EVALUATING AN INTEGRATED MUSCULOSKELETAL MODEL OF THE HUMAN ARM

A simplified model of the mechanical properties of muscle and of the m usculo-skeletal geometry was used to predict torques at the shoulder a nd elbow during arm movements in the sagittal plane. Subjects made mov ements to 20 targets spaced on the diameter of a circle centered on th e initial location of the hand. Movement kinematics and the electromyo graphic (EMG) activity of nine shoulder and elbow muscles were recorde d. Muscle force was predicted using rectified EMG activity as an input to a Hill-type model of muscle dynamics. The model also made simplify ing assumptions about muscle geometry. Muscle force was then converted to torque and the individual muscle torques were weighted to provide the best fit to the joint torque completed from the kinematic data. Th e overall fit of the model was reasonably good, but the goodness of fi t was not uniform over all movement directions. The results suggest th at the assumptions about the musculo-skeletal geometry, the model of m uscle dynamics, and muscles not included in the analysis all contribut ed to the error.