Youth Ice Hockey Related Injury and Concussion: Informing Prevention Through Modifiable Risk Factors

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2021-04-30 Youth Ice Hockey Related Injury and Concussion: Informing Prevention Through Modifiable Risk Factors

Eliason, Paul Hamilton

Eliason, P. H. (2021). Youth Ice Hockey Related Injury and Concussion: Informing Prevention Through Modifiable Risk Factors (Unpublished doctoral thesis). University of Calgary, Calgary, AB. http://hdl.handle.net/1880/113348 doctoral thesis

University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY

Youth Ice Hockey Related Injury and Concussion: Informing Prevention Through Modifiable

Risk Factors

Paul Hamilton Eliason

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF DOCTOR OF PHILOSOPHY

GRADUATE PROGRAM IN KINESIOLOGY

CALGARY, ALBERTA

APRIL, 2021

Ice hockey is a popular sport in Canada, yet is considered a high-risk sport for injury. To prevent these injuries, potential risk factors must be identified to inform injury prevention strategies. Further, injury prevention strategies that have been implemented should be evaluated to ensure no unintended injury consequences have occurred.

In this dissertation, the potential risk factors for injury and prevention strategies in youth ice hockey are reviewed and limitations of the literature are discussed to help inform the next steps for injury prevention. The association between on-ice skill performance and injury is also examined. This will help provide a better understanding of the potentially modifiable risk factors for injury in youth ice hockey and will further aid in the development of targeted interventions.

Additionally, the rates of injury and concussion among under-15 (ages 13-14) ice hockey players playing in leagues allowing body checking, but who have varying years of body checking experience is explored. Finally, the association of body checking experience and rates of injury and concussion in under-18 players (ages 15-17) are assessed. These evaluations will provide important evidence for recent and potentially future body checking policy changes in youth ice hockey.

Policy permitting body checking continues to be the most relevant modifiable risk factor in youth ice hockey. A faster time on the transition agility (suggesting higher skill) was associated with a higher rate of injury among 11-17-year-olds. Among 13-14-year-olds participating in a body checking league, there were no significant differences in the rates of injury or concussion among players that had no body checking experience and those that had either 1 year or 2+ years of experience. Among 15-17-year-olds, the adjusted rates of injury and concussion were higher among those with more body checking experience (≥3 years) than those

ii with less experience (≤2 years). These studies provide further evidence in support of disallowing body checking in younger age groups in youth ice hockey to reduce injury and concussion rates, with no adverse consequences related to less body checking experience when engaged in leagues allowing body checking in older age groups (ages 13-17).

iii Acknowledgements

This dissertation is the result of the many people who have been a part of this chapter in my life.

First and foremost, I would like to acknowledge my mentor and supervisor, Dr. Carolyn Emery. I cannot thank her enough for her tremendous guidance, encouragement, and for the support she has provided both professionally and personally. This was especially true during challenging times. I am forever indebted to her for the opportunities she has provided me.

To my committee members, Dr. Luz Palacios-Derflingher and Dr. Brent Hagel, thank you for your continued direction on these projects. Your time, knowledge, and ongoing support have been instrumental in getting me to this point. A special thank you to Dr. Willem Meeuwisse for encouraging me to further my education and for his mentorship. I would also like to thank Dr.

Kati Pasanen who kindly agreed to supervise me while Dr. Emery was on sabbatical.

As I reflect on my graduate experience, I find myself extremely fortunate to have had such amazing peer-mentorship. These friends and colleagues, listed in no particular order, include Dr.

Amanda Black, Dr. Sarah Kenny, Dr. Kerry MacDonald, Dr. Tracy Blake, Dr. Carly McKay, and Dr. Jackie Whittaker. I will always smile when I think about our times at SIPRC together and look forward to whenever our paths cross.

I met some incredible friends along this journey. These people know who they are, and I thank them all for the memories we have shared. I eagerly await to see where the next pages take us.

Lastly, to my family, who keep my heart full of love. This is as much yours as it is mine.

iv Dedication

This dissertation is dedicated to the man I aspire to be, my dad.

v Table of Contents

Abstract ...... ii Acknowledgements ...... iv Dedication ...... v Table of Contents ...... vi List of Tables ...... x List of Figures and Illustrations ...... xi List of Symbols, Abbreviations and Nomenclature ...... xii

CHAPTER ONE: INTRODUCTION ...... 1 1.1 Background ...... 1 1.1.1 Sport Injury Prevention ...... 2 1.1.2 Sequence of Sport Injury Prevention ...... 2 1.1.3 Sport Injury Prevention Strategies and Unintended Consequences ...... 2 1.2 Research Rationale ...... 3 1.3 Purpose ...... 4 1.4 Summary of Format ...... 4

CHAPTER TWO: INJURIES IN YOUTH ICE HOCKEY: INFORMING THE NEXT STEPS FOR INJURY PREVENTION ...... 6 2.1 Participation and Injury Burden ...... 6 2.2 Sequence of Sport Injury Prevention ...... 7 2.3 Dynamic, Recursive Model of Etiology for Sport Injury ...... 8 2.4 Injury Rates ...... 9 2.5 Potential Risk Factors for Injury in Youth Ice Hockey ...... 10 2.5.1 Extrinsic, Non-modifiable Risk Factors ...... 11 2.5.1.1 Age Group and Relative Age ...... 11 2.5.1.2 Session Type ...... 12 2.5.1.3 Level of Play ...... 12 2.5.1.4 Player Position ...... 13 2.5.1.5 Team Performance ...... 13 2.5.2 Intrinsic, Non-modifiable Risk Factors ...... 13 2.5.2.1 Sex and Gender ...... 13 2.5.2.2 Previous Injury/Concussion History ...... 14 2.5.2.3 Player Size ...... 14 2.5.3 Intrinsic, Potentially Modifiable Risk Factors ...... 15 2.5.3.1 Preseason Reporting of Neck Pain, Headaches, and/or Dizziness ...... 15 2.5.3.2 Strength Measures ...... 15 2.5.3.3 Psychosocial Factors ...... 15 2.5.3.4 Physical Activity Levels ...... 16 2.5.4 Extrinsic, Potentially Modifiable Risk Factors ...... 16 2.5.4.1 Equipment ...... 16 2.5.4.2 Penalty Minutes ...... 17 2.5.4.3 Body Checking Policy ...... 17 2.5.5 Summary of Limitations in the Research Examining Potential Risk Factors .18 2.6 Injury Prevention Strategy Evaluation ...... 19

vi 2.6.1 Neuromuscular Training Programs ...... 19 2.6.2 Equipment ...... 20 2.6.3 Ice Hockey Policy and Rules ...... 21 2.6.3.1 Estimated Injuries Prevented due to Body Checking Policy Change ....22 2.6.3.2 Non-evidence Informed Policy Change ...... 22 2.6.3.3 Unintended Consequences of Body Checking Policy Change ...... 23 2.7 Conclusions and Recommendations for Future Research ...... 24

CHAPTER THREE: DOES SPORT-SPECIFIC SKILL PERFORMANCE INFLUENCE INJURY OR CONCUSSION RATES IN YOUTH ICE HOCKEY PLAYERS? ....25 3.1 Abstract ...... 25 3.2 Introduction ...... 27 3.3 Methods ...... 29 3.3.1 Design ...... 29 3.3.2 Participants ...... 29 3.3.3 Procedures ...... 30 3.4 Statistical Analyses ...... 32 3.5 Results ...... 34 3.5.1 Participants in ‘girls-only’ leagues ...... 40 3.6 Discussion ...... 41 3.6.1 Participants in ‘girls-only’ leagues ...... 43 3.7 Limitations ...... 43 3.8 Conclusions ...... 45

CHAPTER FOUR: RATE OF INJURY AND CONCUSSION ASSOCIATED WITH BODY CHECKING EXPERIENCE AMONG 13 TO 14-YEAR OLD ICE HOCKEY PLAYERS ...... 46 4.1 Abstract ...... 46 4.2 Introduction ...... 48 4.3 Methods ...... 50 4.3.1 Design ...... 50 4.3.2 Participants ...... 50 4.3.3 Procedures ...... 51 4.4 Statistical Analyses ...... 52 4.5 Results ...... 54 4.6 Discussion ...... 64 4.7 Limitations ...... 66 4.8 Conclusions ...... 68

CHAPTER FIVE: THE ASSOCIATION OF BODY CHECKING EXPERIENCE AND RATES OF INJURY AMONG 15 TO 17-YEAR OLD ICE HOCKEY PLAYERS: IS IT TIME TO END THE DEBATE? ...... 69 5.1 Abstract ...... 69 5.2 Introduction ...... 71 5.3 Methods ...... 72 5.3.1 Study Design and Participants ...... 72 5.3.2 Data Collection ...... 73

vii 5.3.3 Outcome Measures ...... 74 5.4 Statistical Analyses ...... 74 5.5 Results ...... 76 5.6 Interpretation ...... 85 5.7 Limitations ...... 87 5.8 Conclusions ...... 88

CHAPTER SIX: CONCLUSIONS AND FUTURE DIRECTIONS ...... 89 6.1 Chapter Summaries ...... 89 6.1.1 Chapter Two ...... 89 6.1.2 Chapter Three ...... 90 6.1.3 Chapter Four ...... 91 6.1.4 Chapter Five ...... 92 6.2 Future Directions ...... 92 6.2.1 Analytical Approaches ...... 93 6.2.1.1 Poisson Regression ...... 93 6.2.1.2 Frailty Models ...... 93 6.2.1.3 Complex Systems Approach ...... 94 6.3 Conclusions ...... 94

REFERENCES ...... 95

APPENDIX A: PRE-SEASON BASELINE QUESTIONNAIRE (2013-2015) ...... 106

APPENDIX B: PRE-SEASON BASELINE QUESTIONNAIRE (2015-2017) ...... 111

APPENDIX C: PRE-SEASON BASELINE QUESTIONNAIRE (2017-2018) ...... 114

APPENDIX D: WEEKLY EXPOSURE SHEET ...... 117

APPENDIX E: INJURY REPORT FORM (2013-2015) ...... 119

APPENDIX F: INJURY REPORT FORM (2015-2017) ...... 125

APPENDIX G: INJURY REPORT FORM (2017-2018) ...... 128

APPENDIX H: COMPONENTS OF THE HOCKEY CANADA SKILLS TEST ...... 131

APPENDIX I: HOCKEY CANADA SKILLS TEST RECORDING SHEETS ...... 143

APPENDIX J: CORRELATION MATRIX OF THE HOCKEY CANADA SKILLS TEST COMPONENTS ...... 145

APPENDIX K: SCATTERPLOTS OF SELECTED HOCKEY CANADA SKILLS TEST COMPONENTS ...... 146

APPENDIX L: CRUDE INCIDENCE RATE RATIOS BASED ON SENSITIVITY ANALYSIS ...... 148

viii APPENDIX M: MULTIPLE INCIDENCE RATE RATIOS BASED ON SENSITIVITY ANALYSIS ...... 149

APPENDIX N: BASELINE CHARACTERISTICS OF PARTICIPANTS IN FEMALE- ONLY LEAGUES ...... 151

APPENDIX O: BASELINE HOCKEY CANADA SKILLS TEST COMPONENTS OF PARTICIPANTS IN FEMALE-ONLY LEAGUES ...... 152

APPENDIX P: BOXPLOTS AND SCATTERPLOTS OF SELECT HOCKEY CANADA SKILLS COMPONENTS BY INJURY STATUS FOR PARTICIPANTS IN FEMALE-ONLY LEAGUES ...... 153

APPENDIX Q: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-15 ICE HOCKEY PLAYERS BASED ON COMPLETE CASE ANALYSIS ...... 156

APPENDIX R: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE HOCKEY PLAYERS WITH CATEGORIZED WEIGHT ...... 157

APPENDIX S: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE HOCKEY PLAYERS BASED ON COMPLTE CASE ANALYSIS ...... 158

APPENDIX T: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE HOCKEY PLAYERS INCLUDING YEAR OF PLAY ...... 159

APPENDIX U: COPYRIGHT PERMISSIONS ...... 160

ix List of Tables

Table 2.1 Potential risk factors for injury in youth ice hockey...... 11

Table 3.1 Baseline characteristics by age groups (under-13, under-15, and under-18) by injury status ...... 35

Table 3.2 Baseline HCST components by age group (under-13, under-15, and under-18) and injury status ...... 36

Table 3.3 Incidence rate ratios for game-related injury and concussion by each HCST component (analyzed continuously) based on crude multilevel Poisson regression analyses ...... 38

Table 3.4 Adjusted incidence rate ratios for game-related injury and concussion outcomes based on multiple multilevel Poisson regression analyses ...... 40

Table 4.1 Baseline characteristics for under-15 ice hockey players’ years of body checking experience over 5 seasons (2013-2018) ...... 55

Table 4.2 Summary of game-related injury outcomes for under-15 ice hockey players by years of body checking experience ...... 57

Table 4.3 Summary of game-related concussion outcomes for under-15 ice hockey players by years of body checking experience ...... 58

Table 4.4 Adjusted incidence rate ratios for game-related injury and concussion outcomes for under-15 ice hockey players by years of body checking experience ...... 60

Table 4.5 Number and rates of game-related injuries per 1000 player-hours among under-15 ice hockey players by years of body checking experience and location and injury type 63

Table 5.1 Baseline characteristics for under-18 ice hockey players’ years of body checking experience over 5 seasons (2013-2018) ...... 78

Table 5.2 Summary of game-related injury outcomes for under-18 ice hockey players by years of body checking experience ...... 80

Table 5.3 Adjusted incidence rate ratios for game-related injury and concussion outcomes for under-18 ice hockey players by years of body checking experience ...... 81

Table 5.4 Number and rates of game-related injuries per 1000 player-hours among under-18 ice hockey players by years of body checking experience and location and injury type 84

x List of Figures and Illustrations

Figure 2.1 The sequence of prevention of sports injuries, van Mechelen et al. (1992)34 (reproduced with permission) ...... 8

Figure 2.2 The dynamic, recursive model of etiology for sport injury, Meeuwisse et al. (2007)41 (reproduced with permission) ...... 9

xi List of Symbols, Abbreviations and Nomenclature

Bwd Backwards CI Confidence interval Fwd Forwards HCST Hockey Canada Skills Test ICC Intraclass correlation coefficient IQR Interquartile range IRF Injury report form IRR Incidence rate ratio LOA Limits of agreement NA Not applicable NMT Neuromuscular training OR Odds ratio PBQ Preseason baseline questionnaire Q1 First quartile Q3 Third Quartile VIF Variance inflation factor WES Weekly exposure sheet

xii

Chapter One: Introduction

1.1 Background

Youth have high rates of sport participation which has important positive health implications such as improved physical fitness, health benefits, quality of life, and higher self- esteem.1-4 While sport participation is both important and popular, it is one of the leading causes of injury in youth and results in a significant health burden.5-9 Canadian studies suggest that 30-

40% of youth ages 11-18 seek medical attention for a sport-related injury annually.10,11 Of all injury types, concussion is one of the most common in youth sport and accounts for 15-20% of all sport-related injuries.10,11 Further, it is expected that annually one in ten youth will incur a sport-related concussion.5,10,11 Many of these concussions are recurrent which may lead to long term health consequences.12-15 Individuals who participate in collision sports have been identified as having the highest risk of injury, including concussion.5,16 Ice hockey is a collision sport and is one of Canada’s most popular sports enjoyed by youth.17 Regrettably, ice hockey is among the highest risk sports for injury and accounts for over 10% of all youth sport-related injuries.5,11,16

Concussion is also one of the most common injuries reported resulting in medical attention or time loss from ice hockey.10,18-25 The rates of injury have been estimated to be as high as 7.98 injuries/1000 game-hours and 3.34 concussions/1000 game-hours in 11-17 year old leagues permitting body checking.5,16,19,22-24,26-30

Arguably, injuries are predictable, and therefore, are preventable.31-33 While not all injuries can or will be prevented, the number and severity of these injuries can be greatly reduced through injury prevention strategies.33 The reduction of injury risk in youth ice hockey would

have a major impact on the quality of life in Canadian youth, and have important national public health implications including the reduction of injury and health care costs.

1.1.1 Sport Injury Prevention

Sport injury prevention can be understood across a continuum of prevention including primary (preventing or reducing the risk of injury), secondary (early diagnosis and prevention of recurrence), and tertiary prevention (ensuring full recovery and prevention of injury consequences). While all aspects of injury prevention are important, shifting our approach to primary prevention will have the most impact on reducing the burden of all injury, including concussion, in youth ice hockey.

1.1.2 Sequence of Sport Injury Prevention

Critical to informing primary injury prevention program is the identification of the risk factors for injury.34 While some potential risk factors for injury in youth ice hockey have been consistently identified, some remain inconclusive.26 A better understanding of the potential risk factors for injury in youth ice hockey will have important implications for informing policy decisions and primary injury prevention strategies.

1.1.3 Sport Injury Prevention Strategies and Unintended Consequences

Once the potential risk factors for injury have been identified, an injury prevention initiative can then be developed and implemented.34 In youth ice hockey, the most successful

injury prevention strategy has been policy change disallowing body checking. A recent meta- analysis estimated a combined effect of a 67% reduction in concussion risk across all youth ice hockey leagues where policy disallows body checking [incidence rate ratio (IRR)=0.33; 95% CI:

0.25-0.45].5 This highlights the significant effect that policy can have on injury prevention in youth ice hockey.

Ideally, the injury prevention program that is developed and implemented is successful in reducing injury of a specific type or population. However, it is important to consider that the same injury prevention program may inadvertently increase the risk of injury of a different injury type or in a different or future population.35-37 As such, any injury prevention program that is implemented in youth sport, including policy change, should be evaluated to ensure that there are no unintended consequences.

1.2 Research Rationale

Injuries, including concussions, are a major health concern for youth ice hockey players.

These injuries are predictable, and therefore, are preventable through injury prevention strategies.31-33 Evaluating potentially modifiable risk factors in the popular sport of ice hockey will provide valuable information regarding policy decisions and primary injury prevention strategies. This will have important national public health implications including the reduction of injury and health care costs. Further, primary injury prevention strategies that have been implemented in youth ice hockey should be evaluated to ensure that there are no unintended consequences.

1.3 Purpose

The primary aim of this research is to provide a better understanding of the potentially modifiable risk factors for injury in youth ice hockey to further aid in the development of targeted interventions. The secondary aim is to ensure that no unintended injury consequences have resulted from policy changes in youth ice hockey.

The specific objectives will be addressed in this doctoral research are:

1. To identify, summarize, and evaluate the existing research examining potential risk

factors for injury and concussion and injury prevention strategies in youth ice hockey

players.

2. To evaluate whether a potentially modifiable risk factor, sport-specific skill performance,

influences injury or concussion rates in youth ice hockey players ages 11-17.

3. To examine the association between body checking experience and rates of injury and

concussion in 13-14-year-old ice hockey players.

4. To evaluate the association between body checking experience and injury in 15-17-year-

old ice hockey players.

1.4 Summary of Format

Chapter two of this thesis reviews the current body of knowledge with regards to the potential risk factors for injury in youth ice hockey, and lays the foundation for the next steps to inform injury prevention. Chapter three explores the association between on-ice skills performance and rates of injury and concussion in 11-17-year-old ice hockey players. This

chapter will provide a better understanding of potentially modifiable risk factors for injury in youth ice hockey and will further aid in the development of targeted interventions. Chapter four investigates the association between body checking experience and rates of injury in 13-14-year- olds. Chapter five investigates the association between body checking experience and rates of injury and concussion in 15-17 year olds. These chapters will provide important evidence for recent and future body checking policy decisions that may be implemented in youth ice hockey.

Finally, chapter six summarizes the findings of all four manuscripts and provides recommendations for future research.

Chapter Two: Injuries in Youth Ice Hockey: Informing the Next Steps for Injury

Prevention

2.1 Participation and Injury Burden

Ice hockey is a popular international sport with registered players in over 75 Ice Hockey

Federations.38 Among these Federations, Hockey Canada leads the world in registration numbers with over 450,000 youth participants (<19 years), including over 25% female participation.10,11,17

While youth enjoy many benefits from participating in sporting activity, such as improved physical and mental health,2,39,40 ice hockey is considered a high-risk sport for injury. It is among the top three injury-producing sports in youth in Canada and accounts for over 10% of all youth sport-related injuries.11 Of all injury types, concussion specifically is of paramount concern. In a systematic review including a meta-analysis, ice hockey was identified as having the second highest incidence of concussion among thirteen youth sports, behind only rugby.16 Further, concussion has been reported to account for between 18-66% of all youth ice hockey injuries.19,21-24,29

Given the large burden of injury in youth ice hockey, potential long-term consequences of these injuries, and associated health care costs, a multitude of studies have been conducted to identify potential risk factors for injury and concussion specifically in youth ice hockey. The identification of modifiable risk factors is critical to develop focused intervention strategies to ameliorate risk. Further, a better understanding of potential risk factors (including non- modifiable) will help target specific youth ice hockey prevention strategies toward the highest risk population. Finally, it is important to consider injury prevention strategies that have been

implemented and evaluated in youth ice hockey, as well as the implications of these strategies, to further inform the next steps for injury prevention in this population. Therefore, this chapter will introduce the sequence of sport injury prevention, review potential risk factors for injury in youth ice hockey that have been examined, discuss the limitations of this literature, summarize injury prevention programs that have been implemented and the scientific evaluations of these programs, and conclude with recommendations for future injury prevention research in youth ice hockey.

2.2 Sequence of Sport Injury Prevention

The sequence of sport injury prevention initially described by van Mechelen is a systematic approach to injury surveillance to establish the extent of the injury, identify risk factors for injury, develop and implement injury prevention strategies, and evaluate the effectiveness of the program through injury surveillance methodology (Figure 2.1).34 Critical to informing injury prevention strategies is the identification of the risk factors for injury. Risk factors are any factors that may increase the potential for injury to occur.32 These may be extrinsic (e.g., equipment use, ice conditions, body checking policy) or intrinsic to the sport participant (e.g., age, skill performance, previous injury). They can further be defined as either modifiable or non-modifiable. Modifiable risk factors are those that can be altered through injury prevention strategies (e.g., skill, strength, helmet fit). Non-modifiable risk factors cannot be altered (e.g., sex, age, previous injury), but may affect the relationship between modifiable risk factors and injury.33 While identifying the risk factors for sport injury is important, there is

particular emphasis on the identification of modifiable risk factors (either extrinsic or intrinsic), as these have the most potential to inform primary injury prevention strategies.

Figure 2.1 The sequence of prevention of sports injuries, van Mechelen et al. (1992)34

(reproduced with permission)

2.3 Dynamic, Recursive Model of Etiology for Sport Injury

Meeuwisse et al.41 describes the dynamic, recursive nature of sport injury (Figure 2.2).

This model illustrates how both the intrinsic risk factors and extrinsic risk factors combine with an event-specific circumstance to produce an opportunity for injury to occur. There is recognition within the model that intrinsic risk factors can change over time with exposure to the extrinsic risk factors and participation in sport, regardless of the outcome of injury.41 These changes can either result in adaptation which may reduce intrinsic risk, or maladaptation which

may increase intrinsic risk. The dynamic, recursive model has also been recently adapted for concussion specifically.42

Figure 2.2 The dynamic, recursive model of etiology for sport injury, Meeuwisse et al.

(2007)41 (reproduced with permission)

2.4 Injury Rates

The overall injury rates in youth ice hockey have been estimated to be between 11.7-34.4 injuries/1000 player-hours and from 1.18-43.99 injuries/100 players.26 Based on combined concussion incidence rates in a meta-analysis examining youth ice hockey players, the concussion rate has been estimated to be 1.20 concussions/1000 athlete-exposures.16 However, it

is important to note that these rates should be considered within the context of the individual studies given different definitions of injury and study populations examined.16,26 More recent literature has estimated injury rates among leagues permitting body checking to be as high as

4.37 injuries/1000 player-hours at the under-13 age group19,29 and 7.98 injuries/1000 player- hours at the under-15 age group.25 The concussion rates were estimated to be as high as 2.79 concussions/1000 player-hours among the under-13 age group and 3.34 concussions/1000 player-hours among the under-15 age group.19,25,29,43

2.5 Potential Risk Factors for Injury in Youth Ice Hockey

Several potential risk factors for injury in youth sport, including ice hockey, have been considered.33 These have been adapted for ice hockey where applicable, and are listed in Table

2.1.

Table 2.1 Potential risk factors for injury in youth ice hockey.

Extrinsic risk factors Intrinsic risk factors Non-modifiable Non-modifiable Age group Age Session type Sex and gender Level of play Previous injury/concussion history Position of play Player size

Potentially modifiable Potentially modifiable Rules Strength Ice surface size and quality Psychosocial factors Physical activity Fitness level Training Balance/proprioception Preseason reporting of neck pain, headaches, and/or dizziness

2.5.1 Extrinsic, Non-modifiable Risk Factors

2.5.1.1 Age Group and Relative Age

Age group has been reported as a potential risk factor for injury and concussion in youth ice hockey in several studies. For reference, the categories of youth ice hockey in Canada are predominantly separated by age groups into under-18 (ages 15-17; formerly called Midget), under-15 (ages 13-14; formerly called Bantam), under-13 (ages 11-12; formerly called Pee Wee), under-11 (ages 10-11, formerly called Atom), and under-9 (ages 8-9; formerly called Novice).

Generally, it has been reported that injury rates increase with increasing age,25,26,29,44 although

some studies have suggested the contrary.26 It is also important to consider that the injury rates can vary significantly by additional factors (e.g., body checking policy) within each age group.

It is also important to highlight that relative age within each age group (sometimes referred to as “year of play”) may be examined. For instance, most age groups include two years of play, except for the under-18 age category which includes three years. Some studies have demonstrated that first year players are at greater risk of injury and concussion than second or third year players in the same age group.19,22,23,29,30,45 This finding is not supported in all studies.25

2.5.1.2 Session Type

Injury and concussion rates have consistently been identified as being significantly higher in games relative to practices or training sessions,43 with estimated incidence rate ratios ranging between 2.45-6.32.26

2.5.1.3 Level of Play

Several studies examining level of play (i.e., the skill division a player participates in) have produced inconsistent findings. These studies have generally identified that injury rates were highest at the most elite levels of play across all age groups.23,26 Recently, cohort studies in under-13 and under-15 age groups do not support these findings.19,22,29

2.5.1.4 Player Position

Player position has also produced inconsistent findings in the literature as to whether forwards or defense are at a greater risk of injury at the youth level.26 Recent literature has suggested no significant difference in the rates of injury between forwards and defense.19,25,29

However, multiple studies have suggested the lowest injury rates in goaltenders compared to other player positions (offensive and defensive).19,22,25,26,29,46

2.5.1.5 Team Performance

Under-13 and under-15 teams with better winning percentages (i.e., winning >50% of all games in the season) have been associated with a 22% lower rate of injury (IRR=0.78; 95% CI:

0.64-0.95) and 36% lower rate of injury resulting in >7 days of time loss (IRR=0.64; 95% CI:

0.47-0.88).47

2.5.2 Intrinsic, Non-modifiable Risk Factors

2.5.2.1 Sex and Gender

Previous youth ice hockey studies have typically only considered sex as a potential risk factor. When considering sex in terms of biological attributes, it has been reported that injury rates in ice hockey are higher in males relative to females;48 however, this study was based on a relatively small number of girls participating and did not have sufficient sample size to draw any conclusion regarding sex as a potential risk factor.26 Most youth ice hockey studies are limited by the relatively small number of females participating in predominantly male leagues to sufficiently examine this variable.19,22,23,25,29 The consideration of gender differences such as

socially constructed roles, behaviours, expression, and identities remain an opportunity for future evaluation in youth ice hockey studies.

