Force Measurement and Ankle Motion of the Forward Skating and Crossovers with a Standard Hockey Skate and a Modified

Force measurement and ankle motion of the forward skating and crossovers with a standard hockey skate and a modified

hockey skate

Xavier Robert-Lachaîne

Department of Kinesiology and Physical Education

McGill University, Montreal

Quebec, Canada

August 2010

A thesis submitted to McGill University in partial fulfillment of the requirements of

the degree of Masters of Science

STATEMENT OF ORIGINALITY

All material presented in this thesis contains original work completed by the author with the help of McGill’s biomechanics laboratory, except external contributions via references where noted. It is the belief of the author that the material presented contributes to analysis of the kinetics and kinematics of ice hockey skating, as well providing insights into the impact of hockey skate design modifications on skating performance.

ACKNOWLEDGEMENTS

I would like to thank Dr. René Turcotte, my supervisor, for giving me direction in the writing of this thesis. His thoughtful advices were based on his experience and answered most of my questions. He was always available to discuss about any aspect of the project. René made sure to give structure to the thesis and assisted me with writing in English, which is my second language. It was fun to work with René who often relaxes the working environment with hockey comments.

The contribution of David Pearsall was also considerate. He always put the biomechanical perspective in thought. The technological aspect of the project was evolving a step further with his notable interventions. David insured to get to maximum out of my potential by discussing about the improvement of the methodology and setting deadlines to accomplish specified objectives.

The presence of Phil Dixon in the laboratory was an immense source of support. He was often the first person to assist me with any kind of problems during my project. His competence in various fields made him a perfect teacher.

Without your help Phil, I would still be in the laboratory writing Matlab functions.

Thanks!

The help of Yannick Michaud-Paquette was always appreciated. He was ready to assist me whenever he could. Yan made lunchtime entertaining with the various TV shows that brought people together.

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Sylvain Gaudet gave me a good support during the construction of the lever and the subsequent calibration. He showed great interest in the project and helped during the data collection. I would also like to thank Adrian De Vincenzo who assisted me for testing during the pilot studies.

Ryan was a great help; his expertise in the electronics gave more professionalism to my project.

Thanks to Jonathan, Ashley, Zubair, Antoine and Rob for their help with the instrumentation of the skates, testing or data collection.

Thanks to Pat and Joe Leamy for providing me with ice times for my data collection. Thanks to McGill Redmen hockey players and other hockey players who freely participated in this study and gave interest throughout.

The partnership with Bauer hockey was important for this thesis; they provided the laboratory with hockey equipment, especially the DROM skates.

Chris Langevin and Ken Covo also gave depth to the project.

Finally, the support of my family was constant throughout my graduate studies. Specifically, my father Serge who gave me the desire to pursue my interests in life and my wife Pierina who is always by my side whatever happens.

Thanks to my newly born Selena for all the love you bring.

CONTRIBUTION OF AUTHORS

The following thesis will be submitted for a publication. The paper will be co-authored by Dr. René Turcotte and Dr. David Pearsall; I will be the primary author. I was responsible of conducting the research and writing the thesis. I have instrumented and calibrated the skates, collected the data, processed the data and made a statistical analysis. I was writing the chapters involving introduction, review of literature, methods, results and discussion. Dr. Turcotte was providing comments throughout the writing of the thesis and insured a coherent English. He helped defining the rationale of the study and the experimental design and suggested articles to discuss. Dr. Pearsall was influential in the development of the methods, he also made comments on the chapters and helped in the structure of the ideas.

ABSTRACT

Dynamic forces were measured during skating directly on-ice using a Bauer

One95 and a second One95 with a modified tendon guard and eyelet configuration (DROM). The intent was to determine if mechanical differences exist in push-off force and ankle kinematics between the two skates. The right skate of each type was instrumented with a calibrated force transducer system to measure medial-lateral and vertical forces during ice skating. In addition, a goniometer was installed about the ankle to measure kinematics during skating.

The ten subjects executed three skills: forward skating and forward crossovers in both directions. The DROM skate demonstrated significant gains in plantarflexion and net plantar-dorsiflexion ROM. In general this was not reflected in greater kinetic output except for greater medial-lateral forces. Total peak force occurred later during plantarflexion, suggesting that the increased ROM resulted in a more prolonged force generation during a given skating stride. The 14 to 20% increases in work and power output while wearing the DROM skates did not translate into improved times for these skating tasks. These apparently contradictory findings may well be attributed to lack of player familiarity with the modified skate’s greater ankle mobility. Hence, to determine the DROM skate’s true performance benefits, a longitudinal study of a cohort of players training with the DROM skate is required.

ABRÉGÉ

Les forces de patinage ont été mesurées directement sur glace avec un

Bauer One95 (Régulier) et un second One95 qui détenait un protecteur du tendon d’Achille modifié et une configuration différente des œillets pour lacets (DROM).

Le but était de déterminer si des différences mécaniques existent dans la force de propulsion et la cinématique de la cheville entre les deux modèles. Le patin droit

était instrumenté d’un système calibré d’estimation de la force qui permettait la mesure dynamique des forces durant le patinage. De plus, un goniomètre était installé autour de la cheville pour mesurer la cinématique durant le patinage. Les dix sujets accomplissaient le patinage avant et le croisé-avant dans les deux directions. Le patin DROM démontrait des gains significatifs en flexion plantaire et amplitude de mouvement frontale. En général, ces résultats ne se sont pas reflétés en bénéfices cinétiques, à l’exception des forces médio-latérales. La force totale maximale était délayée avec le DROM, suggérant une production de force prolongée qui résultait de l’amplitude de mouvement supplémentaire. Les augmentations de 14 à 20% en travail et puissance avec le DROM ne se sont pas traduites en amélioration de vitesse. Ces trouvailles apparemment contradictoires pourraient être attribuables au manque d’accoutumance des joueurs avec le patin modifié qui procure une mobilité supérieure à la cheville. Afin de déterminer le potentiel optimal du DROM sur la performance, une étude longitudinale avec un groupe de joueurs s’entraînant avec le DROM est nécessaire.

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TABLE OF CONTENTS

STATEMENT OF ORIGINALITY ...... II

ACKNOWLEDGEMENTS ...... III

CONTRIBUTION OF AUTHORS ...... V

ABSTRACT...... VI

ABRÉGÉ...... VII

TABLE OF CONTENTS ...... VIII

LIST OF FIGURES ...... XI

LIST OF TABLES ...... XIV

CHAPTER 1 – INTRODUCTION ...... 1 1.1 THESIS OUTLINE ...... 1 1.2 NOMENCLATURE, OPERATIONAL DEFINITIONS AND ABBREVIATIONS ...... 1 1.3 RATIONALE ...... 6 1.4 PURPOSE ...... 12 1.5 HYPOTHESES ...... 12 1.6 LIMITATIONS ...... 13 1.7 DELIMITATIONS...... 13

CHAPTER 2 – REVIEW OF LITERATURE ...... 15 2.1 HISTORY OF HOCKEY ...... 15 2.1.1 Evolution of the skate ...... 15 2.2 HOCKEY SKILLS CLASSIFICATION ...... 16 2.2.1 Internal factors affecting performance...... 17 2.2.2 External factors affecting performance...... 19 2.2.2.1 Air friction...... 19 2.2.2.2 Ice friction...... 20

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2.2.2.3 Skate properties ...... 22 2.2.2.3.1 Boot stiffness...... 22 2.2.2.3.2 Range of motion (ROM) ...... 23 2.2.2.3.3 Blade edge...... 24 2.3 SKATING MECHANICS ...... 25 2.3.1 Linear movement ...... 25 2.3.2 Angular movement ...... 27 2.3.3 Starts ...... 29 2.4 SKATING ANALYSIS ...... 30 2.4.1 Kinematics...... 31 2.4.2 Kinetics ...... 35 2.4.3 Pressure distribution ...... 40 2.4.4 Task analysis ...... 42 2.4.5 Physiology of skating...... 44 2.4.6 Muscle coordination...... 46 2.4.7 Prediction models...... 49

CHAPTER 3 – METHODS ...... 53 3.1 SUBJECTS ...... 53 3.2 EXPERIMENTAL PROTOCOL ...... 53 3.2.1 Environment ...... 53 3.2.2 Setup...... 54 3.2.3 Pre-testing ...... 57 3.2.4 Testing ...... 57 3.2.4.1 Forward skating ...... 58 3.2.4.2 Forward crossovers...... 59 3.3 EQUIPMENT ...... 60 3.3.1 Instrumented force transducer system ...... 60 3.3.2 Data acquisition...... 62 3.3.3 Calibration of the force transducer system ...... 63 3.3.3.1 Theory for calibration ...... 67 3.3.4 Goniometry ...... 73 3.4 DATA PROCESSING ...... 75

3.5 DATA ANALYSIS ...... 80 3.6 STATISTICAL ANALYSIS ...... 81 3.6.1 Power analysis...... 81 3.7 ETHICAL CONSIDERATIONS ...... 82

CHAPTER 4 – RESULTS ...... 84 4.1 TIME MEASURES ...... 84 4.2 KINEMATICS ...... 85 4.2.1 Inversion / Eversion...... 86 4.2.2 Dorsiflexion / Plantarflexion...... 88 4.2.3 Kinematics at peak force...... 90 4.3 KINETICS ...... 92 4.3.1 Vertical force ...... 92 4.3.2 Total force ...... 93 4.3.3 Medial-lateral force...... 95 4.3.4 Impulse...... 96 4.3.5 Work and power ...... 97 4.4 COMPLETE RESULTS ...... 98

CHAPTER 5 – DISCUSSION ...... 100 5.1 TIME MEASURES ...... 100 5.2 KINEMATICS ...... 100 5.3 KINETICS ...... 103 5.4 FUTURE DIRECTIONS ...... 111 5.5 CONCLUSION ...... 112

REFERENCES ...... 114

APPENDIX 1 – INFORMATION AND CONSENT DOCUMENT . 121

APPENDIX 2 – PLAYER PROFILE FORM ...... 124

APPENDIX 3 – MANOVAS TABLES...... 125

LIST OF FIGURES

Figure 1 – Structural components of a standard ice hockey skate...... 5 Figure 2 – Orientation of the forces during skating...... 5 Figure 3– Skating classification (from Pearsall, Turcotte and Murphy, 2000). ...17 Figure 4 – Ankle kinematics during forward skating: (A) Plantar/dorsiflexion. (B) Inversion and eversion (from Pearsall et al., 2001)...... 34 Figure 5 – Positioning of the strain gauges on the plastic blade holder (from Lamontagne and Doré, 1983)...... 38 Figure 6 – Calibration setup: (A) Vertical loading. (B) Medial-lateral loading (from Lamontagne and Doré, 1983)...... 38 Figure 7 – Kinetics of a representative subject for the right skate, including contact time and stride time information (from Stidwill, 2009)...... 40 Figure 8 – (A) Medial and posterior view of the Regular skate (B) Medial and posterior view of the DROM skate with the flexible tendon guard...... 54 Figure 9 – Picture of the goniometer placement on the right foot (A) Previous studies placement: upper part behind the shank and lower part behind the calcaneus inside the boot (B) Placement in the present study: upper part on the medial side of the shank and lower part on the medial outside of the boot...... 56 Figure 10 – The path of the skater during the three tasks: forward skating (fs), crossovers inside foot (coi), crossovers outside foot (coo). The arrows represent the skating direction, the orange circle the pylons and the green triangles the camera placement...... 59 Figure 11 – Picture of the strain gauges on a DROM skate. The arrows indicate which strain gauges are shown. The lateral strain gauges are at the same position as the anterior gauges, but on the opposite side...... 60 Figure 12 – (A) Circuit board design (2:5 scale). (B) Resistors and dummy strain gauge under the board (2:5 scale)...... 62 Figure 13 – Lateral calibration setup (top view)...... 64 Figure 14 – Vertical calibration setup. (A) Wooden foot. (B) Real setup. (C) Model setup...... 66

Figure 15 – Linear relationship of strain to force...... 68 Figure 16 – Cross-correlation example...... 69 Figure 17 – Example of a comparison of the calibrated strain signal and the force signal...... 59 Figure 18 – Representative bodyweight trial from a subject...... 70 Figure 19 – Typical bodyweight trial from the investigator...... 72 Figure 20 – SG series twin axis electrogoniometer...... 74 Figure 21 – FFT of strain gauge data (the cutoff frequency was set at 6 Hz). ..75 Figure 22 – Force data during a crossovers (inside foot) trial with the Regular skate...... 77 Figure 23 – Force data during a forward skating trial with the Regular skate. ...77 Figure 24 – Kinematics of the ankle during a forward skating trial with the DROM skate...... 80 Figure 25 – Contact time (mean ± SD) in the three skills by skate types...... 84 Figure 26 – Stride rate (mean ± SD) in the three skills by skate types...... 85 Figure 27 – Time to completion (mean ± SD) in the three skills by skate types...... 85 Figure 28 – Mean inversion (± SD) in the three skills by skate types (* p < 0.05)...... 87 Figure 29 – Maximal eversion (± SD) in the three skills by skate types...... 87 Figure 30 – Inversion and eversion range of motion (± SD) in the three skills by skate type...... 88 Figure 31 – Mean dorsiflexion (± SD) in the three skills by skate types (* p < 0.05)...... 89 Figure 32 – Maximal plantarflexion (± SD) in the three skills by skate types (* p < 0.05)...... 89 Figure 33 – Mean plantar/dorsiflexion ROM (± SD) in the three skills by skate types (* p < 0.05)...... 90 Figure 34 – Mean eversion angle at peak force (± SD) in the three skills by skate types...... 90 Figure 35 – Mean plantarflexion angles at peak force (± SD) in the three skills by skate types (* p < 0.05)...... 91

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Figure 36 – Mean plantarflexion angles at peak force (± SD) in the forward skating (task), and phases of acceleration and constant speed by skate types (* p < 0.05)...... 91 Figure 37 – Mean vertical average force (± SD) in the three skills by skate types...... 93 Figure 38 – Mean vertical peak force (± SD) in the three skills by skate types...... 93 Figure 39 – Mean total average force (± SD) in the three skills by skate types...... 94 Figure 40 – Mean total peak force (± SD) in the three skills by skate types. ....94 Figure 41 – Mean medial-lateral (+ve Medial; -ve Lateral) average force (± SD) in the three skills by skate types (* p < 0.05)...... 95 Figure 42 – Mean medial-lateral (+ve Medial; -ve Lateral) peak force (± SD) in the three skills by skate types (* p < 0.05)...... 96 Figure 43 – Mean impulse (± SD) in the three skills by skate types...... 96 Figure 44 – Mean work (± SD normalized to bodyweight) in the three skills by skate types...... 97 Figure 45 –Mean power (± SD normalized to bodyweight) in the three skills by skate types...... 97

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LIST OF TABLES

Table 1 – Calibration results for the Regular skates ...... 70 Table 2 – Calibration results for the DROM skates...... 71 Table 3 – Biometrics Ltd. electrogoniometer specifications ...... 74 Table 4 – Description of the variables...... 81 Table 5 – Complete results including means with standard deviations in parentheses and significance between skate types...... 98 Table 6 – MANOVA for forward skating kinetics ...... 125 Table 7 – MANOVA for the crossovers (outside foot) kinetics...... 127 Table 8 – MANOVA for the crossovers (inside foot) kinetics ...... 128 Table 9 – MANOVA for the forward skating kinematics...... 129 Table 10 – MANOVA for the crossovers (outside foot) kinematics...... 131 Table 11 – MANOVA for the crossovers (inside foot) kinematics ...... 132

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CHAPTER 1 - INTRODUCTION

1.1 THESIS OUTLINE

The purpose of this thesis is to compare a standard ice hockey skate to a modified one by means of a kinetic and kinematics analysis of the ankle during skating.

Chapter 1 presents the thesis outline, the definition of the nomenclature, the rationale for this study, purpose and hypotheses, limitations and delimitations of the study and a description of the variables investigated. Chapter 2 provides a review of literature related mostly to the history of hockey and the skate, the classification of hockey skills and factors affecting performance, the skating mechanics and the skating analysis including kinematics and kinetics. Chapter 3 defines the methodology of the thesis research. This section includes the presentation of the subjects, a complete and detailed research protocol, the explanation of all equipment utilized including the calibration procedure, the statistical methods and the definition of the data acquisition and processing.

Chapter 4 presents the results of the study and chapter 5 serves as the discussion of the previously presented results.

1.2 NOMENCLATURE, OPERATIONAL DEFINITIONS AND ABBREVIATIONS

The following are nomenclature, operational definitions, and abbreviations used throughout this thesis.

Achilles tendon guard: Rear upper part of the skate that protects the Achilles

tendon and creates a leverage point for the push-off (figure 1).

Blade holder: The plastic molding, which holds the skate blade or runner (figure

1).

Contact Time: The total time that the skate is in contact with the ice surface.

DROM skate: Modified hockey skate including a flexible Achilles tendon guard and

modified eyelet placement.

Electrogoniometers (goniometers): The instrument with which joint angle

measures will be captured (Biometrics Ltd. Gwent, UK).

Eyelets: Spaces on the top of skate that allow laces to fasten and adjust tension

of the skate laces (figure 1).

Force Transducer: A device used to estimate forces based on strains exerted by

an external load (Winter, 2005).

Heel counter: Rear lower part of skate that protects the heel and prevents the

foot from moving inside the skate (figure 1).

Impulse: The change in momentum produced by an external force, defined as the

integral of force with respect to time (Winter, 2005).

Kinematics: The area of biomechanics, which describes movement without

consideration of the forces leading to that motion (Winter, 2005).

Kinetics: The area of biomechanics concerned with the forces that produce given

movements (Winter, 2005).

Medial-Lateral Force (ML): A force applied by a subject or skater perpendicular to

the orientation of the skate’s blade (figure 2).

Skate runner: The only part of the skate that comes in contact with the ice

allowing push-off and glide on the ice (figure 1).

Padded tongue: The upper front part of the skate that covers and supports the

lower part of the tibia (figure 1).

Power: The rate at which work is performed.

Range of Motion (ROM): The difference between the maximum and minimum

angle attained by a body joint.

Regular skate: Standard modern hockey skate

Rigid sole: Solid point of attachment of the blade holder (figure 1).

Skate boot: A molded skate boot that forms the upper part of the skate (figure

1).

Skating Stride: The biphasic motion of skating, which begins when the foot

contacts the ice with the blade and progresses through glide, push-off, and

recovery of the ipsi-lateral limb (Upjohn et al., 2008).

Strain Gauges: The equipment used to convert the mechanical deformations of

materials into an electrical signal.

