Spastic paresis: impaired spinal reflexes and intact motor programs.

Leg muscle EMG responses evoked by short treadmill acceleration impulses applied during stance were analysed in patients with spastic hemiparesis. The compensatory reactions on the unaffected side consisted of a diphasic pattern of leg muscle activation. The first response could best be described as a polysynaptic spinal stretch reflex response. This response was absent on the spastic side, except for its later, declining component. This remainder of the first response and the following activation of the antagonistic muscle was identical on both the unaffected and the spastic side. This part of the pattern is assumed to be centrally programmed (at the spinal level) and triggered by the termination of the acceleration impulse.