2.5.2.2 Previous Injury/Concussion History

Players with a previous history of injury or concussion have regularly been identified as having higher rates of injury and concussion, respectively.19,22,23,29,30 However, further research is needed to better understand this complex relationship in youth ice hockey and other sports.49-54

2.5.2.3 Player Size

Studies have generally examined weight as an indication of player size and have yielded mixed results. While some studies have suggested lighter players to be at an increased risk of injury and concussion,23,26 others have suggested heavier players are,25,26 or have found no relationship.22,29 Potentially, these findings may be related to size differential, which may be more relevant at the younger age groups where greater size disparities between players may exist. Height may also be related to injury incidence,26 although the literature has not examined this variable as in depth.

2.5.3 Intrinsic, Potentially Modifiable Risk Factors

2.5.3.1 Preseason Reporting of Neck Pain, Headaches, and/or Dizziness

Among under-15 and under-13 players, preseason reporting of neck pain and headache was identified as potential risk factors for concussion (IRR=1.67; 95% CI: 1.15-2.41, and

IRR=1.47; 95% CI: 1.01-3.12, respectively).55 Dizziness was associated with rates of concussion in non-body checking under-13 players (IRR=3.11; 95% CI:1.33-7.26).55 Finally, a combination of any two of these three symptoms was identified as a potential risk factor for concussion in the non-body checking under-13 age group (IRR=3.65; 95% CI: 1.20-11.05) and the under-15 age group (IRR=2.40; 95% CI: 1.15-4.97).55

2.5.3.2 Strength Measures

Baseline strength measures based on hand grip, squat jumps, and countermovement jumps were not associated with concussion incidence in 8-14 year old players.56 Cervical muscle endurance also does not appear to be related with concussion incidence specifically in youth ice hockey,57 although may be related in other youth sporting contexts.58

2.5.3.3 Psychosocial Factors

Several psychosocial factors such as athletic identity (degree to which an individual identifies with an athlete role),59 competitive state anxiety (situational mood state characterized by consciously perceived feelings of apprehension or tension),60 and fear of re-injury have been examined in elite (A, AA, AAA) under-15 and under-18 teams. Players that scored below the

25th percentile in athletic identity have been associated with an increased rate of first injury

(IRR=1.53; 95% CI: 1.05-1.22), but players that scored above the 25th percentile were associated with increased rate of subsequent injury (IRR=2.28; 95% CI: 1.01-6.04).61 Competitive state anxiety and re-injury fear were not associated with rates of first injury or subsequent injury in this poulation.61 Several studies examining player attitudes towards body checking have suggested this factor does not influence rates of injury.19,22,23,29,62

2.5.3.4 Physical Activity Levels

The concussion rate was significantly higher in players who did not meet the Canadian physical activity guidelines (one hour of daily physical activity),63-65 relative to those that did among under-13 (IRR=2.94; 95% CI: 1.30-6.64), under-15 (IRR=2.18; 95% CI: 1.21-3.93), and non-elite (lower 70% by division of play) players aged 11-14 (IRR=2.45; 95% CI: 1.33-4.51).66

This relationship was not observed at the under-18 age category or in elite level (top 30% by division of play) players.66

2.5.4 Extrinsic, Potentially Modifiable Risk Factors

2.5.4.1 Equipment

There is limited evidence based on a systematic review that full face shields reduce the risk of concussion,67 although one study has suggested that full facial protection may reduce concussion severity at the collegiate level [1.71 sessions missed (95% CI: 1.32-2.18) in players with full face shield vs 4.07 sessions missed (95% CI: 2.48-4.74) in players wearing half shields].68 However, full facial protection has been mandated for decades in youth (<18 years old) ice hockey and has been shown to reduce the frequency of facial, dental, and eye

injuries.67,69,70 Wearing a mouth guard was recently shown to reduce the odds of concussion by

64% (OR=0.36; 95% CI: 0.17-0.73).71 Additional studies examining mouth guard use and type are recommended using appropriate approaches to further evaluate injury risk with consideration of potential confounding and more rigorous injury surveillance methodologies.5 Inadequate helmet fit has also been suggested to increase the odds of concussion [odds ratio (OR)=2.67;

95% CI: 1.04-6.81],72 although this requires further investigation with larger sample sizes.

2.5.4.2 Penalty Minutes

Relative to teams that were <50th percentile in penalty minutes, no association was found in the rates of injury (IRR=0.99; 95% CI: 0.80-1.22) or concussion (IRR=0.79; 95% CI: 0.58-

1.07) among teams that were >50th percentile.47

2.5.4.3 Body Checking Policy

Of all the potential risk factors that have been examined, body checking policy has been identified as the single most consistent factor for injury and concussion.5,26 Prior to 2013 when body checking policy change was introduced in Canada, a systematic review including meta- analysis suggested participating in a league permitting body checking league was associated with a 2.45 (95% CI: 1.70-3.60) times higher rate of injury and 1.71 (95% CI: 1.20-2.44) times higher rate of concussion among under-18 age groups.26 Further, a landmark study suggested that playing with policy allowing body checking at the under-13 age group was associated with a

3.26 (95% CI: 2.31-4.60) times greater rate of game-related injury and 3.88 (95% CI: 1.91-7.79) times greater rate of concussion.23 This strong evidence eventually led to national policy change,

which has been evaluated and is discussed further in this chapter in examining injury prevention strategy evaluation ice (section 2.6.3 Hockey Policy and Rules).

2.5.5 Summary of Limitations in the Research Examining Potential Risk Factors

Several general limitations in the literature examining potential risk factors for injury in youth ice hockey should be highlighted. Injury definitions are often not stated or inconsistent between studies, which limits the ability to accurately compare studies. Further, studies that only report injuries per 100 players do not consider the importance of exposure to risk (e.g., player exposure-hours, player exposures). Consistent reporting of injury rates by player hours (e.g., per

1000 game-hours, per 1000 practice-hours) would allow for more accurate comparisons between studies. Many studies had a relatively small sample size and frequently did not provide a power calculation. As such, these studies were vulnerable to committing a type II error. The validity of the injury surveillance system was unknown or not stated in many studies. In injury prevention research, the validation of the injury surveillance system is imperative.9,73 The most concerning and a significant source of bias was a lack of measurement and control for important and potentially confounding covariables. Further, few studies adjusted for cluster by team. Effect estimates and variability in the context of team sports, such as ice hockey, require control for clustering by team in the analysis. As such, future youth ice hockey studies examining potential risk factors are warranted which are well-designed, of sufficient sample size, use a strict injury definition, utilize a validated injury surveillance methodology, and with consideration of additional covariates and clustering.

2.6 Injury Prevention Strategy Evaluation

There has been an increasing number of epidemiological studies evaluating injury prevention strategies in youth sport. These strategies include the evaluation of intrinsic and extrinsic modifiable risk factors and generally cross three targets for prevention including; 1) training strategies, 2) equipment recommendations, and 3) rule modifications and policy changes.5,74,75 While not all potential injury prevention strategies have been evaluated exclusively in youth ice hockey, studies investigating other sports may also be relevant to inform injury prevention in this population.

2.6.1 Neuromuscular Training Programs

Neuromuscular training (NMT) programs typically consist of exercises designed to improve strength, balance, and agility and are usually introduced in part of an extended warm-up routine.75,76 Several systematic reviews including meta-analyses have examined the protective effect of exercise intervention programs on reducing the risk of sport-related injury. One systematic review and meta-analysis combining injury rates from 25 randomized controlled trials across a variety of sports (i.e., soccer, European handball, Australian rules football, floorball, basketball) and age groups suggested a 37% reduction in overall injury rates (IRR=0.63; 95% CI:

0.53-0.75), 35% reduction in acute injury rates (IRR=0.53; 95% CI: 0.37-0.75), and a 47% reduction in overuse injury rates (IRR=0.53; 95% CI: 0.37-0.75).77 An even greater preventive effect was seen when the NMT intervention focused on proprioception/balance (IRR=0.55; 95%

CI: 0.35-0.87) and strength (IRR=0.32; 95% CI: 0.21-0.48), while no preventative effect was seen with programs that focused on stretching (IRR=0.96; 95% 0.85-1.10).77 The overall

protective effect of NMT programs has also been supported in youth sports with a systematic review including meta-analysis suggesting a combined 36% reduction in the risk of lower extremity injury (IRR=0.64; 95% CI: 0.49-0.84) among various youth sports (i.e., handball, soccer, and basketball).8 Recently, a NMT program has also been shown to reduce the incidence of concussion among youth rugby players (aged 14-18) who performed the program exercises at least three times per week (IRR=0.41; 95% CI: 0.17-0.99).78 It stands to reason that the development and implementation of an ice hockey-specific NMT program is worthwhile, but as of yet, remains an opportunity for future research.

2.6.2 Equipment

While protective equipment plays a crucial role in the prevention of injury in youth ice hockey, further evaluation of the effectiveness of certain personal protective equipment (i.e., helmets, full facial protection) is challenging as a control condition is not ethical as policy mandates its use. Full facial protection was mandated across all youth ice hockey associations in the 1970’s and has led to reductions in the frequency of facial, dental, and eye injuries.67,69,70

Recent evaluations of mouth guard use suggests that youth ice hockey players should be mandated to wear mouth guards.5,71 Continued evaluation of mouth guard use and type would be beneficial to affirm or refute these recent evaluations. A properly fitted helmet is recommended although further research examining helmet fit and risk of injury is also warranted.72

2.6.3 Ice Hockey Policy and Rules

Most injury prevention strategy evaluations in youth ice hockey have examined rule modifications and policy changes.5,74 A fair play program where teams get additional points that count towards the season standings for having low penalty minutes was associated with a lower odds of injury compared with a league that did not have the fair play program, although this was not statistically significant (OR=2.43; 95% CI: 0.68-9.05).79 Other studies examining fair play suggested no difference in concussion risk with or without fair play rules in tournament play;80,81 however, Smith et al. indicated fewer non-injurious head contacts with ‘intensified’ fair play

(i.e., fair play was emphasized and influenced team standings) compared with ‘non-intensified’ fair play rules (i.e., fair play was not emphasized).81

Policy permitting body checking has been identified as the single most consistent risk factor for injury and concussion in youth ice hockey.5,23,26 This research led to an evidence informed body checking policy change to disallow body checking at the under-13 age group nationally (USA Hockey 2011, Hockey Canada 2013), as well as regionally/provincially in certain non-elite divisions of play in the under-15 and under-18 age categories.23,26-28 In evaluation of these policy changes, disallowing body checking was associated with a 50% reduction in the rate of injury (IRR=0.50; 95% CI: 0.33-0.75) and 64% reduction in the rate of concussion (IRR=0.36; 95% CI: 0.22-0.58) at the under-13 age group.29 The rates of all injury, which included concussion, was also significantly reduced by 64% in the non-elite under-15 age category (IRR=0.44; 95% CI: 0.27-0.74), although the reduction was not statistically significant for concussion only (IRR=0.60; 95% CI: 0.31-1.18).25 Most recent evaluations at the under-18

age group have further suggested significant reductions in the rate of injury and concussion.44 A recent meta-analysis estimated a combined effect of a 67% reduction in concussion rate across all youth ice hockey leagues where policy disallows body checking (IRR=0.33; 95% CI: 0.25-

0.45).5

2.6.3.1 Estimated Injuries Prevented due to Body Checking Policy Change

It is also important to consider the number of injuries estimated to be prevented due to these policy changes. For instance, it has been estimated that over 6300 injuries (95% CI: 3770-

8978) and 4800 concussions (95% CI: 2791-6791) could be prevented annually in Canada at the under-13 age group alone as a result of the national policy change.29 A similar number of injuries would be prevented annually at the under-15 age group if policy limiting body checking to the most elite levels of play was adopted across Canada (6386 injuries; 95% CI: 2667-8615).25 It is also important to consider the substantial health care cost savings associated with these policy changes.28,82

2.6.3.2 Non-evidence Informed Policy Change

Ideally, any policy change that is made in sport is evidence-informed; however, this is not always the case. For instance, in 2011, Hockey Canada introduced policy to reduce the number of head contact injuries.83 Rule 6.5, the “zero tolerance for head contact” rule, penalized all contact to the head of an opponent at all levels of play, regardless of whether the contact was intentional or unintentional. In evaluation of this policy, the rate of game-related concussion increased after the policy was implemented in both the under-13 (IRR=1.85; 95% 1.20-2.86) and under-15 (IRR=2.48; 95% 1.17-5.24) age group.30 It was noted that the increased concussion

awareness and education after the policy may have contributed to the increased risk of concussions found after the policy.30 No differences were found in the rates of primary/direct head contacts (IRR=1.05; 95% CI: 0.86-1.28) or secondary/indirect contacts via the boards, glass, or ice surface (IRR=0.74; 95% CI: 0.50-1.11) among under-15 players after the implementation of this policy.84

2.6.3.3 Unintended Consequences of Body Checking Policy Change

While evaluation of body checking policy changes in different age groups (age 11-17) and levels of play have consistently shown a protective effect in reducing injury and concussion rates and significant health care cost savings, it is important for continued research to ensure no other unintended injury ‘trade-offs’ or consequences have arisen as a result. This is because the introduction of any injury prevention initiative may produce unintended ‘side effects’ or consequences in either the same or a different population.35,85 For instance, some proponents for permitting body checking argue that gaining body checking experience earlier may protect players from injuries in the later age categories. Before the national body checking policy change, this was initially evaluated using a prospective cohort study based on the 2008/09 season of play that compared under-15 players who had body checking experience at the under-13 level with players who had no prior body checking experience. The results showed similar overall injury (IRR=0.85; 95% CI: 0.63-1.16) and concussion rates (IRR=0.84; 95% CI: 0.48-1.48) between the cohorts, although the rate of injury resulting in time-loss greater than 7 days was

33% lower among those that had body checking experience at the under-13 level than those who did not (IRR=0.67; 95% CI 0.46-0.99).22 It is important to highlight that these findings should be

interpreted alongside the research evaluating body checking policy change reducing the rate of severe injury by 60% in under-13 leagues disallowing body checking.29 Given the most recent policy changes nationally in under-13 and at non-elite levels (lower 70% by division of play) in under-15 in some jurisdictions, further evaluations of the association of body checking experience and rates of injury and concussion is warranted.

2.7 Conclusions and Recommendations for Future Research

The public health impact of injury in youth ice hockey is large. While a myriad of studies has examined potential risk factors for injury in youth ice hockey, many of these potential risk factors remain inconclusive. A clear understanding of potentially modifiable risk factors is required to design, implement, and evaluate appropriate interventions to reduce the burden of injury. As such, continued research into the identification of potentially modifiable risk factors using prospective designs and valid injury surveillance methodologies is warranted to further inform primary injury prevention programs. Further, body checking policy change has successfully prevented injuries in youth ice hockey; however, it is important that research continues to ensure that no unintended consequences have been created because of the recent policy changes. A better understanding of this effect will provide important evidence for the current and any future body checking policy decisions in youth ice hockey.

Chapter Three: Does sport-specific skill performance influence injury or concussion rates

in youth ice hockey players?

3.1 Abstract

Objective: To evaluate the association between ice hockey skill performance and rates of injury and concussion in youth ice hockey players.

Methods: In a prospective cohort study (Safe2Play), youth ice hockey players aged 11-17 were recruited from teams in Calgary, Alberta and surrounding areas over 5 seasons of play (2013/14 to 2017/18). Skill performance was based on three selected components of the Hockey Canada

Skills Test (HCST), which included forward-to-backward transition agility, forward speed, and a

6-repeat endurance skate (all measured in seconds). All ice hockey game-related injuries resulting in medical attention, inability to complete a session and/or time loss from hockey were identified using a validated injury surveillance methodology. Players with a suspected concussion were referred to a study sport medicine physician for diagnosis and management.

Multiple multilevel Poisson regression analysis was performed to examine each HCST component and injury (IRRI) and concussion rate ratios (IRRC), adjusted for age group, year of play, previous injury/concussion, position, and body checking policy, with a random effect at a team level and offset by game exposure hours.

Results: In total, 870 players were recruited and participated in HCST (118 participated in more than one season), representing 1001 player-seasons. This represents 18.27% of total player-

seasons (3352 players representing 5479 player-seasons) in the Safe2Play cohort. There were

107 injuries (including 56 concussions) sustained during the playing season and after HCST was measured in the same season. For every one second increase in time on transition agility, there was an estimated 14% decrease in the rate of injury (IRRI=0.86; 95% CI: 0.74-0.99), but time on transition agility was not associated with rates of concussion (IRRC=0.90; 95% CI: 0.78-1.04).

Forward speed was not associated with adjusted rates of injury (IRRI=1.02; 95% CI: 0.53-1.95) or concussion (IRRC=1.67; 95% CI: 0.91-3.09). Drop-off time was also not associated with injury (IRRI=1.09; 95% CI: 0.92-1.31) or concussion rates (IRRC=1.03; 95% CI: 0.83-1.28).

Conclusions: A faster time on the transition agility skate was associated with a higher rate of injury among youth ice hockey players (aged 11-17). Forward speed and drop-off time were not associated with adjusted rates of injury or concussion. Future studies investigating skill performance and injury in youth ice hockey are warranted.

3.2 Introduction

Ice hockey is a popular sport in Canada with high annual participation rates.86 Regrettably,

Canadian data has suggested that youth ice hockey is among the highest injury-producing sports and accounts for over 10% of all sport-related injuries.11 In the sequence of sport injury prevention, the risk factors for these injuries must be identified in order to properly develop prevention measures.34,87 Previous youth ice hockey studies have consistently identified policy permitting body checking to be associated with increased rates of injury and concussion,5,19,23,25,26,29 but many other potential risk factors such as age, position, and player skill performance remain inconclusive.26 Among these inconclusive factors, player skill performance may have the potential to inform injury prevention strategies because it can be modified through targeted intervention. Few studies have examined the relationship between skill performance and risk of injury and has only been explored in football (soccer),88 skiers and snowboarders,89,90 and professional rugby league players.91 While ice hockey skill performance measures have been measured after returning from injury,92-98 it is unknown whether pre-injury skill performance is related to future injury occurrence.

One of the challenges in examining skill performance in ice hockey is how it should be quantified. The prior studies that have examined skill performance after returning from injury in professional ice hockey players have primarily considered point-based game-related outcome measures (e.g., goals, assists), although more advanced measures (e.g., plus-minus, Corsi,

Fenwick) were recently examined.92-95 However, there are many additional factors that may contribute to these types of performance measures such as amount of playing time, quality of

teammates, coaching style, and the tactical system used by the coach.96 As such, prior youth ice hockey studies investigating ice hockey skill performance have utilized the Hockey Canada

Skills Test (HCST). Developed by Hockey Canada, the national governing body of ice hockey in

Canada, the HCST is one of the first structured protocols designed to measure an array of fundamental hockey skills both with and without the puck. As the HCST is not a point-based measure of performance, it may be a better indication of youth level skill performance, and has been previously shown to be a reliable method to measure skill performance in youth ice hockey players.96 More specifically, the test-retest reliability of the various components of the HCST were assessed using intraclass correlations (ICC) and Bland-Altman Limits of Agreement

(LOA). The ICC estimates ranged from 0.50 to 0.92 (moderate to excellent), with mean differences ranging from 0.001 to -0.397 seconds and 95% LOA ranged approximately ± 1 second.96

To our knowledge, no previous study has examined the relationship between ice hockey skill performance and injury in youth ice hockey. As such, the purpose of this study was to examine the association between on-ice sport-specific skill performance using the HCST and rates of injury and concussion in youth ice hockey players. This study aims to provide a better understanding of the potentially modifiable risk factors for injury in youth ice hockey and will further aid in the development of targeted interventions.

3.3 Methods

3.3.1 Design

This was a prospective cohort study conducted over 5 seasons of play (2013/14 to

2017/18) and included under-13, under-15, and under-18 leagues from Calgary, Alberta,

(Canada) and surrounding area.

3.3.2 Participants

As data were collected in part of a larger longitudinal cohort study (Safe2Play) in youth ice hockey players (3352 players representing 5479 player-seasons including all player-seasons that completed the HCST), no a-priori sample size was calculated. However, this study was informed based on a previous sample size calculation to investigate history of concussion and one component of the HCST, which suggested a sample size of 518 players was required to identify a difference in those with and without a history of concussion. Specifically, the sample size was powered on the proportion of those with and without a previous history of concussion that were in the highest 25th percentile (the slowest players) on the HCST component forward agility weave without the puck (α=0.05, β=0.20; proportion in those without a history of concussion=0.34; proportion in those with a history of concussion=0.46).99

An inclusive sampling strategy was used for the Safe2Play longitudinal cohort study. All under-13, under-15, and under-18 hockey associations affiliated with Hockey Calgary and

Airdrie Minor Hockey Association were invited to participate. Recruitment began at the

association level. If the associations agreed to allow researchers to contact team managers/coaches, the teams were invited to participate. Teams were included if they could identify a team designate to report weekly participation and injuries. All players recruited into

Safe2Play were eligible to complete HCST.

The study population comprised youth ice hockey players (aged 11-17) across all levels of play. Inclusion criteria were: (1) players 11-17 years of age; (2) male or female players; (3) written informed player and parent consent; (4) players registered in under-13, under-15, or under-18 age categories with Hockey Calgary or Airdrie Minor Hockey; (5) agreement of the head coach; (6) agreement of a team designate (e.g., manager) to collect player participation and injury information; and (7) completion of the HCST. Goaltenders were excluded from analysis as the HCST components tested are less relevant to this position, as were players that had a previous injury or illness that prevented full participation in hockey at the beginning of the season. Female players that participated in ‘girls-only’ leagues were analyzed and reported separately so players were examined relative to their own playing cohort.

3.3.3 Procedures

A validated community youth ice hockey injury surveillance methodology was used, which included a preseason baseline questionnaire (PBQ; Appendix A, B, C), a weekly exposure sheet (WES; Appendix D), and an injury report form (IRF; Appendix E, F, G).24 Each team designate collected WES information and identified any players that were injured, including suspected concussions. A study athletic therapist verified all injuries reported by the team

designate on the IRF, or if a player’s WES indicated the player missed participation due to an injury. The specific details of the validated injury surveillance system have been previously published.22,25,28,29 All game-related injuries resulting in medical attention, the inability to complete a session, and/or time loss from hockey were included. For suspected concussions, players were eligible to visit a study sport medicine physician within 72 hours. Study physicians followed the return to play protocols based on the 4th International Consensus Statement on

Concussion in Sport.100 All concussions meeting the definition as per the Consensus Statement on Concussion in Sport were included.100

Players completed HCST at pre-season camps or at a team practice during the playing season. The HCST components include measures of agility (forward-to-backward transition agility, forward agility weave), speed (forward speed, backward speed), and endurance (6-repeat endurance skate) (Appendix H). Each component was measured once with and once without a puck except for the 6-repeat endurance, which was measured without a puck only. All components were measured as the time taken to complete the drill (measured to the nearest hundredth of a second), and were recorded during the same ice session (Appendix I). The final component, the 6-repeat endurance skate, was completed after the transition agility and forward speed skate. A measurement from the 6-repeat endurance skate (“drop-off time”) indicates a player’ endurance, and was measured by subtracting the time of the slowest lap from the time of the fastest lap.

The dimensions of each drill as well as the descriptions can be found on Hockey Canada’s website: https://www.hockeycanada.ca/en-ca/hockey-programs/players/skills-testing. The

specific details of the measurement of the HCST components have been previously published.96

From the HCST components measured, transition agility with the puck was selected as the primary objective based on discussions with community partners as this measure contains components of agility and speed, and is arguably the most technically difficult component.

Forward speed with the puck and drop-off time were considered as secondary objectives.

3.4 Statistical Analyses

All data were analyzed using the statistical software Stata version 15.101 Baseline characteristics and HCST components, shown as either frequencies and percentages or medians and interquartile range, were stratified on age group (under-13, under-15, and under-18) and by players who sustained at least one game-related injury during the study period.

A correlation matrix between all HCST components was calculated to examine relationships between the components due to concerns with multicollinearity (i.e., players with fast times on one component are likely to also have fast times on the other components), to evaluate if each HCST component should be analyzed in different models. Scatterplots of the three selected components were further examined. Separate crude game-related injury and concussion incidence rate ratios (IRRs) with corresponding 95% CIs were estimated for each individual HCST component (time in seconds, analyzed continuously) using multilevel Poisson regression with one random effect at the team level and one random effect at the individual level

(offset by game-hours). Only injuries and game-exposure after completing HCST were included.

An estimation approach based on weekly means was performed within participant, or based on

team information, or within city and division if weekly game exposures were missing. This recommended methodological approach has been supported in several previous youth ice hockey studies.23,25,29,102 The a-priori alpha (�) level was set at 0.05 for the analyses.

Additionally, separate multiple multilevel Poisson regression models for game-related injury and concussion based on complete case analysis were used to evaluate the association between the HCST components and each game-related outcome. The regression models were adjusted for important covariates including; previous injury in the last 12 months (for the injury outcome), previous lifetime concussion history (for the concussion outcome), age group (under-

18, under-15, and under-13), year of play (1st, 2nd, or 3rd), position (defence or forward), and body checking policy (body checking permitted or not permitted). Player game-hours were used as an offset in all models (after completing HCST). Random effects at a team level and individual level were examined to account for clustering. An interaction term between each

HCST component and age group was examined for effect measure modification in each model, and examined using the likelihood ratio test (statistical significance set at alpha=0.05). The variance inflation factor was also examined to further determine if each HCST component should be analyzed in different models. Sex was not considered due to the relatively low numbers of female players playing in the predominantly male leagues. A separate exploratory analysis was conducted for participants in ‘girls-only’ leagues.

A sensitivity analysis was conducted replacing missing HCST values with the most extreme assumptions of 1) fastest times recorded by age group and 2) slowest times recorded by age group for the crude and multiple multilevel Poisson regression models.

3.5 Results

A total of 870 unique players were recruited from 460 teams to participate in the study and completed HCST during the season in which they participated. Of these, 118 players participated in more than one season for a combined 1001 player-seasons (752 players participated in one season, 106 participated in two seasons, 11 participated in three seasons, and 1 participated in four seasons). Table 3.1 summarizes the baseline characteristics by age group and injury status

(if at least one game-related injury was sustained). The baseline characteristics of all HCST components by age group and injury status are presented in Table 3.2.