Stride Phases:

1) Initial Contact: Initial blade to skating surface contact.

2) Glide: Following initial contact, the phase of the stride in which no propulsion

is occurring. The orientation of the blade of the skate on the ice is guiding

the movement of the body.

3) Push-Off: Following the glide, the phase in which the blade turns outward

(external rotation), creating propulsion from extension of the hip, knee,

and ankle.

4) Swing: Flexion of the non-weight bearing limb, allowing it to swing forward to

begin the next stride.

Toe box: The front part of the skate that protects the toes (figure 1).

Total Force (TF): The summation of vertical and horizontal (medial-lateral) force

vectors estimated from strain gauge readings (figure 2).

Vertical Force (V): A force applied by a skater parallel to the orientation of the

skate’s blade estimated from strain gauge readings (figure 2).

Work: The amount of energy transferred by a force acting through a distance

(Work = Force x Distance).

Padded tongue Achilles tendon guard Eyelets

Toe box Boot

Heel counter

Rigid sole

Blade holder

Metal blade

Figure 1 – Structural components of a standard ice hockey skate

Vertical Total component Reactive Force (ice on skate)

Horizontal Horizontal component component

(Lateral) (Medial) Total Applied Force Figure 2 – Orientation of the forces during skating (skate on ice)

1.3 RATIONALE

Ice hockey research has focused on the physiology of training and conditioning, skill development, safety and injury prevention while paying little attention to biomechanics (Pearsall, Turcotte and Murphy, 2000). In striving for performance improvements, manipulation of internal factors of the participants are more often considered than external factors such as equipment and environment. Historically, the evolution of the skate has been modified via the use of improved materials and changing the design and fit of the skate

(Goodman, 1882; Minetti, 2004). The research conducted on the klapskate in speed skating has demonstrated the importance of skate design on skating performance. Although speed skating skills are considered “closed” and ice hockey is a game that consists of a variety of skills and is considered “open”, skating mechanics of the two sports are similar, especially for forward skating and crossovers. Many experts consider skating skills the most important in ice hockey (Renger, 1994; Twist and Rhodes, 1993; Bracko, 2004). Forward skating performance is dependent on the ability to accelerate in two or three strides, and short periods of high intensity skating (Marino, 1983; Bracko et al., 1998;

Montgomery et al., 2004).

Ingen Schenau et al. (1985) showed that speed skaters appear to lift the push-off skate from the ice at a knee angle of 160° during forward skating. Since this phenomenon is not observed in running or jumping, the absence of plantarflexion is a likely explanation for the difference when comparing these

different skills. Ingen Schenau et al. (1985) hypothesized that extension of the knee was completed only after the foot lifted off the ice. This hypothesis was confirmed by Houdjik et al. (2000) who compared the push-off mechanics in speed skating of conventional skates and klapskates. Ice friction, body kinematics and electromyographic data of the lower limb were similar for the two skates. But, a difference in power during the last 50 m of the push-off as measured by the strain gauges technology (Jobse et al., 1990) was observed between the two skate types. With the klapskate, this last portion of the push- off force was directed perpendicular to the blade by generating greater knee extension and ankle plantarflexion torque. The long length of the blade makes it impossible for the conventional skate to direct the force perpendicularly to the ice. The increase in mean power output of 10% with the klapskate can be explained by an increase in work per stroke (6%) and higher stroke frequency

(4%) (Houdjik et al., 2000). The innovation of the klapskate demonstrated the importance of the ankle range of motion (ROM) for an increased power generation with the contribution of the calf muscles in the push-off in speed skating.

In ice hockey, one of the oldest studies done on the kinematics of skating identified several aspects of the skating stride that remain key observations to this day (Marino, 1977). It was noted in this study that ice skating consisted of a bi-phasic movement pattern including single and double support. The double support phase is represented by the propulsion, while the single support phase

consists of the gliding. The horizontal velocity produced by skating can be determined by the product of stride rate and stride length. Marino (1977) also analyzed the kinematics of ice skating at different speeds in order to quantify and compare the temporal aspects of skating. The results showed that as speed increases, stride length remained fairly constant while stride rate increases.

These results suggest that increasing speed on ice is due more to the number of times force is applied rather than the amount of force produced during propulsion. Single and double support times were inversely related to stride rate and the time spent in single support with increasing speed. The acceleration occurring in the middle of single support was marked by external rotation of the thigh and simultaneous initial extension of the hip and knee (Marino, 1979).

When the swinging limb hits the ice it provided stability and balance of the body and propulsion continued through full knee extension, hyperextension of the hip and finished with plantarflexion of the ankle.

Hoshizaki, Kirchner and Hall (1989) evaluated different hockey skates including a test skate. The test skate was manufactured as a regular skate with the ankle support above the subtalar joint removed (resulting in no ankle support above the malleolus). Eight performance tests were timed and ROM was calculated statically and dynamically. It was thought that removing ankle supports from hockey skates would not significantly alter the general kinematics of the ankle in the frontal and sagittal planes. Results from the test skate showed a small increase in the pronation angle, which was thought to reflect a

larger degree of muscular control. This design change could also potentially prevent the forces generated from the hip and knee extension from collapsing the ankle in the skate. With proper structural alignment of the mid-tarsal joint all the way to the hip joint, the skater theoretically could benefit from a more solid lever for propulsion (Hoshizaki, Kirchner and Hall, 1989). The authors concluded that the conventional skate boot restricts ROM at the ankle and that a skate must be considered flexible or rigid in each plane separately (frontal and sagittal).

The results of this study implied a potentially important impact of skate design on the kinematics and kinetics of skating in ice hockey.

The proper execution of the skating push-off in ice hockey requires the skate to glide forward. Thus, the point of application of force is continuously displaced relative to the ice. The propulsive force (reaction force from the ice) is perpendicular to the trajectory of the skate. As the center of gravity is displaced forward, the calf muscles are activated to maintain equilibrium. This causes plantarflexion the moment the reaction force on the blade drops. The effect of the push-off is greater if the angle between the blade and the ice is smaller and optimal technique requires a push forward rather than upward (Ingen Schenau et al., 1989). Speed skaters have been taught to sit and push-off on the back part of the skate as the calf muscles contributed to the maintenance of stability.

Ingen Schenau and Bakker (1980) showed that at high speeds during speed skating, the skater cannot push-off on the ice as quickly as the skater is gliding on the ice. Prolonging push-off would result in a negative rather than a

positive impulse. This study suggested that ankle plantarflexion during the last portion of the stride heel-off to toe-off (HO-TO) is of decreasing importance as the speed increases. But this analysis was done with conventional speed skates and under those conditions (ice friction) a false impression of the importance of plantarflexion is conveyed by the study results. With conventional skates, the plantar flexors contributed mostly at the start of the race. This study shows the importance of skate design on the skating technique, and consequently performance.

According to Humble and Gastwirth (1988) who reviewed the biomechanics of forward skating in ice hockey, striding in skating is not done with the entire blade of the skate flat on the ice. In most skating manoeuvres the inside or outside edge of the blade will be used. During the gliding phase, the blade is on the inside edge to allow a better grip on the ice. Also, the angle of propulsion must decrease or the time for leg extension must decrease to gain speed (Lariviere, 1968). These values are consistent with work per stride and stride rate that determine speed skating performance (Houdjik et al., 2000). A better angle of propulsion will lead to greater work per stride as the medial-lateral component of the total force will increase. These suggestions (Houdjik et al,

2000) also imply that freedom of movement is important to optimize orientation of the lower leg presumably improving its mechanical function during striding and perhaps other skating manoeuvres.

Forward acceleration is often used in ice hockey and frequently a linear skating trajectory is used in races for the puck. Two general skating patterns can be described in many situations on ice. The first is an acceleration phase and is typically the first three strides and the second phase, which often begins on or about the fourth stride, occurs when a skater attains maximum skating velocity.

This second phase is considered to represent a typical forward skating stride

(Hoshizaki, 1987). A skating stride also has a contact period and this is divided in two segments: from touchdown to heel-off (TD-HO) and from HO-TO. The TD-

HO phase accounts for 80% of the contact period and the ankle moves in dorsiflexion and pronation. The HO-TO phase accounts for 20% of the contact period and the skater pivots on the anterior portion of the blade with hip external rotation and ankle plantarflexion and supination, which creates the toe of the skate to push back into the ice (Humble and Gastwirth, 1988). The ankle ROM is important in this second phase for power generation; the skate design will determine the contribution of plantarflexion and supination to the stride.

Thus, taken together the previous research provides a rationale for examining potential performance improvements that can be achieved with skate design modifications. Specifically, design changes that can offer biomechanical advantage may in turn result in improved skating performance.

1.4 PURPOSE

The purpose of this study is to determine the effect of a skate with a modified boot design (designed specifically to permit increased dorsiflexion and plantarflexion) on skating mechanics. To this end, using the Bauer One95 skate model (Bauer Hockey Corp.), a standard and a modified skate boot will be compared. Hereafter, these two skates will be referred to as the “Regular” and

“DROM” skates, respectively. The comparison of forces generated during skating and the ankle kinematics will be made across three different skating conditions, including forward skating and crossovers in both directions. Forces and ankle kinematics will be measured using a portable measurement system described below, on the instrumented right skate during the previously mentioned skating tasks.

1.5 HYPOTHESES

Based on pilot data it is anticipated that the use of the DROM skate during the performance of the various skating tasks will result in higher peak forces, average force, impulse and power than the Regular skate for both forward and crossovers skating conditions. Based on pilot data, the plantar/dorsiflexion range of motion in the sagittal plane is expected to be significantly higher with the

DROM compared to the Regular skate for all on-ice skills. Small differences in inversion-eversion (frontal plane) are expected between the two skates. Due to the medial or lateral orientation of the body during the crossovers, the ankle’s

inversion/eversion ROM is expected to be more pronounced and asymmetric compared to forward skating.

1.6 LIMITATIONS

There are some inherent limitations with respect to this study:

1. The subjects did not use their own personal hockey skates, which may

affect their skating patterns.

2. The accuracy of the electrogoniometers can only be applied within the

specific context of skating in the tested range of motion at the ankle.

They provide local angles; they do not provide the angles in a global

reference frame.

3. As presently designed, the strain gauge system is insensitive to loads

produced at the extreme anterior or extreme posterior of the skate blade

holder.

1.7 DELIMITATIONS

The researchers have consciously decided to include the following delimitations:

4. The current study evaluated certain defined aspects of skating: forward

linear skating, forward crossovers skating.

5. The subjects will not be wearing full ice hockey equipment, thus possibly

affecting the kinetics and kinematics of the body.

6. Only male subjects will be analyzed.

7. The subjects included forwards and defensemen only.

8. The subjects were instructed to skate at their maximum velocity during

each task.

9. The subjects were fitted with their usual skate size, but the width size of

the skate will be Regular (‘D’) as no larger (‘E’ or ‘EE’) skates were

instrumented.

CHAPTER 2 – REVIEW OF LITERATURE

2.1 HISTORY OF HOCKEY

The origin of ice hockey is debatable. Some oral historical accounts from the Mi’kmaq First Nation in Eastern Canada mention a hockey-like game being played. European immigrants have brought many variations to hockey-like games in Canada, such as the Irish sport of hurling, the Scottish sport of shinty and versions of field hockey in England. There are reports of hurly being played on ice ponds in Windsor, Nova Scotia, no later than 1810. A major change came in

1875 when McGill University students organized the first indoor ice hockey game at the Victoria Skating rink in Montreal (McKinley, 2006). The establishment of some basic rules contributed to hockey’s development. Playing inside also helped the promotion of the sport, which could be watched by spectators in relative comfort.

2.1.1 EVOLUTION OF THE SKATE

According to Goodman (1882), the blades of ice skates have evolved historically, in three major phases: wooden, bone and iron. Some archaeological discoveries along with old Scandinavian and Icelandic legends show that skating and skiing started more than 3000 years ago (Minetti, 2004). It is thought that prehistoric men moved on snow and ice on pieces of wood to look for food. The distinction between skating and skiing occurred with the introduction of polished bones as a blade. An old wood carving (“The fall of Lidwina of Schiedam” in

1395) suggests that skates with iron blades have existed for over 600 years.

Historical accounts have associated skating with recreational pursuits and a method of transport in northern Europe during the winter. During the iron phase, the wooden footplate and edged iron blade were used until the introduction of the “Norwegian” skate. This new skate allowed a larger horizontal component in the push-off, because the boot was mounted higher above the blade

(preventing the foot from touching the ice). The skates were also adapted to speed skating, ice hockey and figure skating with different design features corresponding to the needs of the sport. In more modern times, skates have evolved mostly by changing specific components and modifications in design.

One very significant development that had an important impact on speed skating was the development of the klapskate (Koning et al., 2000). The difference in this skate lies in the hinge point on the anterior part of the skate between the boot and the blade that permits the skate boot to rotate. The hinge is mounted close to the metatarso-phalangeal joints allowing a similar reaction force on the foot relative to the ankle joint as seen in running or jumping (Ingen Schenau et al.,

1996). The effects of this change will be discussed in the skate properties section (2.2.2.3.2).

2.2 HOCKEY SKILLS CLASSIFICATION

Thus, it is possible to change the design of a skate to provide mechanical and performance advantages. However, in contrast to speed skating, skating in

ice hockey and the use of the skate is a function of a very complex set of skills that a player must be able to perform effectively to have success in the game.

Three major categories of skills including skating, stick (shooting, passing and puckhandling) and checking must all be performed at a high level. Skating skills are arguably the most important and complex skills of ice hockey. Skating is also made up of many sub-set skills (figure 3).

Figure 3 Skating classification (from Pearsall, Turcotte and Murphy, 2000)

2.2.1 INTERNAL FACTORS AFFECTING PERFORMANCE

In ice hockey, both the aerobic and anaerobic systems contribute to the energy requirements (Montgomery, 1988; Cox et al., 1995; Twist, 2007). The aerobic system is essential to the recovery process and builds a base necessary

to handle more intense anaerobic efforts (Montgomery, 1988; Cox et al., 1995;

Twist, 2007). The anaerobic system provides the major source of energy for muscle contraction during exertion phases of hockey (Montgomery, 1988; Cox et al., 1995; Twist, 2007). The maximum efforts over short distances are characteristic of hockey; the ATP-PC and lactic acid systems supply this energy

(Montgomery, 1988; Cox et al., 1995; Twist, 2007). Muscular training of ice hockey players intends to increase lean body mass, improve absolute strength and provide power (Twist and Rhodes, 1993). Added mass affects the skating performance of hockey players; a low body fat percentage around 10-12% should be maintained (Montgomery, 1988; Dewart et al., 1999). The absolute strength and lean mass will help the player withstand contact (Twist and Rhodes,

1993). Muscle balance and flexibility will help to prevent injuries and maximize the efficiency of movement (Montgomery, 1988; Dewart et al., 1999). Power is often considered the differentiation factor between competitive players and elite players (Koch et al., 1999; Bracko, 1998; Twist, 2007). Power, the capacity of recruiting the maximum muscular activity in the shortest time (Weineck, 1997), is needed for all on-ice skills: skating, stick (shooting, passing and puckhandling) and checking (Twist and Rhodes, 1993). Agility is also an important aspect, as hockey game situations constantly require quick reactions and sudden changes in direction (Twist and Rhodes, 1993). Minkoff (1984) was innovative by adding the visual aspect to hockey performance parameters. The visual tests included visual speed and span, eye fusion, horizontal posture, stereoscopic vision and

three-dimensional peripheral blind spots. The total eye score related strongly to shot accuracy, mostly explained by visual span score. Vision span was also related to success in face-offs. It seemed that goalies and all-star players scored higher for these visual tests. More studies are needed to confirm the interaction between visual scores and game performance.

2.2.2 EXTERNAL FACTORS AFFECTING PERFORMANCE

The effect of external factors and their effect on performance are often neglected, but these factors are important to consider for performance optimization. The most important external factors are air friction, ice friction and skate properties.

2.2.2.1 Air friction

Air friction can impede the maintenance of high speeds while skating. The air friction while skating is not different than for other activities following the laws of aerodynamics. Air friction is dependent on the density of the air and the density is not only dependent of altitude, but also of local atmospheric conditions. During speed skating, air friction is the largest external resisting force

(Koning et al., 1992). Skating position affects performance; it is primarily defined by three kinematic angles: trunk position, knee angle and position of the lower leg. Body position has a strong influence on drag. It seems that the capacity to produce more power for the taller speed skater is negated by the

increased air and ice friction. (Ingen Schenau et al., 1989). The body composition will also affect skating speed; the fat percentage should be as low as possible to maximize speed. But, ice hockey is a contact sport, so extra weight can help to overcome impacts during the course of a game. Thus, these factors and how they affect performance are difficult to quantify in the context of an ice hockey game.

2.2.2.2 Ice friction

Ice friction is assumed to be described by the relationship to surface friction (F = µN), where N equals the normal force and µ the ice friction coefficient. The relatively low friction in skating and skiing is due to a thin film of liquid water between the ice surface and ski or blade. The two common ideas explaining this water formation are frictional heating and pressure-melting

(Koning et al., 1992). Koning et al. (1992) measured ice friction forces with stain gauges on an interconnected block between the shoe and the blade. The coefficient of friction seems to increase with increasing speed. The coefficient of friction was also higher in the curves, explained by the larger deformation of the ice during skating the curve. Kobayashi (1973) reported friction coefficients between 0.003 and 0.007; the optimal condition was on natural ice at an ice temperature of -0.6°C. Koning et al. (1992) measured coefficients of ice friction on the straights of 0.0038 to 0.0057. The best surface temperature for speed skating on artificial ice lies between -6 and -9ºC. It seems the advantages of a

higher temperature (better lubrication) and of a lower temperature (minimizing the deformation) cancel each other out at a particular ice temperature. Fedorolf,

Mills and Niggs (2008) reported friction coefficients of 0.0071 with standard ice hockey blades and 0.0056 to 0.0061 with CT Edge ice hockey blades (described in 2.2.2.3.3).

The coefficient of friction varies throughout the stroke and rises to a distinct peak at the end of the push-off (Koning et al., 1992). The klapskate was believed to reduce the power lost to ice friction that results from pressing the tip of the blade into the ice. Houdjik et al. (2001) analyzed the ice friction with an instrumented conventional skate (Jobse et al., 1990). The energy that would be dissipated with the klapskate was estimated from the conventional skate data.

