Slowed Exercise-Onset Vo(2) Kinetics During Submaximal Endurance Exercise in Subjects With Multiple Sclerosis

Abstract

Background. Low physical activity levels in persons with multiple sclerosis (MS) may reduce skeletal muscle oxidative capacity. Rehabilitation strategies might be altered by a measure of capacity that did not require invasive techniques or maximal exercise testing. For this purpose, we measured exercise onset and offset oxygen uptake (Vo(2)) kinetics during endurance exercise. Objective. This study compared exercise-onset and -offset Vo(2) kinetics in mildly affected persons with MS with healthy matched participants. Methods. From 38 MS patients who had a mean Expanded Disability Status Scale of 3.1 and 16 healthy participants, exercise-onset and -offset Vo(2) kinetics (mean response time [MRT]) were determined during two 6-minute submaximal bouts of exercise separated by a 6-minute recovery interval. Blood lactate, heart rate, expiratory volume, and Borg ratings of perceived exertion were assessed during exercise and compared between groups. Relationships between clinical characteristics and MRT were assessed. Results. During exercise, blood lactate, heart rate, and expiratory volume did not differ between groups (P > .05), but exercise-onset MRT was significantly slower in MS versus healthy participants (P = .007). Exercise-onset MRT was independently related to having MS (P = .02). Exercise-offset MRT was not different between groups or was independently related to having MS (P > .05). No independent relationships between clinical characteristics of MS and exercise-onset or -offset MRT were found. Conclusions. Exercise-onset Vo(2) kinetics during submaximal endurance exercise are significantly slowed in mildly disabled persons with MS, suggesting low skeletal muscle oxidative capacity. Using mean response time