Table 3.1 Baseline characteristics by age groups (under-13, under-15, and under-18) by injury status

Under-13 (ages 11-12) Under-15 (ages 13-14) Under-18 (ages 15-17) Injured Not Injured Injured Not Injured Injured Not Injured (n*=20) (n*=434) (n*=49) (n*=334) (n*=29) (n*=135) Year, n (%) 2013-14 7 (35.00) 179 (41.24) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) 2014-15 7 (35.00) 104 (23.96) 11 (22.45) 91 (27.25) 0 (0.00) 0 (0.00) 2015-16 0 (0.00) 4 (0.92) 11 (22.45) 39 (11.68) 9 (31.03) 26 (19.26) 2016-17 2 (10.00) 50 (11.52) 8 (16.44) 58 (17.37) 9 (31.03) 27 (20.00) 2017-18 4 (20.00) 97 (22.35) 19 (38.78) 146 (43.71) 11 (37.93) 82 (60.74) Sex, n (%) Male 17 (85.00) 403 (92.86) 48 (97.96) 324 (97.01) 29 130 (96.30) (100.00) Female 3 (15.00) 29 (6.68) 0 (0.00) 9 (2.69) 0 (0.00) 4 (2.96) Missing/ prefer not to 0 (0.00) 2 (0.46) 1 (2.04) 1 (0.30) 0 (0.00) 1 (0.74) respond Anthropometrics Height, cm, median 152.25 150.40 164.20 165.40 175.35 177.00 (IQR) (13.70) (10.60) (16.80) (12.00) (8.70) (9.10) Missing, n (%) 2 (10.00) 8 (1.84) 0 (0.00) 7 (2.10) 5 (17.24) 11 (8.15) Weight, kg, median 39.20 40.80 52.20 53.60 64.30 66.95 (IQR) (12.90) (10.80) (20.40) (16.30) (9.00) (14.65) Missing, n (%) 1 (5.00) 5 (1.15) 0 (0.00) 10 (2.99) 3 (10.34) 7 (5.19) Body checking policy Body checking 0 (0.00) 0 (0.00) 39(79.59) 227 (67.96) 28 (96.55) 104 (77.04) Non-body checking 20 434 (100.0) 10 (20.41) 103 (30.84) 1 (3.45) 25 (18.52) (100.00) Missing, n (%) 0 (0.00) (0.00) 0 (0.00) 4 (1.20) 0 (0.00) 6 (4.44) Year of play, n (%) First 9 (45.00) 239 (55.07) 22 (44.90) 172 (51.50) 15 (51.72) 66 (48.89) Second 11 (55.00) 192 (44.24) 26 (53.06) 157 (47.01) 8 (27.59) 52 (38.52) Third N/A N/A N/A N/A 4 (13.79) 15 (11.11) Missing 0 (0.00) 3 (0.69) 1 (2.04) 5 (1.50) 2 (6.90) 2 (1.48) Position, n (%) Forward 8 (40.00) 249 (57.37) 23 (46.94) 205 (61.38) 16 (55.17) 77 (57.04) Defence 11 (55.00) 159 (36.64) 24 (48.98) 109 (32.63) 12 (41.38) 48 (35.56) Missing 1 (5.00) 26 (5.99) 2 (4.08) 20 (5.99) 1 (3.45) 10 (7.41) Previous Injurya No 10 (50.00) 281 (64.75) 18 (36.73) 153 (45.81) 7 (24.14) 50 (37.04) Yes 7 (35.00) 103 (23.73) 23 (46.94) 126 (37.72) 18 (62.07) 60 (44.44) Missing 3 (15.00) 50 (11.52) 8 (16.33) 55 (16.47) 4 (13.79) 25 (18.52) Previous Concussionb No 9 (45.00) 297 (68.43) 27 (55.10) 204 (61.08) 12 (41.38) 74 (54.81) Yes 11 (55.00) 130 (29.95) 21 (42.86) 118 (35.33) 17 (58.62) 56 (41.48) Missing 0 (0.00) 7 (1.61) 1 (2.04) 12 (3.59) 0 (0.00) 5 (3.70) IQR: interquartile range *Sum of n is 1001, given that it is player-season (118 players participated in more than one season). aPrevious injury or concussion 12 months prior to baseline test; bPrevious lifetime concussion.

Table 3.2 Baseline HCST components by age group (under-13, under-15, and under-18) and injury status

Under-13 (ages 11-12) Under-15 (ages 13-14) Under-18 (ages 15-17) HCST Component, Injured Not Injured Injured Not Injured Injured Not Injured seconds, median (range) (n*=20) (n*=434) (n*=49) (n*=334) (n*=29) (n*=135) Agility Transition agility with 18.85 19.72 17.70 17.60 16.06 16.58 puck (14.45, (14.73, (13.00, (13.96, (14.10, (13.17, 26.94) 50.44) 28.60) 32.15) 21.55) 24.32) Missing, n (%) 0 (0.00) 0 (0.00) 0 (0.00) 5 (1.50) 0 (0.00) 1 (0.74) Transition agility 16.51 17.00 15.50 15.63 14.44 14.68 without puck (13.09, (12.30, (11.59, (12.81, (12.73, (11.43, 21.12) 32.85) 19.13) 22.67) 17.21) 21.50) Missing, n (%) 0 (0.00) 0 (0.00) 0 (0.00) 2 (0.60) 0 (0.00) 1 (0.74) Forward agility with 14.76 15.59 14.13 14.21 13.22 13.41 puck (12.35, (12.45, (11.33, (11.57, (8.43, (6.75, 22.79) 38.08) 20.03) 21.00) 15.13) 18.63) Missing, n (%) 0 (0.00) 13 (3.00) 0 (0.00) 2 (0.60) 0 (0.00) 1 (0.74) Forward agility without 13.41 13.87 12.80 12.94 12.40 12.34 puck (11.62, (11.22, (10.70, (10.23, (7.85, (6.49, 16.92) 24.11) 16.34) 17.44) 14.65) 17.59) Missing, n (%) 0 (0.00) 11 (2.53) 0 (0.00) 3 (0.90) 0 (0.00) 1 (0.74) Speed Forward speed with 5.82 5.85 5.50 5.50 4.95 5.14 puck (4.99, (4.88, (4.71, (4.55, 7.19) (4.40, (4.42, 7.11) 11.33) 6.57) 6.19) 6.86) Missing, n (%) 0 (0.00) 1 (0.23) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) Forward speed without 5.47 5.55 5.22 5.25 4.77 4.94 puck (4.99, (4.47, (4.50, (4.38, (4.19, (4.14, 6.55) 7.73) 6.13) 6.78) 5.73) 6.40) Missing, n (%) 0 (0.00) 1 (0.23) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) Backward speed with 7.58 8.20 7.22 7.35 6.62 6.66 puck (6.15, (6.19, (5.48, (5.36, (5.00, (5.29, 11.22) 31.96) 11.00) 12.80) 9.80) 9.20) Missing, n (%) 0 (0.00) 2 (0.46) 0 (0.00) 1 (0.30) 0 (0.00) 1 (0.74) Backward speed without 7.25 7.53 6.84 6.88 6.31 6.34 puck (6.21, (6.03, (5.46, (5.19, (5.44, (4.69, 9.44) 17.02) 8.97) 11.06) 8.45) 9.50) Missing, n (%) 0 (0.00) 1 (0.23) 0 (0.00) 1 (0.30) 0 (0.00) 1 (0.74) Endurance Drop-off time 3.64 3.14 2.69 2.74 2.62 2.38 (1.16, (0.68, (0.81, (0.65, (0.74, (0.75, 8.37) 11.15) 9.72) 13.52) 5.31) 6.88) Missing, n (%) 0 (0.00) 29 (6.68) 1 (2.04) 29 (8.68) 0 (0.00) 1 (0.74) *Sum of n is 1001, given that it is player-season (118 players participated in more than one season). Dark shaded region indicates skill category. Lighter shaded region indicates the HCST component selected for analysis.

There were 21 game-related injuries including 14 concussions sustained during 8938.69 hours of game-play from 454 player-seasons in the under-13 age category, 54 injuries (including

25 concussion) during 10521.73 game-hours from 383 player-seasons in the under-15 age category, and 32 injuries (including 17 concussion) during 4860.012 game-hours from 164 player-seasons in the under-18 age category.

The correlation matrix between all HCST components is presented in Appendix J.

Correlations between the three HCST selected for analysis ranged from 0.32-0.69. Scatterplots of the selected HCST components are shown in Appendix K. The crude multilevel Poisson regression models with a random effect at the team level and the individual level failed to converge; thus, models only included a random effect at the team level. For every one second increase in the time to complete transition agility (a slower time), there was an estimated 14% decrease in the rate of injury (IRR=0.86; 95% CI: 0.79-0.94) and a 13% decrease in the rate of concussion (IRR=0.87; 95% CI: 0.78-0.97). A slower time on forward speed was also significantly associated with rates of all injury (IRR=0.55; 95% CI: 0.35-0.87), but not concussion (IRR=0.77; 95% CI: 0.45-1.31). Drop-off time was not associated with rates of either injury (IRR=0.93; 95% CI: 0.81-1.07) or concussion (IRR=0.92; 95% CI: 0.76-1.11) (Table 3.3).

Similar results and interpretations were seen based on the sensitivity analysis replacing missing

HCST with the most extreme assumptions of the slowest and fastest times recorded by each age group (Appendix L).

Table 3.3 Incidence rate ratios for game-related injury and concussion by each HCST component (analyzed continuously) based on crude multilevel Poisson regression analyses

HCST Component All Injurya Concussiona Transition agilityb 0.86 (0.79-0.94)† 0.87 (0.78-0.97)† Forward speedc 0.55 (0.35-0.87)† 0.77 (0.45-1.31) Drop-off timed 0.93 (0.81-1.07) 0.92 (0.76-1.11) aIRRs and corresponding 95% CI based on crude Poisson regression with one random effect at the team level (offset by game- hours). banalysis based on 995 player-seasons canalysis based on 1000 player-seasons danalysis based on 941 player-seasons †Statistically significant at p<0.05.

Results of the mixed multilevel Poisson regression models evaluating the HCST components together with other covariates are summarized in Table 3.4. The variance inflation factor from these models were low (<2.5). Like the crude multilevel models, the multiple multilevel models only converged with one random effect at the team level. There was no evidence of effect measure modification by age group in either model. For every one second in the time taken to complete transition agility, the rate of injury was expected to decrease by 14%

(IRR=0.86; 95% CI: 0.74-0.99). No significant association was found between transition agility time and rates of concussion (IRR=0.90; 95% CI: 0.78-1.04). However, we note the upper limit of the confidence interval was 1.04 and potentially a larger sample size may yield this statistically significant. Relative to forwards, the defensive position was associated with an increased rate of injury (IRR=1.87; 95% CI: 1.20-2.94) and concussion (IRR=2.04; 95% CI:

1.17-3.57). Participation in a body checking league was associated with increased rates of injury

(IRR=3.34; 95% CI: 1.44-7.72) and concussion (IRR=3.10; 95% CI: 1.21-7.97). Having a previous injury was significantly associated with injury (IRR=1.65; 95% CI: 1.03-2.63), as was previous concussion history for the concussion outcome (IRR=2.43; 95% CI: 1.37-4.28). Age

group and year of play were not found to be associated with rates of injury or concussion. The sensitivity analysis generally resulted in similar results and interpretations; however, in the model replacing missing values with the fastest times recorded by age group, the upper confidence interval for transition agility in the all injury outcome included the null value

(IRR=0.88; 95%: 0.76-1.00) (Appendix M). As the null value was the upper limit in this analysis, we note again that an increase in the sample size may have yielded this statistically significant.

Table 3.4 Adjusted incidence rate ratios for game-related injury and concussion outcomes based on multiple multilevel Poisson regression analyses

All Injurya Concussionb HCST Component Transition agility 0.86 (0.74-0.99)† 0.90 (0.78-1.04) Forward speed 1.02 (0.53-1.95) 1.67 (0.91-3.09) Drop-off time 1.09 (0.92-1.31) 1.03 (0.83-1.28) Age group Under-13 1 (Reference) 1 (Reference) Under-15 0.68 (0.27-1.72) 0.65 (0.23-1.82) Under-18 0.55 (0.19-1.61) 0.81 (0.25-2.60) Year of play First 1 (Reference) 1 (Reference) Second 1.04 (0.64-1.70) 0.81 (0.50-1.44) Third 2.42 (0.74-7.95) 0.53 (0.06-4.45) Position Forward 1 (Reference) 1 (Reference) Defence 1.87 (1.20-2.94)† 2.04 (1.17-3.57)† Body checking policy Not Permitted 1 (Reference) 1 (Reference) Permitted 3.34 (1.44-7.72)† 3.10 (1.21-7.97)† Previous injury in the last yearc No 1 (Reference) N/A Yes 1.65 (1.03-2.63)† Previous concussiond No N/A 1 (Reference) Yes 2.43 (1.37-4.28)† Abbreviation: NA, not applicable (based on examining the covariate of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous injury); based on complete case analysis of 742 player-seasons. bIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous concussion); based on complete case analysis of 856 player-seasons. cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. †Statistically significant at p<0.05.

3.5.1 Participants in ‘girls-only’ leagues

A total of 52 unique female players from 27 teams that participated in ‘girls-only’ leagues were recruited to participate in the study and completed HCST over the 5 seasons of play. Of these, 6 players participated in more than one season for a combined 58 player-seasons (46 players participated in one season, and 6 participated in two seasons). The baseline

characteristics by age group and injury status (if at least one game-related injury was sustained) for these participants is reported in Appendix N. Six players were injured and accounted for 7 total injuries. The baseline characteristics of the HCST components by age group and injury status are presented in Appendix O. There were 0 injuries reported in 222.58 game-hours in 5 player-seasons among the under-13 age group, 4 injuries (including 2 concussion) reported in

1578.59 game-hours in 33 player-seasons among the under-15 age group, and 3 injuries

(including 2 concussions) reported in 695.91 game-hours in 20 player-seasons among the under-

18 age group. Due to the low number of injury outcomes among these participants, boxplots and scatterplots of each HCST component and injury status were examined (Appendix P). Based on visual assessment of the plots, the distributions of each selected HCST component appeared similar between injury status.

3.6 Discussion

To our knowledge, this is the first study to examine the association between on-ice skill performance and rates of game-related injury in youth ice hockey. In this 5-year prospective cohort study, a slower time on transition agility was associated with a lower rate of injury. Based on the model adjusted for the additional covariates, for every one second increase in time taken to complete transition agility, the rate of injury is expected to be 14% lower (IRR=0.86; 95% CI:

0.74-0.99). This would suggest that faster players on transition agility have a greater rate of injury. While interesting, this finding should be interpreted with caution as the clinical relevance of this finding is not yet fully understood. A slower time on forward speed with the puck was associated with a lower rate of injury based on a crude analysis, but this was no longer

significant after adjusting for other important covariates. Drop-off time was not associated with rates of injury or concussion in either crude or adjusted analyses.

Previous studies investigating skill performance and injury in different sports have yielded mixed results. Using a retrospective questionnaire of skill performance as rated by their coach,

Soligard et al. found players with higher skill levels were at greater risk of being injured than their less skilled teammates in youth female football (soccer).88 These results were supported by

Goulet et al. and Ogawa et al. in snowboarders and skiers using self-reported assessments of skill level.89,90 Using a prospective cohort of professional rugby league players, Gabbett et al. found that the majority of skill assessments were not related to injury, although players with poor reactive agility (i.e., those with longer decision times) had a lower risk of injury.91 Interestingly, this suggested that poorer perceptual skill was protective against injury.

Unsurprisingly, injury rates were significantly higher in the leagues that permitted body checking compared with leagues that did not. There was a 3-fold greater rate of injury and concussion in leagues permitting body checking based on the multiple multilevel model. These findings are consistent with prior studies in youth ice hockey including a systematic review with a meta-analysis.5,19,23,25,26,29 Players with a previous history of injury or concussion had higher rates of injury and concussion, respectively. These results were also consistent with previous youth ice hockey studies.19,22,23,29,30 Relative to forwards, the defensive position was associated with an almost 2-fold greater rate of injury and concussion. Prior youth studies have produced inconsistent findings with regards to whether forwards or defense are at greater risk of injury.26

Age group was not associated with rates of injury or concussion in the present study. Previous

studies have yielded mixed results, but generally have suggested that the risk of injury increases with older age groups.26 Year of play was not significantly associated with injury or concussion rates, which was inconsistent with previous youth ice hockey studies,19,22,23,29,30 but was consistent with recent findings at the under-15 age category.25

3.6.1 Participants in ‘girls-only’ leagues

Due to low recruitment and few injury outcomes in female participants who participate in

‘girls-only’ leagues, only descriptive boxplots and scatterplots were examined. Based on visual assessment of these plots, the distributions of each HCST component appeared similar by injury status (Appendix P). It is also worth noting that concussion accounted for 57% of the total injuries reported (4/7). While this proportion is based on a relatively small amount of data, this is potentially concerning, particularly as the ‘girls-only’ leagues do not permit body checking at any age group or level of play. While there is a paucity of research that has examined injuries in

‘girls-only’ leagues, the studies that have been conducted have also suggested that concussion is a common injury type.103,104

3.7 Limitations

While this novel study contributes unique information, it is not without limitations.

Position of play as reported at baseline may not have been consistent for all games played throughout the season. Some participants also chose not to see a study physician or seek an alternative medical assessment, which limits the ability to confirm all suspected concussions.

Player motivation to complete the HCST may have varied by participant and throughout data collection. Parents and coaches may or may not have been present at testing sessions, which may have influenced player’s effort on completing the tests. As motivation was unlikely different between faster and slower players and independent of injury outcome, this would have led to a non-differential misclassification bias. However, all players were encouraged to complete the components to the best of their ability and in a competitive sport context, maximal efforts are typically demonstrated.

The HCST was measured once per season, per player. This type of design inherently assumes that each player’s performance was consistent from the time testing was completed throughout the remainder of the season. As performance is likely a dynamic measure that changes over the course of a season, this analysis may not have captured skill performance data at the etiologically relevant time period.41 Future studies should consider measuring skill performance repeatedly throughout the follow-up time. Additionally, although the HCST has been determined to be a reliable measure of on-ice performance in youth ice hockey players, the validity of the components of the protocol remains unknown. Only the 6-repeat drop-off time has been assessed as a valid measure of a player’s anaerobic capacity;105 however, because experts at

Hockey Canada developed the HCST, this testing protocol has sufficient face validity to warrant its use in research studies.96

While this study will yield important information for player development, future studies should consider the examination and validation of a more global skill performance measure that incorporates different components of the HCST. This would allow for a better understanding of a

player’s overall skill level, which may be more relevant than any single skill component. This composite score would also arguably be more meaningful to the hockey community.

3.8 Conclusions

Faster times on the transition agility was associated with a higher rate of injury among youth ice hockey players (aged 11-17). Forward speed and drop-off time were not associated with adjusted rates of injury or concussion. This study will inform future studies examining skill performance and injury. These future studies should repeatedly measure skill development throughout the season, develop and validate a more global measure of player performance, and include more consideration of participants from ‘girls-only’ leagues.

What are the new findings?

• Faster times on the transition agility skate were associated with a higher rate of injury.

• Defensive players had higher rates of injury and concussion than forwards.

• Participating in a league permitting body checking was associated with a 3-fold greater

rate of injury and concussion, and continues to be the most relevant modifiable risk factor

in youth ice hockey.

Chapter Four: Rate of Injury and Concussion Associated with Body Checking Experience

Among 13 to 14-year old ice Hockey Players

4.1 Abstract

Objective: To compare rates of injury and concussion among under-15 (ages 13-14) ice hockey players playing in leagues allowing body checking, but who have a varying number of years of body checking experience.

Methods: This 5-year longitudinal cohort (2013/14 to 2017/18) study included under-15 ice hockey players from two provinces in Canada (Alberta and British Columbia) playing in leagues where policy allowed body checking. Years of body checking experience were classified based on local and national body checking policy. All ice hockey game-related injuries resulting in medical attention, inability to complete a session and/or time-loss from hockey were identified using a valid injury surveillance methodology. Any player with a suspected concussion was referred to a study sport medicine physician for diagnosis and management. Multiple multilevel mixed-effects Poisson regression analysis was performed, adjusting for important covariates (i.e., year of play, level of play, previous injury/concussion, player weight, position) and a random effect at a team level (offset by game exposure hours), to estimate injury and concussion incidence rate ratios (IRRs).

Results: In total, 1647 players participated, contributing 1842 player-seasons, with 195 players participating in two seasons. There were 135 game-related injuries [injury rate (IR)= 8.31 injuries/1000 game-hours (95% CI; 6.94-9.96)] and 64 game-related concussions [concussion

rate (CR)= 3.94 concussions/1000 game-hours (95% CI; 3.03-5.11)] among those that had no body checking experience, 140 injuries [IR= 8.75 injuries/1000 game-hours (95% CI; 7.04-

10.88)] and 61 concussions [CR= 3.81/1000 game-hours (95% CI; 2.83-5.13)] among those with one year of body checking experience, and 127 injuries [IR= 7.26/1000 game-hours (95% CI;

5.31-9.93)] and 49 concussions (CR= 2.80/1000 game-hours (95% CI; 1.90-4.13)] among those with 2+ years of experience. Relative to no body checking experience, there were no significant differences in the adjusted IRRs for game-related injury for players with 1 year (IRR=1.06; 95%

CI: 0.77-1.45) or 2+ years (IRR=1.16; 95% CI: 0.74-1.84). Similarly, there were no differences in the rates of concussion for players with one year (IRR=0.92; 95% CI: 0.59-1.42) or 2+ years

(IRR=0.69; 95% CI: 0.38-1.25) body checking experience.

Conclusions: Among 13-14-year-old ice hockey players participating in leagues permitting body checking, the adjusted rates of injury and concussion were similar between those that had body checking experience and those that did not. These findings do not support the argument that body checking experience reduces the rate of youth ice hockey injuries.

4.2 Introduction

Ice hockey is a very popular sport in Canada with over 500,000 youth under age 18 years participating in 2018.86 Over 72,500 players were registered in the under-15 age category (ages

13-14; formerly called Bantam).86 The benefits to participating in sports such as ice hockey are numerous and include improved physical fitness, self-esteem, and mental health.2,39,40

Regrettably, participation in youth ice hockey is also associated with a high burden of injury. It is among the top three injury-producing sports in youth in Canada and accounts for over 10% of all youth sport-related injuries.11 In youth leagues permitting body checking, the rates of injury are estimated to be as high as 8 injuries/1000 game-hours and 3.34 concussions/1000 game- hours.24,25,106

Body checking is a tactic used in ice hockey when a player intentionally contacts an opponent using their body to stop an attacking player and/or to separate the opponent from the puck.107 Research has informed body checking policy change at the under-13 (ages 11-12; formerly called Pee Wee) level nationally (USA Hockey 2011, Hockey Canada 2013), as well as in non-elite divisions of play in older age categories (ages 13-17).23,26-28 In evaluation of these policy changes, disallowing body checking was associated with a 50% and 64% reduction in the rate of injury and concussion in under-13 players, respectively.29 Reduced injury rates have also been found in the non-elite under-15 and under-18 (15-17 year olds; formerly called Midget) age categories.25,108 Despite this evidence, proponents for permitting body checking argue that gaining body checking experience earlier may protect players from injuries in the later age categories. That is, they argue that introducing body checking at the under-13 level would protect

players who continued to participate in the under-15 level where players are older and presumably bigger and faster. A previous prospective cohort study based on the 2008/09 season of play compared under-15 players in the top 30% by division of play who had 2 years of body checking experience at the under-13 level with players who had no prior body checking experience. This study suggested similar overall injury (IRR=0.85; 95% CI: 0.63-1.16) and concussion rates (IRR=0.84; 95% CI: 0.48-1.48), although the rate of injury resulting in time- loss greater than 7 days was 33% lower among those that had body checking experience at the under-13 level than those who did not (IRR=0.67; 95% CI 0.46-0.99).22 However, it is important to highlight that this finding should be interpreted alongside the research evaluating body checking policy change reducing the rate of injury resulting in >7 days of time-loss by 60% in under-13 leagues disallowing body checking.29

The body checking policy changes nationally in under-13 and at non-elite levels (lower

70% by division of play) in under-15 in some jurisdictions has presented a unique opportunity to evaluate the association of body checking experience and rates of injury and concussion in the under-15 age category in a larger, more recently obtained sample. In addition, it is important to evaluate and ensure that there are no unintended consequences after a governing body implements rule changes. This is because every decision, even if intended as an injury preventative measure, may produce unintended ‘side effects’ or consequences including a potential increased risk of injury in the same or a different population.35-37 As such, the objective of this study was to compare rates of injury and concussion, adjusted for other important covariates, among under-15 (ages 13-14) ice hockey players participating in leagues allowing body checking, but who have a varying number of years of body checking experience. This

evaluation will provide important evidence for the recent and any future body checking policy decisions that may be implemented in youth ice hockey.

4.3 Methods

4.3.1 Design

This was a prospective cohort study conducted over 5 seasons of play (2013/14 to

2017/18) and included under-15 leagues permitting body checking in three cities from two provinces [British Columbia (Vancouver), and Alberta (Calgary, Edmonton)].

4.3.2 Participants

The study population included under-15 players (ages 13-14) across all levels of play participating in leagues permitting body checking. Recruitment numbers varied by city and year as body checking policy changed throughout the study period (Table 4.1). While no a-priori sample size was calculated, it was informed by a previous youth ice hockey study investigating body checking policy at the under-13 age group.19 Specifically, a sample size of 46 teams (13 players per team) was estimated based on: (1) an incidence rate ratio (IRR)=0.5; (2) a concussion rate=1.5/1000 player-hours in a body checking cohort; (3) 75.5 hours of exposure; (4) a team coefficient of variation of 0.58 (planned comparison rates controlling for cluster by team)

(α=0.05, β=0.20); and, (5) an anticipated drop-out rate of 5%.

Cohorts were defined based on their years of body checking experience. Inclusion criteria were: (1) players 13-14 years of age; (2) male or female players; (3) written informed player or parent consent; (4) players registered in under-15 with Hockey Calgary, Hockey Edmonton,

Airdrie Minor Hockey, or BC Hockey; (5) players participated in a league permitting body checking; (6) agreement of the head coach and (7) agreement of a team designate (e.g., manager) to collect player participation and injury information. Players participating in a ‘girls-only’ league or who had a previous injury or illness that prevented full participation in hockey at the beginning of the season were excluded.