The frictional force was found by decomposing the transformed 3D force vector into normal force and frictional force. Pressing the tip of the blade into the ice was accounted for less than 1 W of the power flowing to ice friction during skating at constant speed. This contradicts the old speed skating technique of sitting on the back of the skate and avoiding plantarflexion. Because power dissipation is only affected marginally by ice friction, the enhanced skating performances with the klapskates must be explained by an increase in power output generated by the skater. Lower ice friction and higher power production are the only two factors that can explain increased performance from a skate modification. This extra power production is obviously related to the contribution of the plantarflexion and greater knee extension that the klapskate allows.

2.2.2.3 Skate properties

Performance depends not only on the skills and conditioning of the athletes, but also on the equipment they use (Federolf, Mills and Nigg, 2008).

Skate manufacturers improved the stability, reduced the weight and added protection and comfort to the hockey skate. The effects of these design changes on the actual performance characteristics have not been thoroughly investigated

(Pearsall, Turcotte and Murphy, 2000). There are a few studies that have investigated skate properties of boot stiffness, range of motion and blade edge

(Turcotte, Pearsall and Montgomery, 2001; Hoshizaki, Kirchner and Hall, 1989;

Ingen Schenau et al., 1996; Federolf, Mills and Nigg, 2008).

2.2.2.3.1 Boot stiffness

Research is an important aspect for optimal equipment development in sporting activities. In the ice hockey skate design, the stiffness properties of the skate boot are important. Stiffness about the skating boot upper surrounding the ankle offers stability and control of blade leverage during skating. Turcotte,

Pearsall and Montgomery (2001) designed an apparatus and protocol to measure the stiffness characteristics of various types of ice hockey boots. The apparatus could measure stiffness in inversion, eversion, plantarflexion, dorsiflexion, lateral and medial torsion. The testing included three types of skates (Bauer 5000, Air

90 and Bauer 1000). These skate models were chosen for their known difference in stiffness as defined by the upper construction of the skate boot. The Bauer

5000 had stiffness characteristics that were consistently higher than the Bauer

1000 and to a certain extent were also stiffer than the Air 90. The constructed apparatus and protocol allowed for the adequate measure of stiffness properties of the different types of skate boots.

2.2.2.3.2 Range of motion (ROM)

Ingen Schenau et al. (1996) proposed a new skate design that allowed a more powerful and sustained plantarflexion. This new skate (“klapskate”) allowed plantarflexion without the disadvantage of ice friction, because the blade remains in the horizontal position during the entire push-off. The conventional speed skates create ice friction (the tip of the blade scratching the ice) when the skater initiates plantarflexion at the end of the push-off. When speed skaters used traditional skates they were taught to avoid plantarflexion in order to reduce excessive ice friction during the gliding push-off. This technique also affected the contribution of the knee extensors because push-off was interrupted before full plantarflexion preventing full extension of the knee (Ingen

Schenau, 1985). The performance of the klapskate was compared to normal skates. Performance times over the season improved with the new skate as lowered times for 500 m, 1500 m and 3000 m were seen. The junior klapskaters improved their training performances by 6.2 ± 2.3%, which is significantly larger (p < 0.001) than the mean progress of 2.5 ± 1.6% of the skaters with traditional speed skates over the same period (Ingen Schenau et al.,

1996). The results seem to confirm that this added plantarflexion contributed to improved performance presumably improving the mechanics of leg extension during the skating stride. Reduced feelings of local fatigue reported by subjects were thought to be due to the increased contribution of the calf muscles to external work and the elongation of the push-off phase.

2.2.2.3.3 Blade edge

In speed skating, a thinner blade was always perceived as one that produced less ice friction. However, the various skating skills in ice hockey require a wider more robust blade. CT Edge Skate Design Inc. (Vancouver,

Canada) introduced a new skate blade designed for a better grip on the ice. The lower part of the blade flares outward on both sides, which changes the angle between the ice and the blade and provides a wider contact area. Federolf, Mills and Nigg (2008) determined the frictional properties of three types of CT Edge blades and a standard ice hockey blade. Sled deceleration measurements were executed to compare the different blades. A three-blade configuration was chosen, the weight was evenly distributed with dumbbells and the sled was launched by a separate propulsion system. The sled reduced air drag to a negligible value, thus, most of the resistance was the result of ice friction.

Compared to standard blades, the friction coefficients were lower by about 13%,

21% and 22% for the CT Edge blades with a blade angle of 4º, 6º and 8º, respectively. Increasing the load on the blades reduced the ice friction. Friction

was independent of test velocity, although the testing did not reach the maximal skating speed observed in ice hockey. There were high day-to-day variations observed in the results and a lateral drifting of the sled was unavoidable; the authors could not explain these problems clearly. The results contradict the paradigm “thinner blades cause less friction”. This small reduction in ice friction likely does not have a major impact on ice hockey skating performance, but the application in speed skating or bobsledding could be significant.

2.3 SKATING MECHANICS

2.3.1 LINEAR MOVEMENT

Marino and Dillman (1983) analyzed the mechanics of the acceleration phase of ice skating with multiple regression models. The purpose was to quantify mechanics involved in the acceleration phase of power skating and relate them to performance. High stride rate, significant forward lean, a low takeoff angle and the recovery foot placed directly under the body at the end of the single support phase were the most important factors related to higher acceleration. These advantageous techniques can be implemented to the skating style to improve performance of the acceleration, velocity and skating time.

Greer and Dillman (1984) presented a different model inspired by the previous one. Toe to hip distance, angle at take-off, body weight, stride rate, trunk position at TD and leg length were included in the model. The predicted acceleration time (3.49 m/s2) of 69 subjects was close to the actual time (3.53

m/s2). It seems that improvements in skating acceleration could be achieved by decreasing the leg angle at take-off, decreasing the trunk angle at TD and increasing the stride rate.

Marino and Weese (1979) completed a kinematic analysis of the hockey skating stride. The objective was to clarify the contributions of the two support periods to the development and the maintenance of skating velocity. The acceleration lasts approximately 1.75 seconds and from a standing start it includes up to 4 strides (sometimes there is no double support phase for the first

2 or 3 strides). Players generate propulsion forces in both phases, but most of the propulsion occurs during single support. The typical pattern of the stride consists of deceleration in the first portion of single support followed by acceleration (near the midpoint of single support), which lasted through the end of double support phase. The rate of acceleration began to decrease early during the double support period. The acceleration occurs after the outward rotation of the thigh and coincided with the initial extension movements of the hip and knee.

The researchers divided the stride into 3 phases instead of 2 phases: glide during single support, propulsion during single support and propulsion during double support. The last phase was composed of the final thrust of the driving leg and some plantarflexion as the skate left the ice.

The end of push-off is defined as the moment when the skate is lifted off the ice. The beginning of the push-off is more difficult to define. Djatschkow

(1977) defines this as the moment when the contra-lateral skate leaves the ice.

Coaches have assumed that the weight transfer occurs as soon as the next gliding skate is placed on the ice (van Ingen Schenau, 1989). However, force measurements from a prediction model in speed skating were estimated as negligible at this point in the skating stride (Ingen Schenau, 1981). Djatschkow

(1977) has defined the beginning of the push-off as the moment when the trunk starts its external rotation with respect to the upper leg. Djatschkow emphasized the importance of this passive movement, which is necessary to position the push-off as horizontally as possible. The definitions of the phases of the stride are important in order to facilitate the interpretation of results and to compare results from different research experiments.

2.3.2 ANGULAR MOVEMENT

Ingen Schenau (1981) showed differences during speed skating when comparing skating the straights and skating the curves in an oval speed skating course. The forces that occur when skating the curves involve a shorter stroke time, lower peak forces and the absence of a phase in the middle of the stroke

(where the force is less than body weight). This resulted primarily due to the observation that the skaters did not rotate from the medial to the lateral side of the skate when compared to straight skating. In comparison with skating the straights, the first portion of the gliding phase is bypassed. This could in part explain the higher stride rate and lower peak forces when speed skating in the curves. Thus, the most important difference in skating the curves is that instead

of changing direction alternately to the right and to the left, the change of direction is always on the same side. Skating the curve in speed skating can be compared to crossovers used in ice hockey and thus there may be similarities in the biomechanics of crossover execution in ice hockey as that seen with speed skating.

Yoneyama et al. (2008) analyzed the ski deflection and estimated ski direction and edge angle during downhill skiing. Skiing is a different movement than skating, but turns during skiing relate to the tight turns in ice hockey.

Although, the two skills are different, both techniques use an instrument to apply forces during legged locomotion. First, the factors affecting the shape of the edge in contact with the snow are the ski shape, the ski elastic properties and the forces acting. A sensor beam was mounted on top of the ski containing torsion sensors and bending sensors. A geomagnetic sensor (compass) was added; it was tri-axial and had good stability and angular resolution. The results were shown only as an example, but some features were informative. Near the turn change of direction, there is a rapid almost linear transition of the edge angle.

The effective radius was generally about equal to the side carve radius. The inner ski, although lightly loaded, may have been carving quite effectively and may have assisted the athlete to control the turn. The importance of ski ploughing even in supposedly carved turns is thought to be relevant. The ski ploughing can be related to braking during sharp turns in ice hockey, such a study design as not been explored for ice hockey.

2.3.3 STARTS

There are three conventional starting techniques being used for forward skating: front or standard, side or thrust and glide and crossover. Naud and Holt

(1979) compared the three skating starts on a 20 feet distance. The crossover start was the slowest start, because the first crossover step caused an elevation of the centre of gravity and suspension of the body in the air for a short period of time. The initial acceleration for the side start was greater than the other techniques for the first two strides. However, the front start was executed with the feet perpendicular to the starting line, thus a repositioning was needed to place the feet in a angle close to 45º (“V” start). There was significant difference between the front or side start compared to the crossover. Different studies seem to agree that the front and side starts are superior to the crossover

(Thiffault, 1969; Jones, 1969; Naud and Holt, 1979). Dillman (1984) showed that speed was significantly improved when the leg forces were applied from a flexed position (knees) for a stationary start. Finally, in the previously mentioned study by Marino a multiple regression analysis showed that an increased forward lean, a lower push-off angle and a high stride rate increased skating speed regardless of the starting style (Marino and Dillman, 1983).

The speed skating start is considered a transition from running to gliding by Koning et al. (1995). Koning et al. explored the different techniques used for propulsion during the start in speed skating. The factor limiting velocity in

running is the necessity to maintain backward rotation of the leg relative to the trunk in a sagittal plane. This results in a constant deceleration and acceleration of the push-off leg. These internal losses are reduced in skating because the push-off is not against a fixed position. The first strides of skating are compared to running because the push-off is executed against a fixed point. During these running-like push-offs, the contribution of rotational velocity of the leg is larger than the contribution of extension of the leg for forward velocity. The gliding technique helps to obtain higher velocities and can be observed by an increasing leg extension velocity.

2.4 SKATING ANALYSIS

The analysis of skating is separated in different categories. The kinematics quantifies the movements of the body segments. The kinetics interprets the ice reaction force. Pressure distribution analyzes the exact location of the application of forces in the skate. Muscle coordination analysis intends to relate the skating mechanics to the human anatomy. Task analysis is directed at pinpointing the requirements of a sport. The physiological aspect of skating focuses on the energetic needs of the task. The prediction models attempt to isolate variables in order to theoretically measure their effect. A summary of each of these approaches is presented in the following sections.

2.4.1 KINEMATICS

To quantify technique, kinematic measures are necessary and they have not been extensively examined in ice hockey (Upjohn et al., 2008). There have been several pioneering studies investigating the kinematics of ice skating, generally using cinematography as the method of evaluation (Upjohn et al.,

2008; Marino and Weese, 1979; Marino, 1977; Gagnon, Doré and Lamontagne,

1983; Chang, 2002; Hoshizaki, Kirchner and Hall, 1989; Lafontaine et al., 2007).

Upjohn (2008) examined the lower body kinematic variables that discriminate high-calibre hockey players from lower calibre hockey players when skating on a skating treadmill using four video camcorders. Results showed greater stride length, stride rate, knee and ankle range of motion for the high- calibre skaters. The lesser range of motion of the lower calibre skaters could be attributed to the importance of maintaining stability while skating. The experienced skaters can easily keep balance, thus they can focus on the maximization of force during the push-off, which is associated with greater range of motion and stride length (Upjohn et al., 2008).

A method for determining the tridimensional angular displacements of the skates was developed by Gagnon, Doré and Lamontagne (1983). The application was done a on an ice hockey two-legged stop to determine the magnitude and direction of the forces exerted by the skater. Two orthogonal rods were attached to the rear part of the skate without restricting movements. The skate was placed on a special apparatus allowing angular displacements about three

orthogonal axes for error evaluation. The rods were tracked with two Locam cameras placed orthogonally and the coordinates were calculated with a

Vanguard Motion Analyzer. The degrees of error for the three planes on the apparatus were small (0.7º, 0.3º and 1.2º) and indicate that the criterion angles could be approximated with a reasonable degree of accuracy. During the stop, the skates were not parallel to the lateral direction, but are positioned in a “V” shape. The outside skate was inclined laterally much more considerably than the inside skate. The vertical force increasing and decreasing alternately suggested that the loading alternated in opposite sequences for the inside and outside skates. The horizontal friction force restraining the motion and (creating the stop) was primarily exerted by the outside skate.

Kinematics of the talocrural and subtalar joints during ice hockey forward acceleration were obtained with cinematography by Hoshizaki, Kirchner and Hall

(1989). Between the initiation of contact with the ice and heel-off the ice, the ankle undergoes dorsal flexion and pronation. This position provides a stable base for the forces produced during hip and knee extension, which is followed by plantarflexion and supination at the ankle. From HO-TO, an increased angle of propulsion was observed and a forward lean contributed to forward impulse by reducing air resistance. This allowed a significant force coming from the ankle plantarflexion as the skater pressed the toe of the skate back against the ice.

However, the effectiveness of this action diminished with speed as the skater could no longer plantar flex fast enough to accelerate the center of mass.

Lafontaine (2007) was innovative in his kinematics measurement system using the traditional cameras and body markers, with one camera moving on guided rails along side of the skater. The objective was to describe the kinematics of the knee and ankle during the first three strides of the ice hockey forward acceleration. This was done to demonstrate the usefulness of the data acquisition method and to determine if a kinematic evolution exists from the start to maximum speed during forward skating. The results showed that the range of motion for both joints progressed at every stride and increased velocities resulted from increased joint motion amplitude. The increases in knee range of motion were mainly affected by an increase in touchdown flexion angles. The ankle eversion can be linked to the blades’ “angle of attack” on the ice. The results suggested that as speed increased eversion increased, thus allowing the skater to apply force in a more tangential direction on the ice surface. The author encouraged hockey players to include motions of large amplitudes in their training programmes, such as multiple-stride plyometrics involving progressive knee flexion.

Using a two dimensional system (cinematography) to evaluate three dimensional skating movements is problematic. When skaters travel the length of the ice, it is difficult to establish a properly calibrated field of view of high resolution (Pearsall et al., 2001). Pearsall et al. (2001) directly measured ankle kinematics in forward ice hockey skating with electrogoniometers placed inside the skate. At the initiation of the single support phase, the skate is in 7.1º of

dorsiflexion and increased to 11.8º at the beginning of the double support phase.

During the swing phase, the skater quickly plantar flexed from 11.8º to 1.9º of dorsiflexion. During the glide, the foot was slightly everted and reached its maximal eversion of 7.1º in preparation for the push-off. This maximum eversion represents the need to generate a resultant force on the ice. During the swing phase the ankle underwent inversion exceeding the neutral position (Figure 4).

A B

Figure 4 – Ankle kinematics during forward skating: (A) Plantar/dorsiflexion. (B) Inversion and eversion (from Pearsall et al., 2001)

The previous results differ from Dewan’s (2004) study also calculating ankle kinematics with goniometry. The ankle reached higher degrees of plantarflexion (5º) and dorsiflexion (18º). Stidwill (2009) measured on-ice ankle kinematics with goniometers reaching 12.9º of plantarflexion and 18.6º of dorsiflexion. The different skates used in these studies might explain the

discrepancies. This clearly shows the evolution in a short time (8 years) of hockey skate design towards higher ROM mostly through increased plantarflexion.

2.4.2 KINETICS

Because of the liquid medium between the ice surface and the skate blade, direct kinetic measures traditionally used in biomechanics have been elusive. Of the studies investigating the kinetics of skating, a few have used strain gauges acting as force transducers attached to an interconnected block assembly between the shoe and the blade of speed skates (Koning et al., 1995; Jobse et al., 1990; Boer et al., 1987; Koning et al., 1992). Even fewer studies have presented force data obtained with strain gauges directly bonded on the skate’s blade holder (Lamontagne et al., 1983; Stidwill, 2009).

The most common force measuring device (force transducer) is the force plate, which usually relies on strain gauges, but piezo-resistive, capacitive, air balloon and springs transducers are also available (Winter, 2005). A force transducer functions with the change in the electrical signal that is proportional to the applied force (explained further in section 3.3) (Winter, 2005). The majority of strain gauges are foil types, available in a wide choice �of shapes and sizes to suit a variety of applications. They consist of a � pattern of resistive foil, which is mounted on a backing material. They �operate on the principle that as the foil is subjected to stress, the � resistance of the foil changes in a defined way.

When this foil undergoes change in one of its direction, the mechanical deflection causes a change in resistance of the strain gauge connected to a bridge circuit

(Frederiksson and Akerlind, 2008). For kinetics analysis, the strain gauge offers the possibility of collecting data on a portable system (Yoneyama et al., 2008;

Stidwill, 2009)

Lamontagne and Doré (1983) completed one of the only known studies attempting to directly determine forces (including medial-lateral forces) for ice hockey. They report the use of instrumented skates by Romiweski (1974) for skating kinetics, but this article is only found in Russian. Roy (1978) used a force plate to analyze the front skating start, but the constraints posed by the use of the force plate are huge for the diversity and complexity of skating skills performed in ice hockey. The objective of Lamontagne and Doré (1983) was to develop, validate and apply a measuring system to evaluate the intensity and direction of forces during skating. The authors used strain gauges attached to the blade holder (a plastic and metal one) of the hockey skate to determine force generation when performing a parallel stop. But, in this study it was not possible to measure forces precisely with the plastic blade holder (only the metal blade holder results were presented). The strain gauges were fixed on the blade holder and mounted in full Wheatstone bridges to measure compression and half bridges to measure flexion. For compression, the two strain gauges were placed together (figure 5) one in the axis of the deformation and the other orthogonally to the first as to measure deformation in the blade’s axis. The system allowed

the measurement of forces perpendicular to the blade (medial-lateral) and the point of application of the resultant force. The forces in the axis of the blade are neglected, because of the low coefficient of friction on ice. The calibration was done by weight loading the blade on a support, with a pendulum for vertical loading and with a pulley for the medial-lateral loading (figure 6). The calibration only reached 450 N for the vertical loading, while a skater can reach 1500 N of vertical force during the push-off (Stidwill, 2009). The authors mentioned that the point loading of the weight was more severe than a distributed load along the blade. The vertical and horizontal forces were calculated by vectorially adding the orthogonal components of the compression and flexion forces. The results for the plastic blade holder were not linear for bi-axial loading. The researchers believed the large flexibility of this material produced instability in the readings.

