The higher rates of forward injuries for specific sites of the body has been reported previously (Seward et al., 1993). In the present study, the site that received the most injuries was the head and neck area, with forwards receiving significantly more injuries than backs. Injuries to the head and facial areas, particular lacerations, have been suggested to be much more common in forwards than in backs (Seward et al., 1993).

Forwards experienced higher rates of injury in each of the type category in this study, with the exception of the dislocation and `others' category.

They recorded significantly higher rates for contusions, haematomas and lacerations. The higher rates for lacerations could be as a result of more injuries to the facial region (Seward et al., 1993). In spite of their high incidence, it may be considered fortunate that is rare for such injuries to cause players to miss games (Gibbs, 1993a).

In this study 67.7% of all injuries took place in the tackle, which is a slightly lower than figures than have been previously reported (77.2%)

(Norton and Wilson, 1995). The injury rates were significantly higher when players were carrying the ball and being tackled. It has previously been reported that of all injuries that take place in the tackle, 56.6% of them are to the ball carrier (Norton and Wilson, 1995), whereas the figure 70 in the present study was 68.5%. It has already been reported how forwards tend to be in more physical confrontations than backs in the game, and when examining the activity whilst in possession, (Larder,

1992) reported that forwards were tackled an average of 13.5 times per game, while backs were tackled only times per game. While Robinson

(1996), reported that forwards were tackled 14.2±0.8 (mean±SE), and backs 10.4±0.5 times per game The process of being tackled is an area of the game that carries inherent dangers, including whiplash injuries, the clashing of heads and being knocked over backwards (Larder, 1992).

Several authors have suggested that stricter enforcement of high tackle regulations could reduce the number of injuries (Seward et al., 1993,

Milburn, 1995, Gibbs, 1994).

Similarly, forwards perform on average over twice as many tackles per game as backs (22.8 vs. 10.1) (Larder, 1992), which exposes them to a greater risk of injury and accounts for their significantly higher injury rates than backs. Outside of the tackle situation, backs demonstrated higher injury rates than forwards, which may appear surprising since they are not involved in scrummages, which average 19.4 per game (Larder,

1992). However, there is evidence that they cover greater distances than forwards (7336 vs. 6647m) (Meir et al., 1993), and knee injuries have been reported to occur in non-contact hyperextension and side stepping manoeuvres (Gibbs, 1994). Furthermore, they would tend to be involved in relatively more situations where they were required to gather a high ball, 71 in circumstances where they may be required to jump for the ball, with the opposition approaching towards them. If more than one player is jumping for the ball there is an obvious risk of injury from collision or landing awkwardly, without a tackle taking place. Similar situations have also been described in Rugby Union where the `Garryowen' kick is used as an attacking ploy (O'Brien, 1992).

The only time off category in which there were significant differences between forwards and backs were injuries that require less than one week away from playing and training. The reason for this would most probably be the higher numbers of overall injuries received by forwards. When examining injuries in this way, one characteristic of Rugby League is the larger numbers of injuries requiring one week away from, playing and training, compared with other team sports (Seward et al., 1993). Arguably, a sizeable proportion of these are lacerations, which some studies have chosen not to include. Gibbs (1993b) reported 61 lacerations over a three year period, that did not require a player to miss subsequent games. If they were included they would have increased the overall injuries by 43%.

In Rugby League forward players experience higher rates of injury than backs, in spite of the fact that backs out number forwards seven to six. It has been suggested that if the differing playing units do have different injury profiles, then perhaps specific prevention programmes would be appropriate (Norton and Wilson, 1995). The results of this study support 72 this proposition and offer further evidence as to the different areas of the body, and the specific situations in which forwards and backs receive injuries. Such considerations should be taken into account when designing player conditions and training programmes (Seward et al., 1993). Fitness profiles have shown forwards to be heavier than backs, with greater amounts of body fat (Brewer et al., 1994). It has been argued that forwards need to have such body composition to provide them with protection from the extra collisions in which they are involved (Meir,

1993). Rugby League may have recently demonstrated a trend toward less specialisation (Larder, 1992), and fitness training may be uniform across positions (O'Connor, 1995a), but evidence suggests that forwards' greater physical involvement, places them at a much higher risk of injury. Some investigators have argued that the best way to standardise injury rates in rugby football is to quote incidence and prevalence per 1000 player hours

(Edgar, 1995, Lower, 1995). While others have commented that getting a true reflection of actual exposure time at risk may prove too difficult (van

Mechelen et al., 1992). In Rugby League, future research could possibly address the questions of how physical involvement (tackles and being tackled) influences injury rates, and are their particular tackle situations that expose players to higher injury risks? Why this is the case may be difficult to pinpoint `why does one tackle cause an injury when the previous 50 did not? ' (MacLeod, 1993). Furthermore, within the two playing units of forwards and backs, there are specialist positions such as hooker and half-back, so that future research could be directed towards 73 examining specific injuries that occur across the full range of positions, rather than the two playing units within a team.

Conclusion

The limitations of this study notwithstanding, it is clear that forward players in rugby league demonstrate a higher incidence of injury than back players. Forwards appear to have a higher injury rates because of their greater physical involvement compared to backs. But, to provide a more complete answer, specific analysis of physical involvement in relation to injury rates is required. 74

Injury in summer rugby league football - the experiences of one club

Abstract

Objective - To investigate whether the movement of the playing season would alter the risk of injury whilst playing first team European professional rugby league.

Methods - The study design was a historical cohort design comparing winter and summer seasons in first team European rugby league, which recorded injuries received by players during match play. Each injury was classified according to site, type, player position, activity at the time of injury, and time off as a result of injury.

injury Results - The risk of when playing summer rugby league was higher than in winter rugby league (RR = 1.67 [95% confidence interval

1.18 to 2.17]). Both forwards (1.08 [0.28 to 1.88]) and backs (2.36 [2.03 to

2.69]) demonstrated an increased risk of injury for summer rugby over winter rugby league.

Conclusions - Summer rugby could have resulted in a shift of injury risk factors as exhibited by a change in injury- patterns. This may be due to playing conditions, but there were also some law changes. Also, changes in playing style, team tactics, player equipment, fitness preparations and the reduced preseason break may have had confounding effects on injury risk.

Key words: rugby league, injury, injury risk, summer rugby, cohort study 75

Introduction

Injury studies in rugby league football have previously reported high rates of injury (Gibbs, 1993a, Gissane et al., 1993, Stephenson et al., 1996,

Seward et al., 1993), higher than many other team sports (Seward et al.,

1993). The reason for this high injury rate is probably the high number of physical collisions in which players are involved during the course of a game (Gibbs, 1993a). With increasing professionalism in the sport, player injuries are an important issue, both in terms of team success and the livelihood of the players themselves (Seward et al., 1993).

The year of 1996 saw a bold move with European Rugby League playing in the spring and summer months, as opposed to its more traditional playing time of the autumn, winter and spring. This move meant playing games in higher temperatures (London temperature (mean[range]) - September to

April September April 9.5 °C [6 - 14], to 18.6 °C [13 - 22]) and on harder surfaces. There would however, be one third fewer competitive matches to be played, due to the restructuring of the league (12 teams) and the elimination of two cup competitions. Injury studies carried out in

Australia (Seward et al., 1993, Gibbs, 1993a, Estell et al., 1995), have consistently reported higher injury rates than English studies

(Stephenson et al., 1996, Gissane et al., 1993), and it has been surmised that this might be due to the game being played on harder surfaces

(Stephenson et al., 1996). Playing rugby league in the summer months 76 may also increase the likelihood of players suffering from thermal injuries and heat stroke, due to the combination of higher temperatures and relative humidities (Savdie et al., 1991, Meir et al., 1994b, Meir et al.,

1994a).

It is an unusual event for a sport to completely change the time of its playing calendar, and this move may result in an alteration in the risk of injury to players. Therefore, the purpose of the present study was to ascertain whether or not the movement of the playing season from the autumn and winter months to the spring and summer months would alter the risk of injury whilst playing professional rugby league, in the new

European Super League established in March 1996.

Methodology

During the initial European Super League season all injuries that were reported for the first team at one professional rugby league club were recorded. The injury data were compared with first team data from a previous study on the same club over a period of four seasons reported previously (Stephenson et al., 1996). An injury was defined as a physical impairment received during a competitive match which prevented a player being available for selection for the next competitive game (Gibbs, 1993b).

The games were 7(1.09) [Mean(SD)] days apart. The diagnosis and classification of injury were carried out by the club doctor and 77 physiotherapist. The information recorded about each injury has been reported previously (Gissane et al., 1993, Gissane et al., 1997a,

Stephenson et al., 1996).

The population at risk was defined as the players who were selected to play for the first team in a given match, and the defined time at risk for calculating injury rates was the duration of the games multiplied by the number of players (1.33 hrs. x 13 players) multiplied by the number of games played. The average number of games played during the winter seasons was 34.5 (596.5 player hours), with each player averaging 12.1 appearances per season, and during the summer season, 23 games (397.67 player hours) were played in the Super League of 1996, with each player averaging 8.3 appearances.

Statistical analyses consisted of the calculation of injury rate per 1000 hours of play as a standardised rate of exposure. To calculate the relative risk (RR) of injury between winter and summer rugby league the method using the incidence density ratio (IDR) for the two cohorts was used as described by Hennekens and Buring (1987).

no. of summer injuries/exposure time (hrs) RR (IDR) = no. of winter injuries/exposure time (hrs) 78

Confidence intervals (95%) were calculated using the method as described by McNeil (1996). Where the confidence interval did not contain the null value (RR = 1.0) the RR was taken as being significant at the P<0.05 level.

Results

There was no significant difference between the ages of the two cohorts of players investigated (winter 24.2(2.5), summer 25.7(3.9) yr. [mean(sd)], (t

= 0.76, df = 69, P=0.448). The injury rates for summer and winter rugby league for all players are displayed in Figure 1, in which it can be seen that summer rugby league had a higher injury rate than winter rugby league. Furthermore, the actual risk of injury in summer rugby league was 67% higher than in winter rugby league (RR = 1.67 [95% confidence interval 1.18 to 2.17]).

The injury rates for forwards and backs were analysed separately (Figure

1). From this it can be seen that the forwards' injury rate was slightly higher for summer rugby league, with an increase in the risk of injury for summer rugby of eight percent higher over winter rugby league (RR = 1.08

[0.28 to 1.88]). In comparison, the backs had a much larger increase in injury rates when playing rugby league in the summer, with a resulting higher risk of injury when playing rugby league in the summer. The RR of

2.36 (2.03 to 2.69) indicated that the risk of injury increased 136% from winter to summer rugby. 79

Figure 1. Comparison of injury rates for winter and summer rugby league (with 95% CI).

100

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In table 1 it can be seen that there were significantly increased risks of injury during summer rugby for haematomas, fractures and dislocations, joint injures and others (all P<0.05). Similarly, there were significantly increased risks of injury to the shoulder, arm and `others' sites of the body

(all P<0.05). While overall, there was significantly greater risk of injury to the lower body (P<0.05) (Table 2). There was an increased risk of being injured in the `others' activity category, which included such activities as running and catching high balls, in summer when compared to winter rugby (P<0.05), while the risk for tackling and being tackled did not alter significantly (Table 3).

Discussion

The major findings of the present study were the increased injury rates and the increased risk of injury associated with summer rugby league in both forward and back players, but the data suggest that the increased risk of injury was proportionately greater in backs than forwards.

The data for this study were collected prospectively as part of an ongoing investigation, which is a necessary process so that changing injury rates can be taken into account when designing playing conditions, training and fixtures (Seward et at, 1993). It allowed the comparison of the winter and summer cohorts, to assess changes in injury risk as a result of moving the playing calendar. It has been suggested that historical cohort study designs decrease the comparability of the data (Rudicel, 1988). 81

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However similar data, by the present investigators, were collected for both summer rugby league (current cohort) and winter rugby league (historical cohort), but only three players were present in both the winter and summer cohorts

Injury rates for the summer cohort increased although exposure time was decreased by one third, which may have been due to the playing conditions of warmer temperatures and harder playing surfaces. In support of this,

Australian studies (Gibbs, 1993a, Estell et al., 1995, Seward et al., 1993), where temperatures during the playing season are 18.2 [16 - 22] °C (mean

[range]), have often reported higher injury rates than British studies

(Stephenson et al., 1996, Gissane et al., 1993), even though fewer games were played (1994-95 English League, 30 games vs. 1994 Australia, 22 games). There is also the possibility that some injuries may have been carried over from the previous season. The last winter season prior to the beginning of Super League finished in the first week of February, with the

Super League beginning at the end of March. This was a 51 day period, much shorter than the three and half month time period between seasons previously, which would not allow players the recuperation period that they had previously enjoyed. Furthermore, the move to full time professionalism could have served to predispose players to injury, since full time training, with increased training would allow players much less time for recovery (Arhheim, 1989). 85

Forwards have been reported to receive more injuries than backs (Gibbs,

1993a, Gissane et al., 1993, Norton and Wilson, 1995, Seward et al., 1993), as a result of being involved in more physical contact (Stephenson et al.,

1996, Gissane et al., 1997b). It is therefore unusual to find a higher rate of injury amongst backs, and the subsequently very high relative risk comparing summer and winter rugby. Alexander (1980) found more injuries to backs when the style of play changed to move the ball wider sooner, giving the backs a greater role in the game. Previous research has shown that the ball carrier is the person who is most likely to receive an injury (Gissane et al., 1997b), which would increase the risk of injury to back players by involving them in more physical collisions, and at the same time reduce the amount of physical contact experienced by forwards.

Another possible reason for backs having a higher injury rate than forwards could be the introduction of the zero tackle law, which was not in place when the winter rugby data was collected. The law (2.3.1) states

"When a player gathers the ball from an opposition kick in general play and does not subsequently pass or kick the ball himself, the initial tackle will be counted as a zero tackle" (RFL, 1996). Which effectively gives a team seven `play the balls' or possessions. When the ball is kicked, it is often kicked deep in the field of play and is gathered by a back player, who runs to gain ground, and since the ball carrier is at the highest risk of injury in a tackle (Gissane et al., 1993, Stephenson et al., 1996), these law 86

changes and playing styles could increase the risk of injury in back players.

The findings of the present study also demonstrated that there was an

alteration in the risk of injury when injuries were examined by both type

and site of the body. Injury investigations in other sports have reported

alterations in injury patterns when changing playing surface, in which

hockey (Jamison and Lee, 1989) and American Football (Skovron et al.,

1990) have reported increased injury rates on astroturf. In American

Football the risk of knee (RR = 1.18) and ankle (RR = 1.39) injuries has

also been shown to increase as a result of the change of playing surface

(Powell and Schootman, 1992). The changing relative risks in specific

injuries seen in the present study may be due to similar mechanisms seen

in hockey and American Football. Specifically, Fuller (Fuller, 1990)

claimed that the hard surface of artificial grass allows players to achieve

higher speed, but there is a decreased shock absorption capacity, and the

same situation could be suggested about summer rugby league. The site

category `others' (RR=12.0) contained a number of foot injuries which

previously were extremely rare (Jennings, 1990), but their onset could be

associated with turning and being tackled on the harder surface.

The first season of Super League has exhibited a change in injury

patterns, and could have resulted in a shift of injury risk factors. This

cannot be exclusively explained by the playing conditions, as there are a 87 number of other factors that need to be considered as athletic injuries are likely multifactorial in aetiology, making the identification of simple risk factors difficult (Meeuwisse, 1994). Between the end of data collection for the first cohort and the beginning of data collection for the second cohort, law changes were instituted which could serve to alter the risk of injury.

The shorter preseason break and the increased training volume might influence the factors that predispose a player to injury. Additionally, playing style, team tactics and player equipment may also have altered.

Any of these factors could have a confounding effect on the incidence of injury and further investigation is needed to determine their influence.

Epidemiological investigations are needed to determine the extent of injury rates as an initial investigative step in epidemiology. However, rugby league has taken the very unusual step of moving its playing season, with the result that descriptive investigations need to continue to document the accompanying injury risk. Preliminary findings suggest that it has increased, but surveillance needs to continue, as sport is a dynamic, changeable entity. The 1997 season will see further changes, which will affect the game, the players and almost certainly the risk of injury associated with such exposure. 88

Body mass loss as an indicator of dehydration in summer rugby league

Abstract

Objective - To determine the body mass losses experienced by summer rugby league players.

Methods - Players at one club who took part in 16 summer games had body mass determined before and after playing.

Results - There was a low overall correlation between percentage body mass loss and ambient temperature (r = 0.29, p=0.02), but as playing temperature increased, 13% of players experienced a 2-3% body mass loss in 14 of 16 games played in excess of 19°C ambient temperature.

Conclusions - With the seasonal change new physiological challenges have been placed on players, some of who are demonstrating body mass losses which can affect on field performance and thermoregulatory mechanisms. 89

Introduction

During exercise the metabolic heat produced by the body can increase by

15 to 20 times above that produced at resting levels (Mitchell, 1994), and taking part in activity in hot conditions can cause the body temperature to

rise even more quickly (Brewer, 1997). Moving the English professional

rugby league season from the period September through to April, to March

until September allowed it to be played in parallel to the Australian rugby

league season. However, for players in the European Super League it

meant that the game was to be played in much higher temperatures than

previously, and for a certain portion of the season (June, July and August)

the temperature would be higher than in Sydney, Australia (Pearce and

Smith, 1993). The movement of the season places a responsibility on the

game's administrators, as well as the players, coaches, and sports

medicine teams at club level to define and implement strategies which will

help players to cope with these new playing conditions. The Rugby League

Medical Association (RLMA) expressed concern for the potential problems

associated with heat stress at its 1996 meeting (Stephenson et al., 1996),

and the Rugby Football League has responded by producing guidelines for

players and coaches to avoid dehydration (Brewer, 1997).

A near-fatal accident was reported in Australian Rugby League (ARL)

where a player who suffered heat stroke whilst playing (ambient

temperature 24.1 °C, relative humidity 73%), spent 10 days in a coma and 90 suffered Disseminated Intravascular Coagulation (DIC), along with renal

and heptatic disturbances (Savdie et al., 1991). Strategies to prevent heat

stress are important in order to maintain optimal cardiovascular function

and thermoregulation (Gonzalez-Alsonso et al., 1992), as well as prevent

dehydration by as little as three percent of body mass which has a

detrimental effect on performance (Brack and Ball, 1998), and has been

described as medically dangerous (Mitchell, 1994). At dehydration levels

slightly below this level (2-3%) the body's ability to sweat is decreased, and with it the capability of the thermoregulatory system to maintain core temperature (Sawka et al., 1985). It has also been reported that

dehydration resulting in body mass decreases as low as 2% can noticeably

impair performance by compromising the circulatory and

thermoregulatory functions (Saltin, 1964). The aim of the present

investigation was to determine the extent to which players' body mass

changes may be used as an indicator of dehydration state whilst playing

summer rugby league.

Methodology

The subjects for this study were the members of the playing squad at one

Super League Club, whose physical characteristics are displayed in table

1. 91

Table 1. Physical characteristics of players [mean±SD].

Age (yrs) Mass (kg) Height (cm) All players (n=28) 24.7±4.0 90.9±11.8 181.8±7.2 Backs (n=15) 25.1±4.3 84.6±7.5 178.4±2.1 Forwards (n=13) 24.3±3.8 98.1±12.1 185.4±7.7

Procedure

The members of the squad who were selected for a given game took part in the assessment procedure on that occasion. Players' body mass was determined in the standard position before starting each game in underwear only, after they were towel dried. Each measurement was recorded to the nearest 100 g using a calibrated Seca 770 model scales. A similar procedure was completed on the players' completion of the game with minimal time delay. During the game the mean ambient temperature

(°C) and mean relative humidity (%) was recorded using a Casella polymeter (Model M 112050: Reliability; humidity E5% between 30% and

90% RH, Temperature f1%).

For each game played, each player that played was treated as an independent event making a total of 268 player appearances. Therefore, all data were collected with body mass being determined as the difference between pre-game mass and post-game mass. Players were allowed to drink water ad libitum after pre game body mass determination, during the game and at half time. For the purposes of analysis, only players who 92 completed each full game of 80 minutes were included in the analysis

(n--120).

The statistical analysis consisted of Pearson's correlation to determine associations between variables, and independent t tests to determine differences between forwards and backs. All tests were carried out using

SPSS for Windows 6.1.2.

Results

Data were recorded in a total of 16 games, and the overall mean temperature was 22.95.3 °C, and the mean relative humidity 73-113.6 %.

During these games a total of 36 forwards and 84 backs completed whole

game(s). The mean body mass loss for all the players was 1.1 (95% CI

0.98 to 1.22) kg, in which the forwards and backs had mean body mass

losses of 1.48 (1.25 to 1.7) kg, and 0.94 (0.82 to 1.06) kg respectively (mean

difference = 0.54 (0.3 to 0.78) kg, t=4.48, df = 118 P=0.001). Overall

mean loss for all players was 1.22 (1.1 to 1.34) % of body mass, in which

forwards and backs had mean losses of 1.51 (1.29 to 1.74) % and 1.09 (0.95

to 1.24) % respectively (mean difference = 0.42 (0.16 to 0.69) %, t=3.18, df

= 120 P=0.002).

The overall relationship between the playing temperature and percentage

body mass loss revealed a low correlation (r = 0.29, p=0.02). There were

non significant negative correlations between relative humidity and 93 percentage mass loss (r = -0.28, p=0.08) and relative humidity and temperature (r =-0.15, p=0.59). From table two it can be observed that as the ambient playing temperature increased the number and percentage of players reaching body mass loss relative to the level of dehydration where performance could become impaired increased. Of the players who experienced 2-3% dehydration, one experienced it four times, three other players twice, with four players experiencing a single incident.

Discussion

The major finding of this study was that an increase in ambient temperature resulted in a greater proportion of players reaching levels of body mass decrease relative to a state of dehydration which could

compromise thermoregulatory control system (Sawka et al., 1985).

In this study there was no attempt to control for specific variables that

might influence the test results, such as water intake and exposure to

direct sunlight (Mitchell, 1994). The main aim was to describe the body

mass losses during the course of playing typical rugby league games in the

summer. Although none of the players reached the 3% loss in body mass

that has been shown to be medically dangerous 94

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(Mitchell, 1994), 13 % (16/120) of players lost between 2-3% body mass in

14 of the 16 games played in excess of 19°C ambient temperature.

Thermoregulation mechanisms can be compromised at such levels of body mass change (Mitchell, 1994, Sawka et al., 1985), ] and the associated level of dehydration may adversely affect physical performance by reducing endurance times (Craig and Cummings, 1966).

Previous studies in other sports have monitored fluid intake of players during match play (Kirkendall, 1993, Goodman et at, 1985). They have also involved far fewer subjects than the present study. There are also practical difficulties with measuring fluid intake during matched play.

Water in drinking bottles is used for other purposes such as, rinsing out mouth, washing gum shields, and cooling heads. All of which can lead to errors in estimation.

A number of measures are in place which are designed to assist players in minimising dehydration. Shirts are now made of much lighter material than previously and weigh about 40% less than before (376.8 vs. 218 g)

(Meir et al., 1994a). The Rugby Football League has also issued some guidelines for players and coaches about training and playing in hot environments (Brewer, 1997). These guidelines advise players that they

"need to hydrate before a game and rehydrate properly after a game."

They also warn that those players with higher percentage body fat are most at risk of thermal stress, and since it has been reported that 96 forwards carry more body fat than backs (O'Connor, 1996, Meir, 1993), this may partly explain why forwards are noted to have a greater percentage body mass loss than backs.

The player observed in 1990 who suffered from DIC was febrile, which served to decrease the amount of heat which could be dissipated before overheating (Savdie et al., 1991). The Rugby League have warned players who have been ill or are suffering from a virus that they are more prone to heat stress, and have advised them to seek advice from the club medical personnel before playing or training. Similarly, the RFL warn about excessive use of taping and protective equipment, which can inhibit the thermoregulatory process (Brewer, 1997). The player who suffered from

DIC, had been wearing his kit and a neoprene thigh guard, in total 70% of his body surface area was covered (Savdie et al., 1991). There is also the practice of support staff entering the field of play at stoppages giving the players water, something not enjoyed in other sports (Cullen, 1998), which serves to aid the rehydration process.

In this study the variable examined was body mass loss as a proxy measure for dehydration. This should be considered as a conservative measure of fluid loss as neither fluid intake or urine excretion were measured. There are also other factors beyond those examined in the present study which could exert an influence on body mass loss during 97 games. For example, previous research has reported that percentage body fat can influence the efficiency of thermoregulation (Meir, 1992).

The results of this study demonstrated that players appear to be experiencing new physiological challenges from the heat encountered whilst playing summer rugby league. Although for the majority of cases seen in the present study this did not represent a problem, 13% of players experienced 2-3% body mass loss during a game, which can effect both on field performance and thermoregulatory mechanisms (Sawka et al., 1985,

Saltin, 1964). Research from other sports and Australian rugby league can provide direction for strategies to help overcome the problem. Devising and adopting strategies such as these was formerly the domain of touring teams. Now, however, it is required in the European playing season due to the switch to summer competition. 98

Physical collisions in professional super league rugby, the demands on different player positions

Abstract

Objective - To determine the total number and nature of physical collisions

experienced by players in differing positions in professional rugby league.

Methods - Video recordings of all the regular season games (N=22) played

by one professional super league rugby club were examined. Physical

collisions were classified into tackles, incomplete tackles, "tackled in

possession", "broken tackles" and passes out of the tackle.

Results - Forwards were involved in significantly more collisions (55) than

backs (29) during the course of each game (z=2.73, P <0.0001). Eight

player positions (forwards (n=6) and two half backs (scrum half and stand

off)) were involved in significantly more collisions while defending as

compared to attacking (all P<0.005). The differences for all back three

quarter positions and the full back were not significant.

Conclusions - Players, both backs and forwards experienced more physical

collisions than previously reported, which may be linked to operational

definitions, rule changes and the advent of summer rugby league. Players

were involved in more physical collisions whilst defending, since over two

thirds of tackles involved more than one player tackling the ball carrier.

Key words: professional rugby league, physical collisions, forwards, backs,

tackle 99

Introduction

Rugby League is a game of physical collisions (Kear et al., 1996), in which the tackle has a greater prominence than in rugby union (Gissane et al.,

1993). The high number of physical collisions encountered by players has been suggested as a possible reason why they experience such high injury rates (Gibbs, 1993a). It has been further suggested that the collisions in which players are involved are important from both a physiological as well as an injury prevention perspective (Kear et al., 1996, O'Hare, 1995). A survey of international players found that the two aspects of the game that players found most tiring were being tackled, and tackling other players (Kear et al., 1996). Many coaches acknowledge that it is important to control these aspects of the game since they have a major influence on the outcome of a match (Larder, 1988, Kear et al., 1996). Within team sports players have different demands placed upon them according to the requirements of their position (O'Connor, 1996), and for optimal performance it is necessary to identify the specific characteristics of successful play relative to playing position (O'Connor, 1995a).

To this end, previous research in rugby league has investigated the movement patterns of players during matches (heir et al., 1993), and the differing injury rates of forwards and backs (Gissane et al., 1997a).

However, while other work reported the number of physical collisions in which players are involved during the course of a game, the studies were limited and were often based on data reported from small numbers of 100 matches (Larder, 1992, Robinson, 1996). Furthermore, when examining the physical collisions from an injury prevention point of view, it may be important to take all physical contacts into account, which might include for example, situations where the tackle was not necessarily successful, because it still involved physical contact.

The purpose of the present study was to determine the number and type of physical collisions that rugby league players experience during typical match play. In addition the study determined how total physical collisions were distributed between attack (while in possession of the ball) and defence, and among playing positions.

Methodology

Players representing one professional rugby league comprised subjects for the present study (N=35, forwards n= 15, backs n= 20). In order to assess the number and type of physical collisions in which players were involved while playing, video recordings of all 22 regular season games played during the 1996 Super League season were analysed. This represents a total of 29.3 hours of match-play or 380.4 player hours (13 players x 1.33 hrs x 22 games). The video tapes used were master copies of recordings produced by two T. V. media broadcasting companies (British Sky

Broadcasting, Isleworth and Micron Video, Wigan), and permission to use the material was granted by the Rugby Football League. 101

Each video was a standard VHS (25 frames-sec-1) and was analysed by the principal investigator. Each physical collision that took place was classified into one of the following categories:

Defence (defending collisions)

1. Tackles - where the defending player(s) halted the progress of the ball carrier, and as a result the ball carrier had to play the ball.

2. Incomplete tackles - where the defending player(s) made contact with the ball carrier, but failed to prevent forward progress, or were unable to stop the passing of the ball.

Attack (attacking collisions)

3. "Tackled in possession" - where the ball carrier was tackled whilst in possession of the ball, forward progress was halted and the ball carrier had to play the ball.

4. "Broken tackles" - where the ball carrier was able to break through the tackle and continue forward progress.

5. Passes out of the tackle - where the ball carrier was tackled but was able to pass the ball.

Following this analysis it was possible to calculate each player's total defensive involvement (the sum of tackles and incomplete tackles), total attacking involvement (the sum of "tackled in possession", "broken tackles" and passes out of the tackle), and total physical involvement (in defence and attack) in each game analysed.

Statistical analysis

In order to determine the reliability of the physical collision analysis, three videos were analysed twice (each one week apart) by the principal 102 author and the 95% limits of agreement were calculated using previously recommended methods (Bland and Altman, 1986, Nevill and Atkinson,

1997). Because the differences between readings did not vary in a systematic way across the all values, it was necessary to log transform the original data (Bland and Altman, 1986). Descriptive, statistics (mean and

95% CI) for each physical collision category were computed for each playing position. To determine differences in the number and type of physical collision between forwards and backs, and between attacking involvement and defensive involvement, further analysis was undertaken using a proportion test (Altman, 1991).

