Annual Meeting Abstracts: A-03 – Featured Session: Musculoskeletal Modeling and the Prediction of In Vivo Muscle and Joint Forces
Hamstring Muscle Kinematics During Sprinting
Effective treatment and rehabilitation of individuals with hamstring muscle strain injuries remains a challenge, as demonstrated by an approximately one-third rate of recurrent injuries. An improved scientific understanding of the mechanics and function of the hamstring muscles during potentially injurious tasks, e.g. sprinting, may lend insights into injury mechanisms and provide a basis for evaluating clinical treatment and prevention strategies. PURPOSE: Test the hypothesis that increasing from sub-maximal to maximal sprinting speed increases the magnitude of peak hamstring muscle-tendon lengths and velocities in sprinters. METHODS: Three-dimensional whole body kinematics were recorded at 200 Hz while 8 athletes sprinted at 80, 85, 90, 95 and 100% of maximal running speed on a treadmill. Kinematic data were used together with a scaled, three-dimensional musculoskeletal model to compute the overall muscle-tendon lengths and velocities of the bi-articular hamstring muscles: semimembranosus (SM), semitendinosus (ST) and biceps femoris (BF). Muscle-tendon lengths and velocities were normalized to muscle-tendon lengths in an upright posture. Repeated measures ANOVA was used to determine the effects of speed on peak muscle-tendon lengths and velocities.
RESULTS: Mean sprinting speeds ranged from 7.1 m/s (80% of max) to 8.9 m/s (100%). Peak hamstring muscle-tendon lengths occurred at ∼92% of the gait cycle (terminal swing), with the muscles stretched an average of 7.4% (SM), 8.1% (ST) and 9.5% (BF) beyond nominal upright lengths. The magnitude of peak hamstring muscletendon lengths did not vary significantly with speed over the range considered. Peak lengthening velocities of 1.5 to 2.0 muscle-tendon lengths per second occurred at ∼65% of the gait cycle and increased significantly (p<0.05) with speed. CONCLUSIONS: We used experimental joint kinematics along with a musculoskeletal model to estimate individual hamstring muscle lengths during sprinting, thus providing an indication of overall strain in the muscle-tendon unit. The results suggest that muscle-tendon strains do not vary substantially as sprinting speed is increased from sub-maximal to maximal. We conclude that muscle-tendon kinematics alone may not be indicative of the potential for a hamstring strain injury in sprinters. Kinetic measures that account for the loading of the muscle may be required to more fully characterize the specific mechanisms contributing to increased risk of hamstring muscle strain injuries during sprinting.
ACKNOWLEDGEMENTS: We thank Allison Arnold of Stanford University for the musculoskeletal model. Supported by the UW-Madison Graduate School.©2004The American College of Sports Medicine