The maximal vertical forces obtained during the parallel stop were 130% of bodyweight, while the horizontal forces only reached 5% of bodyweight.

Figure 5 Positioning of the strain gauges on the plastic blade holder (from Lamontagne and Doré, 1983)

Figure 6 – Calibration setup: (A) Vertical loading. (B) Mediallateral loading (from Lamontagne and Doré, 1983)

Stidwill (2009) measured forces during skating from strain gauges bonded directly to the plastic blade holder without modification to the skate. A portable system was used to capture data, thus making it possible to analyze the various hockey skating skills with more freedom than in previous attempts. This system of measurement is the only one known that has been designed to study vertical and medial-lateral forces during ice hockey skating. The peak vertical forces measured were between 150%-200% of bodyweight during the first six strides of forward skating from a stationary start (figure 7). The medial-lateral profiles were different between the subjects and a separation in low (peaks of 0-10% of bodyweight), mid (peaks of 10-25% of bodyweight) and high (peaks of 25-50% of bodyweight) groups was presented; the differences were hypothesized to be related to skating style. This technology was also designed as a valid tool of comparison for skating kinetics. In this study, a comparison of the kinematics of the knee and the ankle and kinetics of forward skating on-ice and on artificial surface was done. The synthetic surface showed no significant differences (p ≥

0.1) with the exception of greater knee extension on the synthetic ice. It seems the synthetic surface may be a good alternative to real ice for hockey studies.

Figure 7 – Kinetics of a representative subject for the right skate, including contact time and stride time information (from Stidwill, 2009).

2.4.3 PRESSURE DISTRIBUTION

Turcotte et al. (2001) measured the plantar pressure patterns during forward skating with ice hockey skates. The pressure sensors were distributed on the insole of the skate. These sensors were separated in six areas including: anterior foot, medial anterior, lateral anterior, mid foot, medial posterior heel and lateral posterior heel. The total force showed a plateau region before the peak force and was related to the gliding phase. The peak forces were similar regardless of skating speed, but contact time decreased with increasing velocity.

A shift in forces from posterior to anterior coincided with heel strike to toe off

phases. The anterior foot showed a greater peak force at higher speeds. During the entire support phase, the medial foot showed either a greater or equal force when compared to the lateral side of the foot.

Eils and Kupelwieser (1998) measured the plantar pressure distribution in straight inline skating. Testing took place at an indoor hockey rink and a Pedar

Mobile system was collecting data at 50 Hz. The straight skating was analyzed at two velocities of 18 km/h and 24 km/h. Eight areas were defined for the pressure distribution: heel, medial midfoot, lateral midfoot, first and second metatarsal head, third to fifth metatarsal head, first toe, second and third toe, and fifth toe. The total area force-time curves for both speeds were similar to walking patterns. The first weight-bearing peak occurred at 20% of the stride and the second push-off peak occurred at 80% of the stride. During the stride a forward translation of the application of force was observed, starting at the heel and moving in direction of the first toe. The heel and the medial structures of the foot were exposed to the higher pressures. The similar average force between speeds and the reduced contact time for higher velocity suggest that skating velocity is regulated by an increased stride frequency (Koning et al., 1987;

Marino, 1977).

Dewan (2004) placed piezo-resistive sensors on the foot and ankle inside the hockey skate to measure pressure distribution during skating. For the plantar medial foot, the pressure was higher in the forefoot than in the heel, and the arch region was negligible. While the plantar lateral foot had higher pressure in the

heel than the arch, and the forefoot pressure was very low. Overall, the plantar pressures were greater on the medial side reaching 32 pounds per square inch

(PSI) compared to a maximum of 18 PSI on the lateral side. The medial inside pressure was distributed on the ankle at the initiation of the stride and on the forefoot during push-off. The lateral inside pressure was located at the ankle during push-off and the lateral metatarsal showed higher pressure at the end of the stride. The dorsal section of the foot showed a peak pressure at the dorsalis pedis at 17% of the stride, while the first metatarsal peaked at 57%. The posterior section of the foot exerted similar peak pressures of lower amplitude

(1.5 PSI) for the calcaneus and Achilles tendon, but the first occurring at 12% of the stride and the second at 61%.

Trumper (2006) compared the pressure profile of elite and recreational players with fifteen piezo-resistive sensors inside a hockey skate boot during forward crossovers. Elite skaters performed the skill faster (p<0.01). The elite skaters also produced higher peak pressures on the plantar surface and lower peak pressures on the medial and lateral surfaces (p<0.05). Higher pressures were observed on the plantar, medial and lateral surfaces of the inside foot compared to the outside foot for both groups.

2.4.4 TASK ANALYSIS

In ice hockey, time-motion analysis has been used to estimate the time on ice, the distance traveled in a game and the average skating velocity.

Montgomery et al. (2004) aimed to quantify various skating activities, hitting, shooting, passing and pass reception. Film data was obtained from 10 National

Hockey League teams including 180 players. The players depending on position

(center, winger or defenseman) averaged 227-270 forward skating movements in a game, the most common being crossovers (54.6-73.1) and starts (56.1-

64.7). The backward skating was less used, the backward movements averaged

43-146; the defensemen were 19.2% of the time in backward skating compared to 4.8% for the centers and 5.7% for the wingers. The typical player received or gave approximately 8-9 hits per game, but the most active players reached 25-

28 contacts per game. The most frequent shot by the forwards was the wrist shot (29-37%), however the snap shots were almost as common (23-29%). The defensemen chose the slap shot in a high proportion (54%) and their shot accuracy was lower, because they often shoot further away from the net. The most frequent type of pass and pass reception is the forehand side of the stick

(more than 50% for all positions); it could be attributed to the shooting side and positions that are adapted in consequence. The results show that the skating patterns differ between forwards and defensemen, especially when looking at backward skating. It suggests that players in different position could benefit from skate design adapted to their skating tasks.

Dillman (1984) ascertained the movement characteristics of ice hockey players during a game. An analysis of 13.5 seconds of skating time was done on

22 players with 3 Locam 16mm cameras. The number of accelerations (3.36)

was slightly more than the number of decelerations (3.23). The mean distance covered by a player was 56.79m over the 13.5 seconds frame. The mean velocity was 4.21 m/s and the mean peak velocity was 5.01 m/s. Surprisingly, the center had the lowest mean peak velocity 4.44 m/s, probably because the races for the puck occur more often in the corners. The results clearly indicate the frequent speed changes and marked acceleration and deceleration experienced by hockey players over a short period of time. In addition, relatively high skating velocities are reached during the course of the game.

2.4.5 PHYSIOLOGY OF SKATING

Ice hockey is characterized by high intensity intermittent skating; the typical player performs 15-20 minutes of a 60 minutes game and each shift lasts from 30 to 80 seconds with 4 to 5 minutes of rest between shifts (Montgomery,

1988; Cox et al., 1995). These parameters directly determine the contribution of the aerobic and anaerobic systems. Different studies agree that the intensity

of the exercise elicits on-ice requirements nearing 70-80% of VO2max and it seems that anaerobic metabolism contributes to 69% and the aerobic metabolism to

31% of the energy during the shift (Montgomery, 1988). According to heart rate telemetry, peak heart rate surpasses 90% of maximum and the average on- ice values were about 85% of maximum (Montgomery, 1988; Twist and Rhodes,

1993). Muscle glycogen declined an average of 60-80% after a hockey game and the depletion was mostly located in the type I fibres (Montgomery, 1988;

Twist and Rhodes, 1993). After continuous skating, muscle lactate was 2.7 mmol/L, while it reached 26.4 mmol/L after intermittent high intensity skating

(Montgomery, 1988). It seems that lactate accumulation is reduced during a game (8.7, 7.3 and 4.9 mmol/L after the first, second and third period)

(Montgomery, 1988; Twist and Rhodes, 1993; Cox et al., 1995). This tendency is in part attributed to the shorter shift durations as the game progresses. The

lactate threshold on average occurs at 82.5% of VO2max and 89.5% of maximum heart rate in ice hockey players (Cox et al., 1995). In addition, during a shift there are often 2 or 3 stoppages, it provides sufficient time for lactate clearance and for a 60-65% phosphocreatine resynthesis for the next effort (Montgomery,

1988). Professional hockey players display a muscle fibre profile similar to the average untrained individual, but the size of the fast twitch fibres is bigger (22% for IIa and 28% for IIb) (Montgomery, 1988). According to different power tests, hockey players show a peak power of 9.8-13.4 W/kg and 30-second anaerobic endurance of 7.7-10.3 W/kg (Montgomery, 1988; Twist and Rhodes, 1993; Cox

et al., 1995). Players have a mean VO2max of 52-62 ml/kg/min evaluated on cycle ergometer and treadmill protocols (Montgomery, 1988; Twist and Rhodes,

1993; Cox et al., 1995; Dewart et al., 1999). It seems that ice hockey players can experience detraining as opposed to overtraining throughout the season.

Heart rate telemetry of hockey practices showed that only 9-33% of the time was above lactate threshold for a hard practice and 0-9% for a light practice (Cox et al., 1995). Moreover, for the same effort on steady-rate cycle ergometer,

lactate levels of hockey players had increased significantly in the last third of the season compared to the first third (Cox et al, 1995). Aerobic and anaerobic systems may be compromised without a properly constructed programme.

2.4.6 MUSCLE COORDINATION

Elite skaters differ from less skilled skaters showing a smaller pre-extension knee angle, higher amount of work per stroke, slightly higher stroke frequency, higher knee extension velocity, short duration powerful push-off and more horizontally directed push-off (Ingen Schenau, Boer and Groot, 1987). Boer et al.

(1987) examined the patterns of moments of force, power output and muscle coordination at the ankle, knee and hip during speed skating. The peak in push- off force occurs in the early phase of knee extension (115º) and the absence of plantarflexion means that the effective knee extension range is very small (115º-

150º). This results in a short an explosive extension of the knee joint. The power output in the push-off is mainly generated by the mono-articular extensor muscles (gluteus maximus and vastus medialis). It seems the power is transported from the hip to the knee by the bi-articular rectus femoris.

Complex movements involving more than one segment coordinate the muscle activity to influence the anatomical and geometrical constraints to control the transfer of rotation into translation (Ingen Schenau et al., 1987). It is the essential action of the bi-articular muscles to transport energy produced in proximal joints to distal joints that allows a delay to the very end of the push-off.

Koning, Groot and Ingen Schenau (1991) investigated the proximo-distal sequence in movements of the trunk, upper leg, lower leg and foot during the speed skating push-off and compared the intermuscular coordination patterns of speed skaters of different levels of performance. A pronounced decrease of semitendinosus activity and simultaneous increase of biceps femoris activity is observed during the gliding phase. During the push-off the decrease of hamstring activity and increase of rectus femoris activity is obvious. A distinct sequence in the rise of the muscle activity between the knee extensors and ankle flexors is not observed. The simultaneous decrease of tibialis anterior activity and increases in both gastrocnemius and soleus activity contribute to the knee extension by pulling the lower leg into a more vertical position without changing foot and skate positions. A velocity difference between the ankle and the mass center of the body reaches its peak 60 ms before the end of the push-off at a knee angle of 154º. After this point the push-off force is lower than bodyweight.

The intermuscular coordination was not significantly different between elite and trained speed skaters. The elite speed skaters were reaching higher peak velocities and higher sideward velocity which results in a higher amount of useful work per stroke and a larger external power output during the push-off. It seems the ability of the elite skaters is to control their joint moments in a way by which the line of action of the push-off force has an advantageous position with respect to the joints. The capacity to maintain a horizontal position of the upper leg directly determines the level of performance of the skater.

Hinrichs (1994) compared the EMG activity of ice skating and treadmill skating in hockey players. Seven muscles of the leg were analyzed: tibialis anterior, gastrocnemius, vastus medialis, rectus femoris, adductor longus, biceps femoris and gluteus maximus. The EMG data were processed as muscle activation is active or inactive. The tibialis anterior was active from to the start of the stride to 50.9%. The vastus medialis and rectus femoris had similar activation patterns, starting from 1% to 68% of the stride. The biceps femoris and gastrocnemius were both active from 3% to 65% of the stride. The gluteus maximus was active from 2% to 63.5% of the skating stride. Finally, the only significant difference occurred for the adductor longus becoming active at 46.3% of the stride on ice, while becoming active at 57.8% of the stride on the treadmill. The results from the other muscles suggest that treadmill skating simulates the skating stride closer than many other training devices.

Dewan (2004) depicted EMG patterns of four leg muscles during ice skating. The vastus medialis was increasing steeply at 87% of the stride and remains active up to a peak at 33%. The tibialis anterior peak occurs during swing at 78% of the stride and quickly becomes inactive before a second peak near 5%. The peroneus longus shows activity at weight acceptance and peaks again approximately at 40% of the stride. The medial gastrocnemius clearly peaks at 42% of the stride, which is 20% before the ankle plantarflexion maximum.

2.4.7 PREDICTION MODELS

At constant speed, the mean power output during skating is approximately equal to power lost to friction (Ingen Schenau, 1982). Using skating position

(knee and trunk), body composition, altitude, air pressure, coefficient of friction and speed, a prediction model can determine power generation (Ingen Schenau,

1982). Mean power output is equal to the product of work per stroke and stroke frequency. Ingen Schenau et al. (1985) showed that the best speed skaters had the highest mean amount of work per stroke at each distance (500 m, 1500 m and 3000 m). These authors encourage coaches to focus on this aspect of skating to improve performance. This study also mentioned that the best skaters had relatively low stroke frequency. However, speed skating is very different from skating in ice hockey and these results cannot be generalized to the ice hockey skating stride or other ice hockey skating skills.

Most studies on external power in speed skating deal with a calculation of external power at constant speeds (Koning, Groot and Ingen Schenau, 1992).

Speed skating performance is determined by external power production to overcome air and ice friction. Using aerobic and anaerobic power produced on bicycle tests, a model of the kinetics of power production was obtained (Koning,

Groot and Ingen Schenau, 1992). The coefficient of correlation between the simulated 500m times and the actual 500m times was 0.90. The distribution of the available anaerobic energy is an important factor in the short lasting events.

Better sprinters appear to create more total energy at the onset of the race for

the same amount of anaerobic energy. It seems that the performance in the

500m sprint is determined primarily by the peak power output than by the anaerobic capacity of the athletes.

Koning et al. (2005) developed the power prediction model a step further by evaluating the kinetics of energy production, skating efficiency and skating technique. These parameters were measured during competitive imitations of skating; these simulations fit reality better than cycling data. Although fatigue affects skating technique, it is an unconscious adaptive response designed to maintain power throughout the race. It seems the athletes retain a considerable amount of anaerobic energy reserve during the closing stages of the event to prevent more deceleration. Whether this phenomenon is neurologically mediated or a feedback process dependent on monitoring metabolite accumulation, phosphagen depletion or other perceptual information is debatable. The predicted velocity during a 1500m race was much more accurate compared to the real 1500m race with the new model.

Since the introduction of the klapskate in speed skating, skaters and manufacturers thrived for the optimal adjustments of the klapskate to maximize the benefits. Houdjik et al. (2003) simulated the effects of the hinge position on the push-off performance. The ratio between the moment arm of the calf muscles and the maximal moment arm of the ground reaction force with respect to the ankle joint can be manipulated to shift the gear ratio of the calf muscles and influence their mechanical performance. The hinge position was modeled as

the length of the foot segment. Effective energy, total muscle work and efficacy ratio were analyzed in the model. The effective foot length in the current klapskates was approximately 205 mm. and the optimal foot length according to the model was 185 mm. The foot length constrains push-off performance because it affects the control of foot rotation. Foot length must be such to allow proper timing of foot rotation in response to the extension of the knee and the hip. When increasing foot length, the work output will increase for the hip and ankle (up to the optimal length) and decrease for the knee. This reduction in knee work could be explained by the energy transporting capacity of bi-articular muscles. The optimum hinge position will probably depend on many factors

(body build, technique, fatigue, etc.) for each skater and might therefore be difficult to determine.

Mechanical output about the ankle joint differs between isokinetic plantarflexion and jumping. It is thought that at a given angular velocity of plantarflexion during jumping, muscle fibres are operating in a more favourable region of their force-length and force-velocity relationships than during isokinetic plantarflexion. Bobbert and Ingen Schenau (1990) compared these two conditions for one leg with the same subjects. A CYBEX II isokinetic dynamometer was used and extended knee jumps and counter movement jumps were executed. Much larger moments at the ankle joint were produced during jumping than during isokinetic plantarflexion. If the angular velocity is increased, the duration of the movement decreases and the active state reached when the

peak moment occurs becomes even more submaximal for the isokinetic condition. Moment-angular velocity relationship obtained in the plantarflexion experiments does not reflect solely the influence of the shortening velocity of muscle fibres on the force, which can be produced by human plantar flexors. In simulated isokinetic plantarflexion at high angular velocities, the duration of the movement is so short that the active state cannot rise to its maximum, and the moment remains submaximal. In addition, the muscle fibres in jumping are operating in a better region of their force-velocity relationship.

CHAPTER 3 – METHODS

3.1 SUBJECTS

The target population for this study was experienced healthy adult male hockey players. The 10 subjects recruited were aged of 22.9 ± 2.2, weight 80.5

± 9 kg, height 178.3 ± 4.5 cm and had 16.8 ± 3.4 years of hockey experience.

The members of the McGill University varsity hockey team and players with experience playing at the Junior “A” level or higher were asked to volunteer as subjects. All subjects completed an informed consent form prior to participation in the study (Appendix 1). Ethics were approved by McGill University’s committee (file #336-0508). A questionnaire was also distributed to verify the health condition and to obtain information on the background experience of the player (See Appendix 2). All subjects reported good health and no significant injury. Four of the subjects were defensemen, two were centers and four were wingers. Six of the participants shot right and four shot left. All the subjects indicated that they were right leg dominant in the player profile form.

3.2 EXPERIMENTAL PROTOCOL

3.2.1 ENVIRONMENT

All testing was done on-ice at the McGill McConnell arena. The temperature and humidity at ice level were recorded for every testing period using a thermometer (Nexxtech model 6301032, Walnut, CA). The average

temperature was 1.5 ± 1ºC and the average humidity was 47 ± 5%. The surface of the ice was freshly resurfaced with a Zamboni™ prior to testing for optimal skating conditions.