Results

Reliability of video tape analyses

The reliability of the physical collision analysis demonstrated that the

95% limits of agreement calculated were 0.92 to 1.08, which indicated that the retest analyses were between eight percent above and below the original readings.

Collision analysis

The mean number of physical collisions for attack, defence and total collisions experienced by player positions is shown in table 1. All players were involved in both defensive collisions (while attempting to tackle the ball carrier) and attacking collisions (being tackled when carrying the 103 ball), which resulted in an average of 41 physical collisions per player per game (27 in defence and 14 in attack). Forward players were involved in an average of 55 physical collisions during a game (39 defence, 16 attack), which was significantly more than the backs who were involved in an average of 29 physical collisions (16 defence, 13 attack) [z = 2.73, p<0.0032]. All of the forwards, plus the serum half and the stand off were involved in a significantly greater number of physical collisions when defending (all p< 0.05) as compared to attacking. Only three player positions, the two wings and the full back, were involved in more attacking than defensive physical collisions but the differences were not significant (z = 1.66, P> 0.09).

The mean number of defensive physical collisions (complete and incomplete tackles) performed by player positions is presented in figure 1.

There were significantly more complete than incomplete tackles (290 vs.

59, z= 12.3, P <0.00006). Overall, only 17% (59/349) of the defensive physical collisions carried out by the players in this study allowed an opponent to break through the tackle or off load the ball. Backs were involved in a significantly greater number of incomplete tackles than forwards (22% vs. 15%, z=6.14, P <0.00006) 104

Table 1. Physical collisions experienced by player positions during match- play.

Defence Attack Total collisions Position Mean 95% CI Mean 95% CI Mean 95% CI Full back 10 8-13 18 16 - 20 28 26-31 Right wing 10 7-12 13 11-15 23 19 - 25 Right centre 18 15-22 12 10 - 14 30 27 - 34 Left Centre 18 15 - 20 14 13 - 15 32 29 - 34 Left Wing 7 5-9 11 10 - 13 18 16 - 20 Stand off 29** 26 - 32 13 12 - 15 42 38 - 45 Scrum half 23** 19 - 27 10 8-11 33 28 - 36 Openside prop 44** 39 - 49 23 20 - 26 67 60 - 74 Hooker 43** 39 - 47 6 4-8 49 45 - 53 Blindside prop 37** 31- 41 20 17 - 24 57 48 - 66 Openside 2nd row 45** 40 - 50 19 15 - 23 64 56 - 72 Blindside 2nd row 39** 36 - 43 16 14 - 17 55 51-59 Loose forward 27** 24 - 30 11 11-13 38 35 - 43

Backs 16 15-18 13 12-14 29 28-31 Forwards 39** 37 - 41 16 15 - 17 55* 52 - 58 All players 27 25-29 14 13-15 41 39-43

* significantly different from backs ** significantly different from attack

The mean number of attacking physical collisions (`tackled in possession",

"broken tackles" and passes out of the tackle) is presented in figure 2.

There were significantly more "tackled in possession", than passes out of the tackle and "broken tackles" (153 vs. 34, z=8.6, P<0.00006) Overall, the ball carrying players under investigation were able to either "bust" a tackle or off load the ball in 18% (34/187) of the attacking physical collisions. There was no significant difference between the forward and 105 back ball players in the proportion of passes out of the tackle and "broken tackles" (19% vs. 18%, z=0.74, P =0.4593)

Discussion

The present study indicated that rugby league players were involved in an average of 41 (95% CI 39 to 43) physical collisions per game, which is above the upper limit of a previous estimate of 20-40 per game (Larder,

1992). This may be due in part to the decision in the present study to include incomplete tackles in the observations which were not reported in previous estimates. If incomplete tackles were removed, the figure would be reduced to an average 37 physical collisions per game (forwards 50 per game, backs 26 per game). However this would still suggest that the current figures were higher than previously reported (Larder, 1992). 106

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Nevertheless, incomplete tackles accounted for 17% of all physical collisions experienced by players, and while coaches would wish to reduce the overall number to improve team defence performance, the occurrence is an important consideration from both a physical conditioning, and injury prevention point of view, as well as influencing the outcome of the game.

A further possible explanation for the present values being higher than previously reported could be the 1994 rule change that required players on the side not in possession to retire 10 metres after the tackle (Brewer and

Davis, 1995), compared with the original requirement of five metres. It has been suggested that this may lead to an increase in the distances covered and, the total amount of high intensity physical activity, of which tackles are part (Brewer and Davis, 1995). Higher intensity activity may also serve to increase the momentum of the players at the point of contact.

In addition, there has also been the introduction of the zero tackle law which states "When a player gathers the ball fron, an opposition kick in general play and does not subsequently pass or kick the ball himself, the initial tackle will be counted as a zero tackle" (RFL, 1996). This effectively gives a team seven `plays of the ball' or possessions, compared with the previous six, which may potentiate additional physical collisions.

Forwards were involved in a greater number of collisions than backs (55 vs. 29) which is in agreement with previously reported work (Robinson, 109

1996, Larder, 1992), although again the figures in the present study are higher than previously reported. One study reported that at club level forwards were involved in 32 physical collisions per game and backs 19 per game (Robinson, 1996), while at international level forwards were involved in 36 and backs 19 collisions (Larder, 1992). However, the games analysed in both previous studies took place before the 1994 rule change, the zero tackle law, and prior to the advent of summer rugby.

Several authors have suggested that the higher numbers of injuries received by forwards during match play (139.4 vs. 92.7 injuries per 1000 player hours) (Gissane et al., 1997a), may be because of the higher number of physical contacts (Gissane et al., 1997a, Gissane et al., 1993, Gibbs,

1993b, Norton and Wilson, 1995). However, if as a result of recent changes in the laws of the game both forwards and backs are experiencing more physical collisions, then the risk of injury should rise proportionately for all players.

It was also interesting to note that eight of the 13 player positions were involved in significantly more physical collisions in defence than attack. A previous study reported that props and hookers spent a greater amount of the time (4.5%) performing defensive tackling than backs (1.8%), and that forwards spent 2.7% of the time taking the ball into the tackle, compared with 1.8% for backs (Meir et al., 1993). This may account for the greater number of physical collisions by forwards made while defending. It should 110 be noted that more than one player can be involved in the tackle, but only one player is carrying the ball whilst being tackled. Previous research on the number and type of contact experienced by individual players found that two thirds of tackles involved more than one defender tackling the ball carrier (Clarke, 1993). However, unlike the present study, previous work did not seek to examine how many players were involved in a given tackling situation on a ball carrier. If more than one player is involved in the tackle this could potentially increase the risk of injury to a player, as well as the number of physical collisions in which that player is involved.

The present findings have implications for both physical conditioning and injury prevention in rugby league. Coaches have recently suggested that the high injury rates reported in the game (Gibbs, 1993a, Gissane et al.,

1993, Gissane et al., 1997a) are due to the ferocity of the physical collision situation (Jones, 1998). However, coaches have also been also been careful to emphasise the importance of safety and self protection when either tackling or being tackled (Corcoran, 1979). The findings of the present study emphasise the different incidence of physical collisions experienced by different player positions. This could serve as an indication to alter the training strategies of different positions and/or playing units, by either increasing or decreasing the number of physical collisions in training in proportion to those experienced in the game. Rugby League has shown a recent trend towards less specialisation between playing positions (Larder,

1992), and there is the suggestion that fitness training for professional 111 rugby league is uniform for all positions (O'Connor, 1995a). However, it has also been argued that training procedures should reflect the breakdown of match play activities, and that these should be position specific (Meir et al., 1993). Similarly, injury prevention strategies could place a differing emphasis on players who are going to be involved in a greater number of physical collisions than others (RFL, 1996).

Conclusion

The present study has provided data on the number and type of physical collisions experienced by players during professional rugby league play. It

should be recognised that playing style might also exert an influence on

the number and types of physical collisions experienced. However,

empirical data as to the specific nature of the physical collisions that

players incur during a game is important. Training needs to conform to

the principle of specificity, and the sheer volume of physical collisions

encountered by some players may influence their injury risk, both from

the physical impact and the possibility of cumulative fatigue. The

numbers of physical collisions documented in the present study are higher

than previously reported, which could be due to the inclusion of

incomplete tackles. However it could be also be due to a change in the

nature of play. The 1994 rule changes moved the defensive line back

further by 5 metres, and the advent of summer rugby league probably

resulted in firmer playing surfaces which allow faster running speeds and

increased momentum at the point of contact in the tackle. Differences in 112 the running speeds of players have been reported to be an important risk factor in rugby union tackles (Garraway et al., 1999). A further study has examined the numbers of players involved in specific tackles, in an

attempt to determine if this has an influence on the risk of injury to the ball carrier and/or the tackler. In addition the follow up study has

attempted to determine if the number of physical collisions experienced by players has a direct influence on the incidence of injury in playing units

and positions (Gissane et al., 2001a).

Acknowledgement

The authors would like to thank Glen Workman and Tony Currie for their

assistance with this investigation. 113

Physical collisions and injury rates in professional super league rugby

Abstract

Objective - To determine if there was a relationship between exposure to physical collisions and injury rates in professional super league rugby football.

Methods - All injuries received during one season's match play were recorded for all games played by one professional super league rugby club.

Each injury was classified according to player position and activity at the time of injury. Physical collisions were determined from video and

classified into tackles, incomplete tackles, "tackled in possession", "broken

tackle" and passes out of the tackle.

Results - Forwards were involved in significantly more physical collisions

per game than backs (55 vs. 29, P=0.003). Overall backs had a

significantly higher injury rate per 10,000 physical collisions (16.3 vs. 7.2,

P=0.0015), but there were no significant differences between the two

playing units-for injuries received whilst attacking or defending.

Conclusions - This study demonstrated that backs have higher

standardised injury rates (per 10,000 collisions) than forwards, in spite of

being involved in fewer physical collisions per game played. The observed

differences could be due to the nature of specific physical collisions

experienced by the respective playing units or intrinsic injury risk factors

among the players involved.

Key words: Rugby League, injury rates, physical collisions 114

Introduction

Injury rates in rugby league football have been reported to be higher than those experienced in other contact team sports (Gissane et al., 1993,

Seward et al., 1993). It has also been reported that the injury rates experienced by players have increased as a result of the recent move to a summer competition (Gissane et al., 1997b, Gissane et al., 1997a,

Hodgson-Phillips et al., 1998). In addition many authors have reported that forward players receive far more injuries that back players (Lythe and Norton, 1992, Norton and Wilson, 1995, Gissane et al., 1993, Seward et al., 1993, Gibbs, 1993a, Gissane et al., 1997a, Gissane et al., 1998). One reason that is often put forward to explain this finding is that forwards are involved in much more physical contact than backs (Gibbs, 1993a,

Gissane et al., 1997b).

Forwards may be involved in more physical contact because of their role in the game, although it has been suggested that there has been a recent trend towards much less specialisation between positions (Larder, 1992), which may have an influence on the contact rates experienced by forwards

It has also been suggested that when the numbers of player positions involved are taken into account, forwards receive relatively more injuries and backs relatively fewer, than might be expected (Gibbs, 1993a).

Front row forwards spend more of their time taking the ball into the tackle than backs (2.7% vs. 1.8%), and over twice as much time tackling 115

(4.5% vs. 1.8%) (Meir et al., 1993). The amount of time spent in these

activities is an important consideration since research has shown that between 67% and 77% of injuries take place in the tackle (Norton and

Wilson, 1995, Gissane et al., 1997b, Gissane et al., 1997a). It has further been reported that both forwards and backs receive significantly more

injuries while being tackled than when tackling, and that forwards receive

significantly more injuries than backs when either tackling or being

tackled (Gissane et al., 1997a). If injuries are to be reduced, it is necessary

to establish if there is a relationship between the exposure risk factors,

such as the number and type of physical collisions, and the incidence of

injury in rugby league football.

The purpose of the present investigation was to examine the relationship

between the rate of injury in rugby league football, and the number and

type of physical collisions in games in which players are involved during

the course of a full playing season by one professional super league rugby

club.

Methods

All injuries that were reported for the first team of one professional super

league rugby club were recorded over one season. An injury was defined as

a physical impairment received during a competitive match which

prevented a player being available for selection for the next competitive

game (Gibbs, 1993a). The position of the player; the site of the injury; the 116 nature of injury; the activity at the time of injury and the time off as a result of injury were recorded for each game played over the full season.

The details of each category have been described previously (Gissane et al., 1998, Gissane et al., 1997a, Gissane et al., 1993).

The population at risk was defined as the players who were selected to play for the first team in a given match, and the defined time at risk for calculating injury rates was the duration of the games multiplied by the number of players (1.33 hrs. x 13 players) multiplied by the number of games played. A total of 23 games (22 regular season plus one play off game) were played during one season (397.7 player hours).

In order to assess the number and type of collisions that players were involved in while playing, video recordings of 22 regular season games played during the 1996 Super League season were analysed (29.3 hours of

match-play, 380.4 player hours). The video tapes used for analysis were

master copies of recordings produced by two TV media broadcasting

companies (British Sky Broadcasting, Isleworth and Micron Video,

Wigan), and permission to use the material was granted through the

Rugby Football League. The categorisation of physical collisions was

carried out as outlined previously (Gissane et al., 2001c).

Following the analysis of physical collision categories, it was possible to

calculate the following; 1) each player's total defensive involvement (the 117

sum of tackles and incomplete tackles), 2) total attacking involvement (the

sum of "tackled in possession", "broken tackle" and passes out of the tackle), 3) total physical involvement (defensive plus attack) in each game

analysed, and 4) the differences in physical collisions incurred by backs

and forwards.

Statistical analyses consisted of the calculation of injury rate per 10,000

physical collisions as standardised rates of exposure, and descriptive

statistics for physical collisions (mean and 95% CI). In order to compare

differences between the proportions of physical collisions a single

proportion test was used (Altman, 1991), while a test for differences

between injury rates used the method of Clarke (Clarke, 1994), and the

relative risk (RR and 95% CI) was computed. In order to analyse the

differences between forwards and backs in the number of games missed by

injured players, the Mann Whitney U and Kruskal Wallis tests were

employed since the data were not normally distributed

Results

The descriptive statistics of the number of physical collisions incurred by

forwards and backs are shown in table 1, which indicates that forwards

were involved in significantly more physical collisions during defensive

tackling than backs (z = 2.73, P=0.0032). Furthermore, forwards were

involved in a significantly greater total number of physical collisions (z = 118

2.97 P=0.0015). This was largely as a result of the increased defensive tackling demands by forwards, since there was no significant difference in the number of attacking collisions incurred by forwards and backs.

The number of injuries received, sub-divided by activity at the time of injury and the standardised injury rates per 10,000 physical collisions

among forwards and backs are shown in table 2. There were no significant

differences between forwards and backs in the total number of injuries received (7 vs. 13, z=1.12, P=0.26). However, examination of the

standardised injury rates revealed that backs had a higher total

standardised injury rate than forwards (z = 2.21, P= 0.027). When injuries

that were received in the tackle (either to the tackler or the player being

tackled) were examined, there was no significant difference in injury rate

between forwards and backs. The forward playing unit demonstrated

higher injury rates for physical collisions when attacking (RR = 3.68

[95%CI 0.62 22.1]), back - compared with the playing unit (RR 1.01 [0.27 -

3.77]). It was also noted that backs had higher injury rates than forwards

in both attack and defence, but these differences were not significant.

Overall, the tackle situation accounted for a majority (14/20) of all injuries

observed.

In the act of tackling an opponent, the upper body incurred the greatest

proportion of injuries (5/7, z= 0.76, P= 0.44), in which there were two arm

injuries (both forwards) and three shoulder injuries (all to backs). The only 119

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Injuries that were received by players and categorised as `other' which did not occur in the tackle included three joint sprains to backs, that were received whilst running and changing direction quickly i. e. not resulting from physical collisions, as well as two incidences of foul play which were

also included in this category.

Overall backs missed more games in total as a result of injury incurred

than forwards (45 vs. 23). However, forwards had higher median scores for

games missed when their injuries were incurred in tackling (five games

vs. two games [Median scores]), and in being tackled (four games vs. two

games), although neither of these differences were significant (P>0.05)

Discussion

The present study revealed a similar findings to other work (Norton and

Wilson, 1995, Gissane et al., 1997a), in that the majority (14/20) of injuries

occurred in the tackle. Half of these (7/14) were to the person being

tackled, which is lower than reported previously (Lythe and Norton, 1992). 122

However, while previous investigations have suggested that injury was probably related to the number of physical collisions that players were involved in during a game (Norton and Wilson, 1995, Gissane et al.,

1997a), the unique finding of the present study was that when the injury rate was standardised, backs had a significantly higher overall injury rate per 10,000 collisions than forwards, suggesting that positional play has an influence on injury rate. However, when the injuries received in the tackle were examined separately, the difference in injury rates between forwards and backs was removed. Nevertheless, in the present study backs experienced higher rates of injury than forwards (per 10,000 physical collisions), whilst being involved in significantly less physical collisions.

This suggests that backs are more likely to be injured outside of the tackle situation.

The collision in rugby league is considered to be a major risk factor

(Norton and Wilson, 1995, Gissane et al., 1997a). It has been argued that extrinsic risk factors are independent of the injured person, and are related to the types of activity during the incident of injury (Taimela et al.,

1990), and the manner in which sport is practised (Lysens et al., 1991).

These observations may be true of the physical collisions experienced in

rugby league, especially when there is usually more than one person

involved in the physical collision such as the tackle (Clarke, 1993).

Therefore, self protection and safety of both the tackler and the person 123 being tackled are important techniques that coaches teach to players

(Gissane et al., 1998, Corcoran, 1979).

Since the tackle is the activity in rugby league in which so many injuries take place, some authors have suggested that injury prevention strategies

directly aimed at making the tackle safer, should be considered (Lythe and

Norton, 1992). Recent developments have seen certain types of physical contact outlawed (e. g. the spear tackle) and the banning of contact with a player who has jumped to catch a high ball (RFL, 1996). However due to the markedly different number of physical collisions in which players are involved, it may be necessary to develop specific injury prevention programmes for the different positional playing units (Lythe and Norton,

1992).

It is also necessary to consider some intrinsic risk factors which may influence injury rates in rugby league players. Several authors have

reported that forward players have a greater body mass, with larger

overall fat-free mass but possess more body fat than backs (O'Connor,

1996, Brewer and Davis, 1995, Meir, 1993). While it has been suggested

that increased body fat may have a protective effect in the collision (Meir,

1993), the larger fat-free mass of forwards would result in these players being relatively stronger, more difficult to tackle and thus halt progress.

Furthermore both upper and lower body strength has been reported to be

significantly higher in forwards than backs; upper body strength is 124 important for making tackles, while leg strength is important for breaking them (O'Connor, 1996). However, increased body fat could also be a

disadvantage in terms of energy expenditure and workload (O'Connor,

1996, Meir, 1993), especially with the game now being played in higher temperatures. Since backs possess lower levels of upper and lower body

strength than forwards, this could make them more susceptible to injury

in the physical collision. Furthermore backs may also be more predisposed to non-collision injury as a result of their style of play which involves more

turning and changing direction during running than forward play.

Not withstanding the injury associated with physical contact, almost one

third (6/20) of injuries in the present study did not take place during

physical contact. Four of these injuries were to backs (three ligament

sprains and a muscle strain) and two to forwards (one joint sprain and one

dislocation). Nevertheless such injuries will undoubtedly have specific

causes, for example backs may be more susceptible to ligament sprains

and muscle strains because they are involved in more changes of direction

during running. In some instances video evidence suggested a likely

possible cause, for example a back player who injured a hamstring whilst

sprinting with the ball.

Recently, concern has been expressed about the ferocity of tackles and the

role this might play in the incidence of injury (Jones, 1998). It has already

been stated that the defending team usually has more than one player 125 tackling the ball carrier (Clarke, 1993), and the implications of this need to be investigated in future research. The present study demonstrated that backs have slightly higher standardised injury rates than forwards, in spite of being involved in fewer physical collisions. The difficulty appears to be deciding why a player gets injured in a particular collision situation (MacLeod, 1993). If it takes more tacklers to halt the progress of a particular player, is that player at greater risk of being injured? Or, could it be the specific types of tackle that backs receive that results in them receiving more injuries per 10,000 physical collisions? Alternatively, the intrinsic injury risk factors such as strength, body composition and flexibility which influence injury incidence, need to be considered. Another important consideration is the momentum of the players at the point of contact. Momentum results from a combination of strength, speed, body mass and distance covered which can serve to increase the force of a given collision and thereby increase the risk of injury. In rugby union it has been suggested that the momentum of the players is an important factor in determining whether a player is injured in a tackle, with most injuries occurring at running or sprinting speeds (Garraway et al., 1999).

Conclusion

The present study found that there was no relationship between the number of individual physical collisions which players incurred, and the incidence of injury. It is possible that the lack of an observed relationship may be due to the small number of injuries in the present study, or 126 because of the confounding effect of an' increased number of non collision injuries in backs. Future research into injury in rugby league football needs to continue to monitor injury incidence and prevalence. The game has undergone a number of changes in recent years, such as modifications in the laws of the game and movement of the playing calendar, which have undoubtedly influenced injury patterns (Gissane et al., 1998). Therefore,

any further changes might have a similar influence and need to be

monitored. Future investigations also need to examine the evidence with

regards to intrinsic injury risk factors exhibited by players. If injury

prevention programmes are to be put in place, they need to be based on

the knowledge of both intrinsic and extrinsic aetiological risk factors that

contribute to increased injury risk (van Mechelen et al., 1996).

Acknowledgement

The authors would like to thank Dr JCG Pearson for his statistical advice. 127

An operational model to investigate contact sports injuries

Abstract

Purpose: A cyclical operational model is proposed to examine the inter- relationship of a number of factors that are involved in sports injury epidemiology. In sports injury research, investigations often attempt to identify a unique risk factor that distinguishes an injured player. However a wide variety of factors can contribute to a sports injury occurring and an understanding of the cause of injury is important to advance knowledge.

Methods: The proposed model identifies a healthy/fit player initially, although the player may exhibit a number of intrinsic risk factors for sports injury. Prior to exposure to extrinsic risk factors, there is the opportunity for implementation of prevention strategies by coaching personnel and the sports medicine team. These strategies might include, among others, appropriate warm up, adequate hydration, wearing protective equipment and prophylactic taping. Additionally, preventative screening could take place to assessthe various intrinsic and extrinsic risk factors that could lead to sports injury. Discussion: Two examples of how the operational model relates to contact sports injury cases are presented.

Participating in sport inevitably exposes the player to external risk factors which predispose towards injury. The treatment of the injured player aims to restore the player to pre-injury playing status and to prevent the injury from becoming chronic. Conclusions: It is suggested that the application of this proposed cyclical model may lead to greater success in understanding the multi-faceted nature of sports injuries, and 128 furthermore help minimise injury risk and support the rehabilitation of injured contact sports participants.

Key words: epidemiology, injury, incidence, prevalence, risk factors, predisposition 129

Introduction

In sports injury research the aim of inquiries has often been to find a unique marker or risk factor that will identify injured players (Meeuwisse,

1991). Usually the frequency of injury is examined in relation to the presence or absence of a specific risk factor (Powell and Schootman, 1992).

However, most sports injuries are rarely attributed to a single risk factor.

Although injuries may sometimes appear to be random accidents, many factors play a role before the actual occurrence of an injury event

(Meeuwisse, 1991). An understanding of the aetiology of injury is also important for the advancement of knowledge (Meeuwisse, 1994).

While sports participation is acknowledged as having a health-promoting benefit, it can also have deleterious effects on health in the form of injuries and accidents (van Mechelen et al., 1992). Action to prevent sports injuries should be based on the knowledge of aetiological factors that contribute to increased injury risk (van Mechelen et al., 1996). Various authors have described many risk factors which are usually grouped into intrinsic

(subject related) factors and extrinsic (externally related) factors (Lysens et al., 1991, Lysens et al., 1984, Caine et al., 1996).

Intrinsic factors have been defined as individual biological, biomechanical and psychosocial characteristics predisposing a person to the outcome of injury (Caine et al., 1996). Extrinsic risk factors are independent of the 130 injured person and are related to the types of activity during the incident of injury (Taimela et al., 1990), and the manner in which sport is practised

(Lysens et al., 1991). A summary of both intrinsic and extrinsic risk factors documented in the sports injury literature is presented in table 1.

However, even the classification of risk factors into intrinsic and extrinsic could be criticised as being artificial (Lysens et al., 1984), since injuries that result from participation are multi-risk phenomena, with a variety of risk factors interacting at a given time (Lysens et al., 1991).

Since sports injuries do not occur independently, previous research has suggested strategies for the investigation of sports injuries (van Mechelen et al., 1992, Watson, 1997), using a sequence of events with four stages

(van Mechelen et al., 1992);

1. The initial stage involves the identification of the problem and the

description of injury in terms of injury incidence and the severity of

injury.

2. The next stage identifies the risk factors and mechanisms that play a

part in sports injury episodes.

3. Once these have been identified, measures that will have the likely

effect of reducing sports injuries can be introduced. These measures are

based on the injury mechanisms and risk factors that have been

identified in stage two. 131

4. The final stage of the sequence is to repeat the initial stage with the

preventive measures in place, in order to determine the extent to which

such measures are effective.

Later work proposed a multifactorial model for the investigation of sports injuries (Meeuwisse, 1994), in which an indefinite number of intrinsic risk factors may predispose an individual to injury (figure 1). If an athlete is predisposed to injury, extrinsic factors could exert their influence i. e. extrinsic risk superimposed upon intrinsic factors.

However, an injury may require a further "initiating event", such as a collision or sudden change of direction. These "initiating events" may be focused on by the practitioner, with little attention being paid to those factors that were more distant f om the event, e.g. how does an athlete become susceptible to injury?

Both the strategy for injury prevention (van Mechelen et al., 1992) and the multifactorial model of aetiology (Meeuwisse, 1994), have valid and important contributions to make for the investigation of sports injuries.

However, a linear model with a beginning and an end point may be too simplistic, since it is logical to assume that these intrinsic risk factors are not fixed and that they can vary over time. Furthermore figure 1 is a linear model which does not account for what happens following injury, how the athlete may return to sport and how the susceptibility to injury changes. 132

Table 1. Intrinsic and extrinsic risk factors reported in the literature.

Intrinsic risk factors Extrinsic risk factors Physical characteristics Exposure (Meeuwisse, 1991) Age(Meeuwisse, 1991, Powell and Type of sports (Meeuwisse, 1991) Schootman, 1992) Sex (Meeuwisse, 1991, Powell and playing time (Meeuwisse, 1991) Schootman, 1992) Somatotype(Meeuwisse, 1991) position in the team (Meeuwisse, 1991) Body size (Powell and Schootman, 1992) level of competition (Meeuwisse, 1991) Previous injury (Meeuwisse, 1991, warm up (Powell and Schootman, 1992) Powell and Schootman, 1992) Physical fitness (Meeuwisse, 1991) personal equipment (Powell and Schootman, 1992) Joint mobility (Meeuwisse, 1991, Powell and Schootman, 1992) Muscle tightness (Meeuwisse, 1991, Training (Meeuwisse, 1991) Powell and Schootman, 1992) Ligamentous laxity (Meeuwisse, 1991) Malalignment of lower extremities Coaching (Powell and Schootman, 1992) (Meeuwisse, 1991, Powell and Schootman, 1992) Dynamic strength (Powell and Schootman, 1992) Static strength (Powell and Schootman, Refereeing (Powell and Schootman, 1992) 1992) Skill level (Powell and Schootman, 1992) control of game (Powell and Schootman, 1992)

Psychological characteristics (Meeuwisse, 1991) Opponents Psychosocial characteristics(Meeuwisse, 1991) Skill level (Powell and Schootman, 1992) foul play (Powell and Schootman, 1992) Willingness to take risks (Powell and opponent's physique (Powell and Schootman, 1992) Schootman, 1992) players Interaction with other (Powell Environment (Meeuwisse, 1991) and Schootman, 1992) Type & condition of playing surface (Meeuwisse, 1991, Powell and Schootman, 1992) Experience of snort (Powell and weather conditions (Meeuwisse, 1991, Schootman, 1992) Powell and Schootman, 1992) Time of day (Meeuwisse, 1991) time of season (Meeuwisse, 1991)

Equipment protective equipment (Meeuwisse, 1991) Footwear (Meeuwisse, 1991) Orthotics (Meeuwisse, 1991) 133

Figure 1. A new multifactorial model of athletic injury etiology.

Exposure to Extrinsic Risk Factor

Age

Flexib' 'ty

Intrinsic d isceptible Inciting Injury risk athlete athlete T factors Previous event injury

somatotype

. ' , Risk factor for injury (distant from outcome) Mechanism of injury (proximal to outcome)

Source: Meeuwisse WH. Assessing causation in sports injury: a multifactorial model. Clin J Sport Med 1994; 4: 166-70. 134

Materials and Methods

A proposed cyclical operational model for the investigation of

contact sports injuries

Traditional approaches to the epidemiological investigation of sports injuries have tended to focus on the incidence and prevalence of injury,

applied both to individual sports, and to overall national statistics. The model developed here aims to expand this traditional approach to take into consideration the multitude of factors which may predispose to injury,

and which may determine the ultimate outcome of the injury for the

contact sport athlete.

