Factors affecting knee flexion during the swing phase of gait

A three-degree-of-freedom sagittal plane musculoskeletal model of the human lower extremity has been developed to simulate the swing phase of normal gait. Values for the joint angles and angular velocities at toe-off and the excitation input to the model's muscles were derived from experimental measurements. The normal swing phase simulation produced joint angles, joint moments, and heel and toe trajectories that corresponded to experimental results. Simulations were run with altered initial joint angular velocities and applied joint moments to determine the effects of each upon peak knee flexion and knee angular acceleration. It was found that knee flexion during the swing phase is caused primarily by a large initial knee flexion velocity at toe-off which is tempered by a knee extension acceleration that is chiefly caused by muscular action.