4.3.3 Procedures

The injury surveillance methodology validated in youth ice hockey included a preseason baseline questionnaire (PBQ; Appendix A, B, C), a weekly exposure sheet (WES; Appendix D), and an injury report form (IRF; Appendix E, F, G).24 Years of body checking experience was classified based on year of study and local and national body checking policy. Each team designate collected WES information and identified players with an injury or suspected concussion. A study athletic therapist validated all injuries that were reported by the team designate on the IRF. The details of this validated injury surveillance system have been previously published.22,25,28,29 All ice hockey injuries resulting in medical attention, the inability to complete a session, and/or time-loss from hockey were identified by the team designate and recorded on an IRF. Every player with a suspected concussion could follow-up with a study sport medicine physician within 72 hours. Standardized follow-up and return to play protocols were followed by all study physicians based on the 4th International Consensus Statement on

Concussion in Sport.100 Concussions that met the definition based on the Consensus Statement on Concussion in Sport were included.100 Further, injuries that resulted in >7 days of time-loss and concussions that resulted in >10 days of time-loss were included as outcomes. The use of a

7-day time-loss cut-point for injury and 10-day time-loss cut-point for concussion have been supported in the literature and allows for comparison with previous studies.22-25,29,109

4.4 Statistical Analyses

The statistical software R and STATA were used for all analyses.101,110 There was relatively few player-seasons with 3 years of body checking experience (n=323), so those with two and three years of body checking experience were collapsed into 2+ years. Baseline characteristics, described as frequencies and percentages or medians and quartiles, were stratified on years of body checking experience (0, 1 and 2+ years) and by players who sustained at least one game-related injury during the study period. If weekly game exposures were missing, an estimation approach based on weekly means was performed within participant, or based on team information, or within city and division as informed by previous youth ice hockey studies and methodological approach as recommended by Kang et al. (2014).23,25,29,102 Crude game-related injury rates (offset for game-hours) were estimated for injury, injury resulting in >7 days of time- loss, all concussion, and concussion resulting in >10 days of time-loss for each study group with

95% Poisson confidence intervals adjusted for cluster by team. Absolute risk reductions (ARR) were calculated based on these injury rates and 95% CI adjusted for cluster by team. Crude incidence rate ratios (IRRs) with corresponding 95% CIs were estimated using multilevel

Poisson regression with one random effect at the team level and one random effect at the individual level (offset by game-hours).

Separate multiple multilevel Poisson regression models for game-related injury, injury resulting in >7 days of time-loss, concussion, and concussion resulting in >10 days of time-loss were used to evaluate the association between years of body checking experience and each outcome. The regression models were adjusted for the following important covariates: previous injury in the last 12 months (for the injury outcomes), previous lifetime concussion history (for the concussion outcomes), year of play (1st or 2nd), player weight [categorised based on the pattern observed between log (rate) and weight when assumption of linearity was not met], level of play [elite divisions of play (top 20% by division of play) and sub-elite (lower 80%)], and position (forward, defence, or goalie). Player game-hours was used as an offset in the models and random effects at the team and individual level were examined to account for clustering. Missing data were imputed using multiple multilevel imputation using chained equations with 30 imputations completed.110 Models analyzed using imputed data were compared with complete case analyses. Sex was not considered due to the low numbers of female players.

Crude injury rates by body location and injury type were calculated with 95% exact

Poisson CIs or adjusted for cluster by team (offset by game-hours) when outcome numbers were sufficient for model convergence.

4.5 Results

In total, 1647 unique players were recruited to participate across all sites over 5 seasons.

Of these, 195 participated in more than one season for a combined 1842 player-seasons (557 with 0 years, 651 with 1 year, and 634 with 2+ years of body checking experience). Table 4.1 summarizes the baseline characteristics of the study cohorts by injury status (if at least 1 game- related injury was sustained). The median number of players recruited per team was 1 in those with no body checking experience (range: 1-15), 1 in those with one year (range: 1-15), and 4 in those with 2+ years body checking experience (range: 1-17).

Table 4.1 Baseline characteristics for under-15 ice hockey players’ years of body checking experience over 5 seasons (2013-2018) 0 Years BC Experience 1 Year BC Experience 2+ Years BC Experience Injured Not Injured Injured Not Injured Injured Not Injured (n*=118) (n*=439) (n*=121) (n*=530) (n*=117) (n*=517) City, n (%) Calgary 86 (72.88) 315 (71.25) 85 (70.25) 359 (67.74) 53 (45.30) 260 (50.29) Edmonton 32 (27.12) 124 (28.25) 24 (19.83) 124 (23.40) 51 (43.59) 198 (38.30) Vancouver 0 (0.00) 0 (0.00) 12 (9.92) 47 (8.87) 13 (11.11) 59 (11.41) Year, n (%) 2013-14 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) 51 (9.86) 2014-15 0 (0.00) 0 (0.00) 62 (51.24) 291 (54.91) 57 (48.72) 237 (45.84) 2015-16 58 (49.15) 207 (47.15) 25 (20.66) 120 (22.64) 60 (51.28) 229 (44.29) 2016-17 30 (25.42) 133 (30.30) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) 2017-18 30 (25.42) 99 (22.55) 34 (28.10) 119 (22.45) 0 (0.00) 0 (0.00) Sex, n (%) Male 118 (100.0) 434 (98.86) 118 (97.52) 518 (97.74) 114 (97.44) 511 (98.84) Female 0 (0.00) 4 (0.91) 3 (2.48) 12 (2.26) 3 (2.56) 6 (1.16) Missing 0 (0.00) 1 (0.23) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) Anthropometrics Height, cm, median (Q1, 161.70 163.50 167.00 166.50 170.20 170.20 Q3) (154.90, (157.50, (159.10, (159.40, (163.40, (164.20, 169.90) 170.50) 172.90) 172.00) 175.26) 176.20) Missing, n (%) 13 (11.02) 61 (13.90) 20 (16.53) 61 (11.51) 6 (5.13) 64 (12.38) Weight, kg, median (Q1, 49.90 51.40 55.10 54.43 59.10 58.97 Q3) (43.20, (45.40, (47.62, (47.17, (54.40, (52.20, 59.00) 58.95) 61.37) 61.50) 65.70) 65.80) Missing, n (%) 16 (13.56) 47 (10.71) 17 (14.05) 55 (10.38) 12 (10.26) 83 (16.05) Level of play, n (%) Elite (top 20%) 91 (77.12) 359 (81.78) 83 (68.60) 388 (73.21) 69 (58.97) 325 (62.86) Sub-elite (lower 80%) 27 (22.88) 80 (18.22) 38 (31.40) 142 (26.79) 48 (41.03) 192 (37.14) Year of play, n (%) First 111 (94.07) 400 (91.12) 62 (51.24) 291 (54.91) 0 (0.00) 21 (4.06) Second 7 (5.93) 39 (8.88) 59 (48.76) 239 (45.09) 117 (100.0) 496 (95.94) Position, n (%) Forward 73 (61.86) 238 (54.21) 67 (55.37) 290 (54.72) 67 (57.26) 279 (53.97) Defence 34 (28.81) 137 (31.21) 45 (37.19) 173 (32.64) 39 (33.33) 152 (29.40) Goalie 6 (5.08) 42 (9.57) 7 (5.79) 46 (8.68) 4 (3.42) 48 (9.28) Missing 5 (4.24) 22 (5.01) 2 (1.65) 21 (3.96) 7 (5.98) 38 (7.35) Previous Injurya No 52 (44.07) 190 (43.28) 52 (42.98) 276 (52.08) 63 (53.85) 273 (52.80) Yes 40 (33.90) 144 (32.80) 52 (42.98) 168 (31.70) 46 (39.32) 177 (34.24) Missing 26 (22.03) 105 (23.92) 17 (14.05) 86 (16.23) 8 (6.84) 67 (12.96) Previous Concussionb No 68 (57.63) 268 (61.05) 66 (54.55) 319 (60.19) 50 (42.74) 309 (59.77) Yes 45 (38.14) 154 (35.08) 48 (39.67) 193 (36.42) 67 (57.26) 195 (37.72) Missing 5 (4.24) 17 (3.87) 7 (5.79) 18 (3.40) 0 (0.00) 13 (2.51) Q1: first quartile; Q3: third quartile. *Sum of n is 1842, given that it is player-season (195 players participated in more than one season). aPrevious injury or concussion 12 months prior to baseline test. bPrevious concussion ever.

Players were followed between 4 to 30 weeks with a median of 20 participation weeks.

Almost all players (96.3%) had at least one week of game exposure estimated. The median number of game weeks estimated per player was 4 (first quartile: 2, third quartile: 14).

There were 135 game-related injuries [injury rate (IR)= 8.31 injuries/1000 game-hours

(95% CI; 6.94-9.96)] and 64 game-related concussions [concussion rate (CR)= 3.94 concussions/1000 game-hours (95% CI; 3.03-5.11)] among those that had no body checking experience, 140 injuries [IR= 8.75 injuries/1000 game-hours (95% CI; 7.04-10.88)] and 61 concussions [CR= 3.81/1000 game-hours (95% CI; 2.83-5.13)] among those with one year of body checking experience, and 127 injuries [IR= 7.26/1000 game-hours (95% CI; 5.31-9.93)] and 49 concussions (CR= 2.80/1000 game-hours (95% CI; 1.90-4.13)] among those with 2+ years of experience. Table 4.2 summarize the analyses assessing body checking experience and all injury outcomes. The crude multilevel Poisson regression models failed to converge with both random effects; therefore, only a random effect at the team level was examined for these models.

Relative to no body checking experience, no differences in the crude rates were found with those with one year of experience for all injury (IRR=0.98; 95% CI: 0.75-1.28) and for injury resulting in >7 days of time-loss (IRR=1.04; 95% CI: 0.75-1.44). Further, no differences were found with those with 2+ years of body checking experience for all injury (IRR=0.97; 95% CI: 0.74-1.28) and injuries with >7 days of time-loss (IRR=0.93; 95% CI: 0.66-1.30).

Table 4.2 Summary of game-related injury outcomes for under-15 ice hockey players by years of body checking experience All Injury Injury>7 days of time-loss BC Experience 0 Years 1 Year 2+ Years 0 Years 1 Year 2+ Years No. of player-seasons 557 651 634 557 651 634 No. of injuries 135 140 127 83 85 78 Player participation (game- 16237.48 15997.68 17496.32 16237.48 15997.68 17496.32 hours) Injury rate, injuries per 1000 8.31 8.75 7.26 5.11 5.31 4.46 player game-hours (95% CI)a (6.94, (7.04, (5.31, (4.07, (4.17, (3.18, 9.96) 10.88) 9.93) 6.43) 6.78) 6.25) Incidence rate ratio (IRR), 1 0.98 0.97 1 1.04 0.93 (95% CI)b (reference) (0.75, (0.74, (reference) (0.75, (0.66, 1.28) 1.28) 1.44) 1.30) Absolute risk reduction (ARR), 1 -0.44 1.06 1 -0.20 0.65 injuries per 1000 player game- (reference) (-2.70, (-1.47, (reference) (-1.84, (-1.84, hours (95% CI) 1.83) 3.59) 1.44) 2.50) Abbreviation: CI, confidence interval. a Crude rates with 95% Poisson CIs adjusted for cluster by team (offset by game-hours) b IRRs and corresponding 95% CI based on multilevel Poisson regression with one random effect at the team level (offset by game-hours)

Concussion outcome analyses are summarized in Table 4.3. There were no differences in the crude rates of concussion (IRR=0.98; 95% CI: 0.67-1.44) or concussion resulting in >10 days of time-loss (IRR=1.01; 95% CI: 0.62-1.67) between those with no body checking experience and those with 1 year of body checking experience. Further, there were no statistically significant differences in the crude rates of concussion (IRR=0.81; 95% CI: 0.54-1.21) or concussion resulting in >10 days of time-loss (IRR=0.88; 95% CI: 0.53-1.47) among those with 2+ years of body checking experience.

Table 4.3 Summary of game-related concussion outcomes for under-15 ice hockey players by years of body checking experience Concussion Concussion>10 days of time-loss BC Experience 0 Years 1 Year 2+ Years 0 Years 1 Year 2+ Years No. of player-seasons 557 651 634 557 651 634 No. of concussions 64 61 49 34 33 30 Player participation (game- 16237.48 15997.68 17496.32 16237.48 15997.68 17496.32 hours) Concussion rate, injuries per 3.94 3.81 2.80 2.09 2.06 1.71 1000 player game-hours (95% (3.03, (2.83, (1.90, (1.52, (1.42, (1.09, CI)a 5.11) 5.13) 4.13) 2.88) 3.00) 2.70) Incidence rate ratio (IRR), (95% 1 0.98 0.81 1 1.01 0.88 CI)b (reference) (0.67, (0.54, (reference) (0.62, (0.53, 1.44) 1.21) 1.67) 1.47) Absolute risk reduction (ARR), 1 0.13 1.14 1 0.03 0.38 injuries per 1000 player game- (reference) (-1.38, (-0.30, (reference) (-1.04, (-0.62, hours (95% CI) 1.63) 2.59) 1.10) 1.37) Abbreviation: CI, confidence interval. a Crude rates with 95% Poisson CIs adjusted for cluster by team (offset by game-hours) b IRRs and corresponding 95% CI based on multilevel Poisson regression with one random effect at the team level (offset by game-hours)

The results of the multiple multilevel Poisson regression models evaluating each game outcome and level of body checking experience are summarized in Table 4.4. Like the crude models, the multiple multilevel models did not converge when both random effects were examined, so only the random effect by team was included. The adjusted IRRs further suggested no significant differences in the rates of any injury outcome and body checking experience as the

IRR confidence intervals all include the null value of 1.0. For all injuries, players less than 40kg had an increased rate of injury relative to players weighing between 40-79kg (IRR=1.64; 95%

CI: 1.10-2.44). Lighter players also had a 74% greater rate of concussion, although this was not statistically significant (IRR=1.74; 95% CI: 0.99-3.04).

Previous injury was associated with an increased rate of all injury (IRR=1.30; 95% CI:

1.03-1.66) and injury resulting in >7 days of time-loss (IRR=1.35; 95% CI: 1.00-1.82).

Similarly, previous concussion history was significantly associated with rates of concussion

(IRR=1.49; 95% CI: 1.09-2.04), but not concussion resulting in >10 days of time-loss

(IRR=1.41; 95% CI: 0.93-2.13). Goaltenders, compared with forwards, had a significantly reduced rate of injury (IRR=0.52; 95% CI: 0.32-0.83) and injury resulting in >7 days of time- loss (IRR=0.43; 95% CI: 0.22-0.85). Year of play and level of play were not associated with rates of injury or concussion outcomes.

Table 4.4 Adjusted incidence rate ratios for game-related injury and concussion outcomes for under-15 ice hockey players by years of body checking experience Incidence Rate Ratio (95% CI) Potential Risk All Injurya Injury >7 days of Concussionb Concussion >10 Factor time-lossa days of time-lossb Body Checking Experience 0 Years 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 1 Years 1.06 (0.77, 1.45) 1.07 (0.73, 1.57) 0.92 (0.59, 1.42) 0.96 (0.55, 1.68) 2+ Years 1.16 (0.74, 1.84) 1.02 (0.60, 1.73) 0.69 (0.38, 1.25) 0.80 (0.38, 1.68) Year of play First 1.17 (0.62, 1.66) 1.09 (0.72, 1.63) 0.84 (0.53, 1.33) 0.83 (0.46, 1.50) Second 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) Level of play Elite (top 20%) 1.15 (0.81, 1.62) 1.04 (0.72, 1.50) 0.99 (0.65, 1.51) 0.81 (0.48, 1.37) Sub-elite (lower 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 80%) Player Weight <40 kg 1.64 (1.10, 2.44)† 1.40 (0.82, 2.41) 1.74 (0.99, 3.04) 1.91 (0.92, 3.98) 40-79 kg 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 80-104 kg 1.20 (0.66, 2.16) 1.14 (0.52, 2.53) 1.21 (0.47, 3.10) 1.36 (0.41, 4.50) Previous injury in the last yearc No 1 (Reference) 1 (Reference) NA NA Yes 1.30 (1.03, 1.66)† 1.35 (1.00, 1.82)† Previous concussiond NA NA 1 (Reference) 1 (Reference) No 1.49 (1.09, 2.04)† 1.41 (0.93, 2.13) Yes Position Forward 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) Defence 0.93 (0.74, 1.16) 0.98 (0.74, 1.30) 1.04 (0.74, 1.47) 1.19 (0.76, 1.85) Goalie 0.52 (0.32, 0.83)† 0.43 (0.22, 0.85)† 0.64 (0.32, 1.28) 0.95 (0.43, 2.10) Abbreviation: CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (year of play, level of play, player weight, previous injury in the last year, and position). bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (year of play, level of play, player weight, previous concussion, and position). cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. † Statistically significant at p<0.05.

Similar results and interpretations were seen in the estimates based on complete case analysis (Appendix Q). Body checking experience was not significantly associated with any injury or concussion outcome. Goaltenders, compared with forwards, were protected from injury

(IRR=0.45; 95% CI: 0.25-0.81) and injury resulting in >7 days of time-loss (IRR=0.45; 95% CI

0.21-0.97). Previous injury was associated with a higher rate of both injury (IRR=1.30; 95% CI:

1.03-1.66) and injury with >7 days of time-loss (IRR=1.35; 95% CI: 1.00-1.82). Previous concussion was also associated with higher rates of concussion (IRR=1.49; 95% CI: 1.09-2.04), but not concussion with >10 days of time-loss (IRR=1.41; 95% CI: 0.93-2.13). The rate of injury in those in the lowest weight category (<40kgs) did not differ from the injury rate in players weighing between 40-79kgs (IRR=1.48; 95% CI: 0.95-2.33). However, those in the lowest weight category had a higher rate of concussion (IRR=1.93, 95% CI: 1.08-3.43).

The head/face was the most common location for each level of body checking experience, accounting for 48% of injuries in those with no body checking experience, 44% in those with 1 year of body checking experience, and 39% in those with 2+ years of body checking experience

(Table 4.5). This was followed by the shoulder/clavicle (12% in no experience, 14% 1 year, 12%

2+ years), then the wrist/hand (8% in no experience, 6% 1 year, 9% 2+ years). Concussion was the most common injury type among all levels of body checking experience accounting for

64/135 injuries (47% among all injuries) in those with no body checking experience, 61/140

(44% among all injuries) in those with 1 year of body checking experience, and 49/127 in those with 2+ years (39% among all injuries) of body checking experience. Fracture was the next most common injury type for those with no body checking experience and 2+ years of body checking

experience, while joint/ligament sprains/dislocations were the second most common type among those with 1 year of body checking experience.

Table 4.5 Number and rates of game-related injuries per 1000 player-hours among under- 15 ice hockey players by years of body checking experience and location and injury type Location and type of injury Rate per 1000 player-hours (95% CI)a 0 Years’ Experience 1 Years’ Experience 2 Years’ Experience (n*=557) (n*=651) (n*=634) Location n Rate n Rate n Rate (/135) (/140) (/127) Head/faceb 65 4.00 62 3.88 49 2.80 (3.03, 5.12) (2.89, 5.19) (1.90, 4.13) Neck/throat 4 0.25 3 0.19 5 0.29 (0.07, 0.63) (0.04, 0.55) (0.09, 0.67) Shoulder/clavicleb 16 0.99 19 1.19 15 0.86 (0.60, 1.63) (0.73, 1.93) (0.46, 1.60) Arm/elbow/forearm 4 0.25 4 0.25 4 0.23 (0.07, 0.63) (0.07, 0.64) (0.06, 0.59) Wrist/handb 11 0.68 9 0.56 12 0.69 (0.38, 1.19) (0.29, 1.10) (0.36, 1.31) Back/side 0 0.00 6 0.38 3 0.17 (0.00, 0.28) (0.14, 0.82) (0.04, 0.50) Chest/ribs/abdomen 4 0.25 3 0.19 4 0.23 (0.07, 0.63) (0.04, 0.55) (0.06, 0.59) Pelvis/hips/groin/upper leg 3 0.18 7 0.44 7 0.40 (0.04, 0.54) (0.18, 0.90) (0.16, 0.82) Knee 9 0.55 7 0.44 5 0.29 (0.25, 1.05) (0.18, 0.90) (0.09, 0.67) Lower leg/ankle/ foot 3 0.18 3 0.19 11 0.63 (0.04, 0.54) (0.04, 0.55) (0.31, 1.12) Other 3 0.18 1 0.06 0 0.00 (0.04, 0.54) (0.00, 0.35) (0.00, 0.21) Missing/unknownb 13 0.80 16 1.00 12 0.69 (0.44, 1.47) (0.55, 1.83) (0.39, 1.21) Type Contusionb 8 0.49 12 0.75 12 0.69 (0.25, 0.96) (0.40, 1.40) (0.35, 1.34) Concussionb 64 3.94 61 3.81 49 2.80 (3.03, 5.12) (2.83, 5.13) (1.90, 4.13) Joint/ligament sprain/dislocationb 13 0.80 17 1.06 14 0.80 (0.48, 1.34) (0.64, 1.76) (0.41, 1.57) Fractureb 23 1.42 16 1.00 20 1.14 (0.94, 2.14) (0.61, 1.65) (0.67, 1.95) Muscle strain/tendonitisb 9 0.55 15 0.94 13 0.74 (0.30, 1.02) (0.54, 1.64) (0.40, 1.39) Abrasion/bleeding/burn/blister 0 0.00 0 0.00 2 0.11 (0.00, 0.28) (0.00, 0.23) (0.01, 0.41) Other 3 0.18 0 0.00 2 0.11 (0.04, 0.54) (0.00, 0.23) (0.01, 0.41) Missing/unknownb 15 0.92 19 1.19 15 0.86 (0.53, 1.60) (0.69, 2.06) (0.51, 1.44) Abbreviation: CI, confidence interval. *Sum of n is 1842, given that it is player-season (195 players participated in more than one season). aCrude rates with 95% exact Poisson CIs bCorresponding 95% Poisson CIs adjusted for cluster by team (offset by game-hours)

4.6 Discussion

In this prospective cohort study involving under-15 ice hockey players, the rates of all injury, injury resulting in >7 days of time-loss, all concussion, and concussion resulting in >10 days of time-loss were not significantly different between those with no body checking experience and those with either one year or 2+ years of body checking experience. These findings suggest that body checking experience is not protective against injury or concussion at the under-15 age category. This is generally consistent with a previous cohort study that found similar rates of all injury, all concussion, and concussion resulting in >10 days of time-loss among under-15 players who had 2 years of body checking experience and those that had none.22

The present study had contrary results in that the rate of injury resulting in >7 days of time-loss was not significantly different among the different levels of body checking experience, but previously was 33% lower among players with 2 years of body checking experience.22

Using a similar methodological approach, Emery et al. was the first to examine body checking experience as a potential risk factor for injury and concussion, although this evaluation was limited in that the comparisons could only be made between teams in different provinces

(i.e., teams in Alberta with 2 years of body checking experience compared with teams in Quebec with none).22 As such, their results may be confounded due to inter-provincial differences such as style of play or coaching tactics. Further, the previous study was limited to the top 30% by division of play and with only one year follow up, while the current study is strengthened by its examination across all levels of play and 5 years of longitudinal data.

Injury rates were significantly higher for players in the lowest weight category (<40kgs) relative to those weighing between 40-79kgs. This finding was inconsistent with previous under-

15 ice hockey studies that found either no difference or an increased rate of injury in heavier players.22,25 Lighter players also had a non-significant 74% greater rate of concussion (IRR=1.74;

95% CI: 0.99-3.04); given the lower limit of the confidence interval was 0.99, potentially a larger sample size may have yielded this statistically significant. A previous under-13 study found lighter players had an increased rate of concussion.23 Differences in our findings with past under-15 studies may be due to different populations of interest and the different categorizations of weight. The present study categorized weight based on the log (rate) to ensure assumptions of linearity were not violated; a technique used in a previous youth ice hockey study.25

Players with a previous history of injury or concussion had a higher rate of injury and concussion, respectively, which was consistent with other youth ice hockey studies.19,22,23,29,30

Goaltenders had a lower injury and concussion rate in the present study, compared with forwards. This was also consistent with previous studies in both under-15 and under-13 age categories.19,22,23,29,30 Year of play was not identified to be a risk factor for injury. Previous studies have suggested first year players to be at greater risk of injury and concussion;19,22,23,29,30 however, the most recent findings at the under-15 age category also did not identify year of play as a significant risk factor.25

The current study is strengthened by its use of multiple imputation of missing covariate data to improve statistical precision and power. If only a complete case analysis were used, approximately 30% of the data from injury outcome models and 20% from concussion outcome

models would not be included in the multiple multilevel analyses (the difference owing to the different amount of missing data for the covariates “previous injury” and “previous concussion”). Generally, similar results and interpretations were seen in the estimates based on complete case analysis. The only noted difference between the analytical approaches, other than variations in the point estimates and confidence intervals, was that in the complete case analysis those in the lowest weight category (<40kgs) were no longer significantly associated with an increased rate of injury, and were significantly associated with an increased rate of concussion.

4.7 Limitations

All concussions were included if they met the study definition; however, it is noted that not all players with a suspected concussion followed up with a physician [51/64 saw a physician

(79.7%) in those with no body checking experience, 53/61 (86.9%) in those with one year of body checking experience, and 43/49 (87.8%) in those with 2+ years of body checking experience]. Many factors may contribute to return to play decisions such as importance of the game, motivation, personality factors, and parental influence. Each of these factors may have affected the precision of the IRR estimate for injury resulting in > 7 days of time-loss and concussion resulting in >10 days of time-loss. The return to play protocols established by the

International Consensus Statement on Concussion in Sport were followed to support harmonization of return to play between physicians and clinics. There is the potential for non- differential misclassification of concussion resulting in >10 days of time-loss if there was a delay of more than three days until the athlete could see a study physician and then progressed through the return to play protocol. Self-reported covariates on the PBQ may be subject to recall bias.

Position of play may not have been consistent for every game during the season for each player as reported at baseline. Socioeconomic status was not collected as part of the study, though the inclusive sampling strategy across city associations and study years should minimize any potential confounding effect. Selection bias may be of concern in that some players could have stopped playing hockey after sustaining a concussion leading to a loss to follow up. The players that continue to participate (the “survivors”) would then have more body checking experience and may have lower rates of injury and concussion. More research is needed to better understand this effect.

The crude and multiple mixed effects Poisson regression models were initially analyzed with random effects at both the team level and subject level; however, these models failed to converge. This is likely due to the relatively small number of players with more than one season of participation (n=195), as well as the even fewer cases that suffered an injury [81/195 (37.9%) suffered one injury and 7/195 (3.6%) suffered two injuries]. As such, the current analysis is limited by treating the season-players that played in several seasons as independent.

Most youth ice hockey studies, including this one, have examined injury rates across levels of covariates (potential risk factors). There are inherent limitations with calculating rates in that they assume that the rate of injury is constant within each season. This constant rate means there is no ability for the probability of injury to change (from injury to injury) within season, since it only depends on the amount of exposure. Further, there is no consideration of the length of time between injuries.111 As such, future analyses should consider time to event analyses such as

Frailty models (e.g., time to injury, and if applicable, re-injury) to ensure consistent identification of potential risk factors in youth sport.

4.8 Conclusions

We did not find that the rate of injury, injury resulting in >7 days of time-loss, concussion, and concussion resulting in >10 days of time-loss was affected by body checking experience.

This contradicts the notion that permitting body checking in under-13 age groups protects players from injury at the under-15 age category. Given the robust research demonstrating that policy disallowing body checking is associated with lower injury and concussion rates, the findings of this study add to the literature that there are no unintended consequences associated with such body checking policy decisions.

What are the new findings?

