A Musculoskeletal Model of the Hand to Investigate the Force Contribution of the Upper Limb Muscles during Wrist Flexion-Extension

The muscular forces of the upper limb while resisting an imposed flexion-extension movement at the wrist were investigated. A normal subject was examined using a robotic apparatus which measured her wrist resistive flexing/extending moments while it was moved with a constant angular speed. A musculoskeletal model of the upper limb was developed, including a mathematical model to simulate the muscles contraction. An optimization algorithm, based on minimum muscle activation, was used to determine the muscles contributions into the resistive moments. Results indicated that the wrist resistive flexor moment was mostly contributed by the flexor carpi ulnaris and carpi radialis, with rates of 65 and 25 percent, respectively. For the wrist resistive extensor moment, extensor carpi radialis brevis and longus contributed the most, with contribution rates of about 40 and 35 percent, respectively. Verification of the results against the subject’s EMG data revealed a reasonable agreement for the flexors activation patterns. Further work is going on to adapt the model for simulation of the neural lesion and muscular spasticity in brain injury subjects, for whom the speed in movement is considered to be a critical factor in the force generation pattern.