The cyclical model consists of five linked stages. First the ostensibly

healthy/fit athlete may be at risk of injury from a number of

predisposing factors. These may, with or without the additional exposure

to external risk factors, in the presence of a- potential injury event,

result in injury incidence. The duration of time that the injury persists,

during treatment and rehabilitation, contribute to the prevalence of the

injury, and the ultimate outcome may be a return to sport at the original

level, thus completing the cycle, or a return at a different level, or even

premature retirement (figure 2). Each of the elements of the model are

now described in greater detail. 135

Figure 2. A cyclical operational model for the investigation of sports injuries.

Intrinsic risk factors

Return of Healthy/ Healthy/Fit player Player Predisposing/ Precipitating f factors

Primary Prevention Medics/Physios/ No injury Coaches \L Outcomes

N Injury ýý\ Recurrence

Exposure Injury to external Incidence risk factors

Prevalence Prematureretirement/ Lower playing level Factors in the mechanismsof injury

Treatment & Management Types/Efficacy/Code of practice 136

The healthy/fit player

Inherent within the ostensibly healthy/fit player, exist a myriad of intrinsic risk factors that have been suggested by the literature

(Meeuwisse, 1994). For example, it has been reported that field hockey, soccer and lacrosse players exhibited an increased risk for ankle sprain when they displayed an increased eversion: inversion strength ratio

(Barker et al., 1997).

At this stage in the cycle the strategies for intervention may be termed

`primary prevention' (Lysens et al., 1991), with the aim of preventing injuries from occurring in the first instance (Fletcher et al., 1996).

Knowledge of the individual's risk factors may be of benefit in primary prevention. These strategies amongst others might include such measures as appropriate warm up, adequate hydration and prophylactic taping.

They might also include the wearing of protective equipment such as gum shields in rugby, hurling (Crowley et al., 1995) and ice hockey (Rampton et al., 1997), or head guards in hurling (Crowley et al., 1995) and ice hockey

(Rampton et al., 1997, Kujala et al., 1995). Such strategies would also include the coaching of proper technique in contact sports when either making or receiving a tackle (Corcoran, 1979), or teaching correct falling technique in judo (Kujala et al., 1995). Coaches and sports medicine practitioners seek to prevent injury, and it is the most logical and least costly method of health care (Meeuwisse, 1991). Additionally, prevention screening could take place to assessintrinsic risk factors that could lead to 137 sports injury problems (McKeag, 1985). For example, it has been shown that postural and mechanical factors can predispose female basketball players (Garraway and MacLeod, 1995), rugby and soccer (Watson, 1995) players to injury, while screening has been advocated for groin injury prevention in rugby league football (O'Connor, 1995b).

Potential Injury Event

In addition to the intrinsic factors, extrinsic factors will play an important part in the potential for injury. The exposure to extrinsic risk factors will undoubtedly vary across sports and may vary within positions in certain sports, as well as the conditions under which sport is played. For example, both field hockey (Jamison and Lee, 1989) and American football

(Skovron et al., 1990) have reported increased injury rates when games are played on astroturf. In American Football, both the risk of knee (RR =

1.18) and ankle (RR = 1.39) injuries are increased when the game is played on artificial compared with real grass (Powell and Schootman,

1992).

The event that initiates an injury is one of the most identifiable parts of the injury process and has been the focus of much research (Meeuwisse,

1994). In contact team sports these events are likely to be highly game specific, and indeed position specific. It has been suggested there are a high number of thigh injuries in professional soccer (Inklaar, 1994), and that these are commonly result from physical contact with an opponent 138

(Ekstrand and Gillquist, 1983). It has also been suggested that with the exception of goalkeepers, there are few upper body injuries that prevent soccer players from playing (McKeag, 1985).

At this stage in the cycle, a player that is not injured can continue to play whilst still exhibiting the same intrinsic risk factors, whereas if he/she becomes injured the player progresses to the next stage of the model.

Injury Incidence

In descriptive sports medicine epidemiological terminology incidence has

been defined by the number of new events or cases of injury that develop

in a population of individuals at risk during a specified time interval

(Henekens and Buring, 1987). The incidence of injury in specific sports is

an area that has received much attention (Kujala et al., 1995, Hickey et

al., 1997, Garraway and MacLeod, 1995). However, the comparison across

studies is often difficult due to the varying definitions of injury that have

been employed (van Mechelen et al., 1996). Nevertheless, where

comparisons can be made, there is a range of injury incidence rates among

contact sports as demonstrated in table 2.

Injury Prevalence

In descriptive sports epidemiology, injury prevalence has been quantified

by the proportion of individuals in a population who have an injury at a 139 specific instant. It provides an estimate of the probability or risk that an individual will be injured at some point in time (Henekens and Buring,

1987). Injury prevalence depends upon both the incidence rate of an injury, and the period of time between the initiating event to the return to full fitness. In sporting terms the prevalence of an injury is an important consideration, since the treatment and rehabilitation of injuries takes time, and this is often a major factor in injury prevalence. It has been suggested that because professional sport is a business, it is often desirable on the part of both the team and the player to keep time lost from playing to a minimum (Lewin, 1989). Prevalence can also be influenced by game regulations, for example in rugby union football a player who is concussed is required not to either play or train for a period of 21 days (International Rugby Football Board resolution 5.7), whereas in rugby league football there is a sliding scale of required abstinence for the severity of injury based on the symptom severity of concussion. Therefore, concussions that are considered relatively minor in rugby league football, would have a far higher prevalence in rugby union football, which could contribute to a distortion in specific injury prevalence among similar sports

The type and duration of treatment of the athlete is dependent upon each specific injury which the player is has sustained. For example it has been reported that 44% of rugby injuries only require treatment with RICE 140

(rest, ice, compression and elevation), while others may require surgical intervention (Stephenson et al., 1996).

Table 2. Injury incidence rates across team sports.

Sport Injuries per 1000 Reference

player hours

Rugby League 34* Stephenson et al., 1996

Rugby Union 20* Hughes and Fricker, 1994

Australian Rules 35 Seward et al., 1993

Soccer 22.6 Inklaar et al., 1996

*Injuries requiring a player to be unable to play for more than one week

During the rehabilitation process, both secondary and tertiary prevention can take place. The aim of secondary prevention is to restore health when it is impaired (Last, 1995). In sports medicine it is defined as the process of preventing or delaying the development of irreversible structural damage, by therapeutic intervention (Lysens et al., 1991). These measures can influence the prevalence of injury by reducing the amount of time that a person remains injured, but not the incidence. Appropriate and early management of soft tissue injury in particular, has been shown to promote early recovery (MacLeod, 1993).

Therapy that seeks to limit the injury process from becoming either chronic or persistent has been termed tertiary prevention (Lysens et al.,

1991). The aim of tertiary prevention is to reduce both the incidence and 141 prevalence of long term disability (Lysens et al., 1991). Sound treatment and rehabilitation have been suggested to be one of the most adequate preventive measures for secondary and tertiary prevention (Lysens et al.,

1984).

Event Outcomes

In the proposed cyclical operational model for the investigation of sports injuries (figure 2), an injury has three possible event outcomes. A player

can return to a healthy/fit state, the injury can recur, and either, the player can retire from competition at that level, or continue participating

at a lower level The obvious ideal is to return to playing at the pre-injury

level of performance. In order for an athlete to be regarded as healthy they

must be able to take part fully in both training and playing (Lysens et al.,

1991). However, professional athletes are unlike a number of other

occupational groups in that they are often quite willing to train and play

in spite of injury, compared with others, who normally return to work only

when they are completely recovered (Schootman et al., 1994b).

Recurrent injuries are also a major problem in sport and have been

reported to account for 16.5% of all injuries in rugby union football

(Garraway and MacLeod, 1995). Recurrent injuries increase the

incidence rate and the amount of time lost for an injured player, thus

also increasing the prevalence rate of injury. Furthermore, one of the 142 greatest risk factors for injury is the history of previous injury (Watson,

1997).

In extreme circumstances professional sport players are sometimes forced into premature retirement because of injury. In such cases, it has been reported that rugby league football players who suffered long term consequences of injury after their playing careers, experienced difficulties, which included job limitations, reduced income earning potential and increased personal medical costs (Meir et al., 1997).

In certain situations players will be unable to return to playing and the management of such an injury may seek to maximise the quality of life rather than fully remediate the injury (Lysens et al., 1984). Previous work has described cervical spine injuries of two rugby union football players who could no longer return to play (Secin et al., 1999). These players are now members of the Rugby Amistat Foundation, which is dedicated to the well being of players who have suffered physical and mental trauma following disabling injury (Secin et al., 1999).

The overall design of the proposed operational model is cyclical because even if a player returns to health/fitness, the sports injury itself may constitute an intrinsic risk factor for the predisposition of future injury.

Even if a player is fortunate enough to avoid an injury, the individual's intrinsic risk factors are unlikely to remain the same over time. For example, at the beginning of every season a player has another year of 143 experience and is another year older, both of which have been described as potential sports injury risk factors (Lysens et al., 1991, Watson, 1997).

This will serve to alter the nature of intrinsic risk factors present. In addition to this, coaches in contact sports often emphasise increasing muscle bulk during the closed season (heir, 1993), which may also serve to alter an individual's intrinsic risk factors.

Discussion

The advantage of the cyclical model over the previous linear model

(Meeuwisse, 1994) is that knowledge and awareness of the factors involved at each stage of the model, allows for the development of appropriate strategies for the prevention of injury at the primary, secondary and tertiary levels. Therefore, the practical application of this model may help the sports medicine practitioner deal more effectively with the injury problems of athletes in contact sports.

This paper proposes to provide an example of the application of this model to two specific sports situations in the contact sport of rugby union football.

Case 1. First Rib Synchondrosis

An injury to the first rib synchondrosis in a rugby football player is an example of an acute injury, caused primarily as a consequenceof extrinsic 144 factors (Kemp and Targett, 1999). However, the muscle bulk in the shoulder area and the strength of the muscles represent the player's internal (intrinsic) risk factors. The external exposure to a (extrinsic) risk factor would be the contact with the opposing player, and the opposing player's physique.

In this example the specific injury incidence was a first rib synchondrosis.

The injury contributed to the incidence as an injury event, and the treatment which t was described as conservative, and lasting for 12 weeks contributed to the prevalence throughout the recovery period. At the end of the treatment, the event outcome was that the player was pain free and a repeated CT scan showed that the injury had healed. The player was then allowed to resume contact sport at the same level, which would return him to the start of the cycle, where this injury may or may not represent an intrinsic risk factor to future injury.

Case 2. Incarcerated Hernia

An incarcerated hernia during a lineout (Thomas and Thomas, 1999) might fit into the model as follows; this is an acute injury superimposed upon an intrinsic weakness. For this injury, the intrinsic risk factors would include the pre-existing hernia, the player's position, somatotype and gender, while the predisposing external risk factors would include the fact that it took place in a lineout. This is an area of the game that has recently been the subject of some rule changes, which has resulted in 145 lineout jumpers being supported and lifted by adjacent players. This is a technique that is coached and rehearsed during practice sessions. The act of being supported in an unstable mid air position could be considered to be an external risk factor. The exertion of jumping may have increased the intra-abdominal pressure, thus increasing the size of the hernia. This would be compounded by the increased external pressure to the groin area, transmitted through the shorts, with the action of two other players lifting and holding the lineout jumper.

The particular injury was the hernia, which required treatment with surgery. The prevalence of the injury was for a period of five weeks in total, after which the event outcome was the player being able to return to play, again completing the cycle.

Conclusions

The model that has been proposed seeks to acknowledge the multifactorial nature of sports injury. It further recognises that the sports injury is not an endpoint (Meeuwisse, 1994), since rehabilitation and recovery are part of the continuing process. In so doing, it attempts to bridge the gap between descriptive and analytical sports injury epidemiology. Sports participants almost always seek to return to play, but on their return their intrinsic risk factors and the external risk factors will undoubtedly be different. While the model has been applied to rugby football and the 146 myriad of factors that can influence injury, the situation will undoubtedly be different in other sports and needs to be investigated further.

The previously published work underpinning the development of the proposed cyclical model (figure 2) has been presented in order to illustrate the application to sports injury research and demonstrate the advantages over the previously proposed linear model (figure 1). Furthermore, it is envisaged that the new model may be used to further develop current descriptive and future analytical epidemiological approaches to sports injury research.

Acknowledgement

The authors would like to thank Peter J. Maud FACSM for his comments on earlier versions of this manuscript. 147

A pooled data analysis of injury incidence in rugby league football:

Summary

The aim of this study was to summarise the injury rates in professional

Rugby League Football. Previously published studies were identified from

database searches of literature from Medline, Sports Discus, and Web of

Science. A total of 18 articles, which reported the prospective injury data

collection for at least one playing season in professional rugby league

worldwide, were included. The definition of injury adopted required an

injured player to miss the subsequent game through injury. Ten studies

satisfied the injury definition criteria for inclusion. A review of articles

and extraction of relevant data was carried out independently by two

authors. A total of 517 injuries were reported during 12,819 man hours

exposure (753 games), which resulted in an overall injury rate of 40.3

injuries per 1,000 hours (95% CI 36.9 to 43.8). The majority of injuries

were to the lower half of the body (20.7 per 1,000 hours, 95%CI 17.7 to 24),

with the trunk receiving the least (6.7 per 1,000 hours, 95%CI 5 to 8.6).

Injury rates in professional rugby league are higher than some other

contact sports, probably due to the large number of physical collisions that

take place. This pooled data analysis provides more accurate estimates of

injury incidence in the game of professional Rugby League Football. 148

Introduction

Rugby League football has been described as a fast moving contact sport

(Alexander et al., 1980), and as a collision sport (Larder, 1988). It is an invasion game, whereby one team attempts to invade the territory of the other team with the object of scoring points, while the opposition uses physical force, within the laws of the game, to try and stop them. To do this, the internal structure of the game demands that the side that is not in possession tackles their opponents who are in possession of the ball.

Tackling can be described as the act of preventing a ball carrier running with the ball, or passing or kicking the ball to another member of the attacking team. The ball carrier can be tackled by any number of the opposing teams players (Federation, 2001).

A Rugby League team consists of 13 players (six forwards and seven backs) who have six possessions to advance the ball down field. The ball must be passed backwards, but can be carried or kicked down field. Unlike

American Football, there are no special teams or sub-units within a team

(other than forwards and backs), so each player has a role to play in both attack and defence.

Research into the incidence of injury in rugby league has shown that injury incidence is high compared to other sports, for example Rugby

Union (Gissane et al., 1993, Seward et al., 1993). However, one 149 shortcoming of many of these studies is that they deal with a relatively small number of players and often only one club, thus reducing their generalisability.

One strategy to enhance the information provided from epidemiological studies is to combine the information from multiple studies into a single estimate (Checkoway, 1991). For this technique to be successful it is important that the studies that are included have compatible structure with respect to inclusion criteria, follow up, and exposure history. The combined data from these individual studies can then be statistically reanalysed to provide more precise injury data (Blettner et al., 1999).

The purpose of the present study was to provide pooled estimates of injury incidence in rugby league football from published studies; more specifically, this will include estimates of injury incidence, injury severity, site of injury, and the comparison of injury rates between forward players and back players.

Methods

These included the development of a search strategy to locate papers investigating injury in rugby league. Inclusion/exclusion criteria were developed to ensure compatibility, and finally, combined analysis was performed. 150

Search strategy for identification of databases

Searching Medline, Sports Discus and Web of Science databases, covering the period from 1985 to 2000 identified 18 studies. The following terms were used, rugby with league and injury.

Inclusion criteria

In the present analysis the authors collated published studies that

reported the incidence of injury in rugby league football. The inclusion

criteria were: -

" Studies published later than 1990; " Data collection carried out prospectively on professional players; "A definition of a recordable injury being one that required an injured player to miss the subsequent game; "A count of the number of games studied to allow the calculation of person time injury rates.

Procedure

A total of 18 articles were identified that reported prospective data

collection of rugby league injury, and details of these studies are shown in

table 1. Of these, only ten satisfied the inclusion criteria (Gissane et al.,

1993, Seward et al., 1993, Estell et al., 1995, Gibbs, 1993b, Gissane et al.,

1997a, Gissane et al., 1998, Hodgson-Phillips et al., 1998, Stephenson et

al., 1996), but two of these studies had to be excluded (Hodgson-Phillips et

at, 1997, Hodgson-Phillips, 1998) for re-reporting the same source data to

a previous paper (Hodgson-Phillips et al., 1998). 151

Upon further examination, it was also apparent that in some of the remaining eight studies that satisfied the inclusion criteria, authors had used the same common baseline data sets to highlight further trends in their data. For example, the data reported by Gissane et al., (Gissane et al., 1993), are contained within the data reported in a later paper

(Stephenson et al., 1996), while, Stephenson et al. (1996) and Gissane et al. (1997) used the same baseline data. But one reported the overall incidence of injury in rugby league (Stephenson et al., 1996), while the other sought to highlight the differences in injury rates between forwards and backs (Gissane et al., 1997a).

This resulted in a total of six studies being included in the final pooled analysis which are highlighted in table 1, three of which reported both first team and reserve grade information (Estell et al., 1995, Gibbs, 1993b,

Stephenson et al., 1996).

Since many studies did not include all areas of interest for analysis, it was necessary to extract specific information from individual studies at different stages of the analytical process. 152

Statistical methods

The data from individual studies were combined using the method described by Breslow and Day (Breslow and Day, 1987), Person-time incidence rates and 95% confidence intervals were calculated using

Confidence Interval Analysis Software (Altman et al., 2000), To test for significant differences, proportion tests (z), chi-squared (X2) goodness of fit tests were used, along with relative risk (RR) where appropriate.

Results

The included studies reported injury data from a total of 753 games, 548 first team and 205 at reserve grade. The total number of hours observation for injury exposure was calculated as 13 players x length of the game x number of games played (two teams of 13 playing for one hour constitute 26 man hours). Games, are usually 80 minutes in length, but in two studies (Estell et al., 1995, Gibbs, 1993a) reserve grade games were 70 minutes long. There was a total of 12,819 man-hours across the six studies, 9474 at first team and 3118 at reserve grade

The injury incidence figures are shown in table 2. There was an overall injury rate of 40.3 injuries per 1000 man-hours. First team players experienced a slightly higher, injury rate than reserve grade players, although the difference was not significant (z = 0.49, p=0.62). 153

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It was possible to pool data on the site of injury from four studies, which totalled 8365 exposure hours (Seward et al., 1993, Stephenson et al., 1996,

Gibbs, 1993a, Gissane et al., 1998) and figure 1 displays the injury rates to the different sites of the body from these studies. There were significant differences between these injury rates (x2 = 12.34, ff = 3, p<0.01) with injuries to the lower limb accounting for 46.4% of the total, followed by, upper limb (20%), head and neck (18.7%) and trunk (14.7%).

Only two studies (Gibbs, 1993a, Gissane et al., 1997a) have reported a comparison between forward and back players for injury rates, which totalled 3673 man-hours of exposure (forwards = 1811.39, backs = 1861.9), giving injury rates of 66 (95%CI 55 to 79) and 61 (50 to 73) for forwards and backs, respectively. The relative risk (RR) of 1.09 demonstrated that playing as a forward increased the risk of injury by only 9%, although the

95% confidence interval for the RR (0.85 to 1.40) indicated that the increased risk was not significant.

Injury severity was graded according to the criteria used by Gibbs (1993a).

An injury was classified as minor (one game missed), moderate (two to four games missed), or major (five or more games missed). It was possible to pool the results from three studies (Gibbs, 1993a, Hodgson-Phillips et al., 1998, Stephenson et al., 1996) that covered a total of 9437 hours of exposure, and the injury rates are shown in table 3. Overall minor injuries accounted 43% of the total, with moderate and severe accounting for 32.9% 155 and 25% respectively. However, the differences between the injury categories were not significant (X2 =5.37, ff = 2, p>0.05)

Discussion

The major findings of the analysis were; 1) that there was no difference between the injury rates of first and reserve grade players; 2) there were significant differences between the injury rates for different sites of the body, with the lower limb having the highest injury rate; 3) there was a small but not significant increased risk of injury when playing as a forward compared to playing as a back, and 4) there was no significant difference among the degree of severity of injuries sustained by players.

Pooling data from a number of studies of similar design is a technique that can produce an overall estimate which incorporates the information provided by those studies (Elwood, 1998). Therefore, the major strength of the present pooled analysis is the fact that it provides more accurate estimates of injury rates than the individual studies which provide the initial raw data. Therefore injury rates from the present study can be compared with injury rates from previous studies. 156

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Table 3. Injury rates for grades of severity.

Rate per 1000 hours 95% CI Minor 16.64 14.1 to 19.5 Moderate 12.7 10.5 to 15.2 Major 9.32 7.5 to 11.5

The combined data found no significant differences between the injury rates for first and reserve teams. Individual studies have also all reported

non-significant differences between grades (Estell et al., 1995, Gibbs,

1993a, Stephenson et al., 1996). Furthermore, this finding was evident in

spite of the definition of injury that was adopted. For example, one study

(Gibbs, 1993a) only reported injuries that required a player to miss more than one game, while the two other studies (Estell et al., 1995, Stephenson et al., 1996) originally reported all injuries that received treatment.

The combined injury estimate of 46.4% to the lower body injuries is very

similar to the 41% (Seward et al., 1993) and 45% (Gissane et al., 1998) previously been reported in individual studies. One major feature of rugby league is the amount of tackling that takes place. The thigh area is where most coaches will instruct players to aim tackles (Kean, 1996, Larder,

1988), which would make it an area of the body susceptible to injury.

However, there is no real evidence to indicate which area of the body is contacted first, or with how much force, in the tackle. But, when tackles 159 are aimed at the upper part of the body, arms and shoulders can be used to protect such areas as the trunk and head, whereas the lower limb will remain somewhat exposed to contact.

Almost half of the injuries in the pooled data analysis were to the lower limb, whereas it has been reported elsewhere that the head and neck were the most frequently injured sites (Gissane et al., 1993). This discrepancy is also likely to be due to differences in injury definition. If all injuries that required treatment were included, then lacerations that require suturing would be counted, however, these would not require a player to miss a subsequent game. Indeed, it has been suggested that including such injuries in addition to those requiring a player to miss a subsequent game, would increase the injury count by as much as 43% (Gibbs, 1993a).

If this study had adopted an injury definition for all injuries that received treatment, it would have limited the number of studies that could be utilised. However, the injury pattern would probably have been somewhat different. Injury rates would have been somewhat higher, for example combining the first and reserve grade estimates of Estell (Estell et al.,

1995), Hodgson-Phillips (Hodgson-Phillips et al., 1998), and Stepehenson

(Stephenson et al., 1996) would increase the overall injury rate to 116.6 injuries per 1000 hours. It is also likely that the site of the body that was most injured would also change to the head and neck (Stephenson et al.,

1996, Gissane et al., 1993). This definition would then include all minor 160 concussions and sutures that would not prevent a player from playing in the next match.

One recognised limitation when compiling the present analysis was that it was not possible to provide an accurate estimate of the phase of play in which injury took place. Although two previous studies (Gissane et al.,

1997a, Stephenson et al., 1996) have suggested that most injuries are received by the ball carrier whilst being tackled, both reported the same baseline data, and furthermore no other investigators have reported injury occurrence in relation to the phase of play.

The aggregation of two data sets (Gibbs, 1993a, Gissane et al., 1997a) revealed that there was no increased risk of injury when playing as a forward compared to playing as a back. Recent work (Gissane et al., 2001c) has shown that forwards are involved in many more physical collisions than backs during the course of a game (55 vs. 29) This situation is similar in forwards compared in both attack (16 vs. 13) and defence (39 vs. 16).

These increased numbers of physical collisions experienced by forwards do not appear to predispose them injury.

The pooled data analysis of three studies (Stephenson et al., 1996,

Hodgson-Phillips et al., 1998, Gibbs, 1993a) indicated that there were no significant differences between categories of severity of injury.

Nevertheless, although 43% of injuries required players to miss only one 161 game, it was disturbing to note that one in every four injuries required a player to miss five or more games. Since recent changes in playing calendars and league structures, five games now represents almost 20% of a season, which will require increased numbers of players to cover for the playing time lost as a result of injury.

Conclusion

Within the limits of the definition of injury used in the present study (an injury requiring a player to miss a subsequent game), the pooled analysis has allowed the calculation of more accurate estimation of injury rates in professional rugby league and has attempted to make the results more generalisable. The resulting combined analysis reduces the variability associated with imprecise estimates and potential biases associated with individual studies. It also removes the influence of individual sub-cohort characteristics, such as playing style (Checkoway, 1991).

To date, rugby league is a sport that has not undergone a comprehensive scientific investigation. However, it may be possible in future to add subsequent studies to the present pooled analysis with a view to improving the understanding of the factors surrounding injury incidence in rugby league football. 162

In order to provide more comprehensive data on injury incidence in rugby league football further prospective studies are required. Furthermore, these studies should use common definitions of injury, the phases of play in which injury occurs, and the precise mechanism of injury. Such approaches would be best facilitated by the adoption of a standardised injury surveillance system that would allow further in depth analyses to be performed. 163

Overall Discussion and Recommendations

When beginning the investigation of injury in rugby league football, it was observed by De Jennings and myself, that there was very little literature on the subject. Also, when our data collection began (July, 1990), the most recent paper at that time was five years old (Walker, 1985).

The first piece of work published was a simple one-season survey of injuries (Gissane et al., 1993). As it only covered one season, it was almost cross-sectional in design and the findings of this could be somewhat distorted. As pointed out by Alexander et al. (1980), the situation had the potential to change markedly from season to season.

The first article presented in this thesis (Stephenson et al., 1996) (see pages 40 to 57) was designed to be a descriptive study so that the injury situation within the English game could be illustrated. Describing the current situation is usually the starting point with epidemiology. The data collection period of four seasons would allow the more accurate determination of injury estimates than the one-year investigation

(Gissane et al., 1993), and reduce the possibility of marked variation between individual seasons.

From descriptive epidemiological studies, hypotheses can be generated to be tested in later analytical studies (Henekens and Buring, 1987, Hart, 164

1996, Caine et al., 1996). One hypothesis put forward by Stephenson et al.

(Stephenson et al., 1996), was that the exposure of forward and backs was different, and that this differing exposure would result in different injury patterns. Gissane et al. (1997a) examined this hypothesis further (see pages 58 to 73), demonstrating that the injury pattern for the two playing units was indeed different, with forwards experiencing much higher rates of injury that backs.

Events within the game itself largely dictated the direction of the next two studies. The decision was made to move the playing calendar in 1996, from the autumn and winter months to the spring and summer months.

Because of previous research in this field, the opportunity presented itself to examine the hypothesis that the injury rate would change along with the move of the playing calendar. Because the injury register was already in place, there was going to be the opportunity to examine the hypothesis using the same data collection techniques, prior to and after the change.

This would mean the minimisation of potential biases, by using the same data collection tool. The hypothesis was tested using a non-concurrent cohort (Gissane et al., 1998) (see pages 74 to 87), and demonstrated that the risk of injury in summer rugby was 67% higher in spite of players being involved in much fewer games.

Similarly, with the move to summer rugby league, it was unclear what effect the environment, namely the temperature, was going to have on 165 players. The calendar move meant that the game was going to be played in much higher temperatures than European players had previously experienced. In epidemiological terms, the specific situation had to be described to determine if there was a potential health problem. So

Jennings et al. (1998) (see pages 88 to 97), seek to describe the how many players were experiencing dehydration during match play. Ideally, it would have been better to have had a comparison group for body mass losses during winter rugby league. But prior to the calendar change, no one had considered it to be a problem.

However, this paper has had a far-reaching effect. The game's administrators are aware of the need for players to hydrate properly, but at the same time they do not want coaches and trainers constantly running on the field of play. This presents a problem, in as much as the investigation can is viewed by the RLMA as a risk assessment. Its findings suggest that we need more people on the field carrying water, rather than less. To compromise an amendment was placed in the laws (Appendix C

Rule 11) that states: -

On Field Trainers - Only two trainers are permitted on the field at any one time and must enter the field from behind their own team. If both teams obtain permission from the referee prior to the commencement of the game, then another trainer will be allowed for the match if the playing conditions would require, e. g., heat (RFL, 2001). 166

This allows an extra water carrier to be used. Also, with prior consultation with the referees they will in junior games ([J 18, U 19 and U 21), stop the game for at approximately halfway through each half.

Several authors have suggested that injury rates in rugby league are high because of the volume of physical collisions in which players are involved

(Stephenson et al., 1996, Gibbs, 1993a, Kear et al., 1996, O'Hare, 1995).

The next two papers in this thesis (Gissane et al., 2001c, Gissane et al.,

2001a) (see pages 98 to 112 and pages 113 to 126), sought to describe the amounts and types of physical collisions and then determine if there was a relationship between collisions and injury rates. The task was made much easier by the move to summer rugby league. The change was brought about by the opportunity for greatly increased media exposure. From a research point of view, this meant that there were professional video recordings of each game available. Using video recordings meant that both the amounts and types of physical collisions could be determined much more accurately. Also, as tapes could be rewound and reviewed, the chances of measurement errors could be very much reduced. All tapes that were used in this study were recorded from a position at approximately the half way line. This view allows the most uninterupted and least obscured scrutiny of the events taking place.

As a result of this research, speculation about which players were involved in the most physical work was partially laid to rest. Forwards were 167 involved in almost twice as much physical contact as backs, and also players got involved in more physical contact while their side was defending. From this it was possible to determine that backs had a significantly higher injury rate per 10,000 physical collisions than forwards (Gissane et al., 2001a) (see pages 113 to 126).

