[Mechanisms of locomotion in mammals]

From biochemical studies of the hindlimb locomotor cycle in the cat, it appears that joint angle excursions are more simple at hip than at more distal joints. The pattern of EMG activity for the different hindlimb muscles is not simple but detailed and is roughly kept the same in the deafferented preparation and in the chronic spinal preparation too: these results show the central and spinal origin of the basic rhythm generation of the locomotor pattern. What is added to this basic mechanism by the supraspinal levels is: (1) a tonic activation which is necessary for the locomotor bursting to be initiated and maintained; (2) an adjustment of four limb posture to ensure equilibrium throughout a locomotor episode. The cerebellum is likely a leader in latter control. The basic spinal pattern is also controlled by peripheral feed-back signals which operate at spinal level and can delay the next locomotor cycle as long as the limb is loaded. On the other hand, a gain control of simple spinal reflexes is achieved by the spinal locomotion generator versus the phase of the locomotor cycle.