• There were no significant differences in the rates of injury or concussion among under-15

players (ages 13-14) that had no body checking experience and those that had either one

year or 2+ years of experience.

• Lighter players (<40 kg) had an increased rate of injury.

• These findings suggest that body checking experience does not protect youth ice hockey

players from injury.

Chapter Five: The association of body checking experience and rates of injury among 15 to

17-year old ice hockey players: Is it time to end the debate?

5.1 Abstract

Background: To evaluate the association between rates of injury and concussion, adjusted for other important covariates, among under-18 (ages 15-17) ice hockey players who play in leagues permitting body checking and who have a varying number of years of body checking experience.

Methods: Using a prospective cohort design, under-18 ice hockey players playing in leagues where policy allowed body checking were recruited over 3 seasons of play (2015/16 to 2017/18).

Years of body checking experience was estimated based on local and national body checking policy and region of play. All ice hockey game-related injuries resulting in medical attention, inability to complete a session and/or time-loss from hockey were identified using a valid ice hockey injury surveillance methodology. Players with a suspected concussion were referred to a study sport medicine physician for diagnosis and management. Multiple multilevel mixed-effects

Poisson regression analysis was performed, adjusted for important covariates (level of play, previous injury/concussion, player weight, and position) and random effects at a team and individual level (offset by game exposure hours), to estimate injury and concussion incidence rate ratios (IRRs).

Results: A total of 941 players contributed to 1168 player-seasons with 205 players participating in more than one season. There were 29 game-related injuries in 148 player-seasons [injury rate

(IR)= 4.82 injuries/1000 game-hours (95% CI; 3.57-6.52)] including 10 game-related

concussions [concussion rate (CR)= 1.66 concussions/1000 game-hours (95% CI; 0.89-3.12)] among those that had ≤2 years of body checking experience, and 309 injuries in 1020 player- seasons [IR= 11.94 injuries/1000 game-hours (95% CI; 9.86-14.46)] including 115 concussions

[CR= 4.44/1000 game-hours (95% CI; 3.57-5.53)] among players with ≥3 years of body checking experience. Based on multiple multilevel mixed-effects Poisson regression, players with ≥3 years of body checking experience had a higher rate of all injury [incidence rate ratio

(IRR)=2.62; 95% CI: 1.61=4.24) and concussion (IRR=2.63; 95% CI: 1.31-5.29), relative to those with ≤2 years.

Interpretations: Among 15-17-year-old ice hockey players participating in leagues permitting body checking, the adjusted rates of injury and concussion were higher among those with more body checking experience. This suggests that body checking experience does not protect under-

18 ice hockey players from injury.

5.2 Introduction

There are over 74,000 registered Canadian youth ice hockey players in the under-18 age category (ages 15-17; formerly called Midget).86 In an effort to reduce the high burden of injury in Canadian youth ice hockey,24,25,106 evidence-informed policy changes have been implemented to restrict body checking nationally at the under-13 age group (ages 11-12; formerly called Pee

Wee) as well as in certain non-elite divisions of play in older age categories (ages 13-17).23,26-28

Evaluations of these policy changes have been associated with reduced rates of all injury, including concussion.25,29,108 Despite this strong evidence, some advocates for permitting body checking argue that gaining body checking experience earlier may protect players from injuries, including concussions, in the older age categories. For instance, by introducing body checking at the under-13 level it would protect players who continued to participate in the under-15 level, which in turn, would protect players who continue to participate in the under-18 age category. A previous prospective cohort study that examined body checking experience and rates of injury and concussion at the under-15 age group (ages 13-14; formerly called Bantam) found similar rates of overall injury and concussion among those with 2 years’ body checking experience and those with none.22

Due to the body checking policy changes nationally in under-13 and at non-elite levels

(lower 60% by division of play) in the older age categories (ages 13-17) in some jurisdictions, it has presented a unique opportunity to evaluate the association of body checking experience and rates of injury and concussion in the under-18 age category. The association between body checking experience and injury rates has not previously been examined at this age category.

Further, this evaluation will provide important evidence for the recent as well as any future body checking policy decisions in youth ice hockey, and help ensure that no unintended consequences have occurred because of these policy changes.35-37 Therefore, the objective of this study is to compare rates of injury and concussion, adjusted for important covariates, among under-18 (ages

15-17) ice hockey players in leagues permitting body checking, but who have varying years of body checking experience.

5.3 Methods

5.3.1 Study Design and Participants

This was a prospective cohort study over 3 seasons of play (2015/16 to 2017/18) and included under-18 leagues permitting body checking in two cities and surrounding area from one province [Alberta (Calgary, Edmonton)]. An inclusive sampling approach was taken. All under-

18 hockey associations affiliated with Hockey Calgary, Airdrie Minor Hockey Association, or

Hockey Edmonton were invited to participate. Recruitment began at the association level and if associations agreed to allow researchers to contact teams, they were invited to participate. Teams were included if they could identify a team designate to report weekly participation and injuries.

The study population included players aged 15-17 years old across all levels of play participating in leagues permitting body checking. While no a-priori sample size was calculated for this study, it was informed by a previous youth ice hockey study investigating differences in injury rates associated with body checking policy that suggested 46 teams (13 players per team) was sufficient to identify a difference between the cohorts [powered based on an incidence rate ratio

(IRR)=0.5; concussion rate=1.5/1000 player-hours; adjusted for cluster by team and an anticipated drop-out of 10% (α=0.05, β=0.20)].19

Study cohorts were defined based on their years of body checking experience. Inclusion criteria were: (1) players 15-17 years of age; (2) male or female players; (3) written informed player or parent consent; (4) players registered in under-18 with Hockey Calgary, Hockey Edmonton, or

Airdrie Minor Hockey (5) players participated in a league permitting body checking; (6) agreement of the head coach and (7) agreement of a team designate (e.g., manager) to collect player participation and injury information. Players participating in a ‘girls-only’ league or who had a previous injury or illness that prevented full participation in hockey at the beginning of the season were excluded.

5.3.2 Data Collection

The injury surveillance methodology validated in youth ice hockey included a preseason baseline questionnaire (PBQ; Appendix A, B, C), a weekly exposure sheet (WES; Appendix D), and an injury report form (IRF; Appendix E, F, G).24 Years of body checking experience was estimated based on year of study, local and national body checking policy, and, if applicable, players PBQ data from repeated years of participation (the PBQ included a question on whether they played in a body checking league or not). Each team designate collected WES information and identified players with an ice hockey-related injury or suspected concussion. All injury report forms were validated by a study athletic therapist. Further details of this validated injury surveillance system have been previously published.22,25,28,29

5.3.3 Outcome Measures

The outcome measures of this study were the incidence rate of game-related injury, injury resulting in >7 days of time-loss, and all concussion. All injuries resulting in medical attention, the inability to complete a session, and/or time-loss from hockey were included. Concussions that met the definition based on the Consensus Statement on Concussion in Sport were included.100

The 7-day cut-point for injury has been supported in the literature and allows for comparison to previous youth ice hockey studies.22-25,29,109 Participants with a suspected concussion could follow-up with a study sport medicine physician within 72 hours. Standardized follow-up and return to play protocols were followed by all study physicians based on the 4th

International Consensus Statement on Concussion in Sport.100

5.4 Statistical Analyses

All analyses were conducted using the statistical software R and Stata.101,110 Few player- seasons had 1 year of body checking experience (n=20) or no experience (n=1); therefore, these players were collapsed into two years or less. Moreover, players with 3 years or more of body checking experience were collapsed into one group. This decision was also supported from a practical perspective in that the comparison can be thought of between players that likely only have body checking experience from participation with body checking in the under-15 age category (i.e., those with two years or less), and those that have more experience (i.e., 3 years or more).

The baseline characteristics, described as frequencies and percentages or medians and quartiles, were stratified on years of body checking experience (≤2 years or ≥3 years) and by players who sustained at least one game-related injury during the study period. Where weekly game exposures were missing, a recommended approach to estimating weekly means was used based on within participant, or based on team information, or within city and division.102 Several youth ice hockey studies have supported this methodological approach.23,25,29 Crude game- related injury rates (offset for game-hours) were estimated for injury, injury resulting in >7 days of time-loss, and all concussion for each study group with 95% Poisson confidence intervals adjusted for cluster by team. Absolute risk reductions (ARR) were calculated based on these injury rates and 95% CIs adjusted for cluster by team. Incidence rate ratios (IRRs) with corresponding 95% CIs were estimated using multilevel Poisson regression models with random effects at the team and individual level and offset by game-hours.

Separate multiple multilevel Poisson regression models for game-related injury, injury resulting in >7 days of time-loss, and concussion were used to evaluate the association between years of body checking experience and each outcome. The regression models were adjusted for the following important covariates: previous injury in the last 12 months (for the injury outcomes), previous lifetime concussion history (for the concussion outcome), player weight, level of play [elite divisions of play (top 20% by division of play) and sub-elite (lower 80%)], and position (forward, defence, or goalie). Player game-hours was used as an offset in all models and a team and subject level random effect was included to account for clustering. Exploratory regression models were examined with the same outcomes and adjusted for covariates except

that weight was categorized into the lowest 25%, middle 50%, and upper 75% based on the data.

We considered those in the lowest 25% and highest 75% to be at the greatest risk of injury.

Missing covariate data were imputed using multivariate imputation by chained equations including linear mixed effects model (30 imputations completed).110 The regression models with imputed data were compared with complete case analyses. Sex was not considered due to the low numbers of female players (n=7). Year of play (1st, 2nd, or 3rd) was not included in the main outcome models due to concerns with multicollinearity with years of body checking experience, although year of play was included as a covariate in exploratory models. A Fisher’s exact test and variance inflation factor (cut-off ≥5) were calculated to assess for multicollinearity.

Crude injury rates by body location and injury type were calculated with 95% exact

Poisson CIs or adjusted for cluster by team (offset by game-hours) when outcome numbers were sufficient for model convergence.

5.5 Results

A total of 941 unique players were recruited to participate over the 3 seasons of play. Of these, 205 participated in more than one season (183 participated in two seasons and 22 participated in three seasons) for a combined 1168 player-seasons (148 with ≤2 years of body checking experience and 1020 with ≥3 years). Table 5.1 summarizes the baseline characteristics of the study cohorts by injury status (if at least 1 game-related injury was sustained). A total of

186 teams were recruited. The median number of players recruited per team was 1 (range 1 to

19) in those with ≤2 years of body checking experience and 5 (range 1 to 20) in those with ≥3 years body checking experience.

Table 5.1 Baseline characteristics for under-18 ice hockey players’ years of body checking experience over 5 seasons (2013-2018)

≤2 Years BC Experience ≥3 Years BC Experience Injured (n*=27) Not Injured Injured (n*=259) Not Injured (n*=121) (n*=761) City, n (%) Calgary 27 (100.00) 121 (100.00) 176 (67.95) 545 (71.62) Edmonton 0 (0.00) 0 (0.00) 83 (32.05) 216 (28.38) Year, n (%) 2015-16 0 (0.00) 1 (0.83) 134 (51.74) 355 (46.65) 2016-17 0 (0.00) 3 (2.48) 78 (30.12) 254 (33.38) 2017-18 27 (100.00) 117 (96.69) 47 (18.15) 152 (19.97) Sex, n (%) Male 27 (100.00) 120 (99.17) 258 (99.61) 750 (98.55) Female 0 (0.00) 1 (0.83) 1 (0.39) 5 (0.66) Prefer not to respond/missing 0 (0.00) 0 (0.00) 0 (0.00) 6 (0.79) Anthropometrics Height, cm, median (Q1, Q3) 176.1 (170.20, 175.6 (170.20, 177.8 (172.70, 177.8 (172.70, 182.20) 179.50) 181.70) 182.90) Missing, n (%) 4 (14.81) 16 (13.22) 44 (16.99) 101 (13.27) Weight, kg, median (Q1, Q3) 65.80 (58.9, 64.55 (59.00, 69.40 (63.25, 70.31 (63.98, 71.1) 72.60) 76.90) 77.35) Missing, n (%) 4 (14.81) 15 (12.40) 47 (18.15) 97 (12.75) Level of play, n (%) Elite (top 20%) 9 (33.33) 41 (33.88) 94 (36.24) 308 (40.47) Sub-elite (lower 80%) 18 (66.67) 80 (66.12) 165 (63.71) 453 (59.53) Year of play, n (%) First 26 (96.30) 118 (97.52) 106 (40.93) 270 (35.48) Second 1 (3.70) 3 (2.48) 103 (39.77) 321 (42.18) Third 0 (0.00) 0 (0.00) 50 (19.31) 170 (22.34) Position, n (%) Forward 15 (55.56) 71 (58.68) 144 (55.60) 385 (50.59) Defence 12 (44.44) 32 (26.45) 83 (32.05) 228 (29.96) Goalie 0 (0.00) 15 (12.40) 14 (5.41) 78 (10.25) Missing 0 (0.00) 3 (2.48) 18 (6.95) 70 (9.20) Previous Injurya No 13 (48.15) 57 (47.11) 80 (30.39) 307 (40.34) Yes 14 (51.85) 63 (52.07) 133 (51.35) 303 (39.82) Missing 0 (0.00) 1 (0.83) 46 (17.76) 151 (19.84) Previous Concussionb No 15 (55.56) 56 (46.28) 100 (38.61) 380 (49.93) Yes 8 (29.63) 50 (41.32) 150 (57.92) 348 (45.73) Missing 4 (14.81) 15 (12.40) 9 (3.47) 33 (4.34) Q1: first quartile; Q3: third quartile. *Sum of n is 1168, given that it is player-season (205 players participated in more than one season). aPrevious injury or concussion 12 months prior to baseline test. bPrevious concussion ever.

Players were followed 7 to 30 weeks (median=20 weeks). Almost all players (98%) had at least 1 week of game exposure estimated. The median number of game weeks estimated per player was 3 (first quartile: 2, third quartile: 4).

There were 29 game-related injuries in 148 player-seasons [injury rate (IR)= 4.82 injuries/1000 game-hours (95% CI; 3.57-6.52)] including 10 game-related concussions

[concussion rate (CR)= 1.66 concussions/1000 game-hours (95% CI; 0.89-3.12)] among those that had ≤2 years of body checking experience, and 309 injuries in 1020 player-seasons [IR=

11.94 injuries/1000 game-hours (95% CI; 9.86-14.46)] including 115 concussions [CR=

4.44/1000 game-hours (95% CI; 3.57-5.53)] among players with ≥3 years of body checking experience. Table 5.2 summarizes the crude analyses assessing body checking experience and all injury outcomes. The crude multilevel Poisson regression models converged with both random effects for the injury outcomes, but failed for the concussion outcome; therefore, the concussion

IRR only includes a random effect at the team level. Relative to those with ≤2 years of body checking experience, those with ≥3 years of experience did not have an increased rate of all injury (IRR=2.53; 95% CI: 0.97-6.61); however, they had a greater rate of injury resulting in >7 days of time-loss (IRR=2.56; 95% CI: 1.61-4.09), and concussion (IRR=2.66; 95% CI: 1.32-

5.38).

Table 5.2 Summary of game-related injury outcomes for under-18 ice hockey players by years of body checking experience

All Injury Injury >7 days of Concussion time-loss BC Experience ≤2 Years ≥3 ≤2 Years ≥3 ≤2 Years ≥3 Years Years Years No. of player-seasons 148 1020 148 1020 148 1020 No. of injuries or concussions 29 309 19 200 10 115 Player participation (game-hours) 6010.615 25877.74 6010.615 25877.74 6010.615 25877.74 Injury rate, injuries per 1000 4.82 11.94 3.16 7.73 1.66 4.44 player game-hours, (3.57, (9.86, (2.00, (6.33, (0.89, (3.57, (95% CI)a 6.52) 14.46) 4.98) 9.44) 3.12) 5.53) Incidence rate ratio (IRR), 1 2.53 1 2.56 1 2.66 (95% CI)b (reference) (0.97, (reference) (1.61. (reference) (1.32, 6.61) 4.09) 5.38) Absolute risk reduction (ARR), 1 -7.12 1 -4.57 1 -2.78 injuries per (reference) (-9.88, (reference) (-6.70, (reference) (-4.22, 1000 player game-hours (95% CI) -4.35) -2.44) -1.34) Abbreviation: CI, confidence interval. a Crude rates with 95% Poisson CIs adjusted for cluster by team (offset by game-hours) b IRRs and corresponding 95% CI based on multilevel Poisson regression (offset by game-hours). For injury outcomes, the analysis is performed with two random effects: one at a team level and one at an individual level. For concussion, the analysis is performed with one random effect at the team level.

Results of the mixed multilevel Poisson regression models evaluating each game outcome and level of body checking experience are summarized in Table 5.3. Like the crude multilevel Poisson models, the all injury and injury resulting in >7 days of time-loss models converged using both random effects, but the concussion outcome only converged with one random effect at the team level. These adjusted IRRs further suggest players with ≥3 years of body checking experience had higher rates of injury (IRR=2.62; 95% CI: 1.61-4.24), injury with

>7 days of time-loss (2.72; 95% CI: 1.54-4.80) and concussion (2.63; 95% CI: 1.31-5.29) relative to those with ≤2 years.

Table 5.3 Adjusted incidence rate ratios for game-related injury and concussion outcomes for under-18 ice hockey players by years of body checking experience

Outcome Potential Risk Factor All Injurya Injury >7 days of Concussionb time-lossa IRR (95% CI) IRR (95% CI) IRR (95% CI) Body Checking Experience ≤2 Years 1 (Reference) 1 (Reference) 1 (Reference) ≥3 Years 2.62 (1.61, 4.24)† 2.72 (1.54, 4.80)† 2.63 (1.31, 5.29)† Level of play Elite (top 20%) 1 (Reference) 1 (Reference) 1 (Reference) Sub-elite (lower 80%) 1.46 (1.01, 2.12)† 1.43 (0.96, 2.11) 1.47 (0.93, 2.34) Player Weight 0.99 (0.98, 1.00) 0.99 (0.97, 1.00) 0.99 (0.98, 1.01) Previous injury in the last yearc No 1 (Reference) 1 (Reference) Yes 1.51 (1.16, 1.96)† 1.41 (1.00, 1.98)† NA Previous concussiond No NA NA 1 (Reference) Yes 1.77 (1.21, 2.57)† Position Forward 1 (Reference) 1 (Reference) 1 (Reference) Defence 1.20 (0.91, 1.56) 1.19 (0.84, 1.67) 1.31 (0.89, 1.91) Goalie 0.69 (0.41, 1.17) 0.82 (0.44, 1.54) 0.93 (0.47, 1.88) Abbreviation: IRR, incidence rate ratio. CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with two random effects: one at a team level and one at a subject level, and adjusted for covariates (level of play, player weight, previous injury in the last year, and position). bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (level of play, player weight, previous concussion, and position). cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. † Statistically significant at p<0.05.

Relative to elite players, sub-elite players had higher rates of all injury (IRR=1.46; 95%

CI: 1.01-2.12), but not injury resulting in >7 days of time-loss (IRR=1.43; 95% CI: 0.96-2.11) or concussion (IRR=1.47; 95% CI: 0.93-2.34). Previous injury was associated with an increased rate of all injury (IRR=1.51; 95% CI: 1.16-1.96) and injury resulting in >7 days of time-loss

(IRR=1.41; 95% CI: 1.00-1.98). Similarly, previous concussion history was significantly associated with concussion (IRR=1.77; 95% CI: 1.21-2.57). No associations were found between

player position and player weight (continuous) for rates of injury nor concussion. Player weight was also not associated with any outcome when categorized (Appendix R).

Similar results and interpretations were seen in the estimates based on complete case analysis (Appendix S). Relative to those with ≤2 years of body checking experience, those with

≥3 years had higher rates of injury (IRR=2.64; 95% CI: 1.67-4.18), injury resulting in >7 days of time-loss (IRR=2.86; 95% CI: 1.54-5.27), and concussion (IRR=2.49; 95% CI: 1.16-5.37).

Associations were found between previous injury and concussion with injury and concussion, respectively. No significant associations were found between level of play, player weight, and position with any outcome.

Year of play was significantly associated with years of body checking experience

(Fisher’s exact test: p<0.001); however, the variance inflation factor from exploratory models including year of play was low (<1.5), suggesting that multicollinearity may not have been a significant issue. Exploratory models including year of play further suggest that greater body checking experience was associated with increased rates of injury and concussion (Appendix T).

Additionally, previous injury and concussion were significantly associated with injury and concussion, respectively. Level of play was significantly associated with each outcome.

Specifically, sub-elite players had higher rates of all injury (IRR=1.55; 95% CI: 1.08-2.24), injury resulting in >7 days of time-loss (IRR=1.50; 95% CI: 1.01-2.23), and concussion

(IRR=1.65; 95% CI: 1.06-2.59). Year of play was not associated with injury or injury resulting in

>7 days of time-loss, but first year players had a 95% greater rate of concussion (IRR=1.95; 95%

CI: 1.10-3.46) relative to third year players.

The head/face was the most common location for both levels of body checking experience. This location accounted for 34% of injuries among those with ≤2 years of body checking experience and 38% among those with ≥3 years (Table 5.4). This was followed by the shoulder/clavicle (24% in those with ≤2 years and 17% in those with ≥3 years), then the wrist/hand (14% in those with ≤2 years and 9% in those with ≥3 years). Concussion was the most common injury type among both levels of experience accounting for 10/29 injuries (34% of all injuries) in those with ≤2 years of body checking experience, and 115/309 (37% of all injuries) in those with ≥3 years. Fracture was the second most common injury type among those with ≤2 years of body checking experience, accounting for 24% of all injuries. Joint and ligament sprains/strains were the second most common injury type among those with ≥3 years of body checking experience, accounting for 19% of all injuries.

Table 5.4 Number and rates of game-related injuries per 1000 player-hours among under- 18 ice hockey players by years of body checking experience and location and injury type

Location and type of injury Rate per 1000 player-hours (95% CI)a ≤2 Years’ Experience ≥3 Years’ Experience (n*=148) (n*=1020) Location n Ratea n Ratea (/29) (/309) Head/faceb 10 1.67 119 4.60 (0.89, 3.12) (3.71, 5.70) Neck/throat 1 0.17 6 0.23 (0.00, 0.93) (0.09, 0.50) Shoulder/clavicle 7 1.16 51 1.97 (0.47, 2.40) (1.47, 2.59) Arm/elbow/forearm 0 0.00 9 0.35 (0.00, 0.61) (0.16, 0.66) Wrist/hand 4 0.67 28 1.08 (0.18, 1.70) (0.72, 1.56) Back/side 2 0.33 9 0.35 (0.04, 1.20) (0.16, 0.66) Chest/ribs/abdomen 0 0.00 3 0.12 (0.00, 0.61) (0.02, 0.34) Pelvis/hips/groin/upper leg 1 0.17 20 0.77 (0.00, 0.93) (0.47, 1.19) Knee 1 0.17 28 1.08 (0.00, 0.93) (0.72, 1.56) Lower leg/ankle/ foot 2 0.33 12 0.46 (0.04, 1.20) (0.24, 0.81) Missing/unknown 1 0.17 24 0.93 (0.00, 0.93) (0.59, 1.38) Type Contusion 2 0.33 23 0.89 (0.04, 1.20) (0.56, 1.33) Concussionb 10 1.67 115 4.44 (0.89, 3.12) (3.57, 5.53) Joint/ligament sprain/dislocation 5 0.83 59 2.28 (0.27, 1.94) (1.74, 2.94) Fracture 7 1.16 40 1.55 (0.47, 2.40) (1.10, 2.10) Muscle strain/tendonitis 3 0.50 30 1.16 (0.10, 1.46) (0.78, 1.65) Abrasion/bleeding/burn/blister 0 0.00 3 0.12 (0.00, 0.61) (0.02, 0.34) Other 0 0.00 9 0.35 (0.00, 0.61) (0.16, 0.66) Missing/unknown 2 0.33 30 1.16 (0.04, 1.20) (0.78, 1.65) Abbreviation: CI, confidence interval. *Sum of n is 1168, given that it is player-season (205 players participated in more than one season). aCrude rates with 95% exact Poisson CIs bCorresponding 95% Poisson CIs adjusted for cluster by team (offset by game-hours)

5.6 Interpretation

Results from this prospective cohort study involving youth ice hockey players 15-17 years old indicated that the rates of all injury, injury resulting in >7 days of time-loss, and concussion were significantly higher among those with more body checking experience (≥3 years) relative to those with less experience (≤2 years). This suggests that greater body checking experience does not protect 15-17-year-old ice hockey players from injury or concussion, and gives support that there are no unintended consequences following policy change to disallow body checking. In addition to the strong evidence evaluating policy change showing reduced rates of injury,25,29,108 these results provide further evidence in support of removing body checking in youth ice hockey to prevent injury. While the effect of body checking experience in this age group has not been previously examined, prior research investigating body checking experience at the under-15 level found similar rates of injury and concussion among players who had 2 years of body checking experience and those that had none.22 The rates of injury resulting in >7 days of time-loss were previously reported to be 33% lower among the under-15 players with more body checking experience.22 However, this finding was considered in light of this body checking policy change reducing the rate of severe injury 70% in under-13 leagues disallowing body checking.22 The present study found over a two-fold greater injury rate (>7 days of time-loss) among those with more body checking experience. The increased rates of injury and concussion with greater body checking experience may be related to increased player skill levels and speeds of play.

In this study, weight analyzed either continuously or categorized by percentiles was not significantly associated with injury or concussion outcomes. This finding was consistent with one previous under-15 youth ice hockey study, but inconsistent with another that suggested an 85

increased rate of injury in heavier players,22,25 or an under-13 study that found lighter players had an increased rate of concussion.23 These results may be related to size differential, which may be more relevant at the younger age groups where greater size disparities between players may exist. Consistent with the youth ice hockey literature, players with a previous history of injury or concussion had higher rates of injury and concussion, respectively.19,22,23,29,30 Position of play was not significantly associated with any outcome in the present study. This was inconsistent with previous studies at the under-13 and under-15 level where goaltenders were protected from injury.19,22,23,29,30

Based on an exploratory model including year of play, first year players had an increased rate of concussion relative to third year players. This finding is supported by previous studies that have suggested first year players to be at greater risk of injury and concussion,19,22,23,29,30 although most recent findings at the under-15 age category did not identify year of play as a significant risk factor.25 It is worth noting that the IRRs for body checking experience were higher in these models compared with the models without year of play. Specifically, the IRR for all injury among those with ≥3 years body checking experience was 3.20 (95% CI: 1.92-5.35) when year of play was included in the model versus 2.62 (95% CI: 1.61-4.24) when it was not included. Similar increases were seen in the injury resulting in >7 days of time-loss and concussion IRRs (Appendix T & Table 5.3).

