Risk factors, assessments and prevention of muscle strain injuries

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


School of Exercise, Biomedical and Health Sciences


Faculty of Computing, Health and Science

First Advisor

Professor John Cronin

Second Advisor

Associate Professor Kasunori (Ken) Nosaka


The relationships between mechanical stiffness, eccentric exercise and muscle strain injury are emerging areas of interest to researchers. For example, asymmetries between lower body limbs during athletic movements (i.e. ground reaction forces or mechanical stiffness) are thought to increase the risk of injury and compromise performance. The first two chapters of this PhD reviewed the literature on the topics of mechanical stiffness, and the effects of eccentric exercise on optimum length for force development. Both chapters included implications for muscle strain injuries. The third chapter reviewed the previous literature that has investigated the effects of eccentric exercise on hamstring injury rates. The interventions used were critiqued, and new eccentric exercises and interventions were introduced. The following four chapters included experimental research on: first) the effects of running velocity on running kinetics (e.g. vertical and leg stiffness) (i.e. chapter 5); second) relationships between hamstring injuries and leg asymmetries during running (i.e. chapter 6); third) the relationships between training background and optimum length, and fascicle length (i.e. chapter 7); forth) a case study on an eccentric exercise intervention for a previously injured athlete (i.e. chapter 8); and, finally) the effects of eccentric exercise on the optimum angle (knee flex ors and extensors) and injury occurrence in professional soccer players (i.e. chapter 9).

The purpose of chapter 5 was to investigate the effects of running velocity of running kinetics and kinematics in Australian Rules football players. Sixteen semiprofessional Australian football players participated in this study. The subjects performed running bouts at 40%, 60%, 80% and 100% of their maximum velocity on a Woodway non-motorized treadmill. The variables of interest included: vertical force (Fv), relative veriical force (RFv), vertical stiffness, leg stiffness, horizontal force (Fb), relative horizontal force (RFb), contact times, impulse, stride frequency and stride length. As running velocity increased from 40% to 60%, RF v and RF h increased by 14.3% ((Effect Size (ES)= 1.0)) and 34.4% (ES= 4.2) respectively. The changes in RFv and RFh from 60% to 80% were 1.0% (ES= 0.05) and 21.0% (ES= 2.9). And finally, the changes in RFv and RFh from 80% to maximum were 2.0% (ES = 0.1) and 24.3% (ES= 3.4) respectively. The total increase in RFh from the slowest running speed (i.e. 40% max) to maximum was 102.0% (ES= 9.3). Vertical stiffness significantly increased between each increasing running velocity (p < 0.05) while leg stiffness remained constant. Both stride frequency and stride length significantly increased with each increasing velocity (p < 0.05). Conversely contact times, impulse and the vertical displacement of the center of mass significantly decreased with running velocity (p < 0.05). A significant positive correlation was found between Fh and maximum running velocity (r = 0.4 7). For the kinematic variables, only stride length was found to have a significant positive correlation with maximum running velocity (r = 0.66). It would seem that increasing maximal sprint velocity may be more dependent on horizontal force prodnction as apposed to vertical force production.

The purpose of chapter 6 was to quantify the magnitnde of leg asymmetry in kinetic and kinematic variables during running in non-injured and previously injured Australian Rules football (ARF) players. The players included a group of non-injured ARF players (n = II) and a group of previously injured ARF players (n = 11; hamstring injuries only). The players in the injured group had at least one acute hamsh·ing injury in the previous two years. The legs of the non-injured players were classified as dominant and non-dominant whereas the legs of the injured players were classified as injured or non-injured. The players ran on a non-motorized force h·eadmill at approximately 80% of their maximum velocity (Vmax). For the noninjured players, there were no significant differences between dominant and nondominant legs for any of the variables. For the injured players, the only variable that was significantly (p<0.001) different between the injured and non-injured leg was horizontal force production (175 ± 30 vs. 324 ± 44 N). Furthermore, the injured leg (injured group) produced significantly less (30.2% and 33.9%) horizontal force than either legs (dominant and non-dominant legs) of the non-injured group, and the noninjured leg produced significantly more (18.2% and 22.5%) horizontal force than either legs of the non-injured group. In the present study, hamstring injures appeared to have an influence on leg asymmetry in horizontal but not vertical force production during running at sub-maximal velocities.

The purpose of chapter 7 was to investigate differences in optimum angle of peak torque (knee extensors and flexors) and muscle architecture ( vastus lateralis) between nine cyclists and nine Australian Rules Football (ARF) players. The angles of peak torque of the ARF players were significantly (p<0.05) greater during knee extension 70.8 ± 3.5° vs. 66.6 ± 5.9° and smaller during knee flexion 26.2 ± 2.9° vs. 32.3 ± 3.8° compared with the cyclists. The ARF players had significantly (P<0.05) smaller pennation angles 19.3 ± 2.0° vs. 24.9 ± 2.5° and longer fascicle lengths 7.9 ± 0.7 cm vs. 6.2 ± 0.8 cm in comparison with the cyclists. There were no significant differences between groups in regards to muscle thickness or peak torque ratios between the quadriceps and hamstrings (Q/H ratio). Muscle architectural changes associated with resistance strength training need to be investigated so as the effects of training on architecture and functional perfonnance can be detennined.

The purpose of chapter 8 was to present an eccentric exercise intervention, including multi-joint and closed chain exercises, for an Australian Football player with a history of acute hamstring injuries. The athlete was a 24 year old Australian Rules football player with a medical history of three hamstring muscle strain injuries to his right hamstring in the previous four years. After the first three phases of the intervention (i.e. nine weeks), the optimum angle of peak torque during knee flexion decreased from 37.3 to 23.9° in the injured leg, and from 24.3 to 20.3° in the healthy leg. After the first nine weeks, the optimum angles remained constant for another 23 weeks. The optimum angle of peak torque was also shifted in the knee extensors by 3.9° (injured leg) and 3.4° (healthy leg) after nine weeks and remained constant for the remaining 23 weeks. Quadriceps to hamstring peak torque ratio's (Q/H ratios) and peak torque during knee flexion and extension remained constant throughout the intervention. An intervention consisting of multi-joint and closed-chain eccentric exercises can be safe and effective for altering the optimum angle of peak torque (i.e. shifting to longer muscle lengths), after acute hamstring injuries.

The purpose of chapter 9 was to investigate the effects of eccentric exercise on injury occurrence (i.e. hamstrings and rectus femoris) and optimum angle of peak torque (i.e. knee flexors and extensors) in professional soccer players. Twenty three members of a Spanish Professional League soccer team (Division II) were randomly assigned to either an eccentric exercise intervention group (EG) or a control group (CG). Both groups performed regular soccer training during the four week study, which was conducted during the clubs pre-season. After the four weeks, the optimum angles of the knee flexors were significantly (p < 0.05) decreased (i.e. increase in optimum length) by 2.0° in the CG and by 4.0° in the EG. The change in the EG was significantly different to the CG. The optimum angles of the knee extensors were significantly increased (i.e. increase in optimum length) in the EG only by 6.7°. Peak torque levels and ratios of quadriceps to hamstring (Q/H ratios) were not significantly altered throughout the study for either group. There were no injuries reported in the EG, but two rectus femoris muscle strain injuries reported in the CG. It appears that eccentric exercise can shift the optimum length of the knee flexors and extensors and these shifts may have a positive influence in reducing the incidence of injury.

LCSH Subject Headings

Edith Cowan University. Faculty of Computing, Health and Science -- Dissertations

Muscles -- Wounds and injuries

Muscles -- Physiology

Exercise -- Physiological aspects

Muscle rigidity

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