The Operational Model (Gissane et al., 2001b) (see pages 127 to 146) was a culmination of many years reading and researching in the area of injury incidence. Quite often injuries are looked at in relation to one factor. But, injuries can come about as a result of many factors and there are many points in the process where injury incidence, prevalence and outcome can be influenced. Its major difference to other proposed models (Meeuwisse,

1994) was that the model was cyclical, which did not see injury as an end point. By doing this, it allowed the inclusion of a player's previous playing and injury experience into the model. Whereas previous authors (Watson,

1997), had included it as an intrinsic risk factor.

It has been suggested that it is often useful to have information from several epidemiological studies combined into a single estimate

(Checkoway, 1991). Typically there are two ways of carrying out this task.

Firstly, a meta-analysis is the process of using statistical methods to combine the results of different studies. Secondly, when possible the raw

data from several studies can be pooled together and re-analysed. To

carryout a pooled data analysis it is necessary to have the raw data 168

(Blettner et al., 1999). Because of the way that injury data are reported in sports medicine studies, it is often possible to pool the raw data without having access to the original data.

This is possible because an injury rate is calculated using the following formula: -

cases rate = x 10n player hours at risk

Because it is a division sum, if any of the two components are known, the third can be calculated as shown below.

injuries rate = " 10 n player hours at risk

( rate injuries player hours at risk = lan ... Jx

injuries player hours at risk = x ion rate

Many studies report the number of injuries that players receive and the number of games played during the course of the study, along with the injury rate. So, it is possible to break the information clown to its

component parts and combine the data together. This allows research a 169 great deal of scope to combine the information reported in a number of small studies. When it is carried out it will allow much more accurate estimates to be presented and will increase the generalisability of the findings.

With the knowledge of both how rates were constructed and the information reported in the literature, it was possible to write the final paper in the series (Gissane et al., 2002) (see pages 148 to 62).

This series of papers has produced evidence that is valuable to a variety of professions in rugby league football. Those who are involved in preventing and treating injuries now have information on the number of type of injuries that occur during the course of match play. This can serve to inform and guide training of health professions within the game. Also, information is available to coaches about how often injuries occur and how this can influence player selection. For both the health professionals and the coaches, information is available on the risk of dehydration. This not only has effects detrimental to health, but also to a player's skills ability.

In addition to this, the work has resulted in rule amendments (RFL 2001), and some of the most detailed investigations of individual player's activities during match play (see pages 98 to 112 and pages 113 to 126).

Beyond this, the technique of pooling data that was employed (Gissane et

al., 2002) (see pages 148 to 62) could be used in many other sports to 170 provide an overall view of a number of studies that have been published.

This technique has never been used before in sports injury research, and it could be used to examine conflicting findings between studies.

Future research

In spite of the work that has been carried out over the last 12 years, there is still a lot of scope for future research, both in sports injury incidence and in rugby league.

Once upon a time, the editor of a paper called the 'Rugby Leaguer' interviewed me about some of my research. He asked me why I had stated in the paper that more research needed to be done (Gissane et al., 1993). 1 replied that it was for the same reason that he published a paper each week. The game, in the same way as any other sport, is a living thing that is constantly changing and evolving. The game changes, and as it changes it presents opportunities for future research.

Injury research of the game has in recent years focussed on the move to summer rugby. But, in epidemiological terms there are many things that still remain to be investigated. For example, for clear evidence on risk factors they need to be examined in a prospective study, with data collected about specific factors prior to the collection of injury data (Waller et al., 1994). This type of research has been carried out in rugby union 171

(Quarrie et al., 2001) and soccer (Inklaar et al., 1996). Prospective cohort

studies such as these would allow targets and strategies for prevention to be established and implemented. Over the last few years in rugby league, the changes seem to have taken place, and then the investigations as to

whether they have hindered or helped players' health have come later.

However, the move to summer was eight seasons ago, and it now looks

permanent. So possibly now the time is right to investigate ways in which

players' injury experiences can be reduced.

The task today would be somewhat easier in terms of data collection.

When De Jennings and I first began to collect data on 4th July 1990.,

neither of us really had any idea how long we would be going about this

task. All the data was collected in a hand written register. If we were to

start again we would undoubtedly use a purpose written database, which

would make our data much more flexible and the task of data

management much easier. For any sports medicine epidemiology

investigation to function efficiently and to produce high quality research,

information technology is going to be essential. 172

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Injury in rugby league: a four year prospective, survey

Sarah Stephenson, Conor Gissane, Deanna Jennings

Abstract time periods, ' ° and the only longitudinal inves- Objective-To investigate the incidence of tigations have been carried out in the Austral- injury in English professional rugby ian game. 's These studies also report widely league over a period of four playing differing findings, which could be due to the seasons. playing conditions, the skill level of players, the Methods-All injuries that were received design of the studies, or the definition' of what by players during match play were re- constitutes an injury. The purpose of this study corded. Each injury was classified accord- was therefore to describe the incidence of ing to site, type, player position, team injury in one professional rugby league club playing for, activity at the time of injury, over a period of four seasons. and time off as a result of injury. Results-The injury 114 overall rate was Methods (95% confidence interval 105 to 124) per All injuries that were reported by players 1000 playing hours, the most frequent type during the four seasons between July 1990 and of injury were muscular injuries [34 (29 to May 1994 were recorded. A season ran from 40) per 1000 playing hours], while the most the beginning of preseason training to the last frequently injured site was the head and , competitive match in either April or May. An neck region [38 (16 to 25) per 1000 playing injury was taken to be the onset of pain or a hours]. Players received the largest per- disability that occurred while playing rugby centage of injuries when being tackled league football. ' The diagnosis and classi- [46.3% (41.9 to 50.7)], most injuries re- fication of injury was carried out by the club quired less than one week away from play- doctor and the physiotherapist. The site and ing and training [70.1% (66.1 to 74.2)], and injuries were categorised as described previ- forwards had a higher injury rate than ously. ' The following details were recorded backs (139 v 93 injuries per 1000 hours). about each injury: Conclusions-The high rates of injury in league due to the rugby are undoubtedly " The position of the player high bodily in the amount of contact " The site of the injury Being tackled has the highest game. risk of " The nature of injury injury, because being hit forcibly by of " Whether the injury occurred in playing or Forwards higher other players. suffer training injury backs, because rates than probably " The team played for (first or "A" team) they are involved in a larger number of Activity injury Physiotherapy " at the time of West physical collisions. Time injury Department, (Br. 7 Sports Med 1996; 30: 331-334) " off as a result of Middlesex University Hospital, Isleworth, The total number of games played during the Key terms: rugby league; injury; injury rate; prospective Middlesex, United four seasons was In total, there `!were study recorded. Kingdom 249 games played [first team 138, alliance S Stephenson, ("A") team 111]. This included all competi- physiotherapist tions and friendlies. Playing hours at risk were Rugby league is a physical game in which play- Department Health calculated as the number of matches played x of ers are required to demonstrate speed, Studies, Brunel 1.33 (each match lasting 80 minutes). Thirteen stamina, strength, and agility. ' It has been sug- hours University College, players in a side constitute 17.29 playing Isleworth, Middlesex, gested that injury rates in rugby league are at risk during a game. Training sessions took United Kingdom higher than in other main body contact sports place at the rate of two or three per week, C Gissane, such as rugby union, " Australian rules foot- involving approximately five hours work on research officer ball, and soccer= The possible reasons for the game skills, with minimal body contact. ' high injury rate are that players are involved in Reigate, Surrey, Statistical analysis consisted of the calcula- 20 to 40 physical "confrontations" per game, ' United Kingdom tion of rates per 1000 hours of play and D and that players wear minimal protective Jennings, general percentages; where appropriate rates were equipment,; such as padding, which is de- practitioner compared using the normal approximation as signed to protect the soft tissues but not the described by Clarke. " Significance was set at Correspondence to: bones and joints, " or padded supports and C Gissane, Department P<0.05 level. of for it has been the Health Studies, Brunel sleeves which, suggested, there is University College, no evidence of protection for injured muscles. ' Isleworth, Middlesex TW7 However, it is acknowledged that research Results 5DU. into many aspects of rugby league is extremely During the four seasons under investigation, limited, ' least incidence Accepted for publication not on the of injury. 599 medical conditions that prevented a player 9 July 1996 Previous investigations have reported on short from either playing or taking part in club train- 332 Stephenson,G ssane,Jennings

Table I Type of injury sustained in matches

AR players Ist Team A Team

Rate per Rate per Rate per Typeof injury Number 1000 hours 95% CI Number 1000 hours 95% CI Number 1000 hours 95% Cl

Haematotnas 68 16 12-20 37 16 11-20 32 17 11-22 Muscle strains 79 18 14-22 51 21 29-44 27 14 9-19 Muscular injuries (total) 147 34 29-40 88. 37 25-37 59 31 23-39 Joint sprain 117 27 22-32 61 26 16-27 56 29 22-37 Laceration 85 20 16-24 66 28 21-34 19 10 6-14 Contusion 51 12 9-15 28 12 7-16 23 12 7-17 Fracture and dislocation 40 9 6-12 25 10 6-15 15 8 4-12 Concussion 35 8 6-11 18 8 4-11 17 9 5-13 Abrasion and skin infection 10 2 1-4 7 3 1-5 3 2 1-5 Others 7 2 1-3 4 2 1-4 3 2 1-5 All types 492 114 105-124 297 124 111-138 195 102 88-115

CI, confidence interval.

Table2 Site of injurysustained in matches

AU players lit Team A Team

Rate per Rau per Rate per Site of injury Number 1000 hours 95% Cl Number 1000 hours 95% Cl Number 1000 hours 95% CI

Head and neck 165 38 33-44 111 47 38-55 54 28 21-36 Thigh and calf 88 20 16-25 49 21 15-26 39 20 14-27 Knee 50 12 8-15 28 12 7-16 22 11 7-16 Thorax and abdomen 45 10 7-14 24 10 6-14 21 11 6-16 Shoulder 41 10 7-12 26 11 7-15 15 8 4-12 Ankle 40 9 6-12 24 10 6-14 16 8 4-12 Arm 32 7 5-10 19 8 4-12 13 7 3-10 Others 31 7 5-10 16 7 3-10 15 8 4-12 All sites 492 114 105-124 297 "124 111-138 195 102 88-115

Cl, confidence interval.

Table3 Activity of being injured at the time .

All players Ist Team A Team

Rate per Rate per Rate per Activity Number 1000 hours 95% Cl Number 1000 hours 95% CI Number 1000 hours 95% CI

Tackled 228 46.3 41.9-50.7 138 46.5 40.8-52.1 90 46.2 38.2-53.2 Other 159 32.3 28.2-36.4 99 33.3 28.0-38.7 60 30.8 24.3-37.2 Tackler 105 21.3 17.7-25.0 60 20.2 15.6-24.8 45 23.1 17.2-29.0 Total 492 100.0 99.3-100 297 100.0 98.8-100 195 100.0 98.1-100

Cl, confidence interval.

ing for rugby league were recorded. Of these, when comparing the first and A teams, 27 were illnesses and conditions such as although the two rates are markedly different sickness, and were excluded from the analysis. (47 v 28 per 1000 hours; first team vA team; z This left a total of 572 sports. injuries, 492 = 3.2, P<0.05). The nextmost commonly (82.1%) of which were received during match injured site in the body was the thigh and calf, play and 80 (13.9%) during training. but the injury rate was less than half that of the Of the 492 match injuries, 297 (60.4%) head and neck (20 per 1000 hours). The least were to first team players and 195 (39.6%) to injured sites of the body were the arm and the A team players. This equates to an overall inci- "others" category, which included such areas dence rate of 114 injuries per 1000 hours of as fingers and toes (both 7 per 1000 hours). match play (first team, 124; A team, 102; z= The figures for the first and A teams are 2.2, P<0.05). given in table 3 and tended to be quite similar. The types of injuries sustained during' match Of all the playing injuries the largest percent- play are shown in table 1. The highest injury age was received when a player was being tack- rates were for muscular injuries (haematomas led (46.3%), while a tackler was injured in and strains) (34 per 1000 hours). When exam- 21.3% of the injury events. The remaining ining the first and A teams separately, the same 32.3% were classified as "others", which type of injury was the most common (first team included injuries during such activities as run- 37, A team 31 per 1000 hours; z=4.7, P< ning and scrummaging. 0.05). The types of injury that were least com- The amount of time off taken by players as a . mon were abrasions and skin infections and result of injury is shown in table 4. It can be "others" (both 2 per 1000 hours). seen that more than two thirds of all injuries The sites of injuries sustained by players are sustained required a player to take less than in shown table 2, which indicated that the one week away from playing and training, a body region of the that suffers the highest relatively small proportion of injuries (7.5%) injury is rates the head and neck (38 per 1000 required a player to be away from training for hours). The same site was also the most injured more than four weeks. Injury in rugby league 333

Table4 Time off as a result of being injured

Allplayers Ist Team A Team

Rau per Rate per Rate per Time off Number 1000 hours 95% CI Number 1000 hours 95% CI Number 1000 hours 95% CI

<1 week 345 70.1 66.1-74.2 225 75.8 70.9-80.6 120 61.5 54.7-68.4 1-2 weeks 67 13.6 10.6-16.6 32 10.8 7.3-14.3 35 17.9 12.6-23.3 2-3 weeks 32 6.5 4.3-8.7 14 4.7 2.3-7.1 18 9.2 5.2-13.3 3-4 weeks 11 2.2 0.9-3.5 5 1.7 0.6-3.9 6 3.1 0.6-5.5 >4 weeks 37 7.5 5.2-9.6 21 7.1 4.2-10.0 16 8.2 4.4-12.1 Total 492 100.0 99.3-100 297 100.0 98.8-100 195 100.0 98.1-100

Cl, confidence interval.

Table5 Distribution of injury betweenforwards and backs

Ail players Ist Team A Team

Rate Rau Rau Per . per per Position Number 1000 hours 95% CI Number hours 95% CI Number hours 1000 " 1000 95% CI Forwards 277 139 124-155 169 153 113-150 108 122 100-144 Backs 215 93 81-105 128 100 83-116 87 84 67-101 Total 492 114 105-124 297 124 111-138 195 102 88-115

CI, confidence interval.

Table6 Classification of concussions

Severity of concussion Action

Mild: no loss of consciousness (LOC) i. Full memory of event Can usually continue playing (after being checked) ii. Memory deficit of event Must cease playing: no training or playing for 48 hours, and on ly after medical check by the club doctor Moderate: (LOC) of up to 2 minutes Must cease playing: no playing or training for 15 days and only after a medical check by the club doctor Severe: i. LOC of up to 3 minutes Must cease playing: no playing or training for 22 days and only after a medical check by the club doctor ii. LOC of over 3 minutes Must cease playing: and be admitted to hospital for observation: no playing or training for 29 days and only after a medical check by the club doctor

All casesof SEVERE concussion should have x rays of the skull and cervical spine. Source: The Rugby Football League (1993).

The incidence of injury for forwards and result in a fixture backlog requiring more than backs is shown in table 5. From this it can be one game to be played per week. seen that forwards are injured more frequently Muscular injuries accounted for 29.9% of all than backs in absolute terms (56.3 v 43.7%, injury types. This is similar to values that have both first and A teams). When the rate is previously been reported. 1213Injuries of this standardised for the number of players (six for- type to the quadriceps have been reported to wards and seven backs), the injury rate be common as this is the first point of contact differences are even larger (forwards 139 v in the tackle. ' It could be argued that a game backs 93 per 1000 hours; z=4.5, P<0.05). which has been likened to being mugged 30 times in 80 minutes, " which involves a player in 20 to 40 physical "confrontations" per Discussion game, ' predisposes players to this type of In this study we found an -overall injury injury. incidence rate in rugby league of 114 injuries The site of the body to which most injuries per 1000 man hours of play. It has been took place was the head and neck region, with suggested that the high injury rate is due to 33.3% of all injuries. This is higher than has repeated hard body contact. ' The injury rate in been previously reported, with studies quoting the current study is higher than the rate of 14 values ranging from 5.8%' to 28.8%' of all minor that has been reported for rugby union, " and injuries. Again, the decision to include also higher than the rate of 45 per 1000 hours injuries may account for part of the difference. that has been reported for Australian rugby But at least one other study chose to include league. ' One probable reason for the differing minor injuries, "' and commented that head and rates between Australian and English rugby neck injuries were on the increase. 'While league, and League and Union was the another reported that head lacerations were decision of previous studies"' only to include very common, although they did not require injuries that required a player to miss a subse- players to miss games. ' quent game, the games being played on a The observation that a -majority of injuries weekly basis. If in the present study injuries are caused in the tackle is common to both requiring less than one week to recover from rugby codes 31 "" The findings of the present are excluded the overall rate is reduced to 34 study show that the player being tackled is per 1000 hours (first team 30, A team 39 per more likely to be injured (46.3%), and this is 1000 hours). However, this may not strictly be also in agreement with previous research. "" In comparable, as situations such as weather con- rugby league, the tackle is a very prominemt in ditions England may result in more than a part of the game, which carries inherent week between games. Then postponed games, dangers such as being knocked over back- which must be played later in the season, could wards, whiplash, and the clashing of heads' 334 Stephenson,Gissane, Jennings

This study also reported that 32.3% of play- cal body contact between players. Injury rates ers were injured in situations classified as "oth- were shown to be higher at the highest ers"; this must be considered a limitation of the standards of play. Forwards experience greater study. With almost one third of injuries falling rates of injury than backs, which is probably into this category, it is clear that it is too large due to their being involved in more repetitive as a general classification, and that future body contact than backs. Perhaps future research should attempt to break this down research should examine the differing injury into more component parts. For example, rates between forwards and backs in relation to some injuries may have occurred as a result of their game-specific work loads, and also foul play but were not recorded as such. analyse what types of injury these respective Nevertheless, the sport is concerned about groups receive during the course of a game. such incidents, and this was emphasised by the Rugby League issuing a directive in January We would like to thank Dr JA White, Dr L Rushton, Dr JCG 1995 specifically making lifting a player and Pearson, and Ms CAC Coupland for their assistance while "spear tackling" him a sending off offence writing this paper. under Law 15.1 d regarding illegal throws. The vast majority of injuries recorded in this (70.1 %) be study required that a player absent Postscript from training and playing for less than a week. During the peer review of this paper, the Part of the reason for this high figure was the reviewers made some extremely useful and decision to include all *injures received while helpful comments. For some of these points, playing. Gibbs, ' who defined an injury as an we had the necessary information available and event that required a player to miss the next could address the issues, while unfortunately week's game, reported that the largest for others we could not do so. proportion (38%) of injuries required players One of these points was related to infor- to miss the next game. If the injuries requiring mation on the incidence of foul play, which was less than one week off play are excluded from not collected. The reason for this was that the current analysis, the largest proportion when the register was begun back in 1990, we one to two weeks absence (46%). required collected what we thought was relevant at the However, classifying injuries in this way can be time. At that time, there were almost no studies shown to miss many minor injuries. " Also, it available on rugby league and an overall should be pointed out that 17% of the injuries picture of the injury situation was needed. This in this study were lacerations. The recorded is not to say that foul play is not an extremely majority of these would have involved the important issue, but with the advent of the "blood-bin", which began in the 1991-2 season Super League concern has shifted. The Rugby over such injuries. Furthermore, after concern League Medical Association is currently more one investigation reported that such injuries concerned with the effect that playing on hard rarely cause a player to miss a game, but ground will have on overall injury rates and counted 101 over five seasons.' If they were with the potential for heat stress injuries. counted, they would add considerably to both the numbers of, and the injury rates. A possible explanation for differences be- 1 Gibbs N. Injuries in professional rugby league: a three year League Union be prospective study of the South Sydney professional rugby tween the and codes might league football club. Am J Spore Med 1993; 21: 696- 700. the specific regulations regarding concussions. 2 Seward H, Orchard J, Hazard H. Football injuries in International Rugby Football Board Australia at the elite level. Med JAutr 1993; 159298-306. The reso- 3 Gissane C, Jennings DC, Standing S. Incidence of injury in lution (5.7) requires a concussed player to rugby league football. Physiotherapy 1993; 79: 305-10. for 4 Larder P. Te rugby leaguecoaching manual, 2nd ed. London: refrain from playing and training a period of Kingswood Press, 1992. at least three weeks after the injury, and subject 5 Gibbs N. Common rugby league -injuries: recommendations by ' for treatment and preventative measures. Sports Med 1994; to being cleared a proper examination. 18:438-50. However, in rugby league, concussion is 6 Doman P Dunn I- Sporting injuries. London: University of by in table 6. This Queensland Press, 1987. graded severity, as shown 7 MacLeod DAD. Risks and injuries in rugby football. In: could result in injuries being recorded but McLatchie GR, Lennox CME, eds. The soft tissues: less from trauma and sports injuries. Oxford: Butterworth- players requiring time away playing Heinnemann, 1993: 371-81. and training. 8 Brewer J, Davies J. Applied physiology of rugby league. The finding backs injured Sports Med 1995;20: 129-35. that are much 9 Alexander D, Kennedy M, Kennedy J. Rugby league more frequently than forwards has' been football injuries over competitive two seasons Med-7 Aust by others. "" It has also been 1980;2: 334-5. observed 10 Clarke GM. Statistics and experimentaldesign: an introduction reported that forwards received a larger than for biologistsand biochemists.London: Edward Arnold, 1994. injuries, based 11 Garroway M, Macleod D. Epidemiology of rugby football expected number of on the injuries. Lancet 1995; 345: 1485-7. number of player positions. ' As backs run the 12 Alexander D, Kennedy M, Kennedy J. Injuries in rugby forwards be involved in league football, Med9Ausr 1979; 2: 341-2. ball more and tend to less ' 13 Walker RD. Sports injuries: rugby league maybe more collisions, then perhaps they should be dangerous than union. Practitioner 1985;229: 205-6. New Scientist more susceptible to injuries. It has also been 14 O'Hare M. In a league of their own. injury between 1995; 1997:30-5. suggested that the pattern of 15 Addley K, Farren J. Irish rugby injury survey: Dungannon forwards and backs might change with an football club (1986-1987). Bra' Sports Med 1988; 22: 22-4. " 16 Inglis GS, Stewart ID. Rugby injury survey 1979. NZMed3 alteration in the style of play. 1981; 11:349-50. The results from our study show that rugby 17 Lythe MA, Norton RN. Rugby League injuries in New Zea- has high injury This is land. NZ I SportsMed 1992;20: 6-7. league very rates. 18, Inklaar H. Soccer injuries I: incidence and severity. Sports undoubtedly due to the large amount of physi- Med 1994; 18:55- 73.

B BMA House, Tavistock Square, London WCIH 9JR. Tel. 0171 383 6305. Fax. 0171 383 6699 ' 1997.All rights of reproductionofthis reprint arereserved in all countriesof theworld Piing Printedin GreatBritain by Meridian Print CentreLtd. Derby. BJSM/Dec/96 Differences in the Incidence of Injury Between Rugby League Forwards and Backs Gissane C, 'Jennings D. C.,2 Cumine A. J.,3 Stephenson S.E., 4 & White J.A. S l Department of Health Studies, Brunel University College, lsleworth, Middlesex, UK. 2General Practitioner, Reigate, Surrey, UK. 3Department of Sport Science and Physical Education, St Mary's University College Strawberry Hill, Twickenham, Middlesex, UK. 4Department of Physiotherapy, West Middlesex University Hospital, lsleworth, Middlesex, UK. 5Department of Public Health Medicine and Epidemiology, Queen's Medical Centre, University Hospital, Nottingham, UK.

ABSTRACT The purposeof this study was to describethe differencesin the Gissane G Jennings D. C., Cumine A. J., Stephenson S.E., & White incidence of injury to forwards and backs, and to determine if JA (1997) Differences in the incidence of injury between rugby there is a greater risk of injury when playing as a forward or a league forwards and backs. The Australian Journal of back in a professionalRugby League club over a period of four Science and Medicine in Sport 29 (4): 91-94 seasons. Evidence with regard to the incidence of injury to forwards and METHODS AND PROCEDURES backs in the game of rugby league is extremely limited. A four year The data to be used in this investigationhave been described prospective study of all the injuries from one professional Rugby previously (Stephenson et al., 1996). All injuries that were League club was conducted All injuries that were received during reportedby players during the four seasons betweenJuly 1990 match play were recorded, and those for forwards and backs and May 1994, at one professional Rugby League club were backs compared. Forwards had a higher overall rates of injury than recorded. A season ran from the beginning of pre-season 1000 hours, (139.4 [124.2 - 154.6] vs. 92.7 [80.9 - 104.6] per player training, to the last competitivematch in either April or May. An body P<0.00006).Forwards had a higher rate of injuries to all sites injury was taken to be the onset of pain or a disability that injury. with the exception of the ankle and the 'others' category of occurred while playing,Rugby League Football (Gissane et al., (11.6 16.9 16.3] They had significantly higher rates for the arm - vs. 1993). Which has been reported to best correspondwith daily .3.9 P=0.005) head [1.4 - 6.4] per 1000 player hours, and, the and reality (Twellaaret al., 1996). The diagnosisand classificationOf [18.7-31.4] injuries 1000 neck (53.9 [43.9 - 63.8] vs. 25.0 per player injurywas carried out by the club doctor and the physiotherapist. injuries hours, P<0.00006). Forwards had significantly more than The site and type of injuries were categorised as described backs (17.1 7.3 1000 hours, P for contusions vs. per player z=2.85, previously (Alexander et al., 1980). The following details were (26.7 13.8 1000 hours, = 0.0044), lacerations vs. per player z=2.92, recordedabout each injury:The positionof the player(forward or P= haematomas (20.6 11.6 1000 hours, 0.0035) and vs. per player z back), the site of the injury, the nature of injury,the team played Forwards likely be injured = 2.29, P=0.02). were also more to when for (first or 'A' team), activity at the time of injury, time off from in ball (70.5 [59.2 81.7] 38.0 [30.2 45.7]), possession of the - vs. - playingand trainingas a result of injury. and tackling (33.2 [25.3 41.1] vs. 16.8[11.6 22.]]). The also when - - During the time of the injury survey a total of 249 games were higher injury by forwards were most likely as a rates of experienced played, which included all pre-season, league, cup and post- result their greater physical involvement in the game, both in of season games.This representeda total of 4305.21player hours attack and in defence. at risk (13 players x 1.33 hours x 249 games),each game lasting 80 minutes.Since a team of 13 is comprisedof six forwardsand backs, forwards for a total of 1987.02playing INTRODUCTION seven were at risk hours, and backs for 2318.19 hours. The age of a player was In many team sports, different demands are made on different taken as the age at the beginningof the season(1st September). playerpositions. Within Rugby League-therehas been a trend to Basedon this, the mean age(±SE)was 24.3±0.27yrs. reduce specialisation, so that the work carried out by players The statistical analysis consisted of the calculation of injury it has varies less from position to position (Larder, 1992) and rates per 1000 hours of play as a standardisedrate of exposure, been suggested that fitness training is uniform for all positions for both forwards and backs. The injury rates for the different (O'Connor, 1995). Nevertheless, match analysis has demon- playing units were comparedusing the normalapproximation as strated that backs cover greater distances iri a game than describedby Clarke (1994): forwards (7336 6647m [Meir 1993]), that vs. et al., and also r, -r2)-0 forwards are involved in a larger number of physical collisions r- +z than backs (36.3 vs. 19.14).(Larder, 1992). It can be said that the ,t1 forwardsmain role in possessionis to gain ground quickly and to put the opposition on the back foot, while backs attempt to move t, t2 the ball wide and exploit space. Similarly, when defending where r1 and -r2are the two rates being examinedand and forwards do the majority of the tackling, attempting to stop the are the respectivetime periods. oppositiongaining ground, and so denyingthem space in which RESULTS to operate. During the four years of the study a total of 492 injuries were With these in demanded the two variations physical effort of 277 to forwards and 215 to backs. The overall injury team it hypothesisedthat there is recorded, playing units within a was a for 114.3 injuriesper 1000 playerhours (95% differing injury, that the injuries by rate all playerswas risk of -and received members CI 104.8 to 123.8).The rates for forwardsand backs were 139.4 of these might differ. It has been demonstrated hours playing units also (124.2to 154.6) and 92.7 (80.9 to 104.6) per 1000 player that forwards do higher injury than backs experience rates of (z 4.45; P<0.0006). The relativerisk of injurywhen comparing (Gibbs,1993; Gissane et al., 1993; Norton& Wilson, 1995) while = forwardsand backs was 1.50 (1.32 to 1.68).. in Rugby Union, it has been reported that 80% of injuries to Figure Injuriesto differentsites of the body are displayedin 1. backs took place whilst players were involved in the tackle backs, Forwardshad higher rates of injury in all categoriesthan situation(Garroway and Macleod,1995). But to date, the specific injury. with the exceptionof the ankle and the 'others'category of questionof whether, and how, differing roles in game situations the Forwardsalso demonstratedhigher injury rates in six of eight altersthe risk of injury has not been addressed. Sport 91 The Australian Journal of Scienceand Medicinein J:Figure 1: Comparison of injury sites for forwards and backs (rate with 95% CI).

70 Forwards E] Backs 60 * Total 50 ' Significantcüfferencas between ö forwardsand backs,Pc0.05 o. 40 0

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Table 1: Type of injury comparison of forwards and backs.

