Tibialis anterior surface EMG parameters change before force output in multiple sclerosis patients

Abstract

Neuromuscular function has been studied in multiple sclerosis patients with differing levels of disability. Force during maximal voluntary ankle dorsiflexion and surface EMG in tibialis anterior for weakest and strongest legs in 31 patients was compared with 16 control subjects. In the most mildly affected patients strength of dorsiflexion for the strongest leg was not significantly different from that of controls, but integrated mean EMG and median frequency of the power spectrum were significantly lower. In all other patient groups, all parameters measured were different from control values. Results indicate an important change in neuromuscular parameters which precedes loss of the ability to recruit normal force levels. Such changes may imply that the muscles of multiple sclerosis patients are affected even before there is significant evidence of neural motor dysfunction.