5.7 Limitations

While this study has many strengths such as a prospective cohort design and a strong analytical approach including multiple imputation of missing covariate data and mixed effects modelling with 2 levels of clustering, there are limitations. Selection bias was possible due to loss to follow-up in the cohort if some players stopped participating in hockey after sustaining an injury. The players that continued to participate would then have more body checking experience and may have lower rates of injury. This would lead to an underestimation of the association between body checking experience and rates of injury. There is also the potential for misclassification of exposure status as body checking experience was assumed based on the year of the study, local and national body checking policy, and, if applicable, based on player PBQ data from repeated measures. In certain circumstances body checking experience was assumed if there was missing data on players. For instance, if players participated in their first year of play and played with body checking, did not participate or had missing data in their second season, and participated again in their third year with body checking, it was assumed they participated with body checking in their second season, which was added to their experience in their third year. We feel this approach was satisfactory as players typically continue to play in leagues with the same body checking policy. Further, any misclassification was likely independent of the outcome (injury) and would result in a bias toward the null. Position of play may also not have been consistent for every game during the season for each player as reported at baseline. It is possible that teams included in this study have increased risk perception and therefore were more likely to report injuries. Using a clear injury definition helps minimize the risk of bias, but it is also unlikely that this differed based on body checking experience. All concussions were

included if they met the study definition, although not all players with a suspected concussion followed up with a physician [8/10 saw a physician (80.0%) in those with ≤2 years of body checking experience, and 98/115 (85.2%) in those with ≥3 years of experience].

5.8 Conclusions

The rates of all injury, injury resulting in >7 days of time-loss, and concussion were significantly higher among under-18 players with more body checking experience (≥3 years) than those with less experience (≤2 years). This suggests that body checking experience does not protect youth ice hockey players from injury, and adds to literature that there are no unintended consequences following policy disallowing body checking. Additionally, this provides further evidence in support of removing body checking in youth ice hockey to reduce injury and concussion rates. Future research includes the examination of body checking skill development, coaching skills, skill progression, and the impact of body checking policy on game contact behaviours and player performance.

Chapter Six: Conclusions and Future Directions

Injuries, including concussions, are a major health concern for youth ice hockey players.

These injuries are predictable, and therefore, are preventable through injury prevention strategies. The aims of this doctoral research have been twofold: 1) to provide a better understanding of the potentially modifiable risk factors for injury in youth ice hockey to further aid in the development of targeted interventions, and 2) to ensure that no unintended injury consequences have resulted from policy changes that have been implemented in youth ice hockey. Each chapter in this thesis is designed to contribute high quality evidence to achieve these aims. A summary of each chapter including specific future directions are highlighted below.

6.1 Chapter Summaries

6.1.1 Chapter Two

Chapter two of this dissertation reviewed the current body of knowledge with regards to the potential risk factors for injury in youth ice hockey, and laid the foundation for the next steps to inform injury prevention. While a myriad of studies has examined potential risk factors for injury in youth ice hockey, many of these remain inconclusive. Of all the potential risk factors that were discussed, body checking policy is the single most consistent factor associated with injury and concussion. Epidemiological studies evaluating injury prevention strategies in youth sport have generally examined three themes; 1) training strategies, 2) equipment recommendations, and 3) rule modifications and policy changes. Neuromuscular training

programs have been shown to reduce the incidence of injury and concussion across many youth sports, yet the development and implementation of an ice hockey-specific neuromuscular training program remains an opportunity for future research. Recent evaluations of mouth guard use and helmet fit suggest that youth ice hockey players should be mandated to wear mouth guards and a properly fitting helmet, although further research examining these are warranted.

Evaluations of body checking policy change to disallow body checking have shown a protective effect in reducing injury and concussion rates and significant health care cost savings. However, this chapter highlights the importance of continued research after any policy change has been implemented to ensure that no unintended consequences have been created.

6.1.2 Chapter Three

This chapter examined the association between on-ice sport-specific skill performance using components of the Hockey Canada Skills Test and adjusted rates of injury and concussion in youth ice hockey players. This provides a better understanding of the potentially modifiable risk factors for injury in youth ice hockey, which will further aid in the development of targeted interventions. A slower time on the transition agility with the puck was associated with a lower rate of injury among youth ice hockey players (aged 11-17), but was not associated with adjusted rates of concussion. Forward speed with the puck and drop-off time were not associated with adjusted rates of injury or concussion. Other significant findings included an almost 2-fold greater rate of injury and concussion for the defensive position, relative to forwards.

Participating in a league permitting body checking was associated with a 3-fold greater rate of injury and concussion, and continues to be the most relevant modifiable risk factor in youth ice

hockey. Future studies should consider the examination and validation of a more global skill performance measure that incorporates different components of the HCST. This would allow for a better understanding of a player’s overall skill level, which may be more relevant than any single skill component. This composite score may also be more meaningful to the hockey community. It is also important that future studies examining skill performance repeatedly measure skill development throughout the season, to better capture skill performance data at a more etiologically relevant time. Finally, future studies investigating youth ice hockey, including those that examine skill performance, should include more consideration of participants from

‘girls-only’ leagues.

6.1.3 Chapter Four

Chapter four compared the rates of injury and concussion among under-15 (ages 13-14) ice hockey players playing in leagues allowing body checking, but who have varying years of body checking experience. This evaluation provides important evidence for the recent and any future body checking policy decisions in youth ice hockey. In this study, no significant differences were found in the rates of injury or concussion among under-15 players that had no body checking experience and those that had either 1 year or 2+ years of experience. These findings then suggest that body checking experience does not protect under-15 ice hockey players from injury. Future studies should evaluate the influence of body checking policy on player contact behaviours and player performance in games after policy change, if measures of data collection are able to do so (i.e., video analysis measures). This information will continue to inform the hockey community as to any consequences of an implemented policy change.

6.1.4 Chapter Five

This chapter examined the association between body checking experience and injury in 15-

17-year-old ice hockey players. Based on multiple multilevel mixed-effects Poisson regression, players with ≥3 years of body checking experience had a higher rate of all injury and concussion, relative to those with ≤2 years. This study provides further evidence in support of removing body checking in youth ice hockey to reduce injury and concussion risk. In addition to the future directions suggested in chapter four, the effect of coaching strategies aimed at teaching body checking awareness and appropriate checking techniques to players who play in leagues permitting body checking is recommended.

6.2 Future Directions

In addition to the future directions specific to each chapter, there is the opportunity for future youth sport epidemiological studies to consider different analytical approaches and techniques. These may be relevant for future youth ice hockey evaluations, and as such, are highlighted in more depth below.

6.2.1 Analytical Approaches

6.2.1.1 Poisson Regression

The analytic approach used in chapters three, four, and five of this thesis was multiple multilevel Poisson regression with random effects at a team level and, when suitable for model convergence, at the individual level considering participation of some players in multiple study years. There are many benefits to this analytical approach including accounting for multiple independent outcomes (i.e., count of injury/concussion), adjustment for other important variables, and the ability to account for clustering at more than one level. Further, the estimation of injury and concussion rates in these chapters allows for more accurate comparisons to previous youth ice hockey studies. While multiple multilevel Poisson regression can adjust for previous injury/concussion history as a covariate, future youth ice hockey may want to further examine recurrent injury. As such, other analytic approaches may also be considered.

6.2.1.2 Frailty Models

A different analytical approach for the analysis of recurrent injury data is using Frailty models.52,111,112 Frailty models are a type of survival analysis that measures the time to a given event of interest, and in the case of sport injury analysis, the time to injury (and if applicable, time to re-injury). These models have not yet been fully integrated into sport injury prevention research and remain an opportunity for future youth ice hockey epidemiological studies.

6.2.1.3 Complex Systems Approach

Recently, a different approach to the examination of sport-related injury has been suggested. A complex system approach argues the identification of predictive factors for sport- related injury have usually assumed a linear relationship between potential risk factors and sport- related injury, and traditional analyses examining sport-related injury have largely focused on the identification of isolated factors. It has been suggested that future epidemiological studies examining potential risk factors for sport-related injury may need to look beyond a linear relationship of isolated potential risk factors, and employ analytical strategies that incorporate the identification of risk pattern recognition (i.e., interactions among a complexity of multiple risk factors) to better understand the complex nature of sport-injury etiology.113 This emerging strategy may be relevant to future youth ice hockey studies.

6.3 Conclusions

In conclusion, the research presented in this PhD dissertation has contributed to the understanding of the potentially modifiable risk factors for injury in youth ice hockey, which will further aid in the development of targeted interventions. Additionally, ensuring that no unintended consequences have resulted from recent body checking policy changes in youth ice hockey will continue to inform the current and future body checking policy decisions implemented in youth ice hockey. Collectively, the studies conducted in this dissertation will have important national public health implications including the reduction of injury and health care costs, ultimately making youth ice hockey safer and more enjoyable for future generations.

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101. StataCorp L. Stata statistical software: Release 15 (2017). College Station, TX: StataCorp LP. 2017. 102. Kang J, Yuan Y, Emery C. Assessing remedies for missing weekly individual exposure in sport injury studies. Injury prevention. 2014;20(3):177-182. 103. Schick DM, Meeuwisse WH. Injury rates and profiles in female ice hockey players. American Journal of Sports Medicine. 2003;31(1):47-52. 104. Keightley M, Reed N, Green S, Taha T. Age and competition level on injuries in female ice hockey. International journal of sports medicine. 2013;34(08):756-759. 105. Reed A, Hansen H, Cotton C, et al. Development and validation of an on-ice hockey fitness test. Canadian Journal of Applied Sport Science. 1979;4(4):245. 106. Schneider KJ, Nettel-Aguirre A, Palacios-Derflingher L, et al. Concussion Burden, Recovery, and Risk Factors in Elite Youth Ice Hockey Players. Clinical journal of sport medicine: official journal of the Canadian Academy of Sport Medicine. 2018. 107. Canada H. Teaching Checking. https://cdn.hockeycanada.ca/hockey-canada/Hockey- Programs/Coaching/Checking/Downloads/teaching_checking_progression_body_checkin g.pdf. Accessed July 17, 2020, 2020. 108. 2019 CASEM Injury Prevention Podium Presentations. Clinical Journal of Sport Medicine. 2019;29(3):e47-e48. 109. Fuller CW, Ekstrand J, Junge A, et al. Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries. Scand J Med Sci Sports. 2006;16(2):83-92. 110. Team RC. R: A language and environment for statistical computing. In: Vienna, Austria; 2013. 111. Finch CF, Marshall SW. Let us stop throwing out the baby with the bathwater: towards better analysis of longitudinal injury data. British journal of sports medicine. 2016;50(12):712-715. 112. Nielsen RO, Shrier I, Casals M, et al. Statement on methods in sport injury research from the first methods matter meeting, Copenhagen, 2019. J Orthop Sports Phys Ther. 2020;50(5):226-233.

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113. Bittencourt N, Meeuwisse W, Mendonça L, Nettel-Aguirre A, Ocarino J, Fonseca S. Complex systems approach for sports injuries: moving from risk factor identification to injury pattern recognition—narrative review and new concept. British journal of sports medicine. 2016:bjsports-2015-095850.

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APPENDIX A: PRE-SEASON BASELINE QUESTIONNAIRE (2013-2015)

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HOCKEY STUDY PRE-SEASON BASELINE QUESTIONNAIRE SSID #: *OFFICE USE ONLY

Name: / / Today's Date: Gender: Male Female Day Month Year

Age: City: Player's Phone No: ( )

Height: feet inches or cm / / Date of Birth: Weight: (lbs) or (kg) Day Month Year

Dominant Hand (for writing): Right Left Level of Play: Pee Wee Bantam Midget

Division: 1 2 3 4 5 6 7 8 9

10 11 12 AA AAA

Position: Forward Defense Goalie Team Name:

Please check off how many years of organized hockey you have played prior to this season (check only one): 0 years 4 years 8 years 12 years 1 year 5 years 9 years 13 years 2 years 6 years 10 years 14 years 3 years 7 years 11 years Other ______Have you ever participated in a Univeristy of Calgary hockey research study? yes no

If "Yes", what year?______EQUIPMENT (check all that apply): a) Mouthguard: At games: always At practices: always less than 75% less than 75% never never Type of mouthguard worn: dentist custom-fit off the shelf b) Helmet: Make: Bauer CCM Itech Jofa Mission Nike RBK Other:

Type: full clear visor full wire cage combination visor/cage Age: new this season new last season 2-3 years old >3 years old

INJURY HISTORY: 1. Have you ever had a concussion or been "knocked out" or had your "bell rung"? Yes No

if "Yes", please list below; Date: Activity at the time Time unconscious Memory loss (yes or no) Time loss before FULL return to sport

eg. (DD/MM/YY) hockey, skateboarding, etc. 0min 30sec no 1 day, 10 days, etc

If you answered yes to Question 1, please indicate whether you have any persistent problems with: a) memory Yes No b) dizziness Yes No c) headaches Yes No

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2. In addition to any injury described in question 1, have you had any other injury requiring medical attention OR at least 1 day of missed participation from sport or physical activity in the past 12 MONTHS? Yes No if "Yes", please describe this injury/these injuries to the best of your ability below; Injury Date Injury type Body part Sport of occurrence Treatment description Time loss before FULL return to sport eg. (DD/MM/YY) sprain, bruise, etc. knee, nose, etc. soccer, wakeboarding, etc. first aid, physio, etc. 1 day, 3 weeks, etc

3a. Do you have any incompletely healed injuries? Yes No If yes, describe this injury to the best of your ability:

3b. Are you currently receiving treatment for this injury/these injuries? Yes No If yes, describe this injury to the best of your ability:

MEDICAL HISTORY

1. Do you take any medications (asthma inhaler, Advil, Tylenol, etc.) on a regular basis ? Yes No If yes, please list:

2. Are you currently taking any supplements (vitamins, minerals, protein powder, etc.) ? Yes No

If yes, please list:

3. Have you been diagnosed by a physician with a bone fracture, arthritis, or other muscle or bone related condition? Yes No If yes, describe your condition(s) to the best of your ability: Year of diagnosis:

4. Have you been diagnosed by a physician with a systemic disease (e.g., cancer, thyroid disease, heart disease)? Yes No If yes, describe your condition(s) to the best of your ability: Year of diagnosis:

5. Have you ever been diagnosed by a physician with a circulation or heart-related problem (e.g., heart murmur, irregular heart beat, congenital deformity of the heart)? Yes No If yes, describe your condition(s) to the best of your ability: Year of diagnosis:

6. Have you been diagnosed by a physician with a neurological disorder (e.g., brain injury, cerebral palsy, pinched nerve, "stinger", multiple sclerosis, etc.)?

Yes No If yes, describe your condition(s) to the best of your ability: Year of diagnosis:

questionnaire continues !

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7a. Have you ever experienced headaches? 7b. If yes, are they associated with (please check all that apply): Yes No Nausea Vomiting Sensitivity to Light Sensitivity to Noise 7c. Does anyone else in your family experience headaches? Yes No If yes, please list which family members:

7d. Have you ever been diagnosed with migraines? Yes No Year of diagnosis:

8a. Have you ever been concerned that you have an attention or learning issue? Yes No If yes, please describe to the best of your ability:

8b. Have you ever been formally diagnosed by a health care professional (physician, psychologist, etc.) as having an attention or learning issue? Yes No If yes, please describe to the best of your ability: Year of diagnosis:

8c. Have you ever been formally diagnosed by a health care professional (physician, psychologist, etc.) with any of the following: (check all that apply)

Cognitive Delay Disruptive Behaviour Disorder Communication Disorder Oppositional Defiant Disorder Pervasive Developmental Disorder Conduct Disorder ADHD Mood Disorder Learning Disability Depression Anxiety Disorder Bi-Polar Other:

The following questions ask about your thoughts on body checking and how you use body checking in hockey. We ask that you answer as honestly as possible, without any influence from other people. Please circle the numer that best matches your answer.

Strongly disagree Disagree a little Neither Agree a little Strongly agree " # $ 1 2 3 4 5

1) I like body checking. 1 2 3 4 5 2) I like to be body checked. 1 2 3 4 5 3) My coach encourages me to body check. 1 2 3 4 5 4) My parents encourage me to body check. 1 2 3 4 5 5) My teammates encourage me to body check. 1 2 3 4 5 6) I could be seriously injured by a body check. 1 2 3 4 5 7) I could seriously injure someone else with a body 1 2 3 4 5 check. 8) I think body checking increases my teams’ 1 2 3 4 5 chances of winning. 9) I would try to harm an opponent with a body check if it 1 2 3 4 5 would increase my team's chance of winning. 10) I think body checking should be allowed in Pee 1 2 3 4 5 Wee hockey. 11) I would body check another player even if I knew 1 2 3 4 5 it would injure them.

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ACTIVITY HISTORY QUESTIONNAIRE

1. In THE LAST SIX WEEKS, how many weeks and how many hours per week (on average) did you participate in PE class? hours per week number of weeks

2. In THE LAST SIX WEEKS, did you participate in any sports (NOT including PE class)? Yes No If yes, please estimate the average number of hours per week you participated in each sport: HOURS PER NUMBER OF HOURS PER NUMBER OF SPORT SPORT WEEK WEEKS WEEK WEEKS Aerobics Lacrosse Alpine skiing Martial arts Badminton Rock climbing Baseball Rollerblading Basketball Rugby Boxing (incl. kick) Running Cross-country skiing Skateboarding Cycling (road or mtn) Snowboarding Dance Soccer Dirt biking Squash Diving Speed skating Field hockey Swimming Figure skating Tennis Floor hockey Track and field Football Volleyball Golf Waterpolo Gymnastics Weight training Hiking/ Scrambling Wrestling Hockey Other (please describe): Horse riding ______3. In THE LAST SIX WEEKS, how many HOURS A WEEK (on average) do you spend on sport-related preparation (e.g. reading and reviewing scouting reports, watching game tape/film sessions, studying playbooks)? hours per week number of weeks

4. How many classes have you taking THIS SEMESTER? 1 2 3 4 5 6 How many hours (on average) do you spend in class in one week? How many hours (on average) do you spend on homework in one week? How many hours (on average) do you spend studying for a test in your hardest class? How many hours (on average) do you spend studying for a test in your easiest class? How many hours (on average) do you use a computer for school? How many hours (on average) do you spend tutoring or being tutored?

5. On average, how many texts messages/BBMs do you send or receive a day?

6. Please answer the following question based on the LAST SIX WEEKS: On, average, how many HOURS A DAY do you spend on the following: Reading (non-academic material such as novels, magazines, comics) Playing Non-Computer Games (e.g., chess, checkers, board games) Playing Games (on gaming systems, computer or phone) Playing Card Games Doing Word/Number Puzzles (e.g., Sudoku, Crosswords, Search-A-Word) Completing Puzzles Watching TV Talking on the Phone Watching Movies Using the Internet Email Social media (Facebook, Twitter, MySpace) Blogging Surfing/Searching Chores (e.g. making bed, doing dishes, mopping, taking out garbage)

7a. In THE LAST SIX WEEKS, have you been employed? Yes No If yes: 7b. What is your job title (e.g. coach,general labourer, server, office assistant): 7c. In THE LAST SIX WEEKS, how many weeks and how many hours per week (on average) did you work? hours per week number of weeks Thank you for your effort and time in completing this questionnaire. Please ensure this form given to the research staff as soon as possible.

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APPENDIX B: PRE-SEASON BASELINE QUESTIONNAIRE (2015-2017)

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OFFICE USE ONLY: _ Pre-season Baseline Questionnaire SSID:______Team number:______

Player name:______Person completing form: _ ❑Mother ❑Father ❑Player ❑Other:______Date (MM/DD/YY): ______/______/______Parent phone#:______Parent email:______

Birth date (MM/DD/YY): _____/_____/_____ Height:______ft/inches OR ______cm City:______

Dominant hand (writing): !Right !Left Association:______Weight:______lbs OR ______kg Sex: !Male !Female Level of Play: !Pee Wee !Bantam !Midget Have you ever participated in a University of Calgary Hockey Study? !No !Yes - If yes, what year?______Team name:______Years of organized hockey you have played prior to this season: Division: !AAA !AA !A !1 !2 !3 !0 yrs !1 yr !2 yrs !3 yrs !4 yrs !5 yrs !6 yrs !7 yrs 4 5 6 7 8 9 !8 yrs !9 yrs !10 yrs !11 yrs !12 yrs !12 yrs !Other:______! ! ! ! ! ! !10 !11 !12 !Rec.

Position: !Forward !Defense !Goalie

EQUIPMENT (check all that apply): Helmet: make: !Bauer !CCM !Itech !Jofa Mouthguard: !Mission !Nike !RBK !Other:______worn at GAMES: !Always !Less than 75% !Never model:______worn at PRACTICE: !Always !Less than 75% !Never type: !Full clear visor !Full wire cage !Combination visor/cage type: !Dentist custom-ﬁt !Off the shelf (incl. boil and bite) age: !New this season !New last season !2-3 yrs old !>3 yrs old

MEDICAL HISTORY: Have you ever been concerned that you have an attention or learning issue? ❑No ❑Yes Have you ever been diagnosed by a physician with a: If yes, describe:______!Bone fracture, arthritis, or other muscle or bone condition? Year:______Describe:______Have you ever been diagnosed by a health care !Systemic disease (eg, cancer, thyroid disease, heart disease)? professional with any of the following (check all that apply): Year:______Describe:______!Cognitive delay !Learning disability !Circulation or heart problem (eg, murmur, congenital deformity, irregular beat)? !ADHD !Persuasive developmental disorder Year:______Describe:______!Mood disorder !Communication disorder !Neurological disorder (eg, cerebral palsy, pinched nerve, “stinger”, MS)? Year:______Describe:______!Anxiety disorder !Disruptive behaviour disorder !Depression !Oppositional deﬁant disorder Have you ever experienced headaches? !No !Yes !Conduct disorder !Bi-polar disorder If yes, are they associated with: !Other:______!Nausea !Vomiting !Light sensitivity !Noise sensitivity Are you currently taking: Have you been diagnosed with migraines? !No !Yes Medications (eg, inhaler, Tylenol, antidepressants, birth control)? If yes, year of diagnosis:______!No !Yes:______Supplements (eg, vitamins, minerals, protein powder)? Do any family members experience headaches? !No !Yes !No !Yes:______If yes, which member?______

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INJURY HISTORY: Have you ever had a concussion (either diagnosed or not) or been “knocked out” or had your “bell rung”? ❑No ❑Yes If yes, please list below: Time loss before FULL Date Sport/activity at the time Time unconscious Memory loss? (MM/DD/YY) (minutes or seconds) return to sport (days)

!No !Yes

If yes, do you have persistent problems with: Memory? !No !Yes Dizziness? !No !Yes Headaches? !No !Yes

In addition to injuries listed above, have you had any injury requiring medical attention OR at least 1 day of missed participation from sport or physical activity in the past 12 months? !No !Yes If yes, please list below: Sport/activity Time loss before FULL Date Injury type Body part Treatment? (MM/DD/YY) at the time (eg, ﬁrst aid, physio, etc.) return to sport (days)

Do you have any incompletely healed injuries? !No !Yes - describe:______If yes, are you currently receiving treatment for this injury/these injuries? !No !Yes - describe:______

The following questions ask about body checking in hockey. We ask that you answer as honestly as possible, without any inﬂuence from other people. Please circle the number that best matches your answer:

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APPENDIX C: PRE-SEASON BASELINE QUESTIONNAIRE (2017-2018)

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OFFICE USE ONLY: _ Pre-season Baseline Questionnaire SSID:______Team number:______

Player name:______Person completing form: _ ❑Mother ❑Father ❑Player ❑Other:______Date (MM/DD/YY): ______/______/______Parent phone#:______Parent email:______

Birth date (MM/DD/YY): _____/_____/_____ Age: ______Will you be playing hockey in the 2017-2018 season? Sex:oMale oFemale oPrefer not to respond Dominant hand (writing): oRight oLeft oNo oYes

Height:______ft/inches OR ______cm If no, please skip the Hockey How do you identify in terms of gender? ______Participation in 2017-18 section. Weight:______lbs OR ______kg

HOCKEY PARTICIPATION in 2017-18 season: City: ______

Association: ______Position (please select one): oForward oDefense oGoalie

Level of Play: oPee Wee oBantam oMidget oJunior Years of organized hockey you have played prior to this season: Division: o0 yrs o1 yr o2 yrs o3 yrs o4 yrs o5 yrs o6 yrs o7 yrs oAAA oAA oA o1 o2 o3 o4 o5 o6 o8 yrs o9 yrs o10 yrs o11 yrs o12 yrs o12 yrs o7 o8 o9 o10 o11 o12 oRec oPick-up/shinny oOther:______

EQUIPMENT (check all that apply): Helmet: make: oBauer oCCM oItech oJofa Mouthguard: oMission oNike oRBK oOther:______worn at GAMES: oAlways oLess than 75% oNever model:______worn at PRACTICE: oAlways oLess than 75% oNever type: oFull clear visor oFull wire cage oCombination visor/cage type: oDentist custom-ﬁt oOff the shelf (incl. boil and bite) oNone of the above age: oNew this season oNew last season o2-3 yrs old o>3 yrs old

MEDICAL HISTORY: Have you ever experienced headaches? oNo oYes If yes, are they associated with: Have you ever been diagnosed by a physician with a: oNausea oVomiting oLight sensitivity Bone fracture, arthritis, or other muscle or bone condition? oNoise sensitivity oNone of the above oNo oYes If yes, Year:______Describe:______Have you been diagnosed with migraines? oNo oYes If yes, year of diagnosis:______Systemic disease (eg, cancer, thyroid disease, heart disease)? oNo oYes Do any family members experience headaches? If yes, Year:______Describe:______oNo oYes If yes, which member(s) ______Circulation or heart problem (eg, murmur, congenital deformity, irregular beat)? Have you ever been concerned that you have an attention or oNo oYes learning issue? oNo oYes If yes, Year:______Describe:______If yes, describe:______Neurological disorder (eg, cerebral palsy, pinched nerve, “stinger”, Have you ever been diagnosed by a health care professional MS)? with any of the following (check all that apply): oNo oYes oCognitive delay oLearning disability If yes, Year:______Describe:______oADHD oPersuasive developmental disorder Are you currently taking: oMood disorder oCommunication disorder Medications (eg, inhaler, Tylenol, antidepressants, birth control)? oAnxiety disorder oDisruptive behaviour disorder oNo oYes:______oDepression oOppositional deﬁant disorder Supplements (eg, vitamins, minerals, protein powder)? oConduct disorder oBi-polar disorder oNo oYes:______oOther:______

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oNo oYes

oNo oYes If yes, do you have persistent problems with: Memory? oNo oYes Dizziness? oNo oYes Headaches? oNo oYes

In addition to injuries listed above, have you had any injury requiring medical attention OR at least 1 day of missed participation from sport or physical activity in the past 12 months? oNo oYes If yes, please list below: Sport/activity Time loss before FULL Date Injury type Body part Treatment? (MM/DD/YY) at the time (eg, ﬁrst aid, physio, etc.) return to sport (days)

Do you have any incompletely healed injuries? oNo oYes - describe:______If yes, are you currently receiving treatment for this injury/these injuries? oNo oYes - describe:______

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APPENDIX D: WEEKLY EXPOSURE SHEET

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(tournament game, skill training, conditioning,game, skill scrimmage, etc.) (tournament Session Description Duration of game or practice (minutes) Game Penalty Minutes by team Score & Game Outcome Session Date PC (Participation Code) O Other S Form) complete Injury Report (Note do not need to injury N Injury Report Form) (Note MUST complete are: theyif indicate please (i.e. coded "P" or "0") participating If athleteNOT is fully I

form to # ID attribute specifies injury reportspecifies

( participation code participation

Injured in hockey PC Sick Non-hockey related Non-hockey related P Please enter a IID (Month/Day)

) ) for each player F R (Reason) 0 indicating:

Partial

(Injury ID #) time loss (Game=G, Practice=(Game=G, P, Dryland=D) Full None ( 75%) (<75%) ( 0 ) (ie. (ie. regular game, season game, playoff Age Group: (Win=W, Tie=T, Loss=L) (your team / opponent) Player name Bantam Pee Wee Midget PC R Monday Weekly Exposure Weekly Sheet Exposure / / YOUTH HOCKEY STUDY IID PC R Tuesday / / IID PC R Wednesday / / Team ID: Team: Division: IID PC R Thursday / / IID PC R Friday / / IID PC R Saturday / / IID PC R Sunday / / IID

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APPENDIX E: INJURY REPORT FORM (2013-2015)

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HOCKEY STUDY INJURY REPORT FORM Injury ID #: Players Phone #: Parent's Email: On this form, please report any injury (new or recurrent) or any suspected concussion occurring during hockey (game, practice or dryland training activity) which either requires; ! medical attention and/or ! results in the inability to complete the session of activity in which the injury occurred ! and/or results in the player to miss at least one day of sporting activity To complete this form please use the assistance of a parent or coach. Please have any attending medical practitioner (physician, nurse, physiotherapist, athletic therapist) complete the details on the last page on this form. Upon completion*, please return this form to your assigned study personnel *Please do not submit form until player has fully returned to competitive play and has completed questions 20 through 26.

