Effects of mass and momentum of inertia alternation on individual muscle forces during swing phase of transtibial amputee gait.

A computer simulation was carried out to investigate the forces of lower extremity muscles in the swing phase of a transtibial amputee gait. With each muscle as an ideal force generator, the lower extremity was simulated as a two-degrees of freedom linkage with the hip and knee as its joints. Kinematic data of hip and knee joints were recorded by a motion analysis system. Through a static optimization approach, the forces exerted by muscles were determined so that recorded hip and knee joint angles were produced. Simulation results showed that when the mass of prosthetic foot is increased, muscle forces increase, too. This result is in accord with experimental and theoretical studies that reported an increase in leg mass lead to higher electromyography activity of muscles, and energetic of walking. However, since prosthetic foot moment of inertia is smaller than that of thigh and prosthetic shank, its alternation does not have noticeable effect on muscle forces.