Motor-evoked potentials in response to fatiguing grip exercise in multiplesclerosis patients

Objective: This study examined central and peripheral effects of fatiguing exercise (3 min maximal grip) in healthy controls (n = 10) and multiple scl erosis (MS) subjects with weakness, MS-W (n = 16) and normal motor function , MS-NM (n = 16) in the studied extremity. Method: Transcranial magnetic stimulation (TMS) was used to assess resting and facilitated motor-evoked potentials (MEPs) of abductor pollicus brevis (APB) and flexor carpi radialis (FCR) muscles before and after fatiguing ex ercise. Exercise-induced depletion and recovery of phosphocreatine (PCr) we re measured using P-31 magnetic resonance spectroscopy ((PMRS)-P-31) in FCR . Results and conclusion: MS subjects demonstrated significantly lower peak f orce and a faster decline in force than controls. Contralateral muscle acti vation (hand grip) before the fatigue protocol resulted in significantly in creased MEP amplitudes in all groups. Contralateral hand grip following fat iguing exercise resulted in significantly higher MEP amplitudes in controls and MS-NM subjects, but not MS-W subjects. Fatiguing exercise resulted in prolonged central motor conduction time (CMCT) in MS subjects, but not cont rols. No group differences in PCr depletion or resynthesis were observed. A ll groups demonstrated significant post-exercise depression (PED) of MEP am plitude that persisted beyond the time course of PCr recovery, indicating f atigue was central in origin. MS subjects were less able than controls to i ncrease cortical excitability using contralateral muscle activation followi ng fatiguing exercise, possibly indicating impaired conduction in the corpu s callosum. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.