Surface EMG of proximal leg muscles in neuromuscular patients and in healthy controls. Relations to force and fatigue

In an effort to find parameters to evaluate patients with neuromuscular dis orders, surface electromyography (SEMG) of proximal leg muscles was perform ed in 33 patients with myotonic dystrophy (MyD), 29 patients with Charcot-M arie-Tooth (CMT) disease and 20 healthy controls. The root mean square (RMS ) of the SEMG amplitude (mu V) was calculated at different torque levels. E ndurance (seconds) and median frequency (F-med) Of the SEMG power spectrum, used as parameters of fatigue, were determined at 80% of MVC. Maximum Volu ntary contraction (MVC) was found to be decreased in patients; the ratio be tween RMS values of antagonists and agonists was increased and torque-EMG r atios (Nm/mu V) were decreased. These differences with respect to controls were more pronounced in MyD than in CMT. The initial F-med value was lowest in CMT. The greatest decrease in F-med was found in MyD. SEMG data in rela tion to force have not been determined before in groups of MyD or CMT patie nts. In both disorders, parameters differed from controls, which means that adding SEMG to strength measurements could be useful in studying the progr ess of the disorder and the effects of interventions. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.