FORWARDS BACKS TOTAL Rate per Rate per Rate per 1000 1000 ' 1000 Number hours 95% Cl Number hours 95% Cl Number hours 9T/. CI

Joint Sprains 60 30.2 22.7-37.7 57 24.6 18.3-30.9 117 27.2 2-2.3-32.0 Dislocation 5. 2.5 3.3-4.7 6 2.6 0.5-4.7 11 2.6 1.1-4.1 Joint injuries (total) 65 32.7 24.9-40.5 63 27.2 20.6-30.8 128 29.7 25.9-36.3,

Muscle strains 38 19.1 13.1-25.2 41 17.7 12.3-23.1 79 18.3 14.3-22.4 Concussions 22 11.1 6.5-15.7 13 5.6 2.6-8.7 35 8.1, 5.5-10.8 Fracture 16 8.1 4.1 -12.0 13 5.6 2.6-8.8 29 6.7 4.3-9.2

Contusions 34 17.1 11.4-22.8 17 7.3 3.9 -10.8 51 11.8 8.6-15.1 liaematomas 41 20.6* 14.4-26.9 27 11.6 7.3-16.0 68 15.8 12.1 -19.5 Total 75 37.7* 29.4-46.1 44 19.0 13.4-24.5 119 27.6 2-2.7-32.5

Abrasions & Skin infect. 5 2.5 3.31-4.72 5 2.2 0.3-4.1 10 2.3 0.9 - 3.8 Lacerations 53 26.7* 19.6-33.8 32 13.8 9.1 -18.6 85 19.7 15.6-23.9 Other 3 1.5 -0.2-3.2 4 1.7 0.0-3.4 7 1.6 ' 0.4-2.8

Total 277 139.4 124.2-154.6 215 " 92.7 80.9-104.6 492 114.3 104.8- 123.8 'signficantiydifferent from backs (P<0.05)

sitecategory classifications, and had significantly higher injury associatedwith most injury. The results indicated that forwards ratesfor head and neck injuries (53.9 vs. 25.0 injuries per 1000 had significantlyhigher rates of injury than backswhen they were Payerhours, z=9.32, P<0.00006),and arm injuries (11.6vs. 3.9 the tackler, i.e. defending(33.2 vs. 16.8 per 1000 player hours,z per1000 player hours, z=2.81, P=0.005). The two categories = 3.35, P=0.00082), and when they were being tackled i.e. in which backs recorded higher injury rates were ankle (9.9 vs: attacking (70.5 vs. 38.0 per 1000 player hours, z =4.52, 8.6per 1000 player hours, z=0.46, P=0.65) and 'others' (7.3 P<0.0006).It was also found that when incidencerates for being vs.7.1 per 1000 player hours, z=0.11, P=0.91), althoughthese tackled and tackling were compared directly, both forwards werenot statisticallysignificant. (tackler 33.2, tackled 70.5 per 1000 player hours, z=5.16, Analysis of the types of injuries sustained (Table 1), P<0.0006)and backs (tackler16.8, tackled 38.0 per 1000'player demonstratedthat forwards and backs had significantlydifferent hours, z=4.35, P<0.0006),were significantlymore likely to be ratesof injury for contusions (17.1 vs. 7.3 per 1000 player hours, injuredwhen being tackled. z=2.85, P=0.0044), lacerations (26.7vs. 13.8 per 1000 player Finally,when the rates for time off as a"result of injury (Figure hours,z=2.92, P=0.0035) and haematomas(20.6 vs. 11.6 per 2) were analysed, the only category in which there were 1000 player hours, z=2.29, P=0.02). It was observed that significantdifferences between forwards and backs was the rate forwardsexhibited higher injury rates for each type of injury with of injury requiring less than one week away from playing and the exception of the dislocations and the others category. training (99.1 vs. 63.9 per 1000 player hours, z=4.01, P= However,in both cases the observed rates were small and the 0.0005). differences (dislocations P=0.96; non-significant z=0.05, others DISCUSSION Z=0.18, P=0.86). The finding this the differing injury rates of Activity at the time of receiving an injury is shown in Table 2. major of study was forwards backs 1000 hoursat risk.The RR of 1.50 From this it can be seen that the tackle is the phase of play and per player

92 The Australian Journal of Science and Medicine in Sport Table 2: Activity at the time of injury.

FORWARDS BACKS TOTAL Rate per Rate per Rate per 1000 1000 1000 Number hours 95% Cl Number hours 95% Cl Number hours 95% Cl Tackler 1 66 33.2* 25.4-41.1 39 16.8 11.6-22.1 105 24.4 19.8-29.0 Tackled . 140 70 5*# 59.2-81.7 88 38.0" 30.2-45.7 228 53.0# 46.3-59.6 The tackle 206 103.7* 90.3-117.1 127 54.8 45.5-64.1 333 73.5 69.4-85.3

Other 71 35.7 27.6-43.9 88 38.0 30.2-45.7 159 36.9 31.3-42.6 Total 277 139.4 124.2 215 92.7 80.9-104.6 -154.6 492 114.3 104.8 -123.8 * significantlydifferent from backs (P<0.05) significantlydifferent from tackling (P<0.05)

Figure 2: Time off as a result of injury for forwards and Forwards experienced higher rates of injury in each type backs (rate with 95% CI). category in this study, with the exceptionof the dislocationand `others'category. They recordedsignificantly higher rates for both contusions, haematomasand lacerations.The higher rates for lacerations could be as a result of more Injuries to the facial 120 Forwards region (Seward et al., 1993). In spite of their high incidence,it may be consideredfortunate that is for injuries Backs rare such to cause 100 F-I playersto miss games(Gibbs, 1994). Total place ö In this study 67.7% of. all injuries took in the tackle, which 80 is a slightly lower than figures that have been g- ' Significantdifferences between previoisly reported (77.2%) (Norton & Wilson, 1995). The injury- forwardsand backs, P<0.05 rates were 60 higher the ball being CL significantly when players were carrying and tackled. It has previously been reported that of all injuries that 40 take place in the tackle, 56.6% of them are to the ball carrier (Norton & Wilson, 1995), whereas the figure in the present study 20 was 68.5%. It has already been reported how forwards tend to be In more physical confrontations than backs in the game, and 0m Si 2 when examining the activity whilst in possession, Larder (1992) mmmm that forwards 333; reported were tackled an average of 13.5 times per v v? N backs pvj game, while were tackled only 9 times per game. Robinson (1996) reported that forwards were tackled 14.2±0.8 (meantSE), and backs 10.4±0.5 times per game. The process of being tackled is indicatesthat forwards had a 50% greater risk of injury than an area of the game that carries inherent dangers, including injuries, backs.Overall, forwards received56.3% of all injuries and backs whiplash the clashing of heads and being knocked backwards (Larder, Several 43.7%. While other. studies have reported that the number of over 1992). authors have that high injuriesto forwards are more numerous than injuries to backs suggested stricter enforcement of tackle (Seward (Gibbs, 1993; Gissane et al., 1993; Norton & Wilson; 1995; regulations could reduce the number of injuries at al., 1993; Gibbs, 1994; Milburn, 1995). Stephensonet al., 1996), injury rates do need to be standardised relativeto exposure,and considerationneeds to be given to the Similarly, forwards perfdrm on average over twice as many fact that forwards have a lower overall game time exposure,as tackles per game as backs (22.8 vs. 10.1) (Larder, 1992),which thereare fewer forwards, six, in a side than backs, seven. When exposes them to a greater risk of injury and accounts for their thesefactors are taken into account,the differencesbetween the significantlyhigher injury rates than backs. Outside of the tackle two playing units are much larger than raw numbers would situation,backs demonstratedhigher injury rates than forwards, convey. It has been suggested that forwards experiencing a which may appear surprising since they are not involved in higher injury rate, may be due to their involvement in more scrummages, which average 19.4 per game (Larder, 1992): physical body contact than backs (Gibbs, 1993). This is However, there is evidence that they cover greater distances supported by match analysis at international level which has than forwards (7336 vs. 6647m) (Meir et al., 1993), and knee shownthat each player in a side is involved in an averageof 27 injuries have been reported to occur in non-contact hyper- physicalconfrontations (tackles and being tackled) per game, extension and side stepping manoeuvres (Gibbs, 1994). forwardsaverage 36.3 physical confrontations and backs only Furthermore,they would tend tobe involved in relatively more 19.1 (Larder, 1992). While at club level Robinson (1996), situations where they were required to gather a high ball, in reportedthat forwards and backs were involved in 32.4±1.2 and circumstanceswhere they may be requiredto jump for the ball, 19.0±0.8 (mean±SE) physical confrontations per game with the oppositionapproaching towards them. If more than one respectively. player is jumpingfor the ball there is an obviousrisk of injury from The higherrates of forward injuriesfor specificsites of the body collision or landing awkwardly,without a tackle tacking place. has been reported previously (Seward et al., 1993). In the Similar situations have also been described in Rugby Union presentstudy, the site that received the most injuries was the where the 'Garryowen'kick is used as an attackingploy (O'Brien, 1992). head and neck area, with forwards receiving significantly more injuries than backs. Injuries to the head and facial areas, The only time off category in which there were significant particularlacerations, have been suggested to be much more differences between forwards and backs were injuries that commonin forwardsthan in backs (Sewardet äI., 1993). require less than one week away from playing and training.The . The AustralianJournal of Scienceand Medicine in Sport 93 TEXT BOUND INTO

THE SPINE reasonfor this would most probably be the higher numbers of Gissane, C., Jennings, D.C. & Standing, P. (1993). Incidence of injury in league football. overallinjuries received by forwards.When examininginjuries in rugby Physiotherapy 79: 305-310. this Larder, P. (1992). The rugby league coaching manual. 2nd ed. Kingswood way, one characteristic of Rugby League is the larger Press, London. numbers injuries from of requiring one week away playing and Lower, T. (1995). Injury data collection in the rugby codes. Australian training,compared with other team sports (Sewardet al., 1993). ' Journal of Science and Medicine in Sport 27(2): 43-47. Arguably,a sizeable proportion of these are lacerations,which Macleod, D.A. D. (1993). Risks and Injuries in rugby football. In: McLatchie somestudies have chosen not to include.Gibbs (1993), reported GR Lennox CME, editors. The soft tissues: trauma and sports injuries. Oxford: Butterworth-Heinnemann X61lacerations over a three year period, that did Ltd: 371-81. not require a Meir, R., Arthur, D. & Forrest, M. (1993). Time playerto miss subsequent games. If they were included they and motion analysis of professional rugby league: a case study. Strength Conditioning Coach wouldhave increasedthe overallinjuries by 43%. 3: 24-29. In Rugby League forward players experiencehigher rates of Meir, R. (1994). Seasonal changes in estimates of body composition in injurythan backs, in spite of the fact that backs out number -professionalrugby league players. Sport Health 11(4): 27-31. Milburn, P. D. (1995). The'rugby forwards to six. It has been that if the differing tackle -a time for review. Journal of seven suggested Physical Education New Zealand 28(1): 9-15. playing do have different injury then units profiles, perhaps Norton, R. & Wilson, MA. (1995). Rugby league injuries and patterns. New specificprevention programmes would be appropriate(Norton & Zealand Journal of Sport Medicine 22: 37-38. Wilson,1995). The results of this study support this proposition O'Brien, C. (1992). Retrospectivesurvey of rugby injuries in Leinster province andoffer further evidence as to the different areas of the body, of Ireland 1987-89. British Journal of Sports Medicine 26: 243-244. andthe specific situations in which forwards and backs receive O'Connor, D. (1995). Fitness profile of professional rugby league players. injuries.Such be taken into Journal of Sports Sciences 13(5): 505. considerationsshould accountwhen Robinson, J.J. (1996). An investigation Into the defensive designing training (Seward offensive and player conditionsand programmes et work rate of rugby league footballers. Unpublished BSc dissertation, al.,1993). Fitness profiles have shown forwards to be heavier Brunel UniversityCollege. thanbacks, with greater amounts of body fat (Brewer at al., Seward, H., Orchard, J. & Hazard H. (1993). Football injuries in Australia at 11994).It has been argued that forwardsneed to have such body the elite level. Medical Journal of Australia 159: 298-306. Stephenson, S., Gissane, C. & Jennings, D. (1996). Injury in league: compositionto provide them with protection from the extra rugby a four year prospective survey. British Journal of Sports Medicine 30(4): collisionsin which they are involved(Meir, 1994). Rugby League 331-334. have demonstrated may recently a trend toward less Twellaar, M., Verstappen, F.T. J. & Huson, A. (1996). Is prevention of sports Specialisation(Larder, 1992), and fitnesstraining may be uniform injuries a realistic goal? A four-year prospective investigation of sports acrosspositions (O'Connor, 1995), but evidence suggests that injuries among"physical education students. American Journal of forwards'greater physical involvement,places them at a much Sports Medicine 24(4): 528-534. Van Mechelen, M., Hlobil, H. & Kemper, H.G. C. (1992). Incidence higherrisk of injury. Some investigators have argued that the severity,. best aetiology and prevention of sports injuries: a review of concepts. Sports way to standardise injury rates in rugby football is to quote Medicine 14(2): 43-47. incidenceand prevalence per 1000 player hours (Edgar, 1995; Lower,1995). While others have commentedthat getting a true reflectionof actual exposure time at risk may prove too difficult (vanMechelen et al., 1992). In Rugby League, future research could possibly address the questions of how physical involvement(tackles and being tackled) influencesinjury rates, h andare their particular tackle situations that expose players to 4, 1997 higherinjury risks? Why this is the case may be difficult to e) pinpoint '.. why does one tackle cause an injury when the Australian previous50 did not?' (Macleod, 1993). Furthermore,within the X twoplaying units of forwards and backs, there are specialist Conference Positions hooker half-back, that future , such as and so research couldbe directed towards examiningspecific injuries that occur Science acrossthe full range of positions,rather than the two playing units -of and withina team. Medicine in Sport CONCLUSION Thelimitations of this study not with standing, it is clear that forwardplayers in rugby league demonstratea higher incidence Ofinjury than back players. Forwards appear to have a higher injuryrates because of their greater physical involvement comparedto backs. But, to provide a more complete answer, Specificanalysis of physical involvementin relationto injury rates AbstractBooks ISrequired. REFERENCES Alexander,D., Kennedy,M. & Kennedy,J. (1980).Rugby league football injuriesover two competitiveseasons. Medical Journal of Australia 2: 334-335. $20. Send to: Brewer,J., Davis, J. & Kear J. (1994). A comparison of physiological your chequeor postal order characteristicsof rugby league forwards and backs. Journal of Sports SportsMedicine Australia Sciences 12: 158. Oiarke,G. M. (1994). Statistics and experimental design: an introduction POBox 897 for biologists and biochemists. Edward Arnold, London. BelconnenACT 2616 Edgar,M. (1995). Tackling rugby injuries. Lancet 345: 1452-1453. Garroway,M. & Macleod, D. (1995). Epidemiology of rugby football injuries. Lancet 345: 1485-1487. Or faxyour creditcard details through to: Gibbs,N. (1994). Common rugby league injuries: recommendations for SportsMedicine Australia treatment and preventative measures. Sports Medicine 18: 438-450. Gibbs, N. (1993). Injuries in professional rugby league: a three year (02)6253 1489 prospectivestudy of the South Sydney professional rugby league football club. American Journal of Sports Medicine 21: 696-700. Forfurther information phone (02) 6251 6944. j94 The AustralianJournal of Science and Medicine in Sport Reprintedfrom BRITISHJOURNAL OF SPORTSMEDICINE, June1998, Vol 32, No 2, p 149-152

Injury in summer rugby league football: the experiences of one club -

C Gissane, D Jennings, j White, A Cumine

Abstract elimination of two cup competitions. Injury Objective-To investigate whether the studies carried out in Australia' 's have consist- movement of the playing season from ently reported higher injury rates than English winter to summer would alter the risk of studies, '' and it was surmised that this was due injury to players taking part in first team to the game being played on harder surfaces. " European professional rugby league. Playing rugby league in the summer months Methods`The study design was a histori- may also increase the likelihood of players suf- cal cohort design comparing winter and fering from thermal injuries and heat stroke, as summer seasons in first team European the result of a combination of higher tempera- " rugby league, which recorded injuries tures and relative humidities. received by players during match play. It is unusual for a sport to completely change Each injury was classified according to its playing calendar, and this move may result site, type, player position, activity at the in an alteration in the risk of injury to players. time of injury, and time off as a result of Therefore the purpose of the present study was injury. to ascertain whether or not the movement of from Results-The risk of injury when playing the playing season the autumn and winter summer rugby league was higher than months to the spring and summer months injury when playing winter rugby league (relative would alter the risk of to players taking in league in risk = 1.67 (95% confidence interval 1.18 to part professional rugby the new 2.17)). Both forwards (1.08 (0.28 to 1.88)) European Super League established in March 1996. and backs (2.36 (2.03 to 2.69)) experienced an increased risk of injury. Conclusions--Summer rugby may have Methods Super League resulted in a shift of injury risk factors as During the initial European sea- for first exhibited by a change in injury patterns. son all injuries that-were reported the league This may be due to playing conditions, but team at one professional rugby club Health injury data Department of there were also some law changes. were recorded. The were compared Studies, Brunel data from Changes in playing style, team tactics, with first team a previous study on University, Isleworth, four ' An player equipment, fitness preparation, the same club over a period of seasons. Middlesex TW7 SDU, injury defined impairment United Kingdom and the reduced preseason break may also was as a physical during competitive C Gissane have had confounding effects on injury received a match which

risk. 100 Reigate, Surrey, (Br-7 Sporu Med 1998; 32: 149-152) ' United Kingdom All players RR=1.67 D Jennings league; injury; injury k Forwards RR =1.08 Keywords: rugby summer 90 rugby; cohort study Backs RR = 2.36 Department of Public Q All 'Health Medicine and so players Epidemiology, Studies injury in league football have " Forwards University Hospital, of rugby U injury' higher Backs Queen's Medical previously reported rates of 70 Centre, Nottingham than for many other team sports. ' The reason NG7 2UH, United for this high injury rate is probably the high CA Kingdom number of physical collisions in which players 60 j White are involved during the course of a game. ' With 0 increasing in the sport, injuries 0 50 Division of Sport professionalism important issue, both in CD Science and Physical are an terms of team CD Education, St Mary's the livelihood the success and of players 40 University College, themselves. ' x Strawberry Hill, The year of 1996 saw a bold move, with Twickenham, European league- taking in the 30 Middlesex TWl 4SX, rugby place its United Kingdom spring and summer months, as opposed to A Cumine more traditional time of autumn, winter, and " kI I'*- spring. This move meant that matches would 20 Correspondence to: be played in higher temperatures (London C Gissane, Brunel- (mean (range)) in September University, Osterley Campus, temperature to 10 Borough Road, Isleworth, April 9.5 (6-14)°C and in April to September Middlesex TW7 5DU, 18.6 (13-22)°C) and on harder surfaces. There United Kingdom. would, however, be one third fewer competitive Winter rugby Summer rugby to be because Accepted for publication matches played, of the restruc- Fig,,, l Comparisonof injury ratesfor winter and interval). I September 1997 turing of the league (12 teams) and the summer rugby league(with 95% confidence 150 Gissane,Jennings, White, Cumine

Table 1 Relative risk of typesof injury

Winter Summer

Rau per 1000 Rau per 1000 No hours No hours RR 95% CI

Haematomas 4 1.68 2 5.03 3.00* 1.3 to 4.7 Muscle strains 18 7.54 1 2.51 0.33 -1.7 to 2.4 Muscular injuries (total) 22 9.22 3 7.54 0.82 -0.4 to 2.0 Joint sprain 25 10.48 8 20.12 1.92* 1.1 to 2.7 Laceration 4 1.68 0 - - - Contusion 4 1.68 0 - - - Fracture and-dislocation 8 3.35 7 17.60 5.25* 4.2 to 6.3 Concussion 8 3.35 1 2.51 0.75 -1.3 to 2.8 Others 1 0.42 1 2.51 6.00* 3.2 to 8.8 All injuries 72 30.18 20 50.29 1.67* 1.2 to 2.2

RR, relative risk Cl, confidence interval. *p<0.05.

prevented a player from being available for Results selection for the next competitive game. ' The There was no significant difference between games were 7 (1.09) (mean (SD)) days apart. the ages of the two cohorts of players The diagnosis and classification of injury was investigated (winter 24.2 (2.5) years, summer carried out by the club doctor and 25.7 (3.9) years (mean (SD)) (t = 0.76, df = physiotherapist. The type of information re- 69, p=0.448). Figure 1 shows the injury rates corded for each injury has been described for summer and winter rugby league for all previously. ' players: summer rugby league had a higher defined The population at risk was as the injury rate than winter rugby league, the actual for first players who were selected to play the risk of injury in summer rugby league being team in a given match, and the defined time at 67% higher than in winter rugby league (RR = duration risk for calculating injury rates was the 1.67 (95% CI 1.18 to 2.17)). by of the games multiplied the number of play- The injury rates for forwards and backs were (1.33 hours 13 by ers x players) multiplied the analysed separately (fig 1). The injury rate for The number of games played. average number forwards was slightly higher for summer. rugby during winter of games played the season was league (an 8% increase; RR = 1.08 (95% CI 34.5 (596.5 hours), player with each player 0.28 to 1.88)). The backs had a much larger 12.1 season, and averaging appearances per increase in injury rates when playing rugby during 23 games (397.67 the summer season league in the summer. The RR of 2.36 (95% CI hours) played in the Super League player were 2.03 to 2.69) indicated that the risk of injury of 1996, with each player averaging 8.3 increased 136% on changing the playing appearances. season from winter to summer. Statistical analyses consisted of the calcula- Table 1 shows that there were significantly tion of injury rate per 1000 hours of play as a ` increased risks during summer rugby of standardised rate of exposure. To calculate haematomas, fractures and dislocations, joint the relative risk (RR) of injury between winter injuries, and others (all p<0.05). Similarly, and summer rugby league, we used the there increased risk of injury incidence density ratio (IDR) method de- was significantly to the shoulder, arm, and other sites of the scribed by Hennekens and Buring" for the two body (all there was cohorts. p<0.05), and overall, significantly greater risk of injury to the lower No of summer injuries/exposuretime (hours) body (p<0.05) (table 2). There RR (IDR) = was an No of winter injuries/exposuretime (hours) increased risk of being injured in the "others" included Confidence intervals (95% CI) were calcu- activity category, which such activities high balls, in lated using the method described by McNeil. 'Z as running and catching summer (p<0.05), Where the CI did not contain the null value when compared with winter rugby being (RR = 1.0), the RR was taken as being signifi- while the injury risk when tackling or (table 3). cant at the p<0.05 level. " tackled did not alter significantly

Table2 Relative risk of injury to anatomical sitesof the body

Winter Summer

Rate per 1000 Rau per 1000 No hours No hours RR 95% CI

2.4 Thigh and calf 13 5.45 2 5.03 0.90 -0.6 to Knee 9 3.77 3 7.54 2.00 0.7 to 3.3 Ankle 8 3.35 1 2.51 0.75 -1.3 to 2.8 Shoulder 7 2.93 3 7.54 2.57* 1.2 to 3.9 Arm 3 1.26 2 5.03 4.00* 2.2 to 5.8 2.2 Head and neck 19 7.96 3 7.54 0.95 -0.3 to 2.6 Thorax and abdomen 11 4.61 2 5.03 1.09 -0.4 to Others 2 0.84 4 10.06 12.00* 10.3 to 13.7 Upper body 41 17.18 10 25.15 1.46 0.8 to 2.1 Lower body 31 12.99 10 25.15 1.94* 1.2 to 2.6

RR, relative risk; CI, confidence interval. *p<0.05. Injury in summer rugby 151

Table3 Acziviry at the time of injury receive an injury. ' Therefore increasing the amount of time that the backs are ball Winter Summer carriers involves them in more physical collisions and No Rate per 1000 hours No Rate per 1000 hours RR 95% CI increases injury; . therefore their risk of at the same time, the amount of physical contact Tackler 15 6.29 7 17.60 2.7 0.9 to 3.7 by forwards is Tackled 39 16.35 7 17.60 1.1 0.3 to 1.9 experienced the reduced. Other 18 7.54 6 15.09 2.0*. 1.1 to 2.9 Another possible reason for backs having a higher injury rate than forwards is the intro- RR, relative risk; Cl, confidence interval. in *p<0.05. duction of the zero tackle law, which was not place when the winter rugby data were Discussion The law. (2.3: "When - collected. 1) states a The -major findings of the present study were player gathers the ball from an opposition kick the increased injury rates and the increased risk in general. play and does not subsequently pass of injury associated with summer rugby league or kick the ball himself, the initial tackle will be in both forward and back players, but the data counted as a zero tackle". " This effectively suggest that the increased risk of injury was gives a team seven "play the balls" or proportionately greater in backs than forwards. possessions. When the ball is kicked, it is often The data for this study were collected deep in the field of play, and it is gathered by a prospectively as part of a continuing investiga- back player, who runs to gain ground; since the tion, which is a necessary process so that ball carrier is at the highest risk of injury in a changing injury rates can be taken into account tackle, Z` these law changes and playing styles when playing conditions, training, and fixtures could increase the risk of injury in back players. are being designed. ' It allowed the winter and The findings of the present study also show summer cohorts to be compared, to assess that there was an alteration in the risk of injury changes in injury risk as a result of moving the when examined by both type and site of the playing calendar. It has been suggested that body. Investigations in other sports have historical cohort study designs decrease the reported alterations in injury patterns when the comparability of data. " However, similar data playing surface has been changed; for hockey" were collected by the present investigators for and American Football" increased injury rates both summer rugby league (current cohort) have been reported since the use of astrotiirf. In and winter rugby league (historical cohort), American Football the risk of knee (RR = 1.18) but only three players were present in both the and ankle (RR = 1.39) injuries has also been winter and summer cohorts. shown to increase as a result of the change of Injury rates for the summer cohort increased playing surface. " The changing relative risks in even though exposure time was decreased by specific injuries seen in the present study may one third, which may have been due to the be due to similar mechanisms. Specifically, altered playing conditions of warmer tempera- Fuller" claimed that the hard surface of artifi- tures and harder playing surfaces. In support of cial grass allows players to achieve higher this, studies in Australia, "' where tempera- speed, but there is decreased shock absorption tures during the playing season are 18.2 capacity, and the same could be suggested for (16-22)°C (mean (range)), have often reported summer rugby league. The site category "oth- higher injury rates than British studies, "' even ers" (RR = 12.0) contained a number of foot though fewer games were played (30 games in injuries which previously were extremely rare, ' the English league in 1994-1995 v 22 games in but their onset could be associated with turning Australia in 1994). There is also the possibility and being tackled on the harder surface. that some injuries may have been carried over The first season of Super League has from the previous season. The last winter sea- produced a change in injury patterns, and may son before the beginning of the Super League have resulted in a shift of injury risk factors. finished in the first week of February, with the This cannot be exclusively explained by. the Super League beginning at the end of March. playing conditions, as there are a number of This was a 51 day period, much shorter than other factors that need to be considered; the three and half months between seasons as athletic injuries usually have many causes, previously; players therefore did not have the making the identification of simple risk factors time to recuperate that they had previously difficult. " Between the end of data collection enjoyed. Furthermore, the move to full time for the first cohort and the beginning of data professionalism could have predisposed players collection for the second cohort, law changes to injury, since full time increased training were instituted, which may have altered the risk would allow players much less time for of injury. The shorter preseason break and the recovery. " increased amount of training may influence the Forwards have been reported to receive more factors that predispose a player to injury. In '' "5 injuries than backs, as a result of being "addition, playing style, team tactics, and player involved in more physical contact. `' It is there- equipment may also have altered. Any of these fore unusual to find a higher rate of injury factors may have a confounding effect on the among backs and the subsequently very high incidence of injury, and further investigation is relative risk in summer rugby. Alexander et alts needed to determine their influence. found more injuries to backs when the style of Epidemiological investigations are needed to play changed to move the ball wider sooner, determine the extent of injury rates as an initial has giving the backs a greater role-in the game. investigative step. However, rugby league Previous research has shown that the ball taken the very unusual step of moving its play- carrier is the person who is most likely to ing season, and descriptive investigations need ý T. .

152 Gissane,Jennings, White, Cumine

to document the 10 Edgar M. Tackling rugby injuries. Lancer 1995; 345: 1452-3. continue to accompanying Hennekens Epidemiology in injury Preliminary findings it 11 CH, Buring JE. medicine. risk. suggest that Boston: Little, Brown and Company, 1987. has increased, but surveillance needs to con- 12 McNeil D. Epidemiological researchmethods. Chichester. John Wiley Sons, tinue, is dynamic The 1997 and 1996. as sport a entity. 13 Rudicel S. How to a study design. Am Sporn Med choose _7 season will see further changes which will affect 1988; 1S:s43-7. the 14 Armheim DD. Modern principles of athletic training. Boston the game, the players, and almost certainly College injury. Mosby Publishing, 1989. risk of 15 Norton R, Wilson MA. Rugby league injuries and patterns. New ZealandJournal of Sport Medicine 1995; 22: 37-8. 16 Alexander D, Kennedy M, Kennedy J. Rugby league I Gibbs N. Injuries in league: professional rugby a three year football injuries Mod Aust the South Sydney over two competitive seasons prospective study of professional rugby 1980,2: 334-5. _7 league football club. Amy Sports Med 1993; 21: 696-700. The Rugby Football Super League: international 2 Gissane C, Jennings DC, Standing S. Incidence of injury in 17 League. the Football Ixague, 1996. rugby league football. Physiotherapy 1993; 79:305-10. lawn of the game. Leeds: The Rugby 3 Seward H, Orchard J, Hazard H. Football injuries in 18 Jamison S, Lee C. The incidence of female injuries on grass Australia at the elite level. Med, JAust 1993; 159:298-306. and synthetic playing surfaces. Aust J Sci Mod Sport 1989; 4 Stephenson S, Gissane C, Jennings D. Injury in rugby 21: 15-17. league: a four year survey. Br Sports Med 19 Skovron ML, Levy MI, Agel, J. Living with artificial grass: a prospective ,3 1996; 30: 331-4. knowledge update. Part 2: epidemiology. Am. 7 Sport Med 5 Estell J, Shenstoite B, Barnsley L. Frequency of injuries in 1990; 18:510-13. different league Aunt-7 Sci age-groups in an elite rugby club. 20 Powell JW, Schootman M. A multivariate risk analysis of Med Sport 1995; 27: 95-7. selected playing surfaces in the national football league: 6 Savdic IF, Prevedorous H, Irish A, et al. Heat stroke follow- 1980 1989. An knee injuries. 636-9. to epidemiological study of ing rugby league football. Med_Must 1991; 155: Am J Sport Med 1992; 20: 686-94. 7 Meir It, Lowden A. Jersey in B, Davie configuration rugby 21 Fuller MI. A injuries in field hockey league: hot handle? Sport Health 1994; 12:22-5. study of women's as too to Physiotherapyin Sport 1990; 12: 8 Meir R, Lowden B, Davie A. The jersey played on synthetic pitches. effect of type on 3-6. thermoregulatory'responses during exercise in a warm 22 Jennings D, Gissane C. T1trf-toe league Br I humid environment. Aust y Sci Med Sport 1994;26: 25-31. - super toe. Gissane C, Jennings DC, Cumine Al, at al. Differences in Sports Med 1997; 31: 164. in injury: the incidence of injury between rugby league forwards and 23 Mceuwisse WH. Assessing causation sports a backs. Aurr-7 Sci Med Sport 1997; 29: 91-4. multifactorial model. Cling Sport Med 1994; 4: 166-70.