3.2.2 SETUP

The subjects wore a “Regular” hockey skate (Bauer One95) and a prototype skate known as the “DROM” (modified Bauer One95) for the study

(Figure 8).

Figure 8

(A) Medial and posterior view of the Regular skate

(B) Medial and posterior view of the DROM skate with the flexible tendon guard

The subjects wore a helmet for security reasons, gloves and sticks to mimic hockey skating, a shirt, track pants or shorts to allow the wires to pass easily from the skates to a backpack containing the data logger. The right skate was instrumented with force transducing strain gauges for both the DROM and

Regular skate models. Wires from the strain gauges were connected to a box

(described in section 3.3.1), which was also linked to a data logger. The strain gauge box and data logger as well as a trigger to start and stop the trials on ice were placed in a backpack attached to the waist. The total weight of the backpack was 1.6 kg; studies have showed that such a weight would not alter skating mechanics (Boer et al., 1987; Millet et al., 1998). Prior to on-ice testing, the strain gauge channels were zeroed on the data logger, with the subject’s right foot lifted in the air and non-weighted. A weight bearing trial was recorded with the strain gauges while the subject applied all his weight on the right foot in a standing position. With the subject’s known weight, it was possible to verify the precision of force transducer system.

In prior studies, the goniometer was positioned behind the heel on the inside of the skate and on the lower part of the leg to measure the ankle kinematics (Chang, 2002; Dewan, 2004; Stidwill, 2009). Since the trials consisted of vigorous skating, the placement of the goniometer in the skate boot resulted in frequent breaking of electrogoniometers. Thus, goniometers were placed on the medial side of the shank and on the medial exterior surface of the boot (Figure 9). This position placed less stress on the goniometer, and

decreased the likelihood of breakage of the goniometer. The original placement behind the heel and a medial setup on the ankle and shank without skates were placed on the same leg and data simultaneously captured for both setups. The results showed a high correlation between the two placements of r = 0.993 for

10 trials of maximal plantar and dorsiflexion and r = 0.958 for 10 trials of maximal inversion and eversion. Thus, placing the goniometer medially was considered a valid representation of the ankle kinematics.

A B

Figure 9 – Picture of the goniometer placement on the right foot. (A) Previous studies placement: upper part behind the shank and lower part behind the calcaneus inside the boot. (B) Placement in the present study: upper part on the medial side of the shank and lower part on the medial outside of the boot.

The goniometer was secured with tape around the skate and around the tibia; the wires from the strain gauges and the goniometer were fixed to the lower limb just below the knee with tape. The installation of the goniometer was

always done by the principal investigator to avoid inter-tester variability. Before collecting data, the reference (zero) position was collected while sitting (the foot and the tibia making a 90º angle). This non-weight bearing position avoided ankle eversion.

3.2.3 PRE-TESTING

The subjects were introduced to the research staff and received an explanation of the protocol. Subjects read and completed an Informed Consent form and a questionnaire regarding their hockey background. Subjects were instructed to warm-up for a period of approximately 10 minutes to be ready for maximal effort trials. This period allowed the subjects to familiarize themselves with the skates, especially for the prototype. This time was also necessary for the strain gauges to adapt to the ice level temperature. The lace width was measured at the top, middle and bottom part of the skate for each model. This was done to insure that lacing was consistent. However, eyelet configuration differed between skate types.

3.2.4 TESTING

The subjects completed three different tasks (Figure 10) consisting of forward skating and forward crossovers on both sides. The subjects were instructed to skate at maximal speed during the performance of these skills.

Skaters performed two good trials for each task and condition. This reduced the

number of trials and decreased the potential of fatigue on performance. Subjects began in a standing position behind the line with the right foot in midair and started after a verbal command from the investigator. Once the investigator had given the command to start, the subject could start whenever he felt ready and the trial began when the subject initiated the ice contact with the right foot. This starting procedure was the same for all other tasks and conditions. The skaters started by pushing off with the right skate (instrumented skate). The participants were given one minute to recover between trials to avoid fatigue

(Weineck, 1997). After every condition (skate type), the data was visualized on the computer monitor to confirm that the trials were successful.

3.2.4.1 Forward skating

Forward skating was evaluated by having the subjects skate from the goal line to the second blue line at maximum speed. The distance covered was

34.25m on an official North American ice hockey rink. It was important that the subject maintained a linear trajectory while covering this distance. The time taken to cover this distance was measured with the signal produced by the strain gauges. The subject was instructed to lift his right foot in midair as he passed the second blue line. This procedure allowed the determination of the end of the trial as the force signal returns to zero. The start of the event was determined as the moment the blade hit the ice and the end of the event was determined to be the moment the skater crossed the second blue line. The camera was positioned

on the red line on the opposite side of the ice from the skater’s path. The camera followed the skater as he skated using a sagittal view.

3.2.4.2 Forward crossovers

In order to analyze the crossovers on the outside as well as the inside leg, a trial was completed with the subject skating to the right, stopping at the blue line and skating to the left (opposite direction). Crossovers were executed by skating behind the net, starting at the blue line and finishing at the same blue line on the opposite side of the rink. The distance covered was 56.60m when properly executed. The path followed by the subjects was restricted with pylons and if the trajectory of the task was not respected, the trial was repeated. The camera was placed on the middle of the rink for both crossovers tasks.

coi fs

coo

Figure 10 – The path of the skater during the three tasks: forward skating (fs), crossovers inside foot (coi), crossovers outside foot (coo). The arrows represent the skating direction, the orange circle the pylons and the green triangles the camera placement.

3.3 EQUIPMENT

3.3.1 INSTRUMENTED FORCE TRANSDUCER SYSTEM

Prior to testing and during pilot work strain gauges were placed on the blade holder of the right skate only, at five different places as described previously (Stidwill, 2009). In order to measure vertical strain, a strain gauge was positioned on top of the blade holder at the bottom of the tuck in the middle of the skate (Figure 11). The four other strain gauges were placed on the sides of the skate; two on the anterior portion and two on the posterior portion (Figure

11). The two anterior strain gauges were paired, as were the two posterior strain gauges and the medial or lateral strain was calculated from the anterior and posterior portion of the blade holder.

Vertica l Posterior Anterior medial Posterior medial A B medial

Figure 11 – Picture of the strain gauges on a DROM skate. The arrows indicate which strain gauges are shown. The lateral strain gauges are at the same position as the anterior gauges, but on the opposite side.

Wires were soldered to the strain gauges and glued on the back of the skate to avoid any interference with the skater’s movements. The wires were connected to a box that contained 3 Wheatstone half-bridges. The half-bridges for the anterior and posterior post of the blade holder are composed of two resistors of 350Ω and two 0.125” long strain gauges (one on the medial side and one on the lateral side) with an excitation voltage of 2V ± 2%. The half- bridge for the vertical strain was paired with a dummy gauge for temperature compensation, which was placed inside the strain gauge box. The circuit (Figure

12) was designed on the Express PCB (Printed Circuit Board) program (Boston,

USA) to guarantee all the components were properly connected. This custom design was printed on paper, transferred on a copper board, which was etched.

Subsequently, all the soldering was done according to the design and the board was placed inside an aluminium box for protection. The strain gauges were the unknown resistor for the bridges as their resistance was changing with the deformation of the blade holder. This circuit allowed the conversion of the resistances from the strain gauges into voltage signals (two strain gauges for one signal). Finally, the strain gauges were covered with a flexible paste to protect the connections and prevent a signal deviation without interfering with the signal.

Figure 12

(A) Circuit board design (2:5 scale)

(B) Resistors and dummy strain gauge under the board (2:5 scale)

A B

3.3.2 DATA ACQUISITION

The measurement system consisted of the instrumented skate, the strain gauge box and a portable 13 bit analog to digital converter (DataLOG model

P3X8, Biometrics Ltd, Gwent, UK) referred to as the data logger. A microprocessor controlled Digital Acquisition Unit (DAQ) saved the strain files to a 512 MB MMC flash memory card onboard the data logger in a proprietary .RWX format. The DAQ was set to a sensitivity of 10 mV, and was sensitive to signal changes of 0.0025 mV.

3.3.3 CALIBRATION OF THE FORCE TRANSDUCER SYSTEM

The strain readings from strain gauge system were converted to force by correlating them to the forces measured on a force plate (AMTI OR-6, Inc.,

Watertown, USA). The calibration was done separately for medial, lateral and vertical force and the procedure was done for every pair of skates (right skate only). The medial and lateral load procedures were similar (only on different sides of the blade). The boot of the skate rested on a wooden base of support that allowed the skate to be at a proper height for the force plate. The blade lay evenly and flat on top of the force plate (the base provided the appropriate angle for the One95 model). Only the blade was in contact with the force plate. To insure proper loads on the force plate, a wooden device was constructed to distribute the force evenly across the anterior and posterior post. The two contact points for force application were on the bottom of the big hole in the blade holder (Figure 13). One contact point was on the anterior portion of the blade holder and the other contact point was on the posterior portion of the blade holder. As the procedure did not allow pushing directly on the blade (the force plate would correctly record, but the strain gauges would not record at all as the signal comes from the blade holder deformation), this part of the blade holder would transfer the force directly to the blade. This wooden device made the calibration consistent, because the manual loads with the hands cannot be evenly distributed without this construction. The calibration included slow, medium and fast loading rates. The objective was to represent the different

forces applied in a manner similar to that seen during skating. The forces were measured for approximately a minute and involved at least 20 loads. The fast loading rate was more frequently used as it presumably reflects skating conditions more realistically. The manual loading also offered the advantage of a dynamic calibration.

Force Plate

Wooden device Figure 13

Lateral calibration Base of setup (top view) support

For the vertical calibration, the support of the skate was different. A wooden foot was constructed to distribute the force evenly inside the skate boot. A hole was pierced in the middle of this wooden foot and other wood pieces mounted on it to allow a metal rod to enter tightly (Figure 14A). A large wooden lever was constructed to generate high vertical forces. The metal rod transferred the forces from the lever directly to the skate and force plate (Figure

14B & 14C). In previous studies (Stidwill, 2009), this procedure was executed by putting the skate on and simply stepping on the force plate. The calibration was adequate, but the peak forces obtained were close to bodyweight. The intent of

the lever setup was to reach higher peak forces similar to on-ice skating. With the lever it was possible to reach peak forces of 2000 Newtons by manually pressing, while on-ice skating peak forces usually reach up to 1500 Newtons or lower (Stidwill, 2009). The lever made it possible to generate high vertical forces in a consistent manner. The objective of this procedure was to avoid extrapolation of the linear regression line for forces over bodyweight. During the calibration the loading procedures were the same as for medial and lateral loading.

Figure 7 – Vertical calibration setup.

(A) Wooden foot (B) Real setup (C) Model setup

A B

Lever

Free Metal Rod Weights

Wooden Foot

Force Plate Skate

3.3.3.1 Theory for calibration

The calibration procedure is based on the linear relationship between strain and force. The plot of strain against force of the calibration shows this linearity

(Figure 15). Solids tend to maintain their shape when forces are applied to them, but they may stretch, twist or be compressed (Myers, 2006). The strain gauges on the plastic blade holder read this deformation. According to Hooke’s law of elasticity, strain is directly proportional to force (the restoring force is equal to the force constant times the displacement from its equilibrium position)

(Woolfson and Woolfson, 2007; Frederiksson and Akerlind, 2008). This formula applies when the elastic limit is not exceeded. During skating, the deformation of the blade holder is on a rather small scale and is only temporary as the blade holder returns to its equilibrium position after the push-off force. The calibration is based on the assumption that the plastic blade holder of the skate is a linear- elastic material. Poisson’s ratio determines the reaction of the materials to strain; when a material is stretched it tends to contract in the other two directions perpendicular to the stretch (Frederiksson and Akerlind, 2008).

Poisson’s ratio equals negative transverse strain over axial strain; since this value is a constant it does not affect the linearity of the relationship for any type of material.

Figure 15 – Linear relationship of strain to force

During the calibration, the signals from the force plate and the strain gauges were recorded. The two signals were synchronized and scaled in Matlab with a cross-correlation between the two signals (Figure 16). The advantage of this method is that both signals are completely included in the calibration compared to a point loaded approach. Theoretically, the correlation coefficient should be equal to 1; the nearer to 1 is the cross-correlation coefficient

(Woolfson and Woolfson, 2007). The cross-correlation aligns the signals to obtain the highest possible correlation coefficient, so there is no need for

synchronization of the signals (Woolfson and Woolfson, 2007). The cross- correlation function is also a powerful method of distinguishing signals from noise

(Woolfson and Woolfson, 2007). An example of the force plate signal compared to the calibrated strain gauge signal can be seen in Figure 17. The cross- correlation resulted in high coefficients of correlation for all the skates with r =

0.95 as a minimum and almost all the calibration procedures correlating to 0.98 or higher (Table 1; Table 2). For each medial and lateral loading calibration, a linear regression was calculated for the anterior post and posterior post. With the use of the slope and intercept of the regression line for each skate, the calculation of force from strain was derived.

Figure 16 – Crosscorrelation example

Figure 17 – Example of a comparison of the calibrated strain signal and force signal

Table 1 Calibration results for the Regular skates

Skate size Calibration Strain Regression line Coefficient of Linear fit gauges correlation (r) (r squared)

7.5 Lateral AML 585.6787x – 2.6406 0.9969 0.9938

PML 291.877x – 8.9541 0.9903 0.9807

Medial AML 447.2728x – 4.2835 0.9961 0.9922

PML 167.4512x – 30.4375 0.9856 0.9714

Vertical V 841.028x + 76.5206 0.9965 0.9931

8 Lateral AML 548.7997x – 19.8011 0.9849 0.9700

PML 381.4782x – 4.5922 0.9831 0.9665

Medial AML 435.3729x – 5.4565 0.9963 0.9926

PML 258.1347x ‐14.1091 0.9958 0.9916

Vertical V 907.2775x – 24.3179 0.9980 0.9960

8.5 Lateral AML 973.0938x ‐4.6092 0.9970 0.9940

PML 275.7718x – 3.8672 0.9963 0.9926

Medial AML 551.938x – 2 454 0.9913 0.9827

PML 167.2126 – 16.3145 0.9905 0.9811

Vertical V 1457.293x + 18.2977 0.9973 0.9947

9 Lateral AML 707.9087x – 6.4666 0.9790 0.9584

PML 335.0752x – 6.9814 0.9859 0.9720

Medial AML 385.355x – 2.9548 0.9987 0.9974

PML 229.9453x ‐0.92476 0.9973 0.9946

Vertical V 898.0484x + 74.8041 0.9941 0.9882

Table 2 Calibration results for the DROM skates

Skate size Calibration Strain Regression line Coefficient of Linear fit (r gauges correlation (r) squared)

7.5 Lateral AML 893.3535x – 6.9401 0.9863 0.9728

PML 425.8155x + 20.8219 0.9787 0.9579

Medial AML 841.097x + 0.94421 0.9881 0.9763

PML 413.9451x – 3.3157 0.9919 0.9839

Vertical V 617.372x – 37.9032 0.9729 0.9466

8 Lateral AML 1383.5855x – 0.78268 0.9900 0.9801

PML 447.1821x – 13.015 0.9871 0.9744

Medial AML 1773.2835x + 7.1604 0.9899 0.9799

PML 397.196x – 7.6085 0.9861 0.9724

Vertical V 1031.29x – 17.8644 0.9975 0.9950

8.5 Lateral AML 997.7994x + 18.809 0.9909 0.9819

PML 443.1652x – 23.3834 0.9887 0.9775

Medial AML 1157.3355x – 4.2707 0.9946 0.9892

PML 263.7522x – 16.1869 0.9924 0.9849

Vertical V 1431.105x + 19.6478 0.9954 0.9908

9 Lateral AML 2558.9731x – 28.8752 0.9836 0.9675

PML 417.7267x + 34.2757 0.9743 0.9493

Medial AML 1112.8447x + 39.8979 0.9229 0.8517

PML 498.223x – 9.2084 0.9793 0.9590

Vertical V 1764.553x + 23.5617 0.9912 0.9826

The subjects performed a bodyweight trial following the warm-up, this procedure intended to validate the strain gauge technology. The subjects were asked to apply all their weight on the right instrumented skate and the strain gauge signal was recorded. Subjects were not able to distribute their weight evenly. The resulting signals fluctuated as seen in the example of Figure 18, thus complicating the identification of the actual weight in the signal.

Figure 18 Representative bodyweight trial from a subject

The investigator tested every pair of skates with its own bodyweight to confirm that the calibration was adequate. The force transducer system

estimated the bodyweight of 553 Newtons for the investigator with precision, averaging 553.6 ± 7.8 Newtons for all eight skates corresponding to an average percentage of error of 0.1 ± 1.4%. The signal was always interpreted when it was the most stable. A typical bodyweight trial from the investigator can be seen in Figure 19.

Figure 19 – Typical bodyweight trial from the investigator

3.3.4 GONIOMETRY

The SG series twin axis electrogoniometer (Figure 20) used is lightweight, flexible and non-invasive. These goniometers consist of two lead wires

protruding from one end block and transferring the electrical signal to the data logger. Ouckama (2007) found that electrogoniometers have a very high correlation (r2 = 0.78-0.97) (p < 0.0001) to motion capture systems at the ankle joint when installed vertically along the posterior of the subjects’ ankle when walking or running.

Figure 20 SG series twin axis electrogoniometer

Biomectrics Ltd. provides the following specifications concerning the electrogoniometer used in this study:

Table 3 – Biometrics Ltd. electrogoniometer specifications

Minimum life cycles 600 000 cycles

Accuracy ± 2º measured over 90º from the neutral position

Repeatability Better than ± 1º

Cross talk ≤ ± 5% over ± 60º

Recommended operating temperature 0 to +40ºC

3.4 DATA PROCESSING

Data acquisition was completed in a similar fashion as done previously and modified during pilot studies (Stidwill, 2009). The data from the strain gauges and the goniometers were recorded at 100 Hz in the data logger carried in the backpack by the subject. DataLOG software (v.3.0; Biometrics Ltd., Gwent, UK) was used to import the .RWX files and save them as binary .LOG files. All of the data manipulation and analysis of the strain and goniometer data were performed on custom made Matlab programs (The Math Works, Inc., Natick, USA). Data were imported into Matlab. The data were then filtered using a fourth order

Butterworth low pass filter with a 14Hz cut-off for the strain data and a 6Hz cutoff for the goniometer data. The cut-off frequency was determined by a Fast

Fourier Transform (FFT) performed on the raw data to decipher true signal from noise. 99% of the signals were below 10 Hz; an example is shown in figure 21.

