Kinematic data acquisition systems and analytical optimization procedures for the study of human gait have been investigated with the goal of ascertaining individual muscle forces during a walking cycle. Improvements on existing approaches were found to be more crucially dependent on the accurate determination of joint angles and the calculation of joint torques than on the particular optimization criteria employed. Physiologically-based information on the functions of, and constraints on, individual muscles supplemented the optimization procedures. The results of the study elucidate the temporal pattern and quantitative levels of muscle force in a walking cycle for a series of normal persons.