Quantitative assessment of motor fatigue in amyotrophic lateral sclerosis

Motor fatigue is a common complaint in patients with amyotrophic, lateral s clerosis (ALS), but is often excluded, unlike weakness, from the clinical a ssessment of these patients. This could be due to the complexity and often painful assessment techniques of this motor deficit. This study examines th e feasibility of quantitative assessment of motor fatigue by modifying pres ently available force measurements. The relationship between weakness and f atigue in ALS patients was also examined. Fifty-four ALS patients and 39 no rmal control subjects performed 30 s. of sustained maximal voluntary isomet ric contraction (MVIC) of elbow flexors (EF), knee extensors (NE), and ankl e dorsiflexors (DF), using a computerized force measurement system and stan dardized testing procedures. Fatigue index (FI) was digitally calculated, f rom the force-time curve, as the percentage of MVIC unable to be sustained over the 30-s period. Fatigue was greater in ALS patients than in normal co ntrol (mean = 23% vs. 15%) in all muscles including muscles that were not c learly weak. Weakness and fatigue were poorly correlated in ALS patients an d may be independent measures of the pathogeneses of ALS. (C) 2001 Elsevier Science B.V. All rights reserved.