Figure 21 – FFT of strain gauge data (the cutoff frequency was set at 6 Hz).

Temperature differences between the ice and the laboratory could affect strain gauge response and thus impact the strain data. Since the calibrations were done in the laboratory at a temperature of 21ºC and the temperature during on-ice testing was closer to 1.5ºC, a correction factor for these temperature differences is needed. Stidwill (2009) completed warm and cold calibrations on the ice rink and in the laboratory used in the present study. The average difference in the strain readings from the in-lab calibration and the on-ice calibration across all subjects represented the temperature correction factor

(1.2) for on-ice conditions.

To identify the start of the trial from the analog data, during testing the subject would begin with the right foot in the air and to preliminarily “zero” the strain channels. Similarly, the subject also finished each trial by lifting is right foot to determine the moment when the trial ended. Subsequently, the data were digitally zeroed (i.e. adjusted to baseline) for every strain channel based on the first ten frames.

The strain data were converted to force units using the calibration equations obtained from pre-testing on the force plate. The total resultant force was calculated by vector addition of the medial-lateral and vertical forces.

Subsequently, the force data was divided by body weight (Newtons) to express measures as a percentage of body weight. Examples of force data for the forward skating with the Regular skate and the crossovers (inside foot) with the

Regular skate are shown in figure 22 and 23.

Figure 22 – Force data during a crossovers (inside foot) trial with the Regular skate

Figure 23 – Force data during a forward skating trial with the Regular skate

For the kinematics data, the reference (zero) position was collected while sitting (the foot and the tibia making a 90º angle). This non-weight bearing position avoids ankle eversion.

To extract skating strides (e.g. skate contact and push-off) of interest, digital video files were referenced. It was possible to evaluate the number of strides occurring during the trials. For forward skating, the first three strides were captured to represent the acceleration phase and the fourth to last stride were captured to represent the maximum velocity phase (Hoshizaki, 1987;

Marino and Weese, 1979). For crossovers, observing the video files, consistent patterns were observed. Usually, the first four strides were forward skating strides and the next five to seven were crossovers strides, so these latter strides were identified as events to represent the skill. The peak forces were recorded for all the forward skating and crossover events for every stride.

Using Matlab scripts, the start and end of every stride were marked as time events so as to calculate the average force, contact time and impulse. Contact time was calculated as the amount of time the force was being applied. Total force, impulse, work and power were calculated from the following equations:

2 2 FT = √(FV + FML )

I = FT x tC

W = FT x ∆d

P = W / tT

where

FT: Total force

FV: Vertical force

FML: Medial-lateral force

I: Impulse

tC: Contact time

W: Work

∆d: distance covered on the ice during a trial

P: Power

tT: Time of the trial

The events of interest for foot and ankle motions were the maximum and minimum values during the strides. The pattern of the kinematics data followed the force data so it was possible to identify movements that occurred during stride contact time (i.e. not during the swing phase). An example of the kinematics data for forward skating with the DROM skate can be found in figure

24.

During the total peak force, the kinematics of the ankle were observed.

While reaching the peak force, the plantarflexion angle and eversion angle were determined.

Figure 24 – Kinematics of the ankle during a forward skating trial with the DROM skate

3.5 DATA ANALYSIS

Each subject wore two different skate models including the Regular and the

DROM. Skate type is the first independent variable. The second independent variable consists of the three skating tasks performed by the subject with each skate model. The variables derived from the strain data and the range of motion data obtained from the goniometers during the skating tasks with the two skate models represent the dependent variables analyzed in this study. All relevant independent and dependent variables are outlined below.

Table 4 – Description of the variables

Variable Type Scale Definition

Skate type Independent Categorical (1) Regular skate variable (2) DROM skate

Skating tasks Independent Categorical (1) Forward skating variable ‐ Acceleration

‐ Maximum speed

(2) Crossovers (inside foot)

(3) Crossovers (outside foot)

Force obtained from Dependent Continuous - Peak force the strain gauges variable - Average force (medial‐lateral, - Contact time and Stride rate vertical and total) - Impulse - Work and Power Ankle kinematics Dependent Continuous - Plantar/dorsiflexion ROM obtained from the variable - Inversion‐eversion ROM goniometer - Angle at peak force

3.6 STATISTICAL ANALYSIS

A two-way multivariate analysis of variance (MANOVA) with repeated measures was conducted to compare the differences between the skate models for the three tasks. The significance level of α = 0.05 was set in order for the results of the statistical analysis to be considered statistically significant.

3.6.1 POWER ANALYSIS

A power analysis was performed with the G*power 3.0.10 (G*power,

Dusseldorf, Germany) software to determine the required sample size for the

study. A MANOVA with repeated measures between factors was conducted.

Using the forward skating data from the pilot study, an a priori procedure was used to compute the required sample size, given α, power and effect size. The effect size was calculated with the means and standard deviations of the pilot study involving three subjects. The alpha level of error was set to α = 0.05 and the power was set to 0.8; these are judged to be acceptable by previous literature (Spatz, 2001). For the average force, 10 subjects was the required sample size, for plantar/dorsiflexion ROM, 8 subjects and for peak medial-lateral force, 10 subjects. Based on the power analysis 10 subjects were recruited. The results of a power analysis conducted by Stidwill (2009) yielded a similar recommendation of 10 subjects and the research design was comparable to the present study.

3.7 ETHICAL CONSIDERATIONS

Since the subjects involved in this study are experienced hockey players, the risks are minimal. The on-ice skating skills represent basic skating abilities for players of this calibre. The subjects will be required to wear a Canadian Standards

Association (CSA) approved helmet during all on-ice skating. The subjects’ information collected prior to the testing will be kept confidential. These records will be maintained at the McGill University Biomechanics Laboratory by the principal investigator and faculty supervisor for five years after the completion of the project. The information will be accessible to the research staff only and in

case of publication of the results, the identification of the subjects will be kept private.

The completion of the informed consent form by the subjects will be mandatory prior to each testing session. The subjects will be advised that their participation in the study is voluntary. If the subjects experience any discomfort or for any reason they are uncomfortable about their participation in the study, they may withdraw from the study. The consent form (Appendix 1) outlines the methodology of the study and explains the risks involved.

This project has been approved by the McGill University Research Ethics

Board (REB file # 336-0508). The approval form is in Appendix 2.

CHAPTER 4 – RESULTS

Descriptive and inferential statistics of these dependant variables are presented below in graphical format including means and standard deviations

(SD). Significant differences set to α = 0.05 are identified in the graphs with asteriks. The exact results are presented in table 5 at the end of the chapter. Full details on the MANOVAS tables are available in Appendix 3.

4.1 TIME MEASURES

When comparing measures between skate types, no differences were seen for contact time, stride rate or total time to complete the task (Figures 25, 26 and 27) during forward skating (both acceleration and constant speed phases) or crossovers turns (both clockwise and counter clock-wise).

Contact time 0.5

0.4

0.3

0.2 Regular DROM 0.1

Contact time (seconds) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 25 – Contact time (mean ± SD) in the three skills involving the two skate types

Stride rate 2 1.75 1.5 1.25 1 Regular 0.75 0.5 DROM 0.25

Stride rate (strides/sec) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 26 – Stride rate (mean ± SD) in the three skills involving the two skate types

Time to completion 9 8 7 6 5 4 Regular 3 DROM

Time (seconds) 2 1 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 27 – Time to completion (mean ± SD) in the three skills involving the two skate types

4.2 KINEMATICS

The kinematics about the foot and ankle include maximal dorsiflexion, plantarflexion, inversion, eversion as well as net range of motion (ROM) in

plantar/dorsiflexion and inversion/eversion during the contact time. The passive movement (i.e. the swing phase) was not included in the calculation. For every condition and subject, the average was calculated for all the strides involved.

The ROM is expressed as angles in degrees. In addition to the above, the kinematic plantar/dorsiflexion and inversion/eversion angles also were presented corresponding to total peak force.

The width of the laces, which reflect how tightly the subjects laced their skates, was measured at the top, middle and bottom for every subject and they were not different between skate type. The width of the laces when the subjects wore the Regular skate at the top, middle and bottom part of the skate averaged

7cm, 7.5cm and 5.8cm, while in the DROM skate laces widths averaged 6.6cm,

7.2cm and 5.9cm respectively. Thus, the lacing between skate types should not have a notable effect on skating kinematics.

4.2.1 INVERSION / EVERSION

Maximal inversion was more pronounced for the DROM skate for all skating tasks. DROM Inversion was significantly greater than the regular skate for the inside foot during crossovers (Figure 28). Inversion attained during forward skating was similar between skates for both acceleration and constant speed phases. The maximal eversion showed no significant differences between skate types for both the forward skating and crossovers (outside foot) skills (Figure

29). The inversion-eversion ROMs were slightly higher (0.5 to 2.0°) for the DROM skate for all on-ice skills but not significantly different (Figure 30).

Maximal Inversion ()

Crossovers Crossovers Forward Skating (outside foot) (inside foot) 0 ‐1 ‐2 ‐3 Regular ‐4 DROM ‐5 ‐6 ‐7 ‐8

Ankle angle (degrees) ‐9 ‐10 * Figure 28 – Mean inversion (± SD) in the three skills by skate types (* p < 0.05)

Maximal Eversion (+) 16 14 12 10 8 6 Regular 4 DROM 2 0 Ankle angle (degrees) ‐2 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 29 – Maximal eversion (± SD) in the three skills by skate types

InversionEversion ROM

20 18 16 14 12 10 Regular 8 6 DROM 4 2

Ankle motion (degrees) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 30 – Inversion and eversion range of motion (± SD) in the three skills by skate type

4.2.2 DORSIFLEXION / PLANTARFLEXION

Maximal dorsiflexion was more pronounced for the DROM skate for all on- ice skills, but significantly different only for the outside foot of crossovers by more than 4º for the DROM versus Regular skate (Figure 31). Similar dorsiflexion angles were found for both forward skating phases of acceleration and constant velocity.

Maximal plantarflexion was significantly higher (3 to 5º) for the DROM skate for all skills (Figure 32). In forward skating this difference was only observed during the acceleration phase.

The ROM was clearly higher for the DROM skate in the plantar/ dorsiflexion plane for all skating tasks. The means were significantly different for the forward skating and crossovers (outside foot) task and close to significance for

crossovers (inside foot) (Figure 33). Both phases of the forward skating yielded a significantly increased plantar/dorsiflexion ROM with the DROM skate.

Maximal dorsilexion ()

Crossovers Crossovers Forward Skating (outside foot) (inside foot) 0 ‐4 Regular ‐8 DROM ‐12 ‐16 ‐20 Ankle angle (degrees) ‐24 *

Figure 31 – Mean dorsiflexion (± SD) in the three skills by skate types (* p < 0.05)

Maximal plantarlexion (+) 25 * 20 *

15 *

10 Regular DROM 5 Ankle angle (degrees) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 32 – Maximal plantarflexion (± SD) in the three skills by skate types (* p < 0.05)

Plantardorsilexion ROM 40 * 35 * 30 25 20 Regular 15 10 DROM 5 Ankle motion (degrees) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 33 – Mean plantar/dorsiflexion ROM (± SD) in the three skills by skate types (* p < 0.05)

4.2.3 KINEMATICS AT PEAK FORCE

The eversion angle at peak force was not significantly different between skate type for all skating tasks (Figure 34). Similarly, these eversion angles were the same for forward acceleration and constant velocity skating.

Eversion (+) angle at peak force 14 12 10 8 6 4 Regular 2 DROM 0 ‐2 Ankle angle (degrees) ‐4 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 34 – Mean eversion angle at peak force (± SD) in the three skills by skate types

With the DROM, significantly more pronounced plantarflexion for all the skating tasks was evident at peak force (Figure 35). This was primarily seen in the acceleration phase (Figure 36).

Plantarlexion (+) angle at peak force

21 * 18 * 15 12 * 9 Regular 6 3 DROM 0 Ankle angle (degrees) ‐3 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 35 – Mean plantarflexion angles at peak force (± SD) in the three skills by skate types (* p < 0.05)

Plantarlexion (+) angle at peak force

18 * * 15 12 9 Regular 6 DROM

Anke angle (degrees) 3 0 Task Acceleration Constant speed

Figure 36 – Mean plantarflexion angles at peak force (± SD) in the forward skating (task), and phases of acceleration and constant speed by skate types (* p < 0.05)

4.3 KINETICS

The force data were normalized as a percentage of body weight. All data were averaged by strides involved in the skill performed and separated per condition. The forward skating task was analyzed a step further by looking at the acceleration phase (defined as the first three strides) and the constant speed phase defined by the fourth to last stride. For the crossovers skating tasks, the strides involved in the skill were only at constant velocity.

4.3.1 VERTICAL FORCE

For all on-ice skills, the DROM skate yielded slightly higher average vertical force (2 to 9 % bodyweight), though not significantly different (Figure 37). No differences were noted during acceleration or constant speed phase. With regards to vertical peak force again no significant differences were found (Figure

38). The vertical peak force did not vary much between the acceleration and constant speed phases of forward skating.

Vertical Average Force 100 90 80 70 60 50 40 Regular 30 DROM 20 10 Force (% Bodyweigth) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 37 – Mean vertical average force (± SD) in the three skills by skate types

Vertical Peak Force 180 160 140 120 100 80 Regular 60 DROM 40 20 Force (% Bodyweigth) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 38 – Mean vertical peak force (± SD) in the three skills by skate types

4.3.2 TOTAL FORCE

The total average forces (the combination of vertical and medial-lateral forces vectors) tended to be greater (5 to 8% of bodyweight) with the DROM

skate for all skating tasks; however, these differences were not significant

(Figure 39). Likewise, no difference in total peak forces were found (Figure 40).

Total Average Force 100 90 80 70 60 50 40 Regular 30 DROM 20 10 Force (% Bodyweigth) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 39 – Mean total average force (± SD) in the three skills by skate types

Total Peak Force 180 160 140 120 100 80 Regular 60 DROM 40 20 Force (% Bodyweigth) 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 40 – Mean total peak force (± SD) in the three skills by skate types

4.3.3 MEDIAL-LATERAL FORCE

The medial-lateral average forces were significantly higher (7 to 10% of bodyweight) in forward skating and the outside foot of crossovers (Figure 41).

This was significantly higher during forward acceleration. The medial-lateral peak forces were higher with the DROM for all on-ice skills, in particular the inside foot of crossovers (Figure 42) and during forward acceleration (p<0.05).

MedialLateral Average Force

60 * * 45 30 15 0 Regular ‐15 DROM ‐30 Force (% Bodyweight) ‐45 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 41 – Mean medial-lateral (+ve Medial; -ve Lateral) average force (± SD) in the three skills by skate types (* p < 0.05)

MedialLateral Peak Force 125 100 75 50 25 Regular 0 ‐25 DROM ‐50 Force (% Bodyweight) ‐75 * Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 42 – Mean medial-lateral (+ve Medial; -ve Lateral) peak force (± SD) in the three skills by skate types (* p < 0.05)

4.3.4 IMPULSE

Impulse did not show a major difference between skate types (Figure 43).

Impulse 35 30 25 20 15 Regular 10 DROM

Impulse (N*sec/kg) 5 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 43 – Mean impulse (± SD normalized to bodyweight) in the three skills by skate types

4.3.5 WORK AND POWER

Total work during the skating tasks tended to be higher for the DROM skate for all on-ice skills, but were not significantly different. (Figure 44). Power measures were similar to work showing greater values and standard deviations for the DROM skate for all on-ice skills (Figure 45).

Work 4000 3500 3000 2500 2000 Regular 1500 1000 DROM Work (Joules/kg) 500 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 44 – Mean work (± SD normalized to bodyweight) in the three skills by skate types

Power

500 450 400 350 300 250 200 Regular 150 DROM 100 Power (watts/kg) 50 0 Forward Skating Crossovers Crossovers (outside foot) (inside foot)

Figure 45 –Mean power (± SD normalized to bodyweight) in the three skills by skate types

4.4 COMPLETE RESULTS

Table 5 Complete results including means with standard deviations in parentheses and significance between skate types

Skating tasks Forward Skating Crossovers Crossovers (outside foot) (inside foot) Skate types Regular DROM Regular DROM Regular DROM Contact time 0.33 0.31 0.37 0.36 0.33 0.33 (sec) (0.05) (0.07) (0.06) (0.13) (0.05) (0.08) p = 0.489 p = 0.682 p = 0.790 Stride rate 1.64 1.67 1.55 1.56 1.67 1.68 (strides/sec) (0.15) (0.13) (0.18) (0.24) (0.24) (0.20) p = 0.630 p = 0.900 p = 0.974 Time to 5.03 5.04 8.12 8.01 7.21 7.30 completion (0.35) (0.29) (0.67) (0.54) (0.53) (0.53) (sec) p = 0.685 p = 0.384 p = 0.669 Minimal -3.17 -4.28 -3.85 -6.01 -3.85 -6.67 inversion (º) (1.74) (3.40) (2.69) (2.77) (1.50) (3.00) p = 0.454 p = 0.164 p = 0.045 Maximal 9.53 10.30 10.07 10.28 5.82 3.73 eversion (º) (2.23) (2.98) (2.31) (4.45) (2.22) (4.54) p = 0.597 p = 0.915 p = 0.295 Inversion- 12.70 14.58 13.92 16.29 9.67 10.41 Eversion ROM (2.79) (3.95) (2.76) (4.17) (1.69) (3.19) (º) p = 0.324 p = 0.234 p = 0.598 Minimal -11.29 -15.22 -11.79 -17.17 -5.89 -7.03 dorsiflexion (º) (3.38) (6.92) (4.09) (4.72) (3.80) (5.36) p = 0.202 p = 0.042 p = 0.653 Maximal 12.98 16.80 7.54 11.49 17.73 21.36 plantarflexion (3.36) (1.97) (3.96) (2.60) (2.89) (2.63) (º) p = 0.023 p = 0.047 p = 0.030 Plantar- 24.27 32.02 19.33 28.67 23.61 28.40 dorsiflexion (3.11) (6.67) (4.90) (5.68) (3.24) (5.95) ROM (º) p = 0.017 p = 0.006 p = 0.086 Eversion at peak 8.78 9.05 8.73 9.20 5.37 2.65 force (º) (2.36) (2.97) (2.48) (4.73) (2.24) (5.20) p = 0.854 p = 0.820 p = 0.228 Plantarflexion at 10.10 13.97 3.47 7.99 16.60 20.22 peak force (º) (2.95) (3.07) (3.98) (2.33) (2.82) (2.46) p = 0.033 p = 0.024 p = 0.025 Vertical average 65.85 75.44 65.26 68.81 71.18 81.05 force (% (12.75) (17.51) (12.19) (18.24) (13.04) (14.90) bodyweight) p = 0.178 p = 0.616 p = 0.132

