The effect of joint stiffness on simulation of the complete gait cycle

A computer simulation of paraplegic, walker assisted gait through multiple gait cycles is described. Computational problems associated with changing constraints during transitions between phases of gait are avoided by modeling foot-to-floor contact as an external force. Net joint torques, computed from kinematic data by inverse dynamics and transformed into sine functions, are used to drive limb motion. Model instability is overcome by emulating the effects of 'stiffness' at the joints by using proportional-derivative (PD) controllers. Maximum joint torques needed to achieve stable gait were found to be within normal physiological range. Joint kinematics and foot contact forces generally followed a normal gait pattern producing a forward displacement of approximately 0.8 m/s at a walking frequency of 0.5 Hz. The most significant deviation from a normal walking pattern was excessive hip abduction during stance phase causing a waddling (medial-lateral sway) motion. A quantitative measurement of the dynamic stability of the simulation is calculated based on Floquet theory. >