The purpose of this research is to characterize motor-unit firing behavior associated with the movement deficits of patients with spastic cerebral palsy (CP). In their previous work, the investigators have identified structural abnormalities in spastic muscle in CP that are similar to changes seen with experimental chronic low frequency stimulation. This evidence suggested that in CP there may be a reduction in motor-unit firing rates, presumably as a result of the interrupted descending signals. Failure to increase firing rates sufficiently during contraction could cause weakness and loss of dexterity as is typically seen in both agonist and antagonist muscles in CP. In the ankle, for example, failure to generate adequate firing rates during voluntary phasic contraction could cause inadequate push off and toe clearance in gait and thus could be a primary cause of equinus gait in CP. For patients with CP, a failure to generate adequate firing rates during contraction may be amenable to treatment. There is early evidence to suggest that electrical stimulation to the calf and tibialis anterior may increase muscle strength, reduce calf spasticity and improve equinus gait. Selective electrical intervention could improve motor control without causing the weakness or sedation that is characteristic of current pharmaceutical and surgical treatments for CP. An essential first step towards designing an effective treatment would be a clear understanding of the mechanisms underlying the movement deficit. The investigators believe that decreased motor-unit firing rates are an important mechanism of the movement deficit in CP. However, motor-unit firing characteristics have not been previously evaluated in patients with CP.
The specific aim of this study, therefore, is to determine the feasibility of evaluating motor-unit firing properties in the gastrocnemius and tibialis anterior muscles in children with spastic CP who have equinus gait. The protocol compares firing characteristics at progressively increasing levels of voluntary contraction in subjects with CP and in matched controls to distinguish differences in motor-unit activation strategies. Based on these preliminary data, a full research proposal will be developed to investigate the relationship between muscle structure, motor unit firing behavior and motor deficit including gait kinematics in patients with CP. This research is envisioned to provide a foundation for the development of selective electrical treatment that could improve motor control in patients with spastic CP.
| Rose, Jessica; McGill, Kevin C (2005) Neuromuscular activation and motor-unit firing characteristics in cerebral palsy. Dev Med Child Neurol 47:329-36 |