Vertical peak 140.02 140.97 111.25 108.73 114.62 129.08 force (% (31.48) (22.27) (23.54) (23.50) (24.58) (23.77) bodyweight) p = 0.939 p = 0.814 p = 0.198 Total average 67.94 77.39 69.16 78.65 69.27 77.92 force (% (9.64) (17.48) (9.27) (16.83) (11.56) (8.67) bodyweight) p = 0.152 p = 0.136 p = 0.074 Total peak force 147.01 145.52 140.16 139.26 136.73 151.28 (% bodyweight) (29.46) (18.21) (22.68) (29.19) (28.88) (26.00) p = 0.893 p = 0.939 p = 0.252 Medial-lateral 19.65 32.78 25.80 40.83 -14.93 -17.37 average force (8.64) (16.30) (8.16) (18.46) (9.50) (22.52) (% bodyweight) p = 0.037 p = 0.030 p = 0.755 Medial-lateral 48.67 70.53 59.55 82.58 -31.42 -48.49 peak force (% (14.38) (30.89) (17.22) (34.68) (15.97) (19.24) bodyweight) p = 0.057 p = 0.076 p = 0.045 Impulse (N x 22.34 23.91 21.41 21.61 19.38 20.58 sec / kg) (4.13) (8.45) (3.63) (8.09) (5.12) (6.59) p = 0.604 p = 0.943 p = 0.654 Work (joules / 1483.14 1839.67 2395.68 2798.99 2408.86 2884.60 kg) (164.34) (584.04) (382.94) (1017.76) (442.08) (905.95) p = 0.332 p = 0.208 p = 0.209 Power (watts / 299.32 359.42 291.86 369.66 331.24 400.79 kg) (41.66) (137.92) (39.62) (147.59) (61.69) (114.19) p = 0.404 p = 0.166 p = 0.289

CHAPTER 5 – DISCUSSION

5.1 TIME MEASURES

Contact times, stride rates and time to completion were similar across skate types and tasks. In general, contact times ranged from 0.30 to 0.35 seconds, were as stride rates ranged from 1.5 to 1.6 strides/second. The time to completions (from a standing start) were approximately 5 seconds over 34.25m during forwarding skating (̃ 6.9 m/s) and 7.5 seconds over 56.60 m during forward crossover skating (̃7.5 m/s). Imprecise timing of the latter measure may have introduced greater variability. Subjects were required to lift the right foot at the end of the trial to signal its end; however, they did not complete this procedure consistently (i.e. lifting the leg slightly before or after the blue line), resulting in slight variation in the skating distance from trial to trial. Nonetheless, as common performance measures, no time differences between the regular and

DROM skates were observed.

5.2 KINEMATICS

In terms of foot and ankle movement several kinematic differences were found between the skate types, primarily with dorsi and plantarflexion variables.

Greater dorsiflexion was found with the DROM skate and reached significant difference for the crossovers (outside foot) task (p < 0.05). This difference is most likely attributable to the modification in the padded tongue and eyelets

100

configuration. The padded tongue is lighter and more flexible and the eyelets are elevated on the boot, which allow an increased dorsiflexion during skating.

Dorsiflexion was more pronounced during weight acceptance. During the crossovers, the weight acceptance is more important for the outside foot, while dorsiflexion values were lower for the inside foot which produces more force and plantarflexion. During the curve, there is a need to create a centripetal force, which is more likely to be executed at the onset of the push-off (during the weight acceptance phase) by the outside foot (Ingen Schenau et al., 1989).

When comparing the inside and outside foot during the crossovers, the results suggest that reaching greater plantarflexion contributes to more force production.

Plantarflexion was significantly greater for all on-ice tasks with the DROM skate compared to the Regular skate (p < 0.05). During the acceleration phase of forward skating, increased plantarflexion in the DROM skate (p < 0.05) was observed, while at constant speed differences were not significant (p > 0.05).

These results confirm our hypothesis: the design changes of the DROM skate enabled greater plantarflexion. The maximal plantarflexion during forward skating was 16.8º and for the outside and inside feet during crossovers 11.5º and 21.4º. All these values were approximately 4 to 5º greater in the DROM skate compared to the

Regular (p < 0.05). This was also shown at the time of peak force where the plantarflexion angles were significantly higher for all on-ice skills by approximately

101

5º with the DROM skate (p < 0.05). These results demonstrate that the skater was actively using the extra plantarflexion during ice contact push-off.

During running, the ankle reaches approximately 25º of plantarflexion, while during walking it reaches approximately 10º (Rose and Gamble, 2006). The plantarflexion values obtained with the DROM skate indicate that the ankle kinematics were more closely related to the running gait than with the Regular skate. Whole body kinematics may more clearly reveal the effect of skate design modifications. Plantarflexion and dorsiflexion increases resulted in a significantly greater ROM in the DROM skate when compared to the Regular skate (p < 0.05).

The increased ROM was primarily due to the increased plantarflexion.

Furthermore, the DROM showed greater net ROMs for the forward skating, outside and inside feet of crossovers were 7.8, 9.3 (p < 0.05) and 4.8º respectively. The construction of this DROM skate was intended to allow more freedom of movement and these results confirm that the design changes succeeded in producing extra ROM compared to a standard skate.

In general, the inversion and eversion kinematics were not significantly different for all on-ice skills. Comparing skate types, a trend of greater inversion values ranged from 3º to 4º for the regular skate versus 4º to 6.5º for the DROM skate. In one instance, greater inversion of the inside crossover foot was shown with the DROM compared to regular skate (p < 0.05). Differences in net inversion-eversion ROM were small but tended to be greater by 1.0º to 2.2º in the

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DROM skate. It would be interesting to test other skating maneuvers to determine if skaters take advantage of the increased freedom of movement.

Finally, though not statistically tested, an asymmetric trend of note was observed in kinematic measures between skate sides. In general, in crossovers the inside foot was more inverted (̃2.5º) and plantarflexed (~10º) while the outside foot was more everted (̃5º) and dorsiflexed (̃10º). These observations may be explained by the upper body lean over the inside foot during crossovers.

Further focused study on this phenomenon is warranted.

5.3 KINETICS

The peak and average medial-lateral forces exerted for all the skating tasks examined ranged from 2% to 25% of bodyweight higher for the DROM skate compared to the Regular. The medial-lateral average force was significantly different (p < 0.05) for forward skating and crossovers (outside foot) and the peak force was significantly different (p < 0.05) for the crossovers (inside foot).

During forward skating, the DROM skate had significantly higher (p < 0.05) medial-lateral peak and average forces during the acceleration phase, but not the constant velocity phase. The increased ROM afforded by the design modifications of the DROM skate may in part explain the increased potential for force production in the medial-lateral plane. It is possible that skaters were able to use their musculature in an advantageous fashion to increase force production

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instead of relying on the usual stiffness of the skate’s structure (Dewan, 2004;

Stidwill, 2009). Another explanation could be that the point of force application is displaced further medially during the push-off with the increased ROM, thus directly increasing the magnitude of the medial force vector (Winter, 2005).

The vertical force and total force patterns were closely related and this can be explained by the fact that the vertical force component accounted for most of the derived total force. The peak values were similar between the two skates for the forward skating and both crossovers tasks. However, the average force tended to be higher for the DROM skate than Regular skate by 8% to 10% of bodyweight for all on-ice skills.

The impulse results did not show a difference for any skating task. The

impulse (FT x tC) is the calculation of the area under the force curve, so this value takes into account the amount of force production and the time during which it was exerted during the stride (Winter, 2005). There was not significantly more gain in linear momentum created at every stride with the DROM skate. The impulse is indicative of the produced linear acceleration at every stride, as the mass of the skater is constant, so impulse is related to the linear velocity of the skater.

The total work developed during the whole skating task of forward skating, crossovers (counter-clockwise) and crossovers (clockwise) tended to be greater but not significantly different with the DROM skate by 225, 395 and 383 Joules

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per kg. With similar skating parameters for both types of skate, the skater using the DROM skate tended to produce more work, which should be beneficial for skating performance. Similarly, power showed to be greater (but not significantly different) for the forward skating, crossovers (outside foot) and crossovers

(inside foot) with an extra 41, 59 and 44 Watts per kg respectively gained with the use of the DROM skate or gains of 14, 20 and 14% respectively (p > 0.05).

The distance measured that was used for the power calculation was important.

Some subjects lifted the right foot 2 or 3 meters before the blue line, resulting in variability in the recorded distance for a given task completed by a given subject.

Regardless of the possible variability in the calculation of total work and power the increases in power and total work were modest and given ice friction and air resistance and the relatively brief length of the tasks performed in the present study it is not surprising that no significant differences are found in task time to completion when skate models are compared. In speed skating, the mean power outputted was 14% higher with klapskates than traditional skates, while the velocity increased by only 5.6% during the second straight of 400m rink (Houdjik et al., 2000). To increase skating velocity, there are three aspects to consider: stride rate, ice friction and work per stride. Since stride length remains constant as speed increases, stride rate is the determinant factor for velocity (Marino,

1977); in the present study stride rate was similar between skate types. In speed skating, no difference in ice friction was noted when the klapskate was compared to a conventional skate (Houdjik et al, 2001). The modification in the DROM

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skate presented no features that might affect ice friction, so it is reasonable to assume that ice friction was similar for the two skate models in the present study. Since the total work produced by skaters during the skating tasks tended to higher values with the DROM skate, work per stride should also be higher. An increased work per stride could imply a greater mechanical efficiency and minimize fatigue during the course of a game or even a single shift. The analysis of skating physiology with the DROM and Regular skates could provide more substantial results.

Speed skating reports have shown that fatigue occurs sooner in the inside leg, perhaps, because it produces more force (Ingen Schenau, 1989). Koning et al. (1991) calculated a higher power output for the inside leg than the outside of speed skaters when skating in turns. In ice hockey, peak pressure values from the sum of pressure sensors on the lateral, medial and plantar surfaces appear to be higher on the inside leg compared to the outside leg when skaters performed crossovers (Trumper, 2006). Our results substantiate this claim, since the difference between the inside (clockwise) and outside (counter-clockwise) foot during forward crossovers showed that the inside foot produces more power

(̃40 W), although statistics were not executed to establish statistical significance between the inside and outside foot on these skating tasks. This phenomenon is probably due to the mechanical constraints between the lower limbs during skating the curves (i.e. the inside leg is closer to the center of mass,

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thus benefiting of a better push-off angle) (Koning et al., 1991; Trumper, 2006;

Ingen Schenau et al., 1989).

Overall, the kinetics results in the present study indicate a clear tendency of the DROM skate to produce more force than the Regular skate although statistical significance was not achieved in all conditions and all tasks. The locomotor aspects of contact time and stride were similar across skate type for all on-ice skills. Logically with more force production, velocity should be increased. The DROM skate allowed for extra force production as reflected in the greater average force, work and power measurements. This phenomenon is likely related to an increased contribution of the calf muscles at the end of the push-off and a fuller knee extension (quadriceps) as observed with the klapskate in speed skating and although the increases were modest they demonstrate that it is possible to innovate design changes with a potentially positive impact on skating in ice hockey (Ingen Schenau et al., 1996; Houdjik et al., 2000).

The potential for kinetic gains when wearing the DROM skate were based on anticipated freer plantar/dorsiflexion kinematics. For example, a figure skating study compared jumping with skates and without skates (Haguenauer, Legreneur and Monteil, 2006). The restriction of ankle amplitude imposed by wearing figure skates was found to significantly limit the knee joint amplitude. Work output at the knee and ankle joints was significantly lowered when wearing skates. The decrease of work at the knee resulted from an early flexing moment causing a

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premature deceleration of the knee and from a reduction of knee ROM. These results show a minimization of the participation of the knee when plantarflexion is limited. It was proposed that constraining the distal joint causes a reorganization of interjoint co-ordinations and a redistribution of the energy produced by knee extensors to the hip and ankle joints (Haguenauer, Legreneur and Monteil, 2006).

This explanation is concordant with Ingen Schenau’s (1985) thoughts on the incomplete knee extension with conventional speed skates related to the absence of plantarflexion. The gastrocnemius, principal plantar flexor, is a bi- articular muscle, which can limit knee extension without a simultaneous plantarflexion.

Plantar flexors have short muscle fibers and long tendons, along with the location of the medial gastrocnemius in the skeletal system, allow high mechanical output (Bobbert and Ingen Schenau, 1988). Biomechanics of running show that the major power generator, the ankle, generates three and two times the power of the knee and hip, respectively (Ounpuu, 1990). A comparison of the mechanical output about the ankle joint in isokinetic plantarflexion and vertical jumping showed that at a given angular velocity, much larger moments were produced during jumping (Bobbert and Ingen Schenau, 1990). One explanation was that in jumping the muscles fibers operate in a more favorable region of the force-velocity relationship for these muscle groups. In a standard ice hockey skate boot, the movement of the ankle joint is limited, especially for

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plantarflexion. Thus, it was expected that the DROM skate, which enables fuller plantarflexion, would also allow the muscle fibers of the plantar flexors to operate in a more favorable region of their force-velocity relationship increasing the potential for force production.

Taking all the above findings and observations from prior literature together, the potential benefits of the DROM skates may be illuminated. The first strides of the acceleration phase are choppy (no glide) with the weight being concentrated on the front and inside of the blades (as in running) as the push-off starts from a fixed point and moves during gliding (Koning et al., 1995; Humble and Gastwirth, 1988). The angle of propulsion of the blade decreases as acceleration progresses (Hoshizaki and Kirchner, 1987). As speed increases, eversion of the lower limb also increases, thus allowing skaters to apply force in a more tangential direction to the ice surface (Lafontaine, 2007). During the acceleration phase of forward skating, medial-lateral average and peak forces, maximal plantarflexion and plantarflexion angle at peak force were all statistically different between skate types (p < 0.05), while they were not for the constant velocity phase. These results from the DROM skate tend to indicate that the transition during the acceleration phase of skating was faster and could be improved with this skate. The acceleration in hockey might arguably represent one of the most important skating skills for ice hockey performance (Greer and

Dillman, 1984; Renger, 1994; Bracko, 1998; Marino, 1983).

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One issue that should be addressed in future studies is familiarization.

Skating is a complex motor skill and many years of practice are necessary to master this skill for high-level performance (Bracko, 1998; Marino, 1984). In the present study, skaters were not able to familiarize themselves to the DROM and perhaps were not able to take full advantage of the skate design modifications in such a short period of time. In spite of this, subjects were able to produce more force from stride to stride in many of the tasks performed in the present study.

It may be that some of the increased force generated by the DROM is lost because of changes in skating technique used by the skaters with the DROM skate. Some undesirable changes in kinematics due to a lack of practice may have resulted in a reduction in mechanical efficiency. The skaters produced more work per stride, but were not able to create more forward momentum. The skating mechanics were obviously affected with the DROM skate, but perhaps the extra work was lost in medial-lateral plane as the skaters experienced a greater sway in centre of mass from side to side with every stride, while it may have been more stable in the more familiar Regular skate. This hypothesis is based on the tendency to obtain greater force output, work and power with the DROM skate, while time to completion of a trial was similar across skate type. The significantly higher medial-lateral forces could cause a slight lateral deviation of the centre of mass, because skaters are not expecting such a higher contribution for this plane of motion with the DROM skate. Some subjects seem to adapt quickly to the

DROM skate mechanics and the kinetic results were favorable, while in others

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kinetics was actually inferior to the Regular skate. The higher standard deviations on kinetics with DROM skate compared to the Regular suggest that some subjects would probably benefit from a longer period of familiarization.

5.4 FUTURE DIRECTIONS

It would be interesting to analyze other skating maneuvers that involve a bigger change of direction than crossovers. Skaters using the DROM skate may react differently while performing other skating tasks (Pearsall, Turcotte and

Murphy, 2000). An improved protocol addressing timing precision could help to more precisely calculate time and power. This would require the use of photoelectric cells to precisely measure the time to complete a given protocol.

Bilateral concurrent measures on both skates would help address this issue and enable a more exhaustive analysis of the push-off force during various on-ice tasks.

The placement of the strain gauges could be improved to more precisely calculate the force distribution from front to back. This could allow more precise determination of the weight distribution and how weight transfer occurs during the skating stride. During running, the point of force translation (POFT) moves by a mean distance of 0.201 m (Lee and Farley, 1998). If POFT is not considered in skating, peak horizontal ground reaction force (GRF) and mechanical work per step are overestimated. Nevertheless, peak vertical GRF, contact time and

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vertical center of mass displacement remain good estimates even without POFT

(Bullimore and Burn, 2005). Similar results should be expected during skating. In the present study, the single strain gauge used to measure vertical force did not consider POFT. When the force is applied directly over that strain gauge, the force estimation should be accurate, but when the force is applied slightly beside of that gauge the precision of force estimation decreases. Using multiple strain gauges mounted into full bridges or in a rosette pattern to determine POFT during the stride should be explored (Lamontagne and Doré, 1983).

5.5 CONCLUSION

From the above results, the DROM skate clearly demonstrated substantial and significant gains in plantarflexion and net dorsi-plantarflexion ROM. Though peak force measures did coincide with greater plantarflexion, in general this was not reflected in greater kinetic output except for greater medial-lateral forces

(peak and average). Total peak force occurred later during plantarflexion, suggesting that the increased ROM resulted in a more prolonged force generation during a given skating stride. The 14 to 20% increases in work and power output while wearing the DROM skates did not translate into improved times for these power skating tasks. These apparently contradictory findings may well be attributed to lack of player familiarity with the modified skate’s greater ankle mobility. Similar observations were reported with the introduction of the

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klapskate technology in the early 1990’s (Koning et al., 2000; Ingen Schenau,

1996): initial performance benefits were not achieved until after athletes committed to remodulate their skating stride technique through intentional practice. By 1994 those athletes who had adopted this technology broke all short and long track speed skating world records. Hence, to determine the DROM skate’s true performance benefits, a longitudinal study of a cohort of players training with the DROM skate is required.