B BMA House, Tavistock Square, London WC1H 9JR. Tel. 0171393 6305. Fax 0171383 6699 ©1998. All rights of reproduction of this reprint arereserved in all countriesof the world. Printed in GreatBritain by Meridian Print CentreLtd. Derby BJsM/Jun/9s =r; ýa `s xý:,,ý

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+ý'"n 'ýYt Coaching and Sport Sciencejournal (1998) 3,3: 31-33 COACHING i <;i &SPORTBody mass loss as an indicator of dehydration SCIENCE in summer rugby league journal S. Jennings', S. Robertson', D. Jennings', J. White°, C. Gissane© ® SeelothSlampa Spartiva 1909 'Department of Orthopaedics, Royal Free Hospital, Pond Street Hampstead, London NW3, UK 2Department of Sport Science, St Mary's University College, Strawberry HillTwickenham Middlesex, TW14SX, UK. 'General Practitioner, Reigate, Surrey, UK. 'Division of Public Health Medicine and Epidemiology, Queen's Medical Centre, University Hospital, Nottingham, NG7 2UH, UK 5Department of Health Studies, Brunel University, Osterley Campus, Isleworth Middlesex, TW7 SDU, UK.

Abstract the players, coaches, and sports medicine teams at club level to define and implement strategies which will help Objective: To determine the body mass losses expe- players to cope with these new playing conditions. The rienced by summer rugby league players. Rugby League Medical Association (RLMA) expressed for heat Methods: Players at one club who took part in 16 sum- concern the potential problems associated with its 1996 [4] Rugby Football games had body mass determined before and after stress at meeting, and the "mer League has by for playing. responded producing guidelines play- ers and coaches to avoid dehydration [2]. Results: There low between was a overall correlation A near-fatal accident was reported in Australian Rug- body loss temperature percentage mass and ambient by League (ARL) where a player who suffered, heat (r=0.29, but increased, p=0.02), as playing temperature stroke whilst playing (ambient temperature 24.1°C rel- 13% body loss in 14 of players experienced a 2-3% mass ative humidity 73%), spent 10 days in a coma and suf- of 16 games played in excessof 19°C ambient temperature. fered Disseminated Intravascular Coagulation (DIC), Conclusions: With the seasonal change new physio- along with renal and heptatic disturbances [5]. Strate- logical challenges have been placed on players, some of gies to prevent heat stress are important in order to who are demonstrating body mass losses which can af- maintain optimal cardiovascular function and ther- fect on field performance and thermoregulatory mech- moregulation, [6] as well as prevent dehydration by as anisms. little as three percent of body mass which has a detri- mental effect on performance, [7] and has been described as medically dangerous [1]. At dehydration levels slight- Introduction ly below this level (2-3%) the body's ability to sweat is decreased, and with it the capability of the thermoreg- During exercise the metabolic heat produced by the ulatory system to maintain core temperature [8]. It has body can increase by 15 to 20 times above that produced also been reported that dehydration resulting in body at resting levels; [1] and taking part in activity in hot con- mass decreases as low as 2% can noticeably impair per- ditions can cause the body temperature to rise even more fdrmance by compromising the circulatory and ther- quickly [2]. Moving the English professional rugby league moregulatory functions [9]. The aim of the present in- season from the period September through to April, to vestigation was to determine the extent to which play- March until September allowed it to be played in parallel ers' body mass changes may be used as an indicator of to the Australian rugby league season. However, for play- dehydration state whilst playing summer rugby league. ers in the European Super. League it meant that the game was to be played in much higher temperatures that previ- ously, and for a certain portion of the season (June, July Methodology and August) the temperature would be higher than in The for the the Sydney, Australia [3]. The movement of the season places subjects this study were members of Super League Club, physical a responsibility on the game's administrators, as well as playing squad at one whose characteristics are displayed in Table 1.

Procedure Correspondence: Conor Gissane Tel 0181 891 0121 x 2636 The members of the squad who were selected for a Fax 0181847 2030 given game took part in the assessment procedure on E-mail: Conor. Gissane@Brunel. ac.uk that occasion. Players' body mass was determined in the

'31' Body mass loss as an indicator-of dehydration-in summer rugby league

Age (yrs) Mass (kg) Height (cm) The overall relationship between the playing tem- perature and percentage body mass loss revealed a low All correlation (r = 0.29, p=0.02). There were non signifi- players 24.7±4.0 90.9±11.8 181.8±7.2 (n 28) cant negative correlations between relative humidity and = loss (r Backs percentage mass = -0.28, p=0.08) and relative 25.1±4.3 84.6±7.5 178.4±2.1 humidity temperature (r= From (n 15) and -0.15, p=0.59). = table two it can be observed that as the ambient play- Forwards ing increased 24.3±3.8 98.1±12.1 185.417.7 temperature the number and percentage (n = 13) of players reaching body mass loss relative to the level dehydration become im- I Table 1. Physical characteristics of players [Mean ± SD]. of where performance could paired increased. Of the players who experienced 2- 3% dehydration, one experienced it four times, three other players twice, with four players experiencing a single in- before in standard position starting each game under- cident. wear only, after they were towel dried. Each measure- ment was recorded to the nearest 100 g using a cali- brated Seca 770 model scales. A similar procedure was Discussion completed on the players' completion of the game with minimal time delay. During the game the mean ambient The major finding of this study was that an increase temperature (°C) and mean relative humidity (%) was in ambient temperature resulted in a greater proportion recordedusing a Casella polymeter (Model M 112050: of players reaching levels of body mass decreale rela- Reliability; humidity t5% between 30% and 90% RH, tive to a'state -of dehydration which could compromise Temperature ±1%). thermoregulatory control system [8]. For each game played, each player that played was In this study there was no attempt to control for spe- treated as an independent event making a total of 268 cific variables that might influence the test results, such player appearances. Therefore, all data was collected as water intake and exposure to direct sunlight [1]. The with body mass being determined as the difference be- main aim was to describe the body mass losses during tween pre-game mass and post-game mass. Players were the course of playing typical rugby league games in the allowed to drink water ad libitum after pre game body summer. Although none of the players reached the 3% mass determination, during the game and at half time. loss in body mass that has been shown to be medically For the purposes of analysis, only players who completed dangerous, [1] 13% (16/120) of players lost between each full game of 80 minutes were included in the analy- 2-3% body mass in 14 of the 16 games played in excess sis (n = 120). of 19°C ambient temperature. Thermoregulation mech- The statistical analysis consisted of Pearson's corre- anisms can be compromised at such levels of body mass lation to determine associations between variables, and change, [1,8] and the associated level of dehydration independent t tests to determine differences between may adversely affect physical performance by reducing forwards and backs. All tests were carried out using SPSS endurance times [10]. for Windows 6.1.2. Previous studies in other sports have monitored flu- id intake of players during match play [11,12]. They have also involved far fewer subjects than the present ý Results study. There are also practical difficulties with measur- ing fluid intake during matched play. Water in drinking Data were recorded in a total of 16 games, and the bottles is used for other purposes such äs, rinsing out overall mean temperature was 22.9±5.3 °C, and the mean mouth, washing gum shields, and cool heads. All of which relative humidity 73±13.6%. During these games a to- can lead to errors in estimation. tal of 36 forwards and 84 backs completed whole game(s). A number of measures are in place which are designed The mean body mass loss for all the players was 1.1 (95% to assist players in minimising dehydration. Shirts are now CI 0.98 to 1.22) kg, in which the forwards and backs had made of much lighter material than previously and weigh mean body mass losses of 1.48 (1.25 to 1.7) kg, and 0.94 about 40% less than before (376.8 vs. 218 g) [13]. The (0.82 to 1.06) kg respectively (mean difference = 0.54 Rugby Football League has also issued some guidelines (0.3 to 0.78) kg, t=4.48, df = 118 P=0.001). Overall for players and coaches about training and playing in hot mean loss for all players was 1.22 (1.1 to 1.34) % of body environments [2]. These guidelines advise players that mass, in which forwards and backs had mean losses of they "need to hydrate before a game and rehydrate prop- 1.51 (1.29 to 1.74)%. and 1.09 (0.95 to 1.24)% respec- erly after a game". They also warn that those players with tively (mean difference = 0.42 (0.16 to 0.69)%, t=3.18, higher percentage body fat are most at risk of thermal df = 120 P=0.002). stress, and since it has been reported that forwards carry

-32 Players completing game 2- 3% body mass loss

Temperature Games Players number percentage 95% CI number percentage 95% CI 18°C below 2 34 16 47.1 29.8-64.9 0 0.0 or - 19 - 23°C 5 83 37 44.6 33.7-55.9 1 2.7 0.1-14.2 24 - 28°C 8 134 60 44.8 63.2-53.6 10 16.7 8.3-28.5 29+°C 1 17 7 41.2 18.4-67.1 5 71.4 29.0-96.3

Total 16 268 120 44.8 39-51 16 13.3 7.8-20.7

Table 2. Ambient temperature and players' body mass losses during rugby league games. more body fat than backs, [14,15] this may partly explain References whyforwards are noted to have a greater percentage body massloss than backs. 1. Mitchell B. AFLMOA position statement on: the prevention The in 1990 from DIC of thermal injuries in AFL football. Sport Health 1994; player observed who suffered 12(4): 10- 8. was febrile, which served to decrease the amount of heat 2. Brewer J. Beat the heat. a strategy for the prevention of dehy- which could be dissipated before overheating [5]. The dration. Leeds: The Rugby Football League, 1997. Rugby League have warned players who have been ill or 3. Pearce EA, Smith CO. The world weather guide. Oord He- are from virus that they to heat. licon, 1993. suffering a are more prone . . stress,and have advised them to seek advice from the club 4. Stephenson S, Gissane C, Jennings D. Injury in rugby league; four medical personnel before playing or training. Similarly, a year prospective survey. Br J Sports Med 1996; 30:331 the RFL warn about excessive taping -4. use of and protec- 5. Savdie E, Prevedoros H, Irish A, Vickers C, Concannon A, Dar- tive equipment which can inhibit the thermoregulatory veniza P.et al. Heat stroke following rugby league football. Med process [2]. The player who suffered from DIC; had been J Aust 1991; 55:636-9. his kit wearing and a neoprene thigh guard, in total 70% 6. Gonzalez-Alonso J, Heaps CL, CoyleEF. Rehydration after ex- of his body surface area was covered [5]. There is also the ercise with common beveragesand water. Int J Spots Med 1992; practice of support staff entering the field of play at stop- 13:399-406. 7. Brack AS, Ball D. Dehydration pages giving the players water, something not enjoyed in and rapid rehydration: effects during brief high intensity [16] to the on performance exercise.Journal of other sports, which serves aid rehydration Sports Sciences 1998; 17:39-40. process. 8. Sawka MN, Young AJ, Francesconi RP, Muza A, Pandolf KB. In the body loss this study variable examined was mass Thermoregulatory and blood responsesduring exerciseat grad- as a proxy measure for dehydration. This should be con- ed hypohydration levels. J Appl Physiol 1985;59(5): 1394-401. sidered as a conservative measure of fluid loss as neither 9. Saltin B. Circulatory responsesto submaximal and maximal ex- fluid intake or urine excretion were measured. There are ercise after thermal dehydration. J Appl Physiol 1964; 19:1125-32. factors beyond those in the also other examined present 10. Craig FN, Cummings EG. Dehydration influence body loss and muscular work. J study which could exert an on mass Appl Physiol 1966; 21:670-4. during For has games. example, previous research re- 11. Goodman C, Cohen I, Walton J. The effect of water intake on ported that percentage body fat can influence the effi- body temperature during rugby matches. S Afr Med J 1985; ciency of thermoregulation [17]. 1 67:542-4. in The results of this study demonstrated that players ap-. 12.Kirkendall DT. Effects of nutrition on performance soccer. pear to be new physiological from Med Sci Sport Exerc 1993;25: 1370-4. experiencing challenges Meir RA, the heat league. 13. Lowden BJ', Davie AJ. The effect of jersey type on encountered whilst playing summer rugby thermoregulatory during in humid Although for the in the responses exercise a warm majority of cases seen present environment. Aust J Sci Med Sport 1994; 26:25-31. this did 13 % study not represent a problem, of players ex- 14.O'Connor D. Physiological characteristics of professional rug- body loss during perienced 2-3% mass a game, which can by league players. Strength and Conditioning Coach 1996; both field thermoregulatory 4:21-6. effect on performance and _ mechanisms [8,9]. Research from other sports and Aus- 15.Meir R. Seasonal changesin estimates of body composition in tralian rugby league can provide direction for strategies professional rugby league' players. Sport Health 1993; 11(4): 27-31. to help overcome the problem. Devising and adopting 16.Cullen M. Will common senseprevail? Br J Sports ivied 1998; strategies such as these was formerly the domain of tour- 32:97. ing teams. Now, however, it is in the European required 17. Meir R. A review of factors complicating performance under due playing season to the switch to summer competition. conditions of thermal stress.Sport Health 1992; 10(1): 16- 25.

. 33 C

Ck f.. dvdkWju-d2001l-4 CJVU Physical Collisions in Professional Super League Rugby, The Demands on Different Player Positions

C. Gissane'MSct, J. White PhD*, K. Kerr PhD, D. Jennings MB 8S*

tDepartment of Health Studies,Brunel University, Osterley Campus,Isleworth, Middlesex, TW7 5DU. - $Division of Public Health Medicine and Epidemiology, University Hospital, Queen's Medical Centre, Nottingham, NG7 2UH. Division of Physiotherapy Education, University of Nottingham,Hucknall Road,Nottingham, NG5 IPG. *GeneralPractitioner, Reigate, Surrey.

Running Header. Physical Collision in Rugby League

Address for correspondence:

Conor Gissane Department of Health Studies Brunel University Osterley Campus Isleworth Middlesex TW75DU Tel 0181 891 0121 x 2636 Fax 0181 847 2030 conor. gissane@brunel. ac.uk

SUMMARY

by Objective - To determine the total number and nature. of physical collisions experienced players in differing positions in professional rugby league.

Methods - Video recordings of all the regular seasongames (W=22) played by one professional superleague rugby club were examined.Physical collisions were classified into tackles,incomplete tackles,"tackled in possession","broken tackles" andpasses out of the tackle.

involved Results - Forwardswere in significantly more collisions (55) than backs(29) during the course of each game (z=2.73, P <0.0001). Eight player positions (forwards (n=6) and two half backs(scrum half and stand off)) were involved in significantly more collisions while defendingas

137 "ý cl-h d. rdcal Jovnaf 2001 w.. 1 ýI.

rý: comparedto attacking (all P<0.005).The differencesfor all back threequarter positions and the full back were not significant

Conclusions - Players, both backs and forwards experienced more physical collisions than previously reported,which may be linked to operationaldefinitions, rule changesand the adventof summer rugby league. Players were involved in more physical collisions whilst defending,since over two thirds of tacklesinvolved more than oneplayer tackling the ball carrier.

Key words: professional rugby league, 'physical collisions, forwards, backs, tackle

INTRODUCTION

(') Rugby League is a game of physical collisions, in which the tackle has a greater prominence than (2) in rugby union. The high number of physical collisions encountered by players has been suggested as a possible reason why they experience such high injury rates.(3) It has been further suggested that the collisions in which players are involved are important from both a physiological (' as well as an injury prevention perspective. 14)A survey of international players found that the two (') aspects of the game that players found most tiring were being tackled, and tackling other players. Many coaches acknowledge that it is important to control these aspects of the game since they have ('-S) a major influence on the outcome of a match. Within team sports players have different demands (6) placed upon them according to the requirements of their position, and for optimal performance it is necessary to identify the specific characteristics of successful play relative to playing position.

To this end, previous research in rugby league has investigated the movement patterns of players (e) (9) during matches, and the differing injury rates of forwards and baclcs. However, while other work reported the number of physical collisions in which players are involved during the course of a game, the studies were limited and were often based on data reported from small numbers of (', ") matches. Furthermore, when examining the physical collisions from an injury prevention point of view, it may be important to take all physical contacts into account, which might include for example, situations where the tackle was not necessarily successful, because it still involved physical contact.

The purpose of the present study was to determine the number and type of physical collisions that rugby league players experience during typical match play. In addition the study determined how

138 ., i"0 Clevslandm. "Jwmt2ont iw. 4

ýC"iYNMS''ý total physical collisions were distributed between attack (while in possession of the ball) and defence, and among playing positions.

METHODOLOGY

Players representing one professional rugby league comprised subjects for the present study (N=35, forwards n= 15, backs n= 20). In order to assessthe number and type of physical collisions in which players were involved while playing, video recordings of all 22 regular season games played during the 1996 Super League season were analysed. This represents a total of 29.3 hours of match-play or 380.4 player hours (13 players x 1.33 hrs x 22 games). The video tapes used were master copies of recordings produced by two T. V. media broadcasting companies (British Sky Broadcasting, Isleworth and Micron Video, Wigan), and permission to use the material was granted by the Rugby Football League.

Each video was a standardVHS (25 fames.sec') and was analysedby the principal investigator. Eachphysical collision that took place was classifiedinto one of the following categories:

Defence (defending collisions)

defending halted ball 1. Tackles - where the player(s) the progress of the carrier, and as a result the ball carrier had to play the ball.

defending 2. Incomplete tackles - where the player(s) made contact with the ball carrier, but failed to prevent forward progress, or were unable to stop the passing of the ball.

Attac (attacking collisions)

1. "Tackled in possession" - where the ball carrier was tackled whilst in possession of the ball, forward progress was halted and the ball carrier had to play the ball.

2. "Broken tackles" - where the ball carrier was able to break through the tackle and continue forward progress.

3. Passes out of the tackle - where the ball carrier was tackled but was able to pass the ball.

Following this analysis it was possible to calculate each player's total defensive involvement (the sum of tackles and incomplete tackles), total attacking involvement (the sum of "tackled in

139 dswla. d wdlcaljo- d JOGI in .4 ý...,

ýýY... ý possession", "broken tackles" and passesout of the tackle), and total physical involvement (in defenceand attack) in eachgame analysed.

STATISTICAL ANALYSIS

In order to determine the reliability of the physical collision analysis, three videos were analysed week twice (each one apart) by the principal author and the 95% limits of agreement were 01,12) calculated using previously recommended methods Because the differences between readings did not vary in a systematic way across the all values, it was necessary to log transform the original (" data. Descriptive statistics (mean and 95% CI) for each physical collision category were computed for each playing position. To determine differences in the number and type of physical collision between forwards and backs, and between attacking involvement and defensive 03) involvement, further analysis was undertaken using a proportion test.

RESULTS ,

Reliability of video We analyses

The reliability of the physical collision analysis demonstrated that the 95% limits of agreement calculated were 0.92 to 1.08, which indicated that the retest analyses were between eight percent above and below the original readings.

Collision analysis

The mean number of physical collisions for attack, defence and total, collisions experienced by player positions is shown in table 1. All players were involved in both defensive collisions (while attempting to tackle the ball carrier) and attacking collisions (being tackled when carrying the ball) which resulted in an average of 41 physical collisions per player per game (27 in defence and 14 in attack). Forward players were involved in an average of 55 physical collisions during a game (39 defence, 16 attack), which was significantly more than the backs who were involved in an average of 29 physical collisions (16 defence, 13 attack) [z = 2.73, p<0.0032]. All of the forwards, plus the scrum half and the stand off were involved in a significantly greater number of physical collisions when defending (all p< 0.05) as compared to attacking. Only three player positions, the two wings and the fill back, were involved in more attacking than defensive physical collisions but the differences were not significant (z = 1.66, P> 0.09).

140 Q, ýä CleirfmdwedidJoand7001 (trw! S

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Table 1. Physical collisions experienced by player positions during match-play.

Defence Attack Total collisions Position Mean 95% Cl Mean 95% Cr Mean 95% Cl Fall back 10 8-13 18 16 - 20 28 26 - 31 Right wing 10 7-12 13 11-15 23 19 - 25 Right centre 18 IS-22 12 10-14 30 27 - 34 Left Centre 18 15- 20 14 13 -15 32 29 - 34 LeftWing 7 5-9 11 10-13 18 16-20 Standoff 29** 26-32 13 12-15 42 38-45 Sctwnhalf 23** 19-27 10 8-11 33 28-36 Openside prop 44** 39 - 49 23 20 - 26 67 60 - 74 Hooker 43** 39 - 47 6 4-8 49 45 - 53 Blindsideprop 37** 31 - 41 20 17 - 24 57 48 - 66 Openside 2nd row 45** 40 - 50 19 15 - 23 64 56 - 72 Blindside2nd row 39** 36 - 43 16 14-17 55 51 - 59 Loose forward 27** 24 - 30 11 11 -13 38 35-43

Backs 16 15-18 13 12-14 29 28-31 Forwards 39'" 37 - 41 16 15-17 55* 52 - 58 All ulayers 27 25 - 29 14 13 -15 41 39 -43

' significantly different from backs '* significantly different from attack

The mean number of defensive physical collisions (complete and incobut the differences were not significant incomplete tackles) performed by player positions is presented in figure 1. There were significantly more complete than incomplete tackles (290 vs. 59, z= 123, P <0.00006). Overall, only 17% (59/349) of the defensive physical collisions carried out by the players in this study allowed an opponent to break through the tackle or off load the ball. Backs were involved in a significantly greater number of incomplete tackles than forwards (22% vs. 15%, z=6.14, P <0.00006)

141 d-l-d -di-IJ-1 1061 s.- 4i

Figure 1. Proportion of complete and incomplete tackles made by playa position.

Loose fora rd

Blmside 2nd nm

Opeaside2nd 'ow

Blindaide pop

Hooker

O Pop

Saum halt UCamplet taekla Stand off R Incomplete tackles Left Wmg

Left Centre

Right centre

Right wing

Full back

os to 15 20 25 30 35 40 as 50

Number per Came

The mean number of attacking physical collisions ("tackled in possession", "broken tackles" and passes out of the tackle) is presented in figure 2. There were significantly more "tackled in possession", than passes out of the tackle and "broken tackles" (153 vs. 34, z=8.6, P<0.00006). Overall, the ball carrying players under investigation were able to either "bust" a tackle or off load the ball in 18% (34/187) of the attacking physical collisions. There was no significant difference between the forward and back ball players in the proportion of passes out of the tackle and "broken tackles" (19% vs. 18%, z=0.74, P x. 4593)

Figure 2. Proportions of"tackled in possession' and 'broken tackles", and passes out of tackles experienced by position.

Lone forwud

BI'udside 2nd row

Opeoside 2nd row

Bliod. idc prop

Hooker

Operi+ide, Prop o'teckin in Scnon half posfesioo" "bmken tackle" k gssa out of fickle Stand off

Left Win g

Left Centre

Rig1>icentre

Rightw{o`

Full book

os io 15 20 25 142 Nmber per pme ä, a ,di "I djm V12001 kaut 4

dpi,. fib DISCUSSION

The present study indicated that rugby league players were involved in an average of 41-(95% CI 39 to 43) physical collisions per game, which is above the upper limit of a previous estimate of 20-40 (s) per game. This may be due in part to the decision in the present study to include incomplete tackles in the observations which were not reported in previous estimates. If incomplete tackles were removed, the figure would be reduced to an average 37 physical collisions-per game (forwards 50 per game, backs 26 per game). However this would still suggest that the current figures were C3) higher than previously reported. Nevertheless, incomplete tackles accounted for 17% of all physical collisions experienced by players, and while coaches would wish to reduce the overall number to improve team defence performance, the occurrence is an important consideration from both a physical conditioning, and injury prevention point of view, as well as influencing the outcomeof the game.

A further possible explanation for the present values being higher than previously reported could be the 1994 rule change that required players on the side not in possession to retire 10 metres after the tackle, (14)compared with the original requirement of five metres. It has been suggested that this may lead to an increase in the distances covered and, the total amount of high intensity physical activity, of which tackles are part915)Higher intensity activity may also serve to increase the momentum of the players at the point of contact In addition, there has also been the introduction of the zero tackle law which states "When aplayer gathers the ball from an opposition kick in general play and does t1ct not subsequently pass or kick the ball himself, the initial tackle will be counted as a zero taclde". This effectively gives a team seven 'plays of the ball' or possessions, compared with the previous six, which may potentate additional physical collisions.

Forwards were involved in a greater number of collisions than backs (55 vs. 29) which is in l5"03 agreement with previously reported work, although again the figures in the present study are higher than previously reported. One study reported that at club level forwards were involved in 32 (1° physical collisions per game and backs 19 per game, while at international level forwards were P5) involved in 36 and backs 19 collisions However, the games analysed in both previous studies took place before the 1994 rule change, the zero tackle law, and prior to the advent of summer rugby.

Several authors have suggested that the higher numbers of injuries received by forwards during (9) match play (139.4 vs. 92.7 injuries per 1000 player hours), may be because of the higher number (ß's'17) of physical contacts However, if as a result of recent changes in the laws of the game both

143 l, k dewfad wýati'caljoýonc12001 km 4

forwards and backs are experiencing more physical collisions, then the risk-of injury should rise proportionately for all players.

It was also interesting to note that eight of the 13 player positions were involved in significantly more physical collisions in defence than attack. A previous study reported that props and hookers spent a greater amount of the time (4.5%) performing defensive tackling than backs (1.8%), and that forwards spent 2.7% of the time taking the ball into the tackle, compared with 1.8% for backs. (s) This may account for the greater number of physical collisions by forwards made while defending. It should be noted that more than one player can be involved in the tackle, but only one player is carrying the ball whilst being tackled. Previous research on the number and type of contact experienced by individual players found that two thirds of tackles involved more than one defender tackling the ball carrier! ") However, unlike the present study, previous work did not seek to examine how many players were involved in a given tackling situation on a ball carrier. If more than one player is involved in the tackle this could potentially increase the risk of injury to a player, as well as the number of physical collisions in which that player is involved.

The present findings have implications for both physical conditioning and injury prevention in rugby league. Coaches have recently suggested that the high injury rates reported in the game"91 (19) are due to the ferocity of the physical collision situation. However, coaches have also been also been careful to emphasise the importance of safety and self protection when either tackling or being tackled. (20)The findings of the present study emphasise the different incidence of physical collisions

experienced by different player positions. This could serve as an indication to alter the training strategies of different positions and/or playing units, by either increasing or decreasing the number of physical collisions in training in proportion to those experienced in the game. Rugby League has 5) shown a recent trend towards less specialisation between playing positions; and there is the suggestion that fitness training for professional rugby league is uniform for all positions. However, it has also been argued that training procedures should reflect the breakdown of match (g) play activities, and that these should be position specific. Similarly, injury prevention strategies could place a differing emphasis on players who are going to be involved in a greater number of physical collisions than others.

144 05

C. v Jd rrrdlcdJ i. ! 2001 6a e 4 lIpt$ CONCLUSION

The present study has provided data on the number and type of physical collisions experienced by players during professional rugby league play. It should be recognised that playing style might also exert an influence on the number and types of physical collisions experienced. However, empirical data as to the specific nature of the physical collisions that players incur during a game is important. Training needs to conform to the principle of specificity, and the sheer volume of physical collisions encountered by some players may influence their injury risk, both from the physical impact and the possibility of cumulative fatigue. The numbers of physical collisions documented in the present study are higher than previously reported, which could be due to the inclusion of incomplete tackles. However it could be also be due to a change in the nature of play. The 1994 rule changes moved the defensive line back further by 5 metres, and the advent of summer rugby league probably resulted in firmer playing surfaces which allow faster running speeds and increased momentum at the point of contact in the tackle. Differences in the running speeds of players have P') been reported to be an important risk factor in rugby union tackles A further study has examined the numbers of players involved in specific tackles, in an attempt to determine if this has an influence on the risk of injury to the ball carrier and/or the tackler. In addition the follow up study has attempted to determine if the number of physical collisions experienced by players has a direct ) influence on the incidence of injury in playing units and positions.

The authors would like to thank Glen Worlanan and Tony Currie for their assistance with this investigation.

