Non-contact anterior cruciate ligament (ACL) injuries are common in sports. Female athletes have a higher incidence of ACL injuries than their male counterparts. Previous studies suggest that gender differences in motor control strategies may play an important role in elevated risk for non-contact ACL injuries in women. The purpose of this study was to develop an electromyography (EMG) driven knee model to estimate and compare dynamic knee muscle force for a stop jump task between genders.

Three-dimensional kinematic and kinetic data of the knee and electrographic data from ten lower leg muscles across the knee joint were collected for ten male and fourteen female recreational athletes for stop-jumping and running tasks. An EMG driven knee model was developed to estimate individual muscle contraction force. Maximum muscle contraction forces and dynamic muscle force patterns were compared between genders. The knee model was validated by using muscle parameters calculated in stop-jump task to predict knee flexion-extension moment during running. Sensitivity analyses were also performed to assess the effect of muscle parameters on estimated muscle contraction force.

The result of the study showed a good relationship between optimized muscle moment and knee resultant flexion-extension moment for the stop-jump task. When muscle specific stress and EMG-to-force transformation coefficients estimated in the stop-jump task were used to predict muscle generated knee flexion-extension moment in the running task, however, the accuracy of the model significantly decreased. Males and females had basically the same quadriceps force in the stance phase of stop-jump. No significant difference in maximum muscle isometric contraction force was found between genders. For dynamic muscle contraction force, females had significantly higher hamstrings co-contraction than males in the stance phase of stop-jump. Males had higher gastrocnemius force in the last 30% phase than females.