A forward musculoskeletal dynamics approach to the motion of metacarpophalangeal joint of index finger

A forward dynamics approach is presented for the motion simulation of the MCP (metacarpophalangeal) joint of index finger, which combines musculotendon dynamics and muscle excitation-contraction dynamics with the multi-segmental dynamics. In the musculotendon dynamics six muscles are taken into consideration. They are flexor digitorum profundus, flexor digitorum superficials, radial interosseous, lumbrical, ulnar interosseous and long extensor. As an example, a fast flexion process of 60° angle of the index finger at MCP joint is simulated based on minimization of motion time, in which there is no form of constraint at the terminal of motion process. The results show that (1) this forward dynamics approach can obtain acceptable accuracy of motion simulation as long as the musculoskeletal anatomical parameters are adequately estimated; (2) during a fast flexion the angular velocity of MCP joint is a fluctuation wave with an approximate peak interval of 0.015 s, however it can converge to a steady state; (3) the variations of the states of all flexor muscles´ activation is nearly in accordance with a typical function of(1-e^-at) during the initial phase of a fast flexion process. Generally speaking, the forward musculoskeletal dynamics approach could be a useful way to obtain a better understanding of human movement especially the underlying redundant control mechanism