Contractile properties and fatigue of quadriceps muscles in multiple sclerosis

Functional characteristics of electrically stimulated quadriceps muscles of patients with multiple sclerosis (MS) were determined to investigate wheth er adaptations in muscle properties contribute to the higher fatigability o f these patients. The estimated maximal isometric force generating capacity of MS patients was only 11.2% (P < 0.05) lower than control subjects. Howe ver, the patients were only able to voluntarily exert 75 +/- 22% (n = 12) o f their maximal capacity, against 94 +/- 6% (n = 7) for the control subject s. There were no differences in muscle speed, suggesting that muscle fiber distribution was not different in the MS patients due to reduced muscle usa ge. During a series of repeated contractions, greater decrements occurred i n isometric force and in maximal rate of force rise in the MS patients (by 31.3 +/- 10.3% and 50.1 +/- 10.0%, respectively; n = 13) than control subje cts (23.8 +/- 6.6% and 39.0 +/- 8.1%, n = 15), suggesting a lower oxidative capacity. The results indicate that increasing the mass of their muscles b y training may help to reduce the excessive muscle fatigue of MS patients. (C) 2000 John Wiley & Sons, Inc.