Unstable states in four-legged locomotion

Walking in completely paralyzed paraplegic persons can be realized by passive mechanical bracing or multichannel functional electrical stimulation (FES) of paralyzed lower extremities. In both cases the equilibrium has to be provided by the use of crutches. Restored walking in completely paralyzed persons can be, therefore, treated as four-legged locomotion, closely resembling the walking patterns encountered in walking machines. In this way the gait pattern can be described as a sequence of the states displaying the contacts of both feet and both crutches with the ground. Improved four-point gait modalities are proposed by introducing unstable states into the walking sequence. The unstable states are defined as passive gait phases where the body is only supported in two contact points and where the center of body is gravity and inertia driven in the direction of progression. Kinematic measurements of the unstable state were performed in paraplegic subject by assessing the horizontal displacement of the center of body (COB) in the plane of progression.