REFERENCES

1. Kear J, Clarke A, Worsnop S. Conditioning for rugby league.Harpenden: Queen Anne Press,1996 2. Gissane C, Jennings DC, Standing S. Incidence of injury in rugby league football. Physiotherapy 1993; 79: 305-10 3. Gibbs N. Injuries in professional rugby league: a three year prospective study of the South Sydney professionalrugby leaguefootball club. Am JSports Med 1993;21: 696-700 4. O'Hare M. In ä leagueof their own. New Scientist 1995; 1997:30-5 5. Larder P. Therugby league coachingmanual. 2nd ed. London: Kingswood Press,1992 6. O'Connor D. Physiological characteristics of professional rugby league players. Strength and Conditioning Coach 1996;4: 21-6 7. O'Connor D. Fitness profile of professional rugby league players. Journal of Sports Sciences 1995;13: 505 8. Meir R. Arthur D, Forrest M. Time and motion analysis of professional rugby league: a case study. Strength Conditioning Coach 1993;3: 24-9 9. GissaneC, Jennings DC, Cumine AJ, StephensonSE, White JA. Differences in the incidence of injury between rugby league forwards and backs. Australian Journal of Science and Medicine in Sport 1997; 29: 91-4 10. Robinson JJ. An investigation into the offensive and defensive work rate of rugby league footballers. Unpublished BSc dissertation, Brunel University College. 1996

145 . ds,. J d dlmljnw. J2OOJlr+uct /-ýý"i .. rý.ý'ý

bam 11. Bland M, Altman, DG. Statistical methods for assessingagreement between two methods of clinical l measurement.Lancet 1986;i: 307-10 12. Nevill AM, Atkinson G. Assessing agreement between measurementsrecorded on the ratio scale in sportsmedicine and sportsscience. BrJSports Med 1997; 31:314-8 13. Altman DG. Practical statisticsfor medical research.London: Chapmanand Hall, 1991 14. The Rugby Football League. Super League: the international laws of the game. Leeds: The Rugby Football League, 1996 15. Brewer J, DaviesJ. Applied physiology of rugby league.Sports Med 1995;20: 129-35 16. Norton R, Wilson M. Rugby leagueinjuries and patterns.NZJSports Med 1995;22: 37-8 17. Clarke A. A major analysis of rugby league football via questionnaire and video analysis. MSc dissertation. Leeds University, 1993 18. JonesC. Is superleague too tough?Super League Week161: 3,19th June 1998 19. CorcoranPD. Australian rugbyfootball leagueskills manual. Sydney: Australian Rugby League,1979 20. Garraway WM, Lee AJ, Macleod DAD, Telfer JW, Deary U, Murray GD. Factors influencing tackle injuries in rugby union football. BrJSports Med 1999; 33:37-41 21. GissancC JenningsD JenningsS White 7 Kerr K. Physical collisions and the injury experiencein rugby league.Cleveland Medical Journal 2000, In submission

146 G. Q C7rwlandm&=1jo-22001 /nrt4 y - CI" rMr"]S". Physical Collisions and Injury Rates in Professional Super League Rugby

C. Gissane MSC*, D. Jennings MB BSf, S. Jennings:, J. White PhD** and K. Kerr PhD fl

*Department of Health Studies, Brunel University, Osterley Campus, Isleworth, Middlesex, TW7 SDU. tGeneral Practitioner, Reigate, Surrey. Department of Orthopaedics, Middlesex Hospital, Mortimer Street, London NW1. **Division of Public Health Medicine and Epidemiology, University. Hospital, Queen's Medical Centre, Nottingham, NG7 2UH. ttDivision of Physiotherapy Education, University of Nottingham, Hucknall Road, Nottingham, NG5 1PG.

Running Header. Collision and Injury in Rugby League

Address for correspondence: Conor Gissane Department of Health Studies Brunel University Osterley Campus Isleworth Middlesex TW7 5DU Tel 0181 891 0121 x 2636 Fax 0181847 2030 conor. gissane®bronel. ac.uk

SUMMARY

if Objective - To determine there was a relationship between exposure to physical collisions and injury rates in professional super league rugby football.

Methods - All injuries received during one season'smatch play were recorded for all games played by one professionalsuper league rugby club. Each injury was classifiedaccording to player position and activity at the time of injury. Physical collisions were determined from video and classified into tackles, incompletetackles, "tackled in possession","broken tackle" and passesout of the tackle.

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Results - Forwards were involved in significantly more physical collisions per game than backs (55 vs. 29, P=0.003). Overall backs had a significantly higher injury rate per 10,000 physical collisions (16.3 vs. 7.2, P=0.0015), but there were no significant differences between the two playing units for injuries receivedwhilst attackingor defending.

Conclusions - This study demonstrated that backs have higher standardised injury rates (per 10,000 collisions) than forwards, in spite of being involved in fewer physical collisions per game played. The observed differences could be due to the nature of specific physical collisions experienced by the respective playing units or intrinsic injury risk factors among the players involved.

Key words: Rugby League, injury rates, physical collisions

INTRODUCTION

Injury rates in rugby league football have been reported to be higher than those experienced in other t"2Z contact team sports. It has also been reported that the injury rates experienced by players have (3'4.5) increased as a result of the recent move to a summer competition. In addition many authors have reported that forward players receive far more injuries that back players0'2'5"6'7'8"9)One reason that is often put forward to explain this finding is that forwards are involved in much more physical t6'ß contact than backs

Forwards may be involved in more physical contact because of their role in the game, although it has been suggested that there has been a recent trend towards much less specialisation between (°) positions, which may have an influence on the contact rates experienced by forwards It has also been suggested that when the numbers of player positions involved are taken into account, forwards (6) receive relatively more injuries and backs relatively fewer, than might be expected.

Front row forwards spendmore of their time taking the ball into the tackle than backs (2.7% vs. 1.8%), and over twice as much time tackling (4.5% vs. 1.8%)X11)The amountof time spentin these activities is an important considerationsince researchhas shown that between67% and 77% of t5'7 injuries take place in the tackle. It has further been reported that both forwards and backs receive significantly more injuries while being tackled than when tackling, and that forwards receive significantly more injuries than backs when either tackling or beingtackled. 0 If injuries are to be reduced,it is necessaryto establishif there is a relationshipbetween the exposurerisk factors,

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such as the number and type of physical collisions, and the incidence of injury in rugby league football.

The purpose of the present investigation was to examine the relationship between the rate of injury in rugby league football, and the number and type of physical collisions in games in which players are involved during the course of a full playing season by one professional super league rugby club.

METHODS

All injuries that were reported for the first team of one professional super league -rugby club were recorded over one season. An injury was defined as a physical impairment received during a competitive match which prevented a player being available for selection for the next competitive (6). game The position of the player, the site of the injury; the nature of injury; the activity at the time of injury and the time off as a result of injury were recorded for each game played over the full ('. S. season. The details of each category have been described previously. 7)

The population at risk was defined as the players who were selected to play for the first team in a given match, and the defined time at risk for calculating injury rates was the duration of the games multiplied by the number of players (1.33 hrs. x 13 players) multiplied by the number of games played. A total of 23 games (22 regular season plus one play off game) were played during one season (397.7 player hours).

To assessthe number and type of collisions that players were involved in while playing, video recordingsof 22 regular seasongames played during the 1996 Super Leagueseason were analysed (29.3 hours of match-play, 380.4 player hours). The video tapes used for analysis were master copies of recordings produced by two TV media broadcasting companies (British Sky Broadcasting,Isleworth and Micron Video, Wigan), and permissionto use the material wasgranted through the Rugby Football League. The categorisationof physical collisions was carried out as outlinedpreviously. (12

Following the analysisof physical collision categories,it was possibleto calculatethe following; 1) each player's total defensive involvement (the sum of tackles and incomplete tackles), 2) total attacking involvement(the sum of "tackled in possession","broken tackle" and passesout of the tackle), 3) total physical involvement (defensiveplus attack) in each game analysed,and 4) the differencesin physical collisions incurredby backsand forwards.

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Statistical analysesconsisted of the calculation of injury rate per 10,000physical collisions as a standardisedrates of exposure,and descriptivestatistics for physical collisions (meanand 95% CI). In order to compare differencesbetween the proportions of physical collisions a single proportion test was used,13 while a test for differencesbetween injury rates usedthe method of Clarke,14 and the relative risk (RR and 95% CI) was computed.In order to analyse the differences between forwards and backs in the number of gamesmissed by injured players, the Mann Whitney U and Kruskal Wallis tests were employedsince the datawere not normally distributed.

RESULTS

The descriptive statistics of the number of physical collisions incurred by forwards and backs are shown in table 1, which indicates that forwards were involved in significantly more physical collisions during defensive tackling than backs (z= 2.73, P=0.0032). Furthermore, forwards were involved in a significantly greater total number of physical collisions (z = 2.97 P=0.0015). This was largely as a result of the increased defensive tackling demands by forwards, since there was no significant difference in the number of attacking collisions incurred by forwards and backs.

Table I. Mean number of physical collisions incurred per game by forwards and backs.

Total Physical Tackling (Defence) Tackled (Attack) Collisons Position Mean 95% CI Mean 95% CI Mean 95%CI

Backs 16 15 -18 13 12 -14 29 28 - 31

Forwards 39* 37 - 41 16 15 -17 55** 52 - 58

All Players 27 25 - 29 14 13 -15 41 39 - 43

* Significantly different from attacks ** Significantly different from backs

The number of injuries received,sub-divided by activity at the time of injury and the standardised injury ratesper 10,000 physical collisions amongforwards and backs are shown in table 2. There

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idrrr_ýw.ý were no significant differences between forwards and backs in the total number of injuries received (7 vs. 13, z=1.12, P=0.26). However, examination of the standardised injury rates revealed that backs had a higher total standardised injury rate than forwards (z = 2.21, P=0.027). When injuries that were received in the tackle (either to the tackler or the player being tackled) were examined, there was no significant difference in injury rate between forwards and backs. The forward playing unit demonstrated higher injury rates for physical collisions when attacking (RR = 3.68 [95%CI [0.27 0.62 - 22.1]), compared with the back playing unit (RR 1.01 - 3.77]). It was also noted that backs had higher injury rates than forwards in both attack and defence, but these differences were not significant. Overall, the tackle situation accounted for a majority (14/20) of all injuries observed.

Table 2. Injury rates per 10,000 physical collisions for forwards and backs J Injury rate per 10.000 Collisions IniuriCollisions

Attack Defence Total Tackled Tackling Other Total Attack Defence Total

Backs 1892 2394 4286 4 5 4 13* 21.14 20.88 16.33 Forwards 2016 4952 6968 3 2 2 7 14.88 4.04 7.17 Teams 3908 7346 11254 7 7 6 20 17.91 9.53 12.44 .

*Significantly difference to forwards

In the act of tackling an opponent, the upper body incurred the greatest proportion of injuries (5/7, z= 0.76, P= 0.44), in which there were two arm injuries (both forwards) and three shoulder injuries (all to backs). The only other two injuries observed were to the foot and both were incurred by backs. In contrast, when being tackled the lower body received the greatest proportion of all injuries (5! 7), with the only two upper body injuries being incurred one to the head (concussion) and the other to the rib area.

Injuries that were received by players and categorised as `other' which did not occur in the tackle included three joint sprains to backs, that were received whilst running and changing direction quickly i. e. not resulting from physical collisions, as well as two incidences of foul play which were also included in this category.

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Overall backsmissed more gamesin total as a result of injury incurred than forwards (45.vs. 23). However, forwardshad higher medianscores for gamesmissed when their injuries were incurredin tackling (5 games vs. 2 games [Median scores]), and in being tackled (4 games vs. 2 games), althoughneither of thesedifferences were significant (P>0.05).

DISCUSSION

) The present study revealed a similar findings to other work, in that the majority (14/20) of injuries occurred in the tackle. Half of these (7/14) were to the person being tackled, which is lower (9) than reported previously. However, while previous investigations have suggested that injury was probably related to the number of physical collisions that players were involved in during a 6.7) game; the unique finding of the present study was that when the injury rate was standardised, backs had a significantly higher overall injury rate per 10,000 collisions than forwards, suggesting that positional play has an influence on injury rate. However, when the injuries received in the tackle were examined separately, the difference in injury rates between forwards and backs was removed. Nevertheless, in the present study backs experienced higher rates of injury than forwards (per 10,000 physical collisions), whilst being involved in significantly less physical collisions. This suggests that backs are more likely to be injured outside of the tackle situation.

t6.7 The collision in rugby league-is considered to be a major risk factor. It has been argued that extrinsic risk factors are independent of the injured person, and are related to the types of activity (16) (17) during the incident of injury, and the manner in which sport is practised. These observations may be true of the physical collisions experienced in rugby league, especially when there is usually (1s) more than one person involved in the physical collision such as the tackle. Therefore, self protection and safety of both the tackler and the person being tackled are important techniques that (5'19) coaches teach to players.

Since the tackle is the activity in rugby league in which so many injuries take place, some authors have suggested that injury prevention strategies directly aimed at making the tackle safer, should be (9) considered. Recent developments have seen certain types of physical contact outlawed (e. g. the ") spear tackle) and the banning of contact with a player who has jumped to catch a high ball! However due to the markedly different number of physical collisions in which players are involved, it may be necessary to develop specific injury prevention programmes for the different positional 9) playing units !

152 0.s.., 4ý-4' gerdmýdiwedlyd/asru72001 4ausl Y ' lYVY1MJ7ý. iCýk It is also necessary to consider some intrinsic risk factors which may influence injury rates in rugby league players. Several authors have reported that forward players have a greater body mass, with larger overall fat-free mass but possess more body fat than backs (20,21,22)While it has been suggested that increased body fat may have a protective effect in the collision, (20)the larger fat-free mass of forwards would result in these players being relatively stronger, more difficult to tackle and thus halt progress. Furthermore both upper and lower body strength has been reported to be significantly higher in forwards than backs; upper body strength is important for making tackles, (21) while leg strength is important for breaking them. However, increased body fat could also be a t20,211 disadvantage in terms of energy expenditure and work load, especially with the game now being played in higher temperatures. Since backs possess lower levels of upper and lower body strength than forwards, this could make them more susceptible to injury in the physical collision. Furthermore backs may also be more predisposed to non-collision injury as a result of their style of play which involves more turning and changing direction during running than forward play.

Not withstanding the injury associated with physical contact, almost one third (6/20) of injuries in the present study did not take place during physical contact. Four of these injuries were to backs (three ligament sprains and a muscle strain) and two to forwards (one joint sprain and one dislocation). Nevertheless such injuries will undoubtedly have specific causes, for example backs may be more susceptible to ligament sprains and muscle strains because they are involved in more changes of direction during running.. In some instances video evidence suggested a likely possible cause, for example a back player who injured a hamstring whilst sprinting with the ball.

Recently, concern has been expressed about the ferocity of tackles and the role this might play in (24) the incidence of injury. It has already been stated that the defending team usually has more than (1e) one player tackling the ball carrier, and the implications of this need to be investigated in future research. The present study demonstrated that backs have slightly higher standardised injury rates than forwards, in spite of being involved in fewer physical collisions. The difficulty appears to be t25» deciding why a player gets injured in a particular collision situation. If it takes more tacklers to halt the progress of a particular player, is that player at greater risk of being injured? Or, could it be the specific types of tackle that backs receive that results in them receiving more injuries per 10,000 physical collisions? Alternatively, the intrinsic injury risk factors such as strength, body composition and flexibility which influence injury incidence need to be considered. Another important consideration is the momentum of the players at the point of contact. Momentum results from a combination of strength, speed, body mass and distance covered which can serve to increase the force of a given collision and thereby increase the risk of injury. In rugby union it has been

153 p"ý d eland.. di. alj. w. d2X1 A, 4

Is,. fl. suggestedthat the momentumof the players is an important factor in determiningwhether a player is injured in a tackle, with most injuries occuring at running or sprinting speeds.()

CONCLUSION

The present study found that there was no relationship between the number of individual physical collisions which players incurred and the incidence of injury. It is possible that the lack of an observed relationship may be due to the small number of injuries in the present study, or because of the confounding effect of an increased number of non collision injuries in backs. Future research into injury in rugby league football needs to continue to monitor injury incidence and prevalence. The game has undergone a number of changes in recentyears, such as modifications in the laws of the game and movement of the playing calendar, which have undoubtedly influenced injury (5) patterns. Therefore, any Rather changes might have a similar influence and need to be monitored. Future investigations also need to examine the evidence with regards to intrinsic injury risk factors exhibited by players. If injury prevention programmes are to be put, in place, they need to be based on the knowledge of both intrinsic and extrinsic aetiological risk factors that contribute to increased (1"5) injury risk.

ACKNOWLEDGEMENT

The authors would like to thank Dr JCG Pearson for his statistical advice.

REFERENCES

1. Gissane C, Jennings DC, Standing S. Incidence of injury in rugby league football. Physiotherapy 1993; 79: 305-10. 2. Seward H, Orchard J, Hazard H Collinson D. Football injuries in Australia at the elite level. Med JAust 1993; 159:298-306. r 3. Gissane C, Phillips LH, JenningsD, White J, Curnine A. Injury in rugby leaguefootball: the new super N league.BrJSports Med 1997;31: 85. 4. Hodgson Phillips L, StandenPJ, Batt ME. Effects of seasonalchange in rugby leagueon the incidence injury. Med 1998;32: 144-8. of Br JSports % 5. Gissane C, JenningsD, White J Cumine A. Injury in summer rugby league football: the experiencesof one club. Br JSports Med 1998;32: 149-52. 6. Gibbs N. Injuries in professional rugby league: a three year prospective study of the South Sydney professional rugby league football club. Am JSports Med 1993; 21: 696-700. 7. Gissane C, Jennings DC, Cumine AJ, Stephenson SE, White JA. Differences in the incidence of injury between rugby league forwards and backs. Australian Journal of Science and Medicine in Sport 1997; 29: 91-4. 8. Norton R, Wilson M. Rugby leagueinjuries and patterns.NZJSports Med 1995;22: 37-8. 9. Lythe MA Norton RN. Rugby Leagueinjuries in New Zealand.NZJ SportsMed 1992;20: 6-7. 10. Larder P. Therugby league coachingmanual. 2nd ed. London: Kingswood Press,1992.

154 X00. CfsreladwdJrnl/ovrd2001 kw 4

: C11AJ

11. Meir R. Arthur D, Forrest M. Time and motion analysis of professional rugby league: a case study. Strength Conditioning Coach 1993;3-. 24-9. Kerr 12. Gissane C, White J, K, Jennings D. Physical collisions in rugby league, the demands on different player positions. Cleveland Medical Journal 2000, in submission. 13. Altman DG. Practical statisticsfor medical research.London: Chapmanand Hall, 1991. 14. Clarke GM. Statistics and experimental design: an introduction for biologists and biochemists. London: Edward Arnold, 1994. 15. Van Mechelen W, Twisk J, Molendijk A, Blom B, Suei J. Kemper HCG. Subject-relatedrisk factors for sports injuries: a 1-yr prospective study in young adults Medicine and Science in Sports and Exercise 1996;28: 1171-9. 16. Taimela S, Kujala UM, Osterman K. Intrinsic risk factors and athletic injuries. Sports Medicine 1990; 9: 205-15. 17. Lyscns RJ, de Weerdt W, Nicuwboer A. Factors associatedwith injury proneness.Sports Medicine 1991; 12: 281-9. 18. Clarke A. A major analysis of rugby league football via questionnaire and video analysis. MSc dissertation. Leeds University, 1993. 19. CorcoranPD. Australian rugbyfootball leagueskills manual. Sydney.Australian Rugby League,1979. 20. Mcir R. Seasonalchanges in estimatesof body composition in professional rugby league players.Sport Health 1993:11(4): 27-31. 21. O'Connor D. Physiological characteristics of professional rugby league players. Strength and Conditioning Coach 1996;4: 21-6. 22. Brewer J, Davis J, Kear J. A- comparison of physiological characteristicsof rugby Ieague forwards and backs.Journal of SportsSciences 1994; 12: 158. 23. The Rugby Football League. Super League: the international laws of the game. Leeds: The Rugby Football League,1996. 24. Jones C. Is super league too tough? Super League Week 161: 3,19th June 1998. 25. Macleod DAD. Risks and Injuries in rugby football In: McLatchie GR Lennox CME, editors. The soft tissues:trauma and sportsinjuries. Oxford. Butterworth-Heinemann Ltd: 1993;371-81. 26. Garraway WM, Lee AJ, Macleod DAD, Telfer 7W, Deary U, Murray GD. Factors influencing tackle injuries in rugby union football. BrJSports Med 1999; 33: 37-41.

155 An operational model to investigate contact sports injuries

CONOR GISSANE, JOHN WHITE, KATHLEEN KERR, and DEANNA JENNINGS Department of Health Studies, Brunel University, Osterley Campus, Isleworth, Middlesex, TW5 7DU, UNITED KINGDOM; Division of Public Health Sciences, Queen's Medical Centre, University Hospital, Nottingham, NG7 2UH, UNITED KINGDOM; Division of Physiotherapy Education, Clinical Sciences Building, University of Nottingham, Nottingham, NG5 IPB, UNITED KINGDOM; and Wall House Surgery, Yorke Road, Reigate, Surrey, RH2 9HG, UNITED KINGDOM

ABSTRACT

GISSANE, C., J. WHTfE, K. KERR, and D. JENNINGS. An operational model to investigate contact sports injuries. Med. Sci. Sports Exerc., Vol. 33, No. 12,2001, pp. 1999-2003. Purpose: A cyclical operational model is proposed to examine the interrelationship of injury investigations identify a number of factors that are involved in sports injury epidemiology. In sports research, often attempt to factors injury a unique risk factor that distinguishes an injured player. However, a wide variety of can contribute to a sports occurring, knowledge. Methods: The identifies healthy/fit and an understanding of the cause of injury is important to advance proposed model a intrinsic factors for injury. Before player initially, although the player may exhibit a number of risk sports exposure to extrinsic risk factors, there is the opportunity for implementation of prevention strategies by coaching personnel and the sports medicine team. These hydration, strategies might include, among others, appropriate warm-up, adequate wearing protective equipment, and prophylactic intrinsic taping. Additionally, preventative screening could take place to assessthe various and extrinsic risk factors that could lead to injury Participating sports injury. Discussion: Two examples of how the operational model relates to contact sports cases are presented. injury. The injured in sport inevitably exposes the player to external risk factors that predispose toward treatment of the player aims injury from becoming Conclusions: It is to restore the player to preinjury playing status and to prevent the chronic. suggested that the lead in the injuries application of this proposed cyclical model may to greater success understanding multifaceted nature of sports and injured Key Words: EPIDEMI- furthermore help minimize injury risk and support the rehabilitation of contact sports participants. OLOGY, INJURY, INCIDENCE, PREVALENCE, RISK FACTORS, PREDISPOSITION

injury (2). Extrinsic sports injury research, the aim of inquiries has often posing a person to the outcome of risk independent been to find a unique marker or risk factor that will factors are of the injured person and are related identify injured players (24). Usually the frequency of to the types of activity during the incident of injury (35) and in is (20). A injury is examined in relation to the presence or absence of the manner which sport practiced summary of Jn intrinsic factors documented in most injuries both the a specific risk factor (28). However, sports are and extrinsic risk injuries injury literature is in Table 1. However, rarely attributed to a single risk factor. Although sports presented fac- factors into intrinsic may sometimes appear to be random accidents, many even the classification of risk and injury be being (19), because tors play a role before the actual occurrence of an extrinsic could criticized as artificial injury is injuries from event (24). An understanding of the etiology of also that result participation are multi-risk phenom- important for the advancement of knowledge (23). ena, with a variety of risk factors.interacting at a given time Although sports participation is acknowledged as having (20). deleterious Because injuries do independently, a health-promoting benefit, it can also have sports not occur pre- (37). has for investigation effects on health in the form of injuries and accidents vious research suggested strategies the Action to prevent sports injuries should be based on the of sports injuries (37,40) by using a sequence of events with knowledge of etiological factors that contribute to increased four stages (37); involves identification injury risk (38). Various authors have described many risk 1. The initial stage the of the injury in injury factors, which are usually grouped into intrinsic (subject problem and the description of terms of factors incidence injury. related) factors and extrinsic (externally related) and the severity of (2,19,20). 2. The next stage identifies the risk factors and mecha- Intrinsic factors have been defined as individual biolog- nisms that play a part in sports injury episodes. ical, biomechanical, and psychosocial characteristics predis- 3. Once these have been identified, measures that will have the likely effect of reducing sports injuries can be introduced. based the injury 0195-9131/01/3312-1999/$3.00/0 -These measures are on mech- in 2. MEDICINE & SCIENCE IN SPORTS& EXERCISE, anisms and risk factors that have been identified stage Copyright 0 2001 by the American College of Sports Medicine 4. The final stage of the sequence is to repeat the initial in in to Submitted for publication June 2000. stage with the preventive measures place, order Accepted for publication March 2001. determine the extent to which such measures are effective. 1999 TABLE1. Intrinsic factors in the literature. intrinsic andextrinsic risk reported risk factors are not fixed and that they can vary over Factors ExtrinsicRisk Factors Intrinsic Risk time. Furthermore, Figure 1 is a linear model that does not Physicalcharacteristics Exposure(20) account for what happens after injury, how the athlete Type (20) may Age (20,40) of sports to how the injury Sex(20,40) Playingtime (20) return sport, and susceptibility to changes. Somatotype(20) PositionIn the team (20) Bodyshe (40) Levelat competition(20) PreviousInjury (20,40) Warm-up(40) MATERIALS AND METHODS Physicalfitness (20) Personalequipment (40) Joint mobility(20.40) Training(20) A proposed cyclical operational model for the Coaching Muscletightness (20,40) (40) investigation injuries. Ligamentouslaxity (20) Refereeing(40) of contact sports Traditional Malalignmentof lowerextremities Controlof game(40) approaches to the epidemiological investigation sports Opponents of (20,40) injuries have tended to focus on the incidence Dynamic (40) Foulplay (40) and preva- strength lence injury, Staticstrength (40) Opponent'sphysique (40) of applied both to individual sports, and to Environment(20) Skill level(40) overall national statistics. The model developed here aims to Psychological (20) Typeand condition of playingsurfe (20,40) characteristics this traditional to take into Psychosocialcharacteristics (20) Weatherconditions (20,40) expand approach consideration Skill level(40) Tlmeof day (20) the multitude of factors that may predispose to injury and Willingnessto take (40) Timeof season(20) risks ------that may determine the ultimate outcome the injury for Interactionwith otherplayers (40) Equipment of Experienceof sport (40) Protectiveequipment (20) the contact sport athlete. Footwear(20) The cyclical five linked First, Orthotics(401 model consists of stages. the ostensibly healthy/fit athlete may be at risk of injury from a number of predisposing factors. These may with or the factors in Later work proposed a multifactorial model for the in- without additional exposure to external risk the injury in injury inci- vestigation of sports injuries (23), in which an indefinite presence of a potential event result dence. The duration time that the injury during number of intrinsic risk factors may predispose an individ- of persists, treatment to ual to injury (Fig. 1). If an athlete is predisposed to injury, and rehabilitation, contributes the prevalence of the injury, the be extrinsic factors could exert their influence, i. e., extrinsic and ultimate outcome may a return to sport the level, thus the risk superimposed upon intrinsic factors. at original completing cycle, or a return at a different level (Fig. 2). Each However, an injury may require a further "initiating or even premature retirement the the is described in event, " such as a collision or sudden change of direction. of elements of model now greater detail. These "initiating events" may be focused upon by the sports The healthy/fit Inherent the medicine practitioner, with little attention being paid to player. within ostensibly healthy/fit intrinsic factors those factors that were more distant from the event, e.g., player exist a myriad of risk have been by literature (23). For how does an athlete become susceptible to injury? that suggested the ex- it has been field hockey, Both the strategy for injury prevention (37) and the mul- ample, reported th at soccer, and lacrosse increased for tifactorial model of etiology (23) have valid and important players exhibited an risk ankle sprain they displayed increased inversion contributions to make for the investigation of sports injuries. when an eversion: strength (1). However, a linear model with a beginning and an endpoint may ratio At in for intervention be too simplistic because it is logical to assume that these this stage the cycle, the strategies may be termed "primary prevention" (20), with the aim of preventing injuries from in the first instance (6). Exposucto occurring Exlrintie Risk Factor Knowledge of the individual's risk factors may be of benefit in primary prevention. These strategies, among others, include Ag might such measures as appropriate warm-up, ade- quate hydration, and prophylactic taping. They might also include Flexibility wearing protective equipment such as gum shields in rugby (14), hurling (4), and ice hockey (29) or head Intrinsic guards in hurling (4) and ice hockey (16,29). Such strategies risk in factors Pz vioue/ would also include coaching proper technique contact injury sports when either making or receiving a tackle (3) and teaching correct falling technique in judo (16). Coaches and somatolypc sports medicine practitioners seek to prevent injury, and it is the most logical and least costly method of health care (24). Additionally, prevention screening could take place to as- sess intrinsic risk factors that could lead to sports injury 1 ' problems (22). For example, it has been shown that postural ...... Risk factor for injury (distant from outcome) ...... Mechmtism oCinjory and mechanical factors can predispose female basketball (proximal to outcome) players (7), rugby, and soccer (39) players to injury, has been for injury FIGURE 1-A new multifactorial model of athletic injury etiology whereas screening advocated groin pre- (from ref. 23). vention in rugby league football (27).

