Perceived Fatigue, Strength and Aerobic Fitness in Persons with Multiple Sclerosis

Abstract

PURPOSE: Excess fatigue in multiple sclerosis (MS) has been attributed to a variety of factors including low physical fitness. Measures of muscle performance, aerobic capacity and walking speed were compared between MS and control subjects to determine whether the higher perceived fatigue in MS is due to their reduced functional capacity. METHODS: Seven mildly-disabled but physic ally-active persons with MS (5 women, 2 men; 37±8 yrs) and an expanded disability status score (EDSS) of 2.1±1.6, and ten controls (8 women, 2 men; 40±10 yrs) matched for age, height, weight, and body fatness volunteered for this study. Muscle strength and endurance of the knee flexors and extensors (flex/ext) were assessed using isokinetic dynamometry. Leg muscle strength was assessed at 0, 90 and 180 °s−1 while endurance was assessed using 30 repetitions of knee flex/ext at 90°s−1 and 180°s−1. Maximum oxygen consumption was estimated from a submaximal graded cycle ergometry (85% of estimated maximal heart rate) test. Performance tests included the 25ft, 100ft and 6-minute walk. Perceived fatigue was assessed using the Modified Fatigue Impact Scale. RESULTS: Cardiorespiratory fitness was similar between MS and controls (2.3 ± 0.9 L/min vs. 2.3 ±0.04 L/min, and 35.4±8 ml/kg/min vs. 33.1±11 ml/kg/min, respectively). Maximal isokinetic torque of the knee flex/ext (0, 90 and 180 °s−1) was similar between the two groups as were measures of muscle endurance at 90°s−1 and 180°s−1. Walking speeds in the 25ft, 100ft and 6-min tests were also similar between groups (p≥0.05). However, self-assessed fatigue was significantly higher in MS (p < 0.05). CONCLUSIONS: MS subjects with low disability are capable of maintaining similar levels of aerobic fitness, muscle strength/endurance, and walking speed compared with matched controls. Excess fatigue experienced in MS subjects with low disability appears unrelated to their functional capacity.