Suprasegmentally induced motor unit activity in paralyzed muscles of patients with established spinal cord injury

Abstract

In an attempt to demonstrate the presence of functional descending fibers in patients with clinically apparent functional spinal cord transection, we examined electromyographically recorded paralyzed leg muscle responses to the Jendrassik and other reinforcement maneuvers. Two patterns were observed: a low-amplitude, short onset time reinforcement maneuver response (RMR) restricted to one to three muscle groups (RMR₁), and a larger-amplitude response with a longer onset time that occurred bilaterally in essentially all of the recorded muscles (RMR₂). The responses imply preserved descending facilitory influence on isolated populations of motor units (RMR₁) or on segmental interneuron pools (RMR₂). Such findings indicate the presence of functioning fibers traversing the injured portion of the spinal cord in patients diagnosed as having a complete lesion. In such cases, it is possible for patients to initiate subclinical motor unit activity or suprasegmentally induced gross movement through reinforcement maneuvers, but not to control the amplitude or duration of the response.