Prediction of muscle force involved in shoulder internal rotation

The estimation of shoulder muscle farce is important to understand the mech anism of rotator cuff injury In general, mean parameter values are used as input For computational models. However, anatomic and biomechanical paramet ers vary widely among people. The purpose of this study was to evaluate sho ulder muscle forces predicted by an electromyography-driven muscle model gi ven neuromuscular parameters generated by Monte Carlo simulation. Normal di stributions were used to model muscle moment arms; electromyographic and mu scle physiological cross-sectional area data were modeled with log-normal d istributions. Eight muscles were included in the model. Muscle Force and jo int moment were predicted on the basis of the simulated parameters. The res ults showed that the subscapularis and pectoralis major were substantial ac tuators for shoulder infernal rotation. During maximum voluntary contractio n the median of the muscle forces of the subscapularis and the pectoralis m ajor were 1030 N and 462 N, respectively This study demonstrated that the M onte Carlo method could be used for muscle Force prediction by integrating population variability of physiological parameter into a biomechanical musc le model.