1. Player's Name: 2. Gender: Male Female 3. Study Subject ID #: 4. Team: 5. Age Group: Pee Wee Bantam Midget 6. Division: 1 2 3 4 5 6 AA 7 8 9 10 11 12 AAA 7. Date of Birth: / / 8. Date of Injury: / / Day Month Year Day Month Year 9. This injury involved: Sudden onset & contact with another player or equipment Sudden onset & NO contact with another player or equipment Gradual onset / overuse Unknown

10. Injury Status: New Injury Recurrence of Injury from this hockey season Recurrence of Injury from previous hockey season

11. Was bracing or taping used on the injured area or limb at the time of injury? Yes No if yes, what type?

12. Injury occurred during: Practice on ice Game (a) regular season (b) warm up tournament 1st period playoff 2nd period exhibition 3rd period Other (e.g., dryland training; please specify):

13. Position playing at the time of injury: Forward (Centre) Forward (Wing) Defense Goalie Other

14. Was the player able to return to the same game or practice in which they were hurt? Yes No N/A

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Injury Report Form Continued Page 2 Injury ID #:

15.a) Describe to the best of your ability the events surrounding the injury:

15.b) Please check off all that apply to describe the cause of the injury: Body Check if yes: Delivered Received Other Intentional Player Contact please specify: Elbowing Slashing Cross-checking Tripping Roughing Head contact Incidental (unintentional) Contact with another player or their equipment Contact with the environment, NOT another player if yes: Puck Boards Net No contact Unknown

16. Was there a penalty called directly related to the injury event? Yes No 16a) If yes, what was the penalty? (check all that apply) Body checking related - Describe:______Stick-related - Describe:______Head contact related - Describe:______Fighting Other, describe______16b) If yes, what was the consequence of the penalty? (check all that apply) Penalty shot Double minor 10 min misconduct Match penalty 2 min minor 5 min major Game misconduct Suspension indicate length of suspension______16c) If yes, who received the penalty? (check all that apply) Injured player Injured player's teammate Opposing team player

17. Protective gear worn at the time of injury (check all that apply): Mouthguard Yes No Don't know if yes, specify: Dentist custom-fit off the shelf Brace Yes No Don't know if yes, specify: Knee Ankle Other* *please describe: ______Tape Yes No Don't know if yes, specify: Knee Ankle Other* *please describe: ______Helmet Make: Bauer CCM Itech Jofa Mission Nike RBK Other Model (eg. Junior 652C, Jr Ignite 4, etc.): describe other; Type: Full clear visor Full wire cage Combination visor/cage Helmet age: New this season New last season 2-3 yrs old >3 years old

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Injury Report Form Continued Page 3 Injury ID #:

18. Injury Location (number all injury locations that apply [i.e., 1, 2, 3...]; circle affected side where applicable): Head Throat Hand (L / R) Pelvis Ankle (L / R) Face Shoulder (L / R) Finger (L / R) Hip (L / R) Foot (L / R) Ears (L / R) Collarbone (L / R) Back Groin (L / R) Toes (L / R) Eye (L / R) Upper arm (L / R) Side (L / R) Genitals Other* Nose Elbow (L / R) Ribs (L / R) Upper Leg (L / R) Teeth Forearm (L / R) Chest Knee (L / R) Neck Wrist (L / R) Abdomen Lower leg (L / R)

19.Type of Injury (number all types of injury that apply [i.e., 1, 2, 3…]; based on injury locations numbered above): Bruise Cut Dislocation Knocked out Burn Blister Broken bone Concussion Bleeding Joint swelling Muscle strain Other, please Abrasion/Scrape Joint/ ligament sprain Tendonitis describe;

**Please do not complete questions 20 through 26 until the player has returned fully to competitive play and has completed all injury-related care. These questions are related to the INJURY AND ITS RELATED CARE. 20. Total number of calendar days the player was unable to participate in: a) Normal activities of daily living (i.e. work, school, camp, other) days b) Any sport due to this injury days c) Hockey days

21. Total number of days (or hours) the parent or guardian missed work as a direct result of the player's injury days hours Please check box if parent/guardian was not working during this time period. 22. Please list parent/guardian's occupation: N/A

23. Did the player see any health care professional(s) for assessment or treatment of THIS INJURY? Yes No (if yes, please check all that apply once you have completed all care for this injury) EMT (Total # visits______) Physiotherapist (Total # visits ) Physician (Family/GP) (Total # visits______) Athletic therapist (Total # visits ) Physician (ER) (Total # visits______) Massage therapist (Total # visits ) Physician (Sport medicine)(Total # visits______) Dentist (Total # visits ) Pediatrician (Total # visits______) Chiropractor (Total # visits ) Surgeon (Total # visits______) Other (Total # visits ) Radiologist (Total # visits______) please specify;______

24. Was an ambulance called for this injury? Yes No If yes: a) Did the player ride to the hospital in the ambulance? Yes No b) Was the player seen by a health professional at the rink? Yes No

25. Did the player receive any other treatment for this injury? Yes No (if yes, please check all that apply) MRI Number:______X-ray Number:______Cast Number:______, Body part:______,Type:______CT scan Number:______Brace Number:______, Body part:______,Type:______Bone scan Number:______Splint Number:______, Body part:______,Type:______Taping # of tape rolls used:____ Surgery Number:______, Body part:______,Type:______Crutches Other, please describe;

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4 Injury Report Form Continued Page 4 Injury ID #:

26. Did the player take any medications for this injury? if yes: a) Name of medication:______b) Type of medication (e.g., oral, injected treatment, etc.):______c) Duration:______

27. Do you take any medications for other reasons (i.e., not for injuries) on a regular basis? (e.g., asthma inhaler, antidepressants, birth control pills etc.) Yes No If yes, please list:

28. Were you admitted to the hospital for this injury? Yes No (if no, please skip to the next question, #27) a) Primary reason for hospitalization:______b) # of nights in the hospital:______c) Did you have surgery while in the hospital? Yes No If yes, what was the name of the surgery? (If you do not know, please describe to the best of your ability:

29. Who provided the player with clearance to return to activity? Self Parent Coach Therapist Physician Other, please describe;

If the player is seen by a physician, physiotherapist, athletic therapist or other medical practitioner for this injury please have them complete one of the following sections: Upon completion, please return this form to your Team Designate

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HOCKEY STUDY 2013-2018 Office use only Athlete's Name: SSID IID

Date: / / Day Month Year

Attending Medical Practitioner’s Name: Occupation (i.e.. Family Physician/Specialist/Therapist/etc): Diagnosis:

Treatment Plan:

Expected/Recommended duration of treatment:

Is this athlete cleared to resume unrestricted competition? Yes No IF NO: Expected date of clearance: Conditions of clearance:

Does this athlete require medical follow up prior to clearance? Yes No

HOCKEY STUDY 2013-2018 Athlete's Name: Office use only SSID IID Date: / / Day Month Year

Attending Medical Practitioner’s Name: Occupation (i.e.. Family Physician/Specialist/Therapist/etc): Diagnosis:

Treatment Plan:

Expected/Recommended duration of treatment:

Is this athlete cleared to resume unrestricted competition? Yes No IF NO: Expected date of clearance: Conditions of clearance:

Does this athlete require medical follow up prior to clearance? Yes No

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APPENDIX F: INJURY REPORT FORM (2015-2017)

125

OFFICE USE ONLY: Hockey Study Injury Report Form Injury ID#: ______ Please complete this form for any injury including suspected concussion Person completing form: ❑Mother ❑Father ❑Player occurring in hockey (game/practice/dryland, etc.) which receives: ❑Team designate ❑Other:______1) medical attention OR Parent phone#:______2) results in the inability to complete the session in which the injury occurred OR Parent email:______3) results in the player missing at least one day of sporting activity 1. Player name:______12. This injury involved: 2. Player SSID#:______3. Team #: ______! Sudden onset & contact with another player ! Sudden onset & NO contact with another player 4. Today’s date (MM/DD/YY): ______/_____/_____ ! Gradual Onset/Overuse (Go to 15) ! Unknown (Go to 13) 13. Cause of injury (check all that apply): 5. Injury date (MM/DD/YY): ______/_____/______! Body check: !Delivered !Received 6. Injury status: ! Other intentional player contact: ! New injury !Elbowing !Roughing !Head contact !Cross-checking ! Recurrence of injury from this hockey season !Tripping !Slashing !High Sticking ! Recurrence of injury from previous hockey season ! Unintentional contact with player or equipment 7. Did the player return to play the same game/practice? ! Contact with the environment, NOT another player !No !Yes !Non-hockey injury (Go to 16) !Puck !Boards !Net !Ice !Other:______8. At the time of injury, were any of the following worn? 14. Mechanism of injury (check all that apply): !Direct blow to head: !Right !Left !Front !Back Mouthguard: !Unknown !No !Yes !Fell & hit head: !Back !Forward !Side Brace: !Unknown !No !Yes: !Left side !Right side !Hit head: !On boards !On ice !On net !Other:______if yes, worn on: !Knee !Ankle !Wrist !Other:______!Non-head injury Tape: !Unknown !No !Yes: !Left side !Right side 15. Was a penalty called directly related to the injury event? ! ! ! ! if yes, worn on: Knee Ankle Wrist Other:______!No !Yes 9. Have you changed any equipment (since baseline?) If yes, !Body checking related !Stick-related !Head-contact !No !Yes !No baseline - entering study at injury !Fighting !Other:______If yes, which? !Mouthguard !Helmet !Other:______If yes, !2 min minor !Double minor !5 min major 10. Position playing at time of injury: !Penalty shot !10 min misconduct !Match penalty !Forward (Centre) !Forward (Wing) !Defense !Game misconduct !Suspension: length______!Goalie !Other:______If yes, who received the penalty ? (check all that apply) 11. Injury occurred during: !Injured player !Injured player’s teammate !Other team 16. Describe events surrounding injury: ! Game a) !Regular season !Tournament !Playoff !Exhibition ______b) !Warm-up !1st period !2nd period !3rd period ______! Practice on ice ! Other (eg, dryland) Please specify:______

17. Injury location for each type of injury (check all boxes that apply AND circle which side the injury occurred on):

Type of Injury Head Face Ears (L /R)Eye (L /R)Nose Teeth Neck Throat Shoulder (LCollarbone / R) Upper (L / R) armElbow (L / R) (L / ForearmR) (LWrist / R) (L / R)Hand (L / R)Finger (L /Back R) Side (L / R)Ribs (L / R)Chest Abdomen Pelvis Hip (L / R)Groin (L / R)Genitals Upper LegKnee (L / R) (L / R)Lower leg Ankle(L / R) (L / FootR) (L / R)Toes (L / R)Other:______Knocked out

Concussion

Bruise

Burn

Bleeding

Abrasion/scrape

Cut

Blister

Joint swelling Joint/ligament sprain

Dislocation

Broken bone

Muscle Strain

Tendonitis

Other:______V.2

126

ONLY complete this section once the athlete has fully returned to play AND has completed all injury related care

18. Date of full medical clearance for return to: Normal daily activities (MM/DD/YY): _____/____/_____

Non-contact sports (full participation) (MM/DD/YY): ______/____/_____

Collision/contact sports (full participation) (MM/DD/YY): ______/____/_____ 19. Who provided clearance to return to play? !Physician !Therapist !Coach !Parent !Self !Other: ______20. Total time parent/guardian missed work as a direct result of the player’s injury: ______days + ______hours !Not working 21. Parent/guardian’s occupation:______!Not working 22. Was an ambulance called? !No !Yes - If yes, did the player ride to the hospital in the ambulance? !No !Yes 23. Was the player admitted to the hospital (other than an emergency department visit)? !No !Yes If yes, primary reason for hospitalization:______# nights in the hospital:______If yes, did the player have surgery in the hospital? !No !Yes - Name or describe the surgery:______24. Did the player see any health care professional(s) for assessment/treatment of this injury? ❑No ❑Yes (check all that apply):

!On-site ﬁrst aid Total # visits:_____ !Paediatrician Total # visits:_____ !Athletic Therapist Total # visits:_____ !EMT/Paramedic Total # visits:_____ !Surgeon Total # visits:_____ !Massage Therapist Total # visits:_____ !Family Physician/GP Total # visits:_____ !Radiologist Total # visits:_____ !Dentist Total # visits:_____ !ER Physician !Chiropractor !Other:______Total # visits:_____ Total # visits:_____ Total # visits:_____ !Sport Med. Physician !Physiotherapist ______Total # visits:_____ Total # visits:_____

25. Did the player have any tests or receive any other treatment for this injury? !No !Yes If yes, check all that apply:

!MRI # of times:_____ Body part:______!Cast # of casts:______Body part:______Type:______!X-ray # of times:_____ Body part:______!Brace # of braces:_____ Body part:______Type:______!CT scan # of times:_____ Body part:______!Splint # of splints:_____ Body part:______Type:______!Bone !Taping # of times:_____ Body part:______# of tape rolls:___ Body part:______Type:______scan !Crutches !Other:______26. Did the player take any medications for this injury? !No !Yes If yes, name:______type (eg, oral, injected):______

duration (days):______frequency (eg, # doses/day):______dosage (eg, 200mg):______

If the player sees a physician, therapist, or other practitioner, have this healthcare provider complete the following section (unless a fee is involved). Upon completion, return to your Team Designate or study personnel.

HOCKEY STUDY 2013-2018 Player’s Name:

Medical practitioner’s name:______Date (MM/DD/YY): _____/_____/_____ Occupation: !Sport Med. Physician !Family Physician/GP !ER Physician Diagnosis/clinical impression (check both if needed): !Athletic Therapist !Physiotherapist !Other:______!Concussion !Other:______

Treatment plan: !Rest until asymptomatic !Begin RTP steps !Return to full participation !Other:

Conditions of clearance: !Asymptomatic !Complete RTP steps !Other:

ONCE PLAYER IS CLEARED TO RETURN TO UNRESTRICTED COMPETITION: Ofﬁce use only IID:______(MM/DD/YY) Date of clearance : _____/_____/_____ UCDC:______

V.2

127

APPENDIX G: INJURY REPORT FORM (2017-2018)

128

OFFICE USE ONLY: Hockey Study Injury Report Form Injury ID#: ______ Please complete this form for any injury including suspected concussion occurring in hockey (game/practice/dryland, etc.) which receives: Person completing form: ❑Mother ❑Father ❑Player 1) medical attention OR ❑Team designate ❑Other:______2) results in the inability to complete the session in which the injury occurred OR Parent phone#:______3) results in the player missing at least one day of sporting activity Parent email:______1. Player name:______12. This injury involved: 2. Player SSID#:______3. Team #: ______o Sudden onset & contact with another player o Sudden onset & NO contact with another player 4. Today’s date (MM/DD/YY): ______/_____/_____ o Gradual Onset/Overuse (Go to 15) o Unknown (Go to 13) 13. Did you/the player anticipate the contact that resulted in 5. Injury date (MM/DD/YY): ______/_____/______injury? 6. Injury status: oNo oYes o New injury 14. Cause of injury (check all that apply): o Recurrence of injury from this hockey season o Body check: oDelivered oReceived o Recurrence of injury from previous hockey season o Other intentional player contact: 7. Did the player return to play the same game/practice? oElbowing oRoughing oHead contact oCross-checking oNo oYes oNon-hockey injury (Go to 16) oTripping oSlashing oHigh Sticking If yes, how long did they continue to play for (minutes)?______o Unintentional contact with player or equipment 8. At the time of injury, were any of the following worn? o Contact with the environment, NOT another player o o o o o Mouthguard: oUnknown oNo oYes Puck Boards Net Ice Other:______Mouthguard type: oDentist custom-ﬁt oOff the shelf 15. Mechanism of injury (check all that apply): oDirect blow to head: oRight oLeft oFront oBack oTop Brace: oUnknown oNo oYes: oLeft side oRight side oFell & hit head: oBack oForward oSide if yes, worn on: oKnee oAnkle oWrist oOther:______oHit head: oOn boards oOn ice oOn net oOther:______Tape: oUnknown oNo oYes: oLeft side oRight side oNon-head injury if yes, worn on: oKnee oAnkle oWrist oOther:______16. Was a penalty called directly related to the injury event? 9. Have you changed any equipment (since baseline?) oNo oYes oNo oYes oNo baseline - entering study at injury If yes, oBody checking related oStick-related oHead-contact If yes, which? oMouthguard oHelmet oOther:______oFighting oOther:______10. Position playing at time of injury: If yes, o2 min minor oDouble minor o5 min major oForward (Centre) oForward (Wing) oDefense oPenalty shot o10 min misconduct oMatch penalty oGoalie oOther:______oGame misconduct oSuspension: length______11. Injury occurred during: If yes, who received the penalty ? (check all that apply) o Game oInjured player oInjured player’s teammate oOther team a) oRegular season oTournament oPlayoff oExhibition 17. Describe events surrounding injury: b) oWarm-up o1st period o2nd period o3rd period ______o Practice on ice o Other (eg, dryland) Please specify:______

18. Injury location for each type of injury (check all boxes that apply AND circle which side the injury occurred on):

Cut o Fall to ground

Blister o Clutch of head

Joint swelling o Dazed Joint/ligament sprain o Blank look Dislocation o Cut/bleeding on your face Broken bone

Muscle Strain

Tendonitis

Other:______V.2

129

ONLY complete this section once the athlete has fully returned to play AND has completed all injury related care

18. Date of full medical clearance for return to: Normal daily activities (MM/DD/YY): _____/____/_____

Non-contact sports (full participation) (MM/DD/YY): ______/____/_____

Collision/contact sports (full participation) (MM/DD/YY): ______/____/_____

Is the player returning to collision/contact sports? oNo oYes 19. Who provided clearance to return to play? oPhysician oTherapist oCoach oParent oSelf oOther: ______20. Total time parent/guardian missed work as a direct result of the player’s injury: ______days + ______hours oNot working 21. Parent/guardian’s occupation:______oNot working 22. Was an ambulance called? oNo oYes - If yes, did the player ride to the hospital in the ambulance? oNo oYes 23. Was the player admitted to the hospital (other than an emergency department visit)? oNo oYes If yes, primary reason for hospitalization:______# nights in the hospital:______If yes, did the player have surgery in the hospital? oNo oYes - Name or describe the surgery:______24. Did the player see any health care professional(s) for assessment/treatment of this injury? ❑No ❑Yes (check all that apply):

oOn-site ﬁrst aid Total # visits:_____ oPaediatrician Total # visits:_____ oAthletic Therapist Total # visits:_____ oEMT/Paramedic Total # visits:_____ oSurgeon Total # visits:_____ oMassage Therapist Total # visits:_____ oFamily Physician/GP Total # visits:_____ oRadiologist Total # visits:_____ oDentist Total # visits:_____ oER Physician Total # visits:_____ oChiropractor Total # visits:_____ oOther:______Total # visits:______oSport Med. Physician Total # visits:_____ oPhysiotherapist Total # visits:_____

25. Did the player have any tests or receive any other treatment for this injury? oNo oYes If yes, check all that apply:

oMRI # of times:_____ Body part:______oCast # of casts:______Body part:______Type:______oX-ray # of times:_____ Body part:______oBrace # of braces:_____ Body part:______Type:______oCT scan # of times:_____ Body part:______oSplint # of splints:_____ Body part:______Type:______oBone # of times:_____ Body part:______oTaping # of tape rolls:___ Body part:______Type:______scan oCrutches oOther:______26. Did the player take any medications for this injury? oNo oYes If yes, name:______type (eg, oral, injected):______

duration (days):______frequency (eg, # doses/day):______dosage (eg, 200mg):______

HOCKEY STUDY 2013-2018 Player’s Name:

Medical practitioner’s name:______Date (MM/DD/YY): _____/_____/_____ Occupation: oSport Med. Physician oFamily Physician/GP oER Physician Diagnosis/clinical impression (check both if needed): oAthletic Therapist oPhysiotherapist oOther:______oConcussion oOther:______

Treatment plan: oRest until asymptomatic oBegin RTP steps oReturn to full participation oOther:

Conditions of clearance: oAsymptomatic oComplete RTP steps oOther:

ONCE PLAYER IS CLEARED TO RETURN TO UNRESTRICTED COMPETITION: Ofﬁce use only IID:______(MM/DD/YY) Date of clearance : _____/_____/_____ UCDC:______

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APPENDIX H: COMPONENTS OF THE HOCKEY CANADA SKILLS TEST

131

National Skills Standards

& Testing Program

Handbook

132

133

134

National Skills Standards & Testing Program

Setting Up the Stations

6 Station Skills Testing Set-Up

1 2 3 3 3 2 C 10 feet btw pylons 1 1 3

2 C X X X X 3

1 24 feet 24 X X 24 feet C 24 feet 4 G C G * * 5 4 feet 24 feet X X C C X X 6 100 feet

Time Description 60 MIN 6 Station Skills Testing Set Up

Option 1 All 6 stations can be run in one practice. It takes approximately 10 minutes to set up, leaving about 8 minutes per station to complete the testing. During the set up period, players can warm up and be given an overview of how the session will work. Depending how many players there are they can be divided into groups as small as two (1 team on the ice) or as many as 6 (2 teams on the ice). Option 1 requires 6 coaches or testing assistants, one for each test station.

Option 2 3 stations can be run one practice, and another 3 stations can be run the next. Option 2 requires at least 3 coaches or testing assistants.

Key Execution Points (KEP) Use parents to act as recorders when entering the scores on the data sheet. Ensure the necessary equipment is on hand.

(30) Pucks (1) Tape Measure – 100 ft (1) Can of spray paint (3) Stop watches (10) Pylons (6) Clipboards

If players fall or perform the skill incorrectly, give them another chance to complete the skill.

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National Skills Standards & Testing Program

STATION ONE: Forehand / Backhand Passing

1 Station 1

C 24 feet 24 X X 1

Time Description 8 MIN Forehand / Backhand Passing

1 player starts with puck standing on edge of circle, a receiver is standing straight across from the passer near the boards.

The passer makes a total of 10 passes, 5 forehand and 5 backhand.

Receivers are 24 feet from passer. At the point where the receiver is located, place two spray paint dots on the ice 1 foot a part.

The passer skates around the pylon on the forehand side, makes a pass to the receiver, then skates around the pylons to pick up another puck to make another moving pass. 5 passes are made on the forehand then change direction and make 5 passes on the backhand.

The receiver is not scored for pass reception. A successful pass is one that goes through the 2 dots on the ice.

Key Execution Points (KEP)

Score is recorded as number of successful passes out of 5 (5 forehand & 5 backhand) by passer only. There is no time limit. Can split into two groups.

136

National Skills Standards & Testing Program

STATION TWO: Forward Weave Agility Skate

Station 2

C X X X X

G Finish

X X X X

Start 10 feet

Time Description 6 MIN Forward Weave Agility Skate

Start at the blue line, skate forward towards the far pylon and make a tight turn around first pylon. Weave back through the pylons, making a tight turn around the last pylon (closest to start line), and weave back through the pylons, making a tight turn around the last one. Sprint back to the blue line which is both the start and finish line.

The first pylon is 10 feet from blue line. (Starting point)

Pylons are set 10 feet apart.

Key Execution Points (KEP)

This is a timed drill.

Do the test without a puck first, then repeat the test with a puck.

Measure distances for pylon placement and use spray paint to mark the spot. Place a pylon over top of each spray painted dots. This ensures that if a pylon gets knocked off down, it will be easy to replace it to the exact spot.

137

National Skills Standards & Testing Program

STATION THREE: Shooting Accuracy / Shooting Speed (option – speed puck)

Station 3 3 3 2 1 1

24 feet

2 3

24 feet

Time Description 8 MIN Shooting Accuracy

Players line up 24 feet from the boards or net. A standard shooter tutor can be used as the target. Players take 10 forehand shots and 10 backhand shots at the target. 3 points are awarded for hitting the top two corners, 2 points for hitting the five hole and 1 point for hitting the bottom two corners. 30 points is the maximum points to be awarded. NOTE: A series of 5 targets could also be placed on the boards, or a comparable target system to that of a shooter tutor that has 5 shooting areas can also be used.

A way of saving time is to split this station into forehand and backhand stations and have two people recording simultaneously – 1 forehand, and 1 backhand.

Shooting Speed Option

A speed puck is required. After each shot, the speed on the puck is noted with the highest speed of the 10 shots being recorded.

Key Execution Points (KEP)

Have 10 pucks ready for each player to shoot.

Have all players go through on forehand first, then on backhand.

Measure the distances, and use spray paint to mark the spot.

138

National Skills Standards & Testing Program

STATION FOUR: Figure “8” Stickhandling

Station 4

* *

* * 4 feet 4 feet

Time Description 8 MIN Figure “8” Stickhandling

Two spray painted dots, or pucks are placed 4 feet apart.

Each player is timed to see how long it takes to do 5 figure 8’s around the dots with the puck.

Player is stationary, and only the puck does the figure 8’s around the dots.

One complete figure 8 is going around both dots / pucks and crossing the middle starting point.

For players 8 years old and under place the dots 3 feet apart instead of 4.

Key Execution Points (KEP)

This is a timed drill. Use water to freeze pucks in place so they don’t move if touched by the player.

139

National Skills Standards & Testing Program

STATION FIVE: Transition - Agility Skate

Station 5

24 feet start / finish X X 24 feet 24 feet X X 24 feet X X

X X 5

Time Description 8 MIN Transition - Agility Skate

Each player starts on line at the bottom of circle. The player skates forward to far right side pylon, pivots and skates backwards to lower right side pylon.