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APPENDIX 1 – INFORMATION AND CONSENT DOCUMENT

Investigator: Xavier Robert‐Lachaine M.Sc. candidate

René A. Turcotte Ph.D. and David J. Pearsall Ph.D. Biomechanics Laboratory, Department of Kinesiology and Physical Education, McGill University Statement of Invitation

You are invited to participate in a research project conducted by the above named investigator. This research project will be performed at McConnell Arena, located at 3883 University Ave., Montreal, Québec, H2W 1S4. You are asked to come to one experimental session that will last up to 1 hour. We greatly appreciate your interest in our work. Purpose of the Study The purpose of this study is to compare a Regular hockey skate (Bauer One95) and a prototype skate known as the DROM (highly modified Bauer One95 without a tendon guard leaving an opened space in the back of the skate). The comparison will be made across four different conditions of skating, including forward skating, crossovers on both sides and backward skating. Specifically, the forces obtained with strain gauges produced by the right skate during the skating strides will be examined. The force data will allow the measurement of many components of the stride including peak forces (vertical, medial‐ lateral and total), average force, impulse, contact time and power. The range of motion (ROM) of the ankle during the skating strides will also be determined with electrogoniometry.

Your participation in this study involves: 1. Providing informed consent prior to the experimental session, 2. Performing four skating tasks using a pair of Nike‐Bauer One95 hockey skates and a prototype model. The procedure listed below is common to the experimental session: a. You will be outfitted with a hockey helmet (Nike‐Bauer 8500, sized accordingly), hockey skates (Nike‐Bauer One95 and prototype model, sized accordingly) b. You will be outfitted with an electrogoniometer about your ankle c. You will be asked to wear shorts or loose track pants and backpack d. You will perform four skating tasks, performing common ice hockey skating maneuvers e. You will be asked to conduct up to 2 trials per task Risks and Discomforts

It is envisioned that you will encounter no significant discomfort during these experiments. It is anticipated that a 10‐15 minute learning curve is associated when first skating with the prototype model; however, after this learning period you will feel comfortable skating with

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this type of skates. There is a slight risk that you could fall on the ice surface; however the danger is no greater than found in Regular hockey and you will be wearing a helmet in case this does occur.

Benefits The personal benefits from the study is to gain insight on the force patterns generated while skating and compare this information with other subjects if they are willing to share their personal results. The results of this study may lead to a greater understanding of the underlying mechanics of ice hockey skating, as well as to provide a tool to compare different hockey techniques.

Confidentiality All the personal information collected during the study concerning you will be encoded in order to protect their confidentiality. These records will be maintained at the Biomechanics Laboratory for 5 years after the end of the project, and will be destroyed afterwards. Only members of the research team will be able to access them. In case of presentation or publication of the results from this study nothing will enable your identification.

Inquiries Concerning this Study If you require information concerning the study (experimental procedures or other details), please do not hesitate to contact Xavier RobertLachaine or René Turcotte, at the numbers or addresses listed below. Xavier Robert‐Lachaine, M.Sc. Candidate, Tel: (514) 398‐4184 x0583, E‐mail: xavier.robert‐ [email protected] René A. Turcotte, PhD, Associate Professor, Tel: (514) 398‐4184 x0488 Fax: (514) 398‐ 4186 E‐mail: [email protected]

Responsibility clause In accepting to participate in this study, you will not relinquish any of your rights and you will not liberate the researchers nor their sponsors or the institutions involved from any of their legal or professional obligations. Consent Please be advised that your participation in this research undertaking is strictly on a voluntary basis, and you may withdraw at any time. A copy of this form will be given to you before the end of the experimental session.

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CONSENT

I, ______, AGREE TO VOLUNTARILY PARTICIPATE IN THE STUDY DESCRIBED ABOVE ABOUT THE KINEMATICS AND KINETICS OF ICE HOCKEY SKATING

I HAVE RECEIVED AND READ A DETAILED DESCRIPTION OF THE EXPERIMENTAL PROTOCOL. I AM FULLY SATISFIED

WITH THE EXPLANATIONS THAT WERE GIVEN TO ME REGARDING THE NATURE OF THIS RESEARCH PROJECT,

INCLUDING THE POTENTIAL RISKS AND DISCOMFORTS RELATED TO MY PARTICIPATION IN THIS STUDY.

I am aware that I have the right to withdraw my consent and discontinue my participation at any time without any prejudices.

Signatures

SUBJECT

______

(signature) (print name)

RESEARCHER

______(signature) (print name)

Date: ______

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APPENDIX 2 – PLAYER PROFILE FORM

Name ______Age ______Height ______

Weight ______Position played ______

Hockey experience (years) ______Highest level of competition______Shooting side (circle) R L

Dominant leg (circle) R L Skate size ______Skates usually worn ______

History of injuries ______Health condition ______

______

Other information (by the investigator): Laces width ‐Regular: Top______Middle______Bottom______‐DROM: Top______Middle______Bottom______

Ice Temperature ______

Humidity ______

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APPENDIX 3 – MANOVAS TABLES

Table 6 – MANOVA for forward skating kinetics

Sum of Dependent variable Analysis Squares df Mean Square F Sig. Medial-Lateral Between Groups 861.940 1 861.940 5.068 .037 Average Force Within Groups 3061.483 18 170.082 Total 3923.423 19 Medial-Lateral Between Groups 1242.657 1 1242.657 6.433 .021 Average Force during Within Groups 3477.194 18 193.177 the acceleration Total 4719.851 19 Medial-Lateral Between Groups 690.330 1 690.330 3.678 .071 Average Force at Within Groups 3378.850 18 187.714 constant speed Total 4069.181 19 Medial-Lateral Peak Between Groups 2391.079 1 2391.079 4.118 .057 Force Within Groups 10451.102 18 580.617 Total 12842.181 19 Medial Lateral Peak Between Groups 3870.020 1 3870.020 8.304 .010 Force during the Within Groups 8389.143 18 466.063 acceleration Total 12259.163 19 Medial-Lateral Peak Between Groups 1842.175 1 1842.175 2.496 .132 Force at constant Within Groups 13283.463 18 737.970 speed Total 15125.638 19 Vertical Average Between Groups 459.946 1 459.946 1.961 .178 Force Within Groups 4220.845 18 234.491 Total 4680.791 19 Vertical Average Between Groups 690.817 1 690.817 2.329 .144 Force during the Within Groups 5339.653 18 296.647 acceleration Total 6030.470 19 Vertical Average Between Groups 351.767 1 351.767 1.351 .260 Force at constant Within Groups 4688.136 18 260.452 speed Total 5039.902 19 Vertical Peak Force Between Groups 4.549 1 4.549 .006 .939 Within Groups 13382.697 18 743.483 Total 13387.245 19 Vertical Peak Force Between Groups 6.664 1 6.664 .007 .935 during the Within Groups 17361.608 18 964.534 acceleration Total 17368.272 19 Vertical Peak Force at Between Groups 10.621 1 10.621 .015 .905 constant speed Within Groups 13040.498 18 724.472

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Total 13051.119 19 Total Average Force Between Groups 446.461 1 446.461 2.241 .152 Within Groups 3585.684 18 199.205 Total 4032.144 19 Total Average Force Between Groups 401.044 1 401.044 2.123 .162 _average_ during the Within Groups 3400.604 18 188.922 acceleration Total 3801.647 19 Total Average Force Between Groups 496.223 1 496.223 2.077 .167 _average_ at constant Within Groups 4299.500 18 238.861 speed Total 4795.723 19 Total Peak Force Between Groups 11.163 1 11.163 .019 .893 Within Groups 10793.635 18 599.646 Total 10804.797 19 Total Peak Force Between Groups 1.144 1 1.144 .001 .971 during the Within Groups 15675.060 18 870.837 acceleration Total 15676.204 19 Total Peak Force at Between Groups 16.998 1 16.998 .033 .859 constant speed Within Groups 9368.333 18 520.463 Total 9385.331 19 Impulse Between Groups 12.337 1 12.337 .279 .604 Within Groups 796.791 18 44.266 Total 809.128 19 Impulse during the Between Groups 21.230 1 21.230 .442 .515 acceleration Within Groups 865.345 18 48.075 Total 886.575 19 Impulse at constant Between Groups 12.772 1 12.772 .230 .637 speed Within Groups 999.211 18 55.512 Total 1011.983 19 Contact time Between Groups .003 1 .003 .499 .489 Within Groups .091 18 .005 Total .094 19 Contact time during Between Groups .001 1 .001 .338 .568 the acceleration Within Groups .079 18 .004 Total .080 19 Contact time at Between Groups .003 1 .003 .382 .544 constant speed Within Groups .124 18 .007 Total .127 19 Number of strides Between Groups .139 1 .139 .279 .604 Within Groups 8.950 18 .497 Total 9.089 19

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Stride rate Between Groups .005 1 .005 .240 .630 Within Groups .340 18 .019 Total .344 19 Time Between Groups .064 1 .064 .170 .685 Within Groups 6.805 18 .378 Total 6.869 19 Work Between Groups 161884.019 1 161884.019 .994 .332 Within Groups 2930893.451 18 162827.414 Total 3092777.470 19 Power Between Groups 3883.830 1 3883.830 .730 .404 Within Groups 95737.999 18 5318.778 Total 99621.829 19

Table 7 – MANOVA for the crossovers (outside foot) kinetics

Sum of Dependent variables Analysis Squares df Mean Square F Sig. Medial-Lateral Between Groups 1129.172 1 1129.172 5.544 .030 Average Force Within Groups 3665.941 18 203.663 Total 4795.113 19 Medial-Lateral Peak Between Groups 2650.944 1 2650.944 3.537 .076 Force Within Groups 13490.079 18 749.449 Total 16141.023 19 Vertical Average Between Groups 62.810 1 62.810 .261 .616 Force Within Groups 4331.253 18 240.625 Total 4394.064 19 Vertical Peak Force Between Groups 31.686 1 31.686 .057 .814 Within Groups 9956.515 18 553.140 Total 9988.201 19 Total Average Force Between Groups 450.038 1 450.038 2.438 .136 Within Groups 3322.283 18 184.571 Total 3772.320 19 Total Peak Force Between Groups 4.070 1 4.070 .006 .939 Within Groups 12296.888 18 683.160 Total 12300.958 19 Impulse Between Groups .207 1 .207 .005 .943 Within Groups 707.894 18 39.327 Total 708.101 19 Contact time Between Groups .002 1 .002 .174 .682 Within Groups .166 18 .009 Total .168 19

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Number of strides Between Groups .139 1 .139 .372 .549 Within Groups 6.717 18 .373 Total 6.856 19 Stride rate Between Groups .001 1 .001 .016 .900 Within Groups .797 18 .044 Total .798 19 Time Between Groups .966 1 .966 .795 .384 Within Groups 21.854 18 1.214 Total 22.820 19 Work Between Groups 449460.29 1 449460.297 1.702 .208 Within Groups 4753934.40 18 264107.467 Total 5203394.69 19 Power Between Groups 8795.507 1 8795.507 2.084 .166 Within Groups 75966.444 18 4220.358 Total 84761.951 19

Table 8 – MANOVA for the crossovers (inside foot) kinetics

Sum of Dependent variables Analysis Squares df Mean Square F Sig. Medial-Lateral Between Groups 29.957 1 29.957 .100 .755 Average Force Within Groups 5377.754 18 298.764 Total 5407.711 19 Medial-Lateral Peak Between Groups 1456.340 1 1456.340 4.660 .045 Force Within Groups 5624.857 18 312.492 Total 7081.197 19 Vertical Average Between Groups 486.842 1 486.842 2.484 .132 Force Within Groups 3527.603 18 195.978 Total 4014.445 19 Vertical Peak Force Between Groups 1045.124 1 1045.124 1.788 .198 Within Groups 10520.946 18 584.497 Total 11566.070 19 Total Average Force Between Groups 374.232 1 374.232 3.586 .074 Within Groups 1878.724 18 104.374 Total 2252.956 19 Total Peak Force Between Groups 1058.546 1 1058.546 1.402 .252 Within Groups 13590.319 18 755.018 Total 14648.866 19 Impulse Between Groups 7.213 1 7.213 .207 .654 Within Groups 626.429 18 34.802 Total 633.642 19

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Contact time Between Groups .000 1 .000 .073 .790 Within Groups .105 18 .006 Total .106 19 Number of strides Between Groups .001 1 .001 .003 .956 Within Groups 7.825 18 .435 Total 7.826 19 Stride rate Between Groups .000 1 .000 .001 .974 Within Groups .861 18 .048 Total .861 19 Time Between Groups .147 1 .147 .189 .669 Within Groups 14.041 18 .780 Total 14.188 19 Work Between Groups 656459.709 1 656459.709 1.697 .209 Within Groups 6962416.322 18 386800.907 Total 7618876.031 19 Power Between Groups 8327.763 1 8327.763 1.196 .289 Within Groups 125312.759 18 6961.820 Total 133640.522 19

Table 9 – MANOVA for the forward skating kinematics

Sum of Dependent variables Analysis Squares df Mean Square F Sig. Eversion at peak Between Groups .257 1 .257 .036 .854 force Within Groups 86.531 12 7.211 Total 86.788 13 Eversion at peak Between Groups .232 1 .232 .034 .857 force during the Within Groups 82.173 12 6.848 acceleration Total 82.405 13 Eversion at peak Between Groups .224 1 .224 .029 .868 force at constant Within Groups 93.190 12 7.766 speed Total 93.414 13 Minimal inversion Between Groups 4.362 1 4.362 .598 .454 Within Groups 87.505 12 7.292 Total 91.866 13 Minimal inversion Between Groups 2.867 1 2.867 .528 .481 during the Within Groups 65.143 12 5.429 acceleration Total 68.010 13 Minimal inversion at Between Groups 5.433 1 5.433 .583 .460 constant speed Within Groups 111.802 12 9.317 Total 117.235 13

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Inversion-eversion Between Groups 12.368 1 12.368 1.058 .324 ROM Within Groups 140.285 12 11.690 Total 152.653 13 Inversion-eversion Between Groups 11.586 1 11.586 1.045 .327 ROM during the Within Groups 133.018 12 11.085 acceleration Total 144.604 13 Inversion-eversion Between Groups 12.694 1 12.694 .958 .347 ROM at constant Within Groups 158.950 12 13.246 speed Total 171.644 13 Maximal eversion Between Groups 2.040 1 2.040 .295 .597 Within Groups 82.997 12 6.916 Total 85.037 13 Maximal eversion Between Groups 2.927 1 2.927 .442 .519 during the Within Groups 79.479 12 6.623 acceleration Total 82.405 13 Maximal eversion at Between Groups 1.518 1 1.518 .210 .655 constant speed Within Groups 86.717 12 7.226 Total 88.235 13 Plantarflexion at peak Between Groups 52.240 1 52.240 5.771 .033 force Within Groups 108.635 12 9.053 Total 160.876 13 Plantarflexion at peak Between Groups 65.316 1 65.316 8.719 .012 force during the Within Groups 89.890 12 7.491 acceleration Total 155.206 13 Plantarflexion at peak Between Groups 44.242 1 44.242 3.588 .083 force at constant Within Groups 147.976 12 12.331 speed Total 192.218 13 Minimal dorsiflexion Between Groups 54.097 1 54.097 1.823 .202 Within Groups 356.068 12 29.672 Total 410.165 13 Minimal dorsiflexion Between Groups 56.071 1 56.071 2.376 .149 during the Within Groups 283.131 12 23.594 acceleration Total 339.203 13 Minimal dorsiflexion Between Groups 53.600 1 53.600 1.505 .243 at constant speed Within Groups 427.495 12 35.625 Total 481.096 13 Plantar/dorsiflexion Between Groups 210.205 1 210.205 7.753 .017 ROM Within Groups 325.346 12 27.112 Total 535.551 13 Plantar/dorsiflexion Between Groups 275.879 1 275.879 10.930 .006 ROM during the acc.

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Within Groups 302.885 12 25.240 Total 578.764 13 Plantar/dorsiflexion Between Groups 176.826 1 176.826 5.719 .034 ROM at constant Within Groups 371.015 12 30.918 speed Total 547.841 13 Maximal Between Groups 51.028 1 51.028 6.736 .023 plantarflexion Within Groups 90.902 12 7.575 Total 141.930 13 Maximal Between Groups 83.203 1 83.203 10.831 .006 plantarflexion during Within Groups 92.181 12 7.682 the acceleration Total 175.384 13 Maximal Between Groups 35.717 1 35.717 4.087 .066 plantarflexion at Within Groups 104.860 12 8.738 constant speed Total 140.577 13

Table 10 – MANOVA for the crossovers (outside foot) kinematics

Sum of Dependent variables Analysis Squares df Mean Square F Sig. Eversion at peak Between Groups .768 1 .768 .054 .820 force Within Groups 171.236 12 14.270 Total 172.003 13 Minimal inversion Between Groups 16.372 1 16.372 2.202 .164 Within Groups 89.227 12 7.436 Total 105.599 13 Inversion-eversion Between Groups 19.661 1 19.661 1.572 .234 ROM Within Groups 150.046 12 12.504 Total 169.707 13 Maximal eversion Between Groups .150 1 .150 .012 .915 Within Groups 150.691 12 12.558 Total 150.842 13 Plantarflexion at peak Between Groups 71.383 1 71.383 6.719 .024 force Within Groups 127.492 12 10.624 Total 198.875 13 Minimal dorsiflexion Between Groups 101.195 1 101.195 5.187 .042 Within Groups 234.135 12 19.511 Total 335.330 13 Plantar-dorsiflexion Between Groups 304.843 1 304.843 10.826 .006 ROM Within Groups 337.889 12 28.157 Total 642.733 13 Maximal Between Groups 54.763 1 54.763 4.886 .047 plantarflexion

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Within Groups 134.507 12 11.209 Total 189.270 13

Table 11 – MANOVA for the crossovers (inside foot) kinematics

Sum of Dependent variables Analysis Squares df Mean Square F Sig. Eversion at peak Between Groups 25.871 1 25.871 1.614 .228 force Within Groups 192.380 12 16.032 Total 218.251 13 Minimal inversion Between Groups 27.985 1 27.985 4.986 .045 Within Groups 67.347 12 5.612 Total 95.332 13 Inversion-eversion Between Groups 1.904 1 1.904 .293 .598 ROM Within Groups 78.065 12 6.505 Total 79.968 13 Maximal eversion Between Groups 15.291 1 15.291 1.199 .295 Within Groups 153.094 12 12.758 Total 168.385 13 Plantarflexion at peak Between Groups 45.798 1 45.798 6.532 .025 force Within Groups 84.138 12 7.012 Total 129.936 13 Minimal dorsiflexion Between Groups 4.591 1 4.591 .212 .653 Within Groups 259.405 12 21.617 Total 263.996 13 Plantar-dorsiflexion Between Groups 80.089 1 80.089 3.490 .086 ROM Within Groups 275.377 12 22.948 Total 355.465 13 Maximal Between Groups 46.329 1 46.329 6.069 .030 plantarflexion Within Groups 91.599 12 7.633 Total 137.928 13

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