Excitability of anterior horn cells after periodic or discrete repetitive movements.

INTRODUCTION/AIMS: It has been well established that spasticity interferes with smooth joint movements. Although the degree of spasticity is related to the excitability of anterior horn cells and is thought to improve after repetitive movements, the effect of the rhythm of repetitive movements on the excitability of anterior horn cells remains unknown. Therefore, we investigated the excitability of anterior horn cells after periodic and discrete repetitive movements using F waves.

METHODS

Right-handed, healthy subjects were recruited for this study. Subjects then performed periodic or discrete repetitive thumb abduction movements for 10 seconds, measuring the F waves before, immediately after, and then 2 and 4 minutes after performing these movements. Specifically, the F waves were recorded from the abductor pollicis brevis muscle, after median nerve stimulation at the wrist. Next, the F/M amplitude ratio, which was used to evaluate the excitability of anterior horn cells, was compared before, immediately after, and 2 and 4 minutes after each task.

RESULTS

A total of 12 subjects participated in this study. In the periodic task, the F/M amplitude ratio was found to be significantly decreased immediately after the task compared with before the task, but there was no significant difference between the other trials. Conversely, in the discrete task, there was no significant difference in the F/M amplitude ratio between trials.

DISCUSSION: Periodic repetitive movements were found to temporarily reduce the excitability of anterior horn cells.