The player then pivots and skates forward to far left side pylon, pivots and skates backwards to lower left side pylon.

The player then pivots and skates forward to designated line, stops, and then skates forward back to starting line.

Complete the test without a puck. Then complete the test with a puck.

Key Execution Points (KEP)

Players must transition from forward to backward and forward to backward at the pylons.

Measure distances, and use spray paint to mark the spot. Place a pylon over top of each spray painted dot. This will ensure accurate placement of the pylon without having to re- measure when pylons are knocked over.

140

National Skills Standards & Testing Program

STATION SIX: Forward / Backward - Speed Skate

Backwards Station 6 With Pucks

Forwards

100 feet Finish

Time Description 8 MIN Forward / Backward - Speed Skate

Players skate as fast as they can straight ahead, first forwards and then backwards.

The distance is 100 feet.

Measure 100 feet starting at the goal line. Use spray paint to draw a line to indicate the finish line.

Complete first without a puck. Then add a puck for the second trial.

Key Execution Points (KEP)

Complete forward skating without a puck then add a puck. Repeat the test backwards first without a puck and then with a puck.

Encourage players to skate through finish line (discourage players from stopping at the finish line).

141

National Skills Standards & Testing Program

Goaltender Tests

1 2a/b 3 Rebound Control Iron Cross Lateral Movement a. 5 shots on ice b. 5 shots in air 8 Feet G G G 4 x

24 Feet a. Shuffle both ways b. Butterfly slide both ways

Time Description 8 MIN Rebound Control – Iron Cross – Lateral Movement

Rebound control is done from 24 feet out measured from the goal line, 10 shots total are taken. 5 in the air, 5 on the ice. The following point system is used to record score.

1 point for trapping or catching the puck ( possession ) 2 points for deflecting the puck to the corners with elevation. 3 points for rebound back in direction of the shot 4 points for a rebound to the weakside 5 points for a goal (The lower the point total, the better the score ) The Iron Cross is a timed drill with two separate tests. The forward and backward portions are the same, with the difference being the first one utilizes a shuffle to go sideways and the second one uses a Butterfly slide to go sideways. (Based on standardized circle width of 30 feet, if circle is not standard size, then mark off 30 feet distance both vertically and horizontally).

The Lateral Movement test is done by moving sideways 8 feet for 4 repetitions, while keeping the outside pad (slide pad) on the ice the entire time (over and back is counted as 1 repetition). Key Execution Points (KEP)

Can be done anywhere on the ice as part of regular team testing or in a separate session. For Rebound control drill try to ensure the shots are consistent for each goalie. Best to do when the ice is fresh, for less pad friction.

142

APPENDIX I: HOCKEY CANADA SKILLS TEST RECORDING SHEETS

143

ment Move- Lateral (secs) (secs) B. Iron Cross (secs) A. Control GOALTENDER TEST RESULTS Re-bound Bwd Puck Email: Speed w/ Signature #2: Bwd Speed w/o Puck Fwd Speed w/ Puck Fwd Speed w/o Puck tion Puck Transi- Agility w/ tion Agility Transi- w/o Puck 8's Figure TEST RESULTS Shooting Accuracy Fwd Puck Agility Weave w/ Fwd Agility Weave NATIONAL SKILLS STANDARDS & TESTING w/o Puck Fh Bh (secs) (secs) Fh Bh (secs) (secs) (secs) (secs) (secs) (secs) (secs) (points)

( / 5) ( /5) ( /30) ( /30)

Passing Accuracy

Gender Position Date of Test: Test #: Signature #1: Team Name: Coach: Phone: Age Division: Level: Name PERSONAL INFORMATION First Last Skills Testing - Data Recording Sheet NOTE: (Bh=backhand, Fh=forehand) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

144

APPENDIX J: CORRELATION MATRIX OF THE HOCKEY CANADA SKILLS TEST

COMPONENTS

Correlation matrix of each HCST component (n=923 player-seasons)

Fwd. Fwd. Transition Transition Fwd. Fwd. Bwd. Bwd. Drop- agility agility agility agility speed speed speed Speed off without with without with puck without with without with time puck puck puck puck puck puck puck

Fwd. 1.0000 agility without puck Fwd. 0.8547 1.0000 agility with puck Transition 0.7284 0.7545 1.0000 agility without puck Transition 0.6759 0.7705 0.8529 1.0000 agility with puck Fwd. 0.5609 0.5778 0.6732 0.6241 1.0000 speed without puck Fwd. 0.5915 0.6455 0.7417 0.6928 0.8217 1.0000 speed with puck Bwd. 0.6744 0.7033 0.8162 0.7879 0.7198 0.7710 1.0000 speed without puck Bwd. 0.6309 0.7066 0.7633 0.8015 0.6343 0.6998 0.8642 1.0000 Speed with puck Drop-off 0.3943 0.3946 0.4118 0.4033 0.2800 0.3225 0.3621 0.3621 1.0000 time Fwd (forwards); Bwd (backwards) Bolded correlations show HCST components analyzed

145

APPENDIX K: SCATTERPLOTS OF SELECTED HOCKEY CANADA SKILLS TEST

COMPONENTS

146

50 40 30 20 Transition puck: with weave agility 10 4 6 8 10 12 Forward speed with puck:

Scatterplot of transition agility with puck and forward speed with puck

50 40 30 20 Transition puck: with weave agility 10 0 5 10 15 Drop off time:

Scatterplot of transition agility with puck and drop-off time

12 10 8 Forward speed with puck: with speed Forward 6 4 0 5 10 15 Drop off time:

Scatterplot of forward speed with puck and drop-off time

147

APPENDIX L: CRUDE INCIDENCE RATE RATIOS BASED ON SENSITIVITY

ANALYSIS

Incidence rate ratios for game-related injury and concussion by each HCST component (analyzed continuously) based on crude multilevel mixed-effects Poisson regression analyses replacing missing HCST times with the slowest times recorded by age group HCST Component All Injurya Concussiona Transition agility 0.86 (0.79-0.94)† 0.87 (0.77-0.97)† Forward speed 0.55 (0.35-0.87)† 0.77 (0.45-1.30) Drop-off time 0.93 (0.83-1.05) 0.89 (0.75-1.05) aIRRs and corresponding 95% CI based on crude Poisson regression with one random effect at the team level (offset by game- hours); based on 1001 player-seasons. †Statistically significant at p<0.05.

Incidence rate ratios for game-related injury and concussion by each HCST component (analyzed continuously) based on crude multilevel mixed-effects Poisson regression analyses replacing missing HCST times with the fastest times recorded by age group HCST Component All Injurya Concussiona Transition agility 0.87 (0.80-0.95)† 0.88 (0.79-0.98)† Forward speed 0.56 (0.36-0.87)† 0.77 (0.45-1.32) Drop-off time 0.94 (0.82-1.08) 0.95 (0.79-1.13) aIRRs and corresponding 95% CI based on crude Poisson regression with one random effect at the team level (offset by game- hours); based on 1001 player-seasons. †Statistically significant at p<0.05.

148

APPENDIX M: MULTIPLE INCIDENCE RATE RATIOS BASED ON SENSITIVITY

ANALYSIS

Adjusted incidence rate ratios for game-related injury and concussion outcomes based on multiple multilevel Poisson regression analyses replacing missing HCST times with the slowest times recorded by age group All Injurya Concussionb HCST Component Transition agility 0.87 (0.76-0.99)† 0.92 (0.81-1.05) Forward speed 1.02 (0.55-1.90) 1.51 (0.90-2.51) Drop-off time 1.00 (0.86-1.15) 0.95 (0.79-1.13) Age group Under-13 1 (Reference) 1 (Reference) Under-15 0.67 (0.26-1.71) 0.64 (0.23-1.80) Under-18 0.55 (0.19-1.59) 0.77 (0.24-2.47) Year of play First 1 (Reference) 1 (Reference) Second 1.04 (0.26-1.71) 0.80 (0.45-1.44) Third 2.62 (0.79-8.68) 0.55 (0.06-4.70) Position Defence 1.93 (1.02-2.60)† 2.09 (1.20-3.65)† Forward 1 (Reference) 1 (Reference) Body checking policy Permitted 3.34 (1.44-7.75)† 3.05 (1.19-7.84)† Not permitted 1 (Reference) 1 (Reference) Previous injury in the last yearc Yes 1.63 (1.02-2.60)† N/A No 1 (Reference) Previous concussiond Yes N/A 2.43 (1.38-4.28)† No 1 (Reference) Abbreviation: NA, not applicable (based on examining the covariate of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous injury); based on complete case analysis of 797 player-seasons. bIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous concussion); based on complete case analysis of 915 player-seasons. cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. †Statistically significant at p<0.05.

149

Adjusted incidence rate ratios for game-related injury and concussion outcomes based on multiple multilevel Poisson regression analyses replacing missing HCST times with the fastest times recorded by age group All Injurya Concussionb HCST Component Transition agility 0.88 (0.76-1.00) 0.91 (0.80-1.05) Forward speed 0.96 (0.50-1.83) 1.52 (0.89-2.61) Drop-off time 1.09 (0.92-1.30) 1.04 (0.85-1.27) Age group Under-13 1 (Reference) 1 (Reference) Under-15 0.64 (0.25-1.64) 0.63 (0.23-1.77) Under-18 0.52 (0.18-1.54) 0.78 (0.24-2.52) Year of play First 1 (Reference) 1 (Reference) Second 1.03 (0.63-1.67) 0.80 (0.45-1.43) Third 2.55 (0.77-8.42) 0.54 (0.06-4.58) Position Defence 1.86 (1.18-2.91)† 2.00 (1.15-3.51)† Forward 1 (Reference) 1 (Reference) Body checking policy Permitted 3.67 (1.60-8.40)† 3.27 (1.29-8.32)† Not permitted 1 (Reference) 1 (Reference) Previous injury in the last yearc Yes 1.62 (1.01-2.58)† N/A No 1 (Reference) Previous concussiond Yes N/A 2.42 (1.37-4.27)† No 1 (Reference) Abbreviation: NA, not applicable (based on examining the covariate of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous injury); based on complete case analysis of 797 player-seasons. bIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (age group, year of play, position, body checking policy, and previous concussion); based on complete case analysis of 915 player-seasons. cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. †Statistically significant at p<0.05.

150

APPENDIX N: BASELINE CHARACTERISTICS OF PARTICIPANTS IN FEMALE-

ONLY LEAGUES

Baseline characteristics of participants in ‘female-only’ leagues comparing age groups (under- 13, under-15, and under-18) by injury status

Under-13 (ages 11-12) Under-15 (ages 13-14) Under-18 (ages 15-17) Injured Not Injured Injured Not Injured Injured Not Injured (n*=0) (n*=5) (n*=3) (n*=30) (n*=3) (n*=17) Anthropometrics Height, cm, median (IQR) N/A 152.00 162.00 163.50 160.00 170.00 (16.00) (7.00) (28.70) (11.60) (17.40) Weight, kg, median (IQR) N/A 42.50 62.50 53.80 72.80 60.00 (5.50) (76.40) (30.40) (33.60) (24.20) Missing, n (%) N/A 0 (0.00) 0 (0.00) 0 (0.00) 1 (33.33) 0 (0.00) Year of play, n (%) First N/A 4 (80.00) 1 (33.33) 14 (46.67) 2 (66.67) 8 (47.06) Second N/A 1 (20.00) 2 (66.67) 16 (53.33) 1 (33.33) 2 (11.76) Third N/A N/A N/A N/A 0 (0.00) 7 (41.18) Position, n (%) Forward N/A 4 (80.00) 1 (33.33) 20 (66.67) 3 (100.00) 10 (58.82) Defence N/A 0 (0.00) 2 (66.67) 10 (33.33) 0 (0.00) 7 (41.18) Missing N/A 1 (20.00) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) Previous Injurya No N/A 5 (100.00) 0 (0.00) 13 (43.33) 1 (33.33) 6 (35.29) Yes N/A 0 (0.00) 3 (100.00) 16 (53.33) 2 (66.67) 11 (64.71) Missing N/A 0 (0.00) 0 (0.00) 1 (3.33) 0 (0.00) 0 (0.00) Previous Concussionb No N/A 5 (100.00) 1 (33.33) 18 (60.00) 1 (33.33) 7 (41.18) Yes N/A 0 (0.00) 2 (66.67) 12 (40.00) 2 (66.67) 9 (52.94) Missing N/A 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00) 1 (5.88) IQR: interquartile range *Sum of n is 58, given that it is player-season (6 players participated in more than one season). aPrevious injury or concussion 12 months prior to baseline test. bPrevious concussion ever.

151

APPENDIX O: BASELINE HOCKEY CANADA SKILLS TEST COMPONENTS OF

PARTICIPANTS IN FEMALE-ONLY LEAGUES

Baseline HCST components of participants in ‘female-only’ leagues by age group (under-13, under-15, and under-18) and injury status Under-13 (ages 11-12) Under-15 (ages 13-14) Under-18 (ages 15-17) Injured Not Injured Injured Not Injured Injured Not Injured (n*=0) (n*=5) (n*3) (n*=30) (n*=3) (n*=17) HCST Component, median (range) Transition agility N/A 23.81 16.75 17.16 18.60 15.50 (20.91, (16.01, (14.87, (17.90, (14.31, 42.09) 22.37) 33.03) 26.98) 21.50) Forward speed N/A 6.38 5.62 5.48 5.79 5.16 (6.15, (5.44, (4.84, (5.18, (4.78, 8.40) 6.43) 6.50) 5.84) 6.84) Drop-off time N/A 5.63 2.56 3.07 3.00 2.59 (3.18, (2.50, (1.01, (2.96, (1.57, 9.11) 5.09) 10.78) 4.60) 6.37) Q1: first quartile; Q3: third quartile. *Sum of n is 58, given that it is player-season (6 players participated in more than one season).

152

APPENDIX P: BOXPLOTS AND SCATTERPLOTS OF SELECT HOCKEY CANADA

SKILLS COMPONENTS BY INJURY STATUS FOR PARTICIPANTS IN FEMALE-

ONLY LEAGUES

40 35 30 25 20 Transition puck: with weave agility 15 Not injured Injured Boxplot of transition agility with puck and injury status for female participants in ‘female-only’ leagues

40 35 30 25 20 Transition puck: with weave agility 15

0 .2 .4 .6 .8 1 Injured or Uninjured

Scatterplot of transition agility with puck and injury status for female participants in ‘female- only’ leagues (0=not injured; 1=injured)

153

9 8 7 6 Forward speed with puck: with speed Forward 5

Not injured Injured Boxplot of forward speed with puck and injury status for female participants in ‘female-only’ leagues

9 8 7 6 Forward speed with puck: with speed Forward 5

0 .2 .4 .6 .8 1 Injured or Uninjured Scatterplot of forward speed with puck and injury status for female participants in ‘female-only’ leagues (0=not injured; 1=injured)

154

10 8 6 Drop offDrop time: 4 2 0 Not injured Injured Boxplot of drop-off time and injury status for female participants in ‘female-only’ leagues

10 8 6 Drop offDrop time: 4 2 0 0 .2 .4 .6 .8 1 Injured or Uninjured Scatterplot of drop-off time and injury status for female participants in ‘female-only’ leagues (0=not injured; 1=injured)

155

APPENDIX Q: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-15 ICE

HOCKEY PLAYERS BASED ON COMPLETE CASE ANALYSIS

Adjusted incidence rate ratios for game-related injury and concussion outcomes for under-15 ice hockey players by years of body checking experience based on complete case analysis Incidence Rate Ratio (95% CI) Potential Risk All Injurya Injury >7 days of Concussionb Concussion >10 Factor time-lossa days of time-lossb Body Checking Experience 0 Years 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 1 Years 1.16 (0.80, 1.66) 1.22 (0.79, 1.91) 0.87 (0.54, 1.41) 0.99 (0.53, 1.85) 2+ Years 1.47 (0.87, 2.50) 1.53 (0.83, 2.84) 0.75 (0.40, 1.41) 1.02 (0.47, 2.21) Year of play First 1.32 (0.88, 1.99) 1.28 (0.79, 2.09) 0.79 (0.48, 1.29) 0.80 (0.46, 1.61) Second 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) Level of play Elite (top 30%) 1.21 (0.85, 1.73) 1.18 (0.81, 1.73) 0.97 (0.62, 1.50) 0.80 (0.48, 1.34) Sub-elite (lower 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 70%) Player Weight <40 kg 1.48 (0.95, 2.33) 1.06 (0.54, 2.07) 1.93 (1.08, 3.43)* 2.00 (0.93, 4.33) 40<80 kg 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) 80-104 kg 1.26 (0.66, 2.39) 1.14 (0.48, 2.64) 1.24 (0.49, 3.16) 1.30 (0.40, 4.22) Previous injury in the last yearc No 1 (Reference) 1 (Reference) NA NA Yes 1.30 (1.02, 1.66)* 1.35 (0.99, 1.84) Previous concussiond NA NA 1 (Reference) 1 (Reference) No 1.58 (1.12, 2.21)* 1.53 (0.98, 2.40) Yes Position Forward 1 (Reference) 1 (Reference) 1 (Reference) 1 (Reference) Defence 0.98 (0.77, 1.27) 1.08 (0.78, 1.48) 1.18 (0.82, 1.68) 1.43 (0.89, 2.29) Goalie 0.45 (0.25, 0.81)* 0.45 (0.21, 0.97)* 0.70 (0.34, 1.46) 1.07 (0.45, 2.52) Abbreviation: CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and adjusted for covariates (year of play, level of play, player weight, previous injury in the last year, and position); based on 1305 observations. bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (year of play, level of play, player weight, previous concussion, and position); based on 1523 observations. cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit.

156

APPENDIX R: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE

HOCKEY PLAYERS WITH CATEGORIZED WEIGHT

Adjusted incidence rate ratios for game-related injury outcomes for under-18 ice hockey players by years of body checking experience with categorized weight

Outcome Potential Risk Factor All Injurya Injury >7 days of Concussionb time-lossa IRR (95% CI) IRR (95% CI) IRR (95% CI) Body Checking Experience ≤2 Years 1 (Reference) 1 (Reference) 1 (Reference) ≥3 Years 2.63 (1.62, 4.26)† 2.71 (1.53, 4.78)† 2.64 (1.31, 5.29)† Level of play Elite (top 20%) 1 (Reference) 1 (Reference) 0.66 (0.42, 1.05) Sub-elite (lower 80%) 1.45 (1.00, 2.10)† 1.42 (0.96, 2.10) 1.51 (0.95, 2.39) Player Weight ≤63.5 1.24 (0.91, 1.68) 1.25 (0.85-1.83) 0.93 (0.59, 1.47) 63.6-77.0 1 (Reference) 1 (Reference) 1 (Reference) ≥77.1 0.89 (0.63, 1.26) 0.93 (0.60, 1.45) 0.79 (0.47, 1.33) Previous injury in the last yearc No 1 (Reference) 1 (Reference) NA Yes 1.51 (1.16, 1.97)† 1.41 (1.00, 1.98)† Previous concussiond No NA NA 1 (Reference) Yes 1.77 (1.21, 2.57)† Position Forward 1 (Reference) 1 (Reference) 1 (Reference) Defence 1.20 (0.92, 1.57) 1.19 (0.84, 1.67) 1.31 (0.90, 1.91) Goalie 0.89 (0.63, 1.26) 0.82 (0.44, 1.54) 0.94 (0.47, 1.89) Abbreviation: IRR, incidence rate ratio. CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with two random effects: one at a team level and one at a subject level, and adjusted for covariates (level of play, categorized player weight, previous injury in the last year, and position). bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (level of play, categorized player weight, previous concussion, and position). cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. † Statistically significant at p<0.05.

157

APPENDIX S: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE

HOCKEY PLAYERS BASED ON COMPLTE CASE ANALYSIS

Adjusted incidence rate ratios for game-related injury outcomes for under-18 ice hockey players by years of body checking experience based on complete case analysis

Outcome Potential Risk Factor All Injurya Injury >7 days of Concussionb time-lossa IRR (95% CI) IRR (95% CI) IRR (95% CI) Body Checking Experience ≤2 Years 1 (Reference) 1 (Reference) 1 (Reference) ≥3 Years 2.64 (1.67, 4.18)† 2.86 (1.54, 5.27)† 2.49 (1.16, 5.37)† Level of play Elite (top 20%) 1 (Reference) 1 (Reference) 1 (Reference) Sub-elite (lower 80%) 1.43 (0.95, 2.14) 1.38 (0.89, 2.14) 1.55 (0.90, 2.67) Player Weight 0.99 (0.98, 1.00) 0.99 (0.98, 1.00) 1.00 (0.98, 1.02) Previous injury in the last yearc No 1 (Reference) 1 (Reference) NA Yes 1.75 (1.25, 2.44)† 1.66 (1.12, 2.47)† Previous concussiond No NA NA 1 (Reference) Yes 1.95 (1.28, 2.98)† Position Forward 1 (Reference) 1 (Reference) 1 (Reference) Defence 1.16 (0.83, 1.62) 1.15 (0.74, 1.77) 1.09 (0.71, 1.69) Goalie 0.75 (0.41, 1.40) 0.97 (0.46, 2.05) 0.93 (0.44, 1.97) Abbreviation: IRR, incidence rate ratio. CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with two random effects: one at a team level and one at a subject level, and adjusted for covariates (level of play, player weight, previous injury in the last year, and position); based on 793 observations. bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (level of play, player weight, previous concussion, and position); based on 926 observations. cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. † Statistically significant at p<0.05.

158

APPENDIX T: ADJUSTED INCIDENCE RATE RATIOS FOR UNDER-18 ICE

HOCKEY PLAYERS INCLUDING YEAR OF PLAY

Adjusted incidence rate ratios for game-related injury outcomes for under-18 ice hockey players by years of body checking experience with year of play

Outcome Potential Risk Factor All Injurya Injury >7 days of time- Concussionb lossa IRR (95% CI) IRR (95% CI) IRR (95% CI) Body Checking Experience ≤2 Years 1 (Reference) 1 (Reference) 1 (Reference) ≥3 Years 3.20 (1.92, 5.35)† 3.13 (1.71, 5.73)† 3.79 (1.84, 7.80)† Year of play First 1.43 (0.95, 2.15) 1.29 (0.80, 2.10) 1.95 (1.10, 3.46)† Second 1.05 (0.73, 1.50) 1.02 (0.66, 1.59) 1.06 (0.61, 1.85) Third 1 (Reference) 1 (Reference) 1 (Reference) Level of play Elite (top 20%) 1 (Reference) 1 (Reference) 1 (Reference) Sub-elite (lower 80%) 1.55 (1.08, 2.24)† 1.50 (1.01, 2.23)† 1.65 (1.06, 2.59)† Player Weight 0.99 (0.98, 1.00) 0.99 (0.98, 1.01) 1.00 (0.98, 1.02) Previous injury in the last yearc No 1 (Reference) 1 (Reference) NA Yes 1.51 (1.16, 1.96)† 1.41 (1.00, 1.98)† Previous concussiond No NA NA 1 (Reference) Yes 1.75 (1.20, 2.55)† Position Forward 1 (Reference) 1 (Reference) 1 (Reference) Defence 1.18 (0.90, 1.54) 1.17 (0.83, 1.66) 1.27 (0.87, 1.85) Goalie 0.68 (0.40, 1.15) 0.81 (0.43, 1.51) 0.90 (0.45, 1.80) Abbreviation: IRR, incidence rate ratio. CI, confidence interval. NA, not applicable (based on examining the risk factor of interest for all previous injury for injury definitions and for previous concussion for concussion definitions). aIncidence rate ratios and corresponding 95% CI based on multiple multilevel Poisson regression analysis offset for exposure game-hours, with two random effects: one at a team level and one at a subject level, and adjusted for covariates (year of play, level of play, player weight, previous injury in the last year, and position). bIncidence rate ratios and corresponding 95% CI based on multiple mixed effects Poisson regression analysis offset for exposure game-hours, with a random effect at a team level, and covariates (year of play, level of play, player weight, previous concussion, and position). cThe covariate “previous injury in the last year” includes any concussion that occurred in the previous 12 months. dThe covariate “previous concussion” includes any concussion without a date limit. † Statistically significant at p<0.05.

159

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Licensed Content Author Willem van Mechelen et al

Licensed Content Date Oct 23, 2012

Type of Use Thesis/Dissertation

Requestor type academic/university or research institute

Format print and electronic

Portion ﬁgures/tables/illustrations

Number of 1 ﬁgures/tables/illustrations

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3/25/2021 RightsLink Printable License Will you be translating? no

Circulation/distribution 1 - 29

Author of this Springer no Nature content

Youth Hockey Related Injury and Concussion: Informing Title Prevention Through Modiﬁable Risk Factors

Institution name University of Calgary

Expected presentation Apr 2021 date

Portions Figure 1: The sequence of prevention of sport injuries

Requestor Location

Canada Attn: Mr. Paul Eliason

Total 0.00 CAD

Terms and Conditions

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Scope of Licence Duration of Licence Post on a website 12 months Presentations 12 months Books and journals Lifetime of the edition in the language purchased

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3/25/2021 RightsLink Printable License homepage. Our required acknowledgement format is in the Appendix below.

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Appendix 1 — Acknowledgements:

For Journal Content: Reprinted by permission from [the Licensor]: [Journal Publisher (e.g. Nature/Springer/Palgrave)] [JOURNAL NAME] [REFERENCE CITATION (Article name, Author(s) Name), [COPYRIGHT] (year of publication)

For Advance Online Publication papers: Reprinted by permission from [the Licensor]: [Journal Publisher (e.g. Nature/Springer/Palgrave)] [JOURNAL NAME] [REFERENCE CITATION (Article name, Author(s) Name), [COPYRIGHT] (year of publication), advance online publication, day month year (doi: 10.1038/sj.[JOURNAL ACRONYM].)

For Adaptations/Translations: Adapted/Translated by permission from [the Licensor]: [Journal Publisher (e.g. Nature/Springer/Palgrave)] [JOURNAL NAME] [REFERENCE CITATION (Article name, Author(s) Name), [COPYRIGHT] (year of publication)

Note: For any republication from the British Journal of Cancer, the following credit line style applies:

Reprinted/adapted/translated by permission from [the Licensor]: on behalf of Cancer Research UK: : [Journal Publisher (e.g. Nature/Springer/Palgrave)] [JOURNAL NAME] [REFERENCE CITATION (Article name, Author(s) Name), [COPYRIGHT] (year of publication)

For Advance Online Publication papers: Reprinted by permission from The [the Licensor]: on behalf of Cancer Research UK: [Journal Publisher (e.g. Nature/Springer/Palgrave)] [JOURNAL NAME] [REFERENCE CITATION (Article name, Author(s) Name), [COPYRIGHT] (year of publication), advance online publication, day month year (doi: 10.1038/sj. [JOURNAL ACRONYM])

For Book content: Reprinted/adapted by permission from [the Licensor]: [Book Publisher (e.g. Palgrave Macmillan, Springer etc) [Book Title] by [Book author(s)] [COPYRIGHT] (year of publication)

Other Conditions:

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