2000 Official Journal of the American College of Sports Medicine http-J/www.acsm-msse. org lntcinsic Risk TABLE2 Injuryincidence rates among team Primary Pmention contact sports. F7pOý ReReturnturn of HeaU1rv/Fi1 Medies1Fhysios/ Injuriesper C Realdo4 t Player 1000Player Player Sport Hours Reference RugbyLeague Football Exl-posm 34* Stephensonat al., 1996(34) to Em RugbyUnion Football 20* Hughes Fricker, \ cmal and 1994(10) Nn Infu \\ k FaUOn AustralianRules Football 35' Seward ry Potennal et al., 1993(32) vent Soccer 22.6 Inklaar 1996 Outcomes `'ý Injury Evan at al., (11) ` I \ Injuries to be to for than1 njury \ requiringa player unable play more wk. Recurrence J , ` ýý i 1n1ý f an individual will be injured at some point in time (8). Injury prevalence dependsupon both the incidence rate of an injury and the period of time between the initiating event to the I Factorsin Prcmidue RetiremeaU the Meohanimu return to full fitness. In sporting terms, the Lower Playing Lcvd Tccabxica[and Rehabilitation of prevalence of an Iniurv injury is an important consideration, because the treatment and rehabilitation of injuries takes time and this is often a FIGURE 2-A cyclical operational model for the investigation of major factor in injury prevalence. It has been that contact sports injuries. suggested becauseprofessional sport is a business, it is often desirable on the part of both the team and the player to keep time lost Potential injury event. In addition to the intrinsic fac- främ playing to a minimum (18). Prevalence can also be tors, extrinsic factors will play an important part in the influenced by game regulations, for example, in rugby union potential for injury. The exposure to extrinsic risk factors football a player who is concussed is required not to either will undoubtedly vary across sports and may vary within play or train for a period of 21 d (International Rugby positions in certain sports, as well as the conditions under Football Board resolution 5.7), whereas in rugby league which sport is played. For example, both field hockey (13) football there is a sliding scale of required abstinence for the and American football (33) have reported increased injury severity of injury based on the symptom severity of con- rates when games are played on Astroturf. In American cussion. Therefore, concussions that are considered rela- football, both the risk of knee (RR = 1.18) and ankle (RR tively minor in rugby league football would have a far = 1.39) injuries are increased when the game is played on higher prevalence in rugby union football, which could artificial compared with real grass (28). contribute to a distortion in specific injury prevalence The event that initiates an injury is one of the most among similar sports. identifiable parts of the injury process and has been the The type and duration of treatment of the athlete is focus of much research (23). In contact team sports, these dependent upon each specific injury that the player has events are likely to be highly game specific, and indeed sustained. For example, it has been reported that 44% of position specific. It has been suggested that there are a high rugby injuries only require treatment with RICE (rest, ice, number of thigh injuries in professional soccer (12) that compression, and elevation) (10), whereas others may re- commonly result from physical contact with an opponent quire surgical intervention (36). (5). It has also been suggested that with the exception of During the rehabilitation process, both secondary and goalkeepers, there are few upper body injuries that prevent tertiary prevention can take place. The aim of secondary soccer players from playing (22). prevention is to restore health when it is impaired (17). In At this stage in the cycle, a player who is not injured can sports medicine, it is defined as the process of preventing continue to play while still exhibiting the same intrinsic risk or delaying the development of irreversible structural factors, whereas if he/she becomes injured the player damage by therapeutic intervention (20). These measures progresses to the next stage of the model. can influence the prevalence of injury by reducing the Injury incidence. In descriptive sports medicine, epi- amount of time that a person remains injured, but not the demiological terminology, incidence has been defined by incidence. Appropriate and early management of soft the number of new events or cases of injury that develop in tissue injury, in particular, has been shown to promote a population of individuals at risk during a specified time early recovery (21). interval (8). The incidence of injury in specific sports is an Therapy that seeks to limit the injury process from be- area that has received much attention (7,9,16). However, the coming either chronic or persistent has been termed tertiary comparison across studies is often difficult due to the vary- prevention (20). The aim of tertiary prevention is to reduce ing definitions of injury that have been employed (38). both the incidence and prevalence of long-term disability Nevertheless, where comparisons can be made, there is a (20). Sound treatment and rehabilitation have been sug- range of injury incidence rates among contact sports as gested to be one of the most adequate preventive measures demonstrated in Table 2. for secondary and tertiary prevention (19). Injury prevalence. In descriptive sports epidemiology, Event outcomes. In the proposed cyclical operational injury prevalence has been quantified by the proportion of model for the investigation of sports -injuries (Fig. 2), an, individuals in a population who have an injury at a specific injury has three possible event outcomes. A player can instant. It provides an estimate of the probability or risk that return to a healthy/fit state, the injury can recur, and either

A MODELTO INVESTIGATECONTACT SPORTS INJURY Medicine & Science in Sports & Exercises 2001 the from that level This player can retire competition at or continue paper proposes to provide an example of the appli- lower level. The ideal is participating at a obvious to return to cation of this model to two specific sports situations in the level playing at the preinjury of performance. For athletes to be contact sport of rugby union football. healthy, be fully in regarded as they must able to take part both Case 1: first rib synchondrosis. An injury to the first training (20). However, in and playing professional athletes are rib synchondrosis a rugby football player is an example of in injury unlike a number of other occupational groups that they are an acute caused primarily as a consequence of ex- to train in injury, factors often quite willing and play spite of compared trinsic (15). However, the muscle bulk in the shoul- der with others, who normally return to work only when they are area and the strength of the muscles represent the play- (30). internal completely recovered er's (intrinsic) risk factors. The external exposure to Recurrent injuries in (extrinsic) are also a major problem sport and a risk factor would be the contact with the op- have been for 16.5% injuries in reported to account of all posing player and the opposing player's physique. football (7). Recurrent injuries increase rugby union the In this example, the specific injury incidence was a first incidence lost for injured rate and the amount of time an rib synchondrosis. The injury contributed to the incidence as increasing player, thus also the prevalence rate of injury. an injury event, and the treatment, which was described as Furthermore, factors injury one of the greatest risk for is the conservative and lasting for 12 wk, contributed to the prev- history injury (40). of previous alence throughout the recovery period. At the end of the In extreme circumstances, professional sport players are treatment, the. event outcome was that the player was pain sometimes forced into premature retirement because of in- free and a repeated CT scan showed that the injury had jury. In it has been healed. such cases, reported that rugby league The player was then allowed to resume contact sport football players who suffered long-term consequences of at the same level, which would return him to the start of the injury after their playing careers experienced difficulties, cycle, where this injury may or may not represent an intrin- which included job limitations, reduced income-earning po- sic risk factor to future injury. tential, and increased personal medical costs (26). Case 2: incarcerated hernia. An incarcerated hernia In certain situations, players will be unable to return to during a lineout (36) might fit into the model as follows; this playing, and the management of such an injury may seek to is an acute injury superimposed upon an intrinsic weakness. maximize the quality of life rather than fully remediate the For this injury, the intrinsic risk factors would include the injury (19). Previous work has described cervical spine preexisting hernia and the player's position, somatotype, injuries of two rugby union football players who could no and gender, whereas the predisposing external risk factors longer return to play (31). These players are now members would include the fact that it took place in a lineout. This is of the Rugby Amistat Foundation, which is dedicated to the an area of the game that has recently been the subject of well-being of players who have suffered physical and men- some rule changes, which has resulted in lineout jumpers tal trauma after disabling injury (31). being supported and lifted by adjacent players. This is a The overall design of the proposed operational model is technique that is coached and rehearsed during practice cyclical because even if a player returns to health/fitness, the sessions. The act of being supported in an unstable mid-air sports injury itself may constitute an intrinsic risk factor for position could be considered to be an external risk factor. the predisposition of future injury. Even if a player is for- The exertion of 'jumping may have increased the intra- tunate enough to avoid an injury, the individual's intrinsic abdominal pressure, thus increasing the size of the hernia. risk factors are unlikely to remain the same over time. For This would be compounded by the increased external pres- example, at the beginning of every season, a player has sure to the groin area, transmitted through the shorts, by the another year of experience and is another year older, both of action of two other players lifting and holding the lineout which have been described as potential sports injury risk jumper. factors (20,40). This will serve to alter the nature of intrinsic The particular injury was the hernia, which required treat- risk factors present. In addition to this, coaches in contact ment with surgery. The prevalence of the injury was for a sports often emphasize increasing muscle bulk during the period of 5 wk in total, after which the event outcome was the closed season (25), which may also serve to alter an indi- player being able to return to play, again completing the cycle. vidual's intrinsic risk factors. CONCLUSIONS has been DISCUSSION The model that proposed seeksto acknowledge the multifactorial nature of sports injury. It further recognizes that The advantage of the cyclical model over the previous the sports injury is not an endpoint (23), becauserehabilitation linear model (23) is that knowledge and awareness of the and recovery are part of the continuing process.In so doing, it factors involved at each stage of the model allows for the attempts to..bridge the gap between descriptive and analytical development of appropriate strategies for the prevention of sports injury epidemiology. Sports participants almost always injury at the primary, secondary, and tertiary levels. There- seek to return to play, but on their return their intrinsic risk fore, the practical application of this model may help the factors and the external risk factors will undoubtedly be dif- deal sports medicine practitioner more effectively with the ferent. Although the model has been applied to rugby football in injury problems of athletes contact sports. and the myriad of factors that can influence injury, the situation American College 2002' Official Journal of the of Sports Medicine http.//www. acsm-msse.org will undoubtedly be different in other sports to be descriptive and needs and future analytical epidemiological ap- investigated further. proacbes to sports injury research. The previously published work underpinning the devel- opment of the proposed cyclical model (Fig. 2) has been The authors would like to thank Peter J. Maud, FACSM, for his comments presented to illustrate the application to sports injury re- on earlier versions of this manuscript Address for correspondence: Conor Gissane, search and demonstrate the advantages over the previously Department of Health Studies, Brunel University, Osterley Campus, Isleworth, proposed linear model (Fig. 1). Furthermore, it is envisaged Middlesex, 1W7 5DU, England, United Kingdom; E-mail: conor. that the new model may be used to further develop current [email protected]. uk.

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A MODELTO INVESTIGATECONTACT SPORTS INJURY Medicine & Science in Sports & Exercises 2003 SP°dsMed2002: 32M. 211-216 ORIGINAL RESEARCHARTICLE 0112-16002/0003-0211425.00ro

® Adis Interrchond limited. AN nghts reiarwd.

A Pooled Data Analysis of Injury Incidence in Rugby League Football

Conor Gissane,l De Jennings,2 Kathleen Kerr3 and John A. White4 1 Department of Health Studies, Brunel University, Osterley Campus, Isleworth, Middlesex, UK 2 Wall House Surgery, Reigate, Surrey, UK 3 Division of Physiotherapy Education, Nottingham University, Nottingham, UK 4 Centre for Sports Medicine, Queen's Medical Centre, University of Nottingham, Nottingham, UK

Abstract Objective: The aim of this study was to summarise the injury rates in professional rugby league football. Methods: Previously -published studies were identified from database searches of the literature from Medline, Sports Discus and Web of Science. A total of 18 articles, which reported the prospective injury data collection for at least one playing seasonin professional rugby league worldwide, were included. The def- inition of injury adopted required an injured player to miss the subsequent game through injury. Ten studies satisfied the injury definition criteria for inclusion. A review of articles and extraction of relevant data were carried out independently by two authors. Results: A total of 517 injuries were reported during 12 819 hours of exposure (753 games), which resulted in an overall injury rate of 40.3 injuries per 1000 hours [95% confidence interval (CI) 36.9 to 43.8]. Most injuries were to the lower half of the body (20.7 per 1000 hours, 95% Cl 17.7 to 24), with the trunk receiving the least (6.7 per 1000 hours, 95% CI 5 to 8.6). Conclusions: Injury rates in professional rugby league are higher than in some other contact sports, probably because of the large number of physical collisions that take place. This pooled data analysis provides more accurate estimates of injury incidence in the game of professional rugby league football.

Rugby League football has been described as a ber of the attacking team. The ball carrier can be fast moving contact sport, (') and as a collision sport.i2l tackled by any number of the opposing team's play- It is an invasion game, whereby one team attempts ers.131 to invade the territory of the other team with the A rugby league team consists of 13 players (six object of scoring points, while the opposition uses forwards and seven backs) who have six posses- physical force, within the laws of the game, to try sions to advance the ball down field. The ball must and stop them. To do this, the internal structure of be passed backwards, but can be carried or kicked the game demands that the side that is not in pos- down field. Unlike American football, there are no session tackles their opponents who are in posses- special teams or sub-units within a team (other than sion of the ball. Tackling can be described as the forwards and backs), so each player has a role to act of preventing a ball carrier, running with the play in both attack and defence. ball, or passing or kicking the ball to another mem- Research into the incidence of injury in rugby 212 Gissaneet al.

league has injury incidence shown that is high com- Data collection carried out prospectively on pared with other sports, for example rugby union. R4I professional players However, one shortcoming of many of these stud- A definition of a recordable injury being one ies is that deal they with a relatively small number that required an injured player to miss the sub- of players and often only one club, thus reducing sequent game their generalisability. A count of the number of games studied to allow One information strategy to enhance the pro- the calculation of player time injury rates. vided from epidemiological studies is to combine the information from multiple studies into a single Procedures estimate. 161For this technique to be successful it is important that the studies that are included have A total of 18 articles were -identified that re- compatible structure with respect to inclusion cri- ported prospective data collection of rugby league teria, follow-up, and exposure history. The com- injury, and details of these studies are shown in bined data from individual I. Of these studies can then table these, only -ten satisfied the inclusion be statistically reanalysed to provide more precise criteria, 14,5.8-13]but two of these studies had to be injury data. (7) excludedt14.'5l for re-reporting the same source data The purpose of the present study was to provide in a previous article. UU21 pooled estimates of injury incidence in. rugby league Upon further examination, it was also apparent football from published studies; more specifically, that in some of the remaining eight studies that sat- this included estimates of injury incidence, injury isfied the inclusion criteria, authors had used the severity, site of injury and the comparison of injury same common baseline data sets to highlight fur- rates between forward players and back players. ther trends in their data. For example, the data re- ported by Gissane et al 141were contained within data [ Methods reported in a later article. 131While Stephenson et al 1131and Gissane et al. 1 01used the same baseline The methodology included the development of data, one group of investigators reported the over- a searchstrategy to locate articles investigating in- all incidence of injury in rugby league, [131while the jury in rugby league. Inclusion/exclusion criteria other sought to highlight the differences in injury were developedto ensure compatibility, and finally, rates between forwards and backs. 110]This resulted combined analysis was performed. in a total of six studies being included in the final pooled analysis, which are highlighted in table I, Search Strategy for Identification three of which reported both first team and reserve {8.9.'31 of Databases grade information. Since many studies did not include all areasof The search strategy involved searching Medl- interest for analysis, it was necessaryto extract spe- ine, Sports Discus and Web of Science databases, cific information from individual studies at differ- covering the period from 1985 to 2000. A total of ent stages of the analytical process. 18 studieswere identified. The following terms were used.,rugby with league and injury. Statistical Analysis

Inclusion Criteria The data from individual studieswere combined using the method describedby Breslow and Day.t 1 In the present analysis the authors collated pub- Person-time incidence rates and 95% confidence lished studies that reported the incidence of injury intervals (CI) were calculated using confidence in- in rugby leaguefootball. The inclusion criteria were: terval analysis software.J241 To test for significant a Studies published later than 1990 differences, proportion tests (z), and chi-squared

O Adis Internationcd Umlied Al rights reserved. SportsMod 2002:32 (3) Injury Incidence in Rugby League Football 213

Table I. Summaryof rugby league Injurystudies that reportedprospective data collection' Study Study design Samplingtime Grade/level Participatingclubs "(no. of seasons) Alexander at a11'61 Prospective 1 1st, reserve, U21 1 Alexander at al t1I Prospective 2 1st, reserve, U21 1 lstell et al. iai Prospective 1 1st, reserve, U21, U19, U17, U15 1 Gabbettir71 Prospective 3 Amateur 3 Gibbst'81 Prospective 3+2 1st, reserve, U21 1 Gibbsl9l Prospective 3 1st, reserve, U21 1 Gissane et al 1'1I Prospective 5 ist 1 Gissane et al. t101 Prospective 4 1st, reserve 1 Gissane et W.141 Prospective 1 1st, reserve 1 Gissaneat al1191 Prospective 1 ist 2 Hodgson-Philiipstt5J Prospective 4 ist 1 Hodgson-Phillips et ai. 1121 Prospective 4 ist 1 Hodgson-Philipset aLI141 Prospective 4 Ist 1 Lytheand Norton1201 Mixed 1 Not stated Not stated Nortonand Wilson[211 Prospective 1 1st, reserve,senior B, open-ageamateur 24 Seward et aLt Prospective 1 1st, reserve,U21 9 Stephenson et al 1'a1 Prospective 4 Ist, reserve 1 Walker[221 Prospective 5 Not stated 1 a Studies in bold Include overallanalysis. U15 = under 15s; U17 = under 17s; U19 = under 19s; U21 = under 21s.

injury (%2)goodness-of-fit testswere used, along with rel- It was possible to pool data on the site of ative risk (RR) where appropriate. from four studies, which totalled 8365 exposure hourstS,h'. '3.25Jand figure I. displays the injury rates Results for the different sites of the body from these studies. There were significant differences between these The included injury data from studies reported injury rates (2 = 12.34, ff = 3, p<0.01) with 753 548 first team 205 a total of games, and at injuries to the lower limb accounting for 46.4% of .. The total hours of obser- i reserve grade. number of the total, followed by the upper limb (20%), head vation for injury exposure was calculated as 13 play- and neck (18.7%) and trunk (14.7%). ers x length of the game x number of games played Only two studies11°' 1have reported a compar- (two teams of 13 playing for 1 hour constitutes ison between forward and back players for injury 26 player hours). Games are usually 80 minutes in rates, which totalled 3673 player-hours of expo- length, but in two studies, 18'251reserve grade games (forwards 1811.39 player-hours, backs = were 70 minutes long. There were a total of 12 819 sure = 1861.9 This gave rise to injury rates player-hours across the six studies, 9474 player- player-hours). 66 1000 hours (95% CI 55 to 79) and 61 per hours at first team and 3344 player-hours at reserve of per (50 73) for forwards backs, grade. 1000 hours to and re- spectively. The RR 1.09demonstrated that The injury incidence figures are shown in table of play- increased injury by II. There was an overall injury rate of 40.3 injuries ing as a forward the risk of only RR (0.85 1.40) per 1000 player-hours. First team players experi- 9%, although the 95% CI for the to enced a slightly higher injury rate than reserve grade indicated that the increasedrisk wasnot significant. players did, although the difference was not signif- Injury severity was graded according to the cri- icant (z = 0.49, p=0.62). teria used by Gibbs. 1151An injury was classified as

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214 Gissaneet al.

Table It. Pooled injury incidence data of included studies Study Grade/ level No. Injuries of seasons Games played Exposure time Injury rate 95% Cl reported (no. ) (no. ) (h) per 1000h 'Z Hodgson-Phillips et al. ist 4 77 115 1988.4 38.7 30.1-47.4 Seward 15l at al. ist 1 151 178 3077.6 49.1 41.2-56.9 Gissane et al1111 ist 1 20 23 397.7 50.3 28.3-72.3 1' 1 Stephenson et al 1st 4 72 138 2386.0 30.2 23.2-37.1 151 Estee et al. ist 1 20 28 484.1 41.3 23.2-59.4 Gibbsl°I 1st 3 47 66 1141.1 41.2 29.4-53.0

Combined let 387 548 9474.9 40.8 38.8-44.8 Gibbelol Reserve 3 41 68 1001.0 41.0 29.4-55.6 Stephenson et 81.1'31 Reserve 4 75 111 1919.2 39.1 30.7-49.0 Estell at a081 Reserve 1 14 28 424.7 33.0 15.7-50.2

Combined Reserve 130 205 3344.9 38.9 32.2-45.8 Overall 517 753 12819.8 40.3 36.9.43.8 Cl = confidenceinterval. minor (one game missed), moderate (two to four rates of first and reserve grade players; (ii) there games missed), or major (five or more games miss- were significant differences between the injury rates ed). It was possible to pool the results from three for different sites of the body, with the lower limb studies['2.13.25)that covered a total of 9437 hours of having the highest injury rate; (iii) there was a small in III. exposure, and the injury rates are shown table but. not significant increased risk of injury when Overall, injuries for 43% minor accounted of the playing as a forward compared with playing as a injuries total, with moderate and severe accounting back; and (iv) there was no significant difference for 32.9 25%, However, dif- and respectively. the between the degree of severity of injuries sustained ferences between injury the categories were not sig- by players. (x2 5.37, df 2, nificant = = p>0.05). Pooling data from a number of studies of similar design is a technique that can produce an overall es- Discussion timate which incorporates the information provided by those studies. 1261Therefore, the major strength The major findings of the current analysis were: of the present pooled analysis is the fact that it pro- (i) that there was no difference between the injury vides more accurate estimates of injury rates than the individual studies which provided the initial raw data. Therefore, injury rates from the present 30 study can be compared with injury rates from pre- 25 vious studies. The combined data demonstrated no significant ý20 differences between injury for first 15 the rates and re- serve teams. Individual studies have also all reported W [8,13,251 ci 10 nonsignificant differences between grades. 5 Furthermore, this finding was evident irrespective of the definition of injury that was adopted. For Head Upper limb Trunk Lower limb example, one studylu1 only reported injuries that and neck required a player to miss more than one game, while Site of Injury the two studiesl8-131originally reported all in- Fig. 1. Pooled data for site of injury (rates per 1000 hours with other 95% confidence interval). juries that received treatment.

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The injury 46.4% combined estimate of of the clude all minor concussionsand suturesthat would for lower body injuries is total very similar to the not prevent a player from playing in the next match. 41151and 45%1111reported in individual studies. One One recognised limitation when compiling the major feature of rugby league is the amount of tack- present analysis was that it was not possible to pro- ling that takes place. The thigh area is where most vide an accurate estimate of the phase of play in coaches will instruct players to aim tackles, 12.271 which injury took place. Although two previous 131 which would tend to. make it an area of the body studies(to. have suggestedthat most injuries are by more susceptible to injury. However, there is no received the ball carrier whilst being tackled, both baseline data, it real evidence to indicate which area of the body is reported the same so is essen- tially Furthermore, inves- contacted first, or with how much force, in the tackle. a single study. no other tigators have injury in Furthermore, when tackles are aimed at the upper reported occurrence relation to the phase of play. part of the body, arms and shoulders can be used to The aggregation of two data setst10.251revealed protect such areas as the trunk and head, whereas that there was no increased risk of injury when play- the lower limb will remain somewhat exposed to ing as a forward compared with playing as a back. contact. Recent workt28) has shown that forwards are in- The finding that half the injuries in the almost of volved in many more physical collisions than backs data to the lower limb is in pooled analysis were during the course of a game (55 vs 29). This situa- the head contrast to an earlier report that and neck tion is similar in forwards compared in both attack frequently injured t41This dis- were the most sites. (16 vs 13) and defence (39 vs 16). These increased crepancy may also be caused by differences in in- numbers of physical collisions experienced by for- jury definition. If all injuries that required treat- wards do not appear to predispose them to injury. ment were included, then lacerations that rgquired The pooled data analysis of three studies('2'13,251 suturing would be counted, even though these would indicated that there were no significant differences not require a player to miss a subsequent game. between categoriesof severity of injury. Neverthe- Indeed, it has been suggested that including such less, although 43% of injuries required players to injuries, in addition to those requiring a player to miss only one game, it was disturbing to note that miss a subsequent game, would increase the injury one in every four injuries required a player to miss count by as much as 43%. (251 five or more games.Since recent changesin play- ing league five If this study had adopted an injury definition for calendarsand structures, gamesnow 20% all injuries that received treatment, it would have represent almost of a season,which will re- increased of to cover for the increased the number of studies that could be utilised. quire numbers players time lost as a result of injury. However, at the same time this would have reduced playing the number of hours of observation, as several large- Conclusion scale studies employed the injury definition of play- ers missing a subsequent game. (5.9.IEI Nevertheless, Within the limits of the definition of injury used the injury pattern would probably have been rather in the present study (an injury requiring a player to has different. Injury rates would have been somewhat miss a subsequentgame), the pooled analysis higher, for example, combining the first and re- serve grade estimates of Estell et al., 181Hodgson- Table Ill. Injury ratesfor gradesof severity Phillips et al. (121and Stephenson et 1131 al. would Seyeity Rate per 1000h 95% Cl increase the injury 116.6 injuries overall rate to per Minor 16.64 14.1-19.5 1000 hours. It is also likely that the site of the body Moderate 12.7 10.5-15.2 that was most injured would also change to the Major 9.32 7.5-11.5 head and neck. (4.13)This definition would then in- Cl = confidenceInterval.

0 Adis Interns onal Limited. AAfights reserved SporteIvied 2002,32 (3) 216 Gissaneet al

allowed the calculation of more accurate estima- 9. GibbsN. Transientpost-traumatic cortical blindness in a rugby leagueplay: a casereport. AustJ Sci Med Sport 1993;25 (3). tions of injury rates in professional rugby league and 95-6 has attempted to make the results more generalis- 10. Gissane C, Jennings D, Cumine A, et al. Differences in the incidence of injury between rugby league forwards and backs. ' able. The resulting combined analysis reduces the Aust J Sci Med Sport 1997; 29 (4): 91-4 variability associated with imprecise estimates and 11. Gissane C, Jennings D. White J, et al. Injury in summer rugby biases individual league football: the experiences of one club. Br J Sports Med potential associated with studies. 1998; 32: 149-52 influence individual It also removes the of sub-cohort 12. Hodgson-PhillipsL, StandenP, Batt M. Effectsof seasonalchange characteristics, such as playing style. « in rugby leagueon the incidenceof injtuy. Br J SportsMed 1998;32: 144-8 league is has To date, rugby a sport that not un- 13. Stephenson S, Gissane C. Jennings D. Injury in rugby league: a dergone a comprehensive scientific investigation. four year prospective survey. Br J Sports Med 1996; 30 (4): 341-5 However, it be in future to may possible add sub- 14. Hodgson-Phillips L. Standen P, Batt M. The effects of seasonal sequent studies to the present pooled analysis with change in rugby league on the incidence of injury [abstract]. Br J Sports Mod 1997; 31 (4): 354 to improving the factors a view understanding of 1S.Hodgson-Phillips 1.. The in foot- effects of seasonalchange rugby surrounding injury incidence in rugby league leagueon the incidenceof injury. PhysiotherSport 1998;XXI ball. (1): 13-4 16. Alexander D, Kennedy M, Kennedy J. Injuries in rugby league To provide more comprehensive data on injury football. Med J Aust 1979; 2: 341-2 in incidence Injury between incidence in rugby league football further prospec- 17. GabbettT. Differences the of ama- teur league forwards backs. 5th International Olympic Furthermore, these rugby and tive studies are required. stud- Committee World Congress of Sports Sciences; 1999 Oct 31- ies should include the common definitions of in- Nov 5; Sydney 18. Gibbs N. Common leagueinjuries: recommendations for jury, the of play in which injury occurs, and rugby phases' treatmentand preventativemeasures. Sports Med 1994; 18 the precise mechanism of injury. Such approaches (6): 438-50 19. Gissane C, Phillips LH, Jennings D, et al. Injury in rugby league: would be best facilitated by the adoption of a stand- the new super league. Br 1 Sports Med 1997; 31(1): 85 ardised injury surveillance system that would al- 20. Lythe M, Norton R. Rugby leagueinjuries in New Zealand. low further in-depth analysis to be performed. SportsMed 1992;20 (1): 6-7 21. Norton R, Wilson M. Rugby league injuries and patterns. Sports Med 1995; 22: 37-8 dangerous Acknowledgements 22. Walker R. Sports injuries: rugby league-may be less than union. Practitioner 1985; 229: 205-6 23. Breslow N, Day N. Statistical in cancer research; The authorshave no conflicts of interest. methods the design and analysis of cohort studies. Vol. II. - Lyon: IARC, 1987 References 24. Altman D, Machin D. Bryant T, et al. Statistics with confidence. London: 2000 1. AlexanderD, KennedyM, Kennedy1. Rugby league football 2nd od. BMJ Books, league: injuries over two competitive seasons.Med J Aust 1980; 2 25. Gibbs N. Injuries in professional rugby a three-year (6): 334-5 prospective study of the South Sydney professional 21 (5): 2. LarderP. Therugby league coachingmanual. London: Heinemann rugby leaguefootball club. Am J SportsMed 1993; Kingswood, 1998 696-700 3. Rugby LeagueInternational Federation. Rugby league laws of 26. Elwood M. Critical appraisal of epidemiological studies and trials. 2nd Oxford. Oxford University Press, 1999 the game.Leeds (UK): Rugby FootballLeague, 2001 clinical ed. J. Skills development for league. Harpenden; Queen 4. Gissane C, Jennings D, Standing P. Incidence of injury in rugby 27. Kcar rugby league football. Physiotherapy 1993; 79 (5): 305-10 Anne Press, 1996 White J, Kerr K. Physical in 5. SewardH, OrchardJ, HazardH, et aLFootball injuries in Aus- 28. GissaneC, et al. collisions profes- league demands different tralia at the elite level. Med J Aust 1993;'159 (5): 298-301 sional super rugby, the of player Cleve Med J 2001; 4: 137-46 6. CheckowayH. Data pooling in occupationalstudies. J Occup positions. Med 1991;33: 1275-80 7. Blettner M, Sauerbrei W, Schlehofer B, et al. Traditional re- in views, meta-analyses and pooled analyses epidemiology. Correspondence and offprints: Conor Gissane,Department Int J Epidemiol 1999; 28: 1-9 Health Studies, Brunel University, Osterley Campus, 8. Estell J, Shenstone B, Barnsley L. Frequency of injuries in dif- of Middlesex, TW7 SDU, UK. ferent age groups in an elite rugby league club. AustJ Sei Med lsleworth, Sport 1995; 27 (4): 95-7 E-mail: conor.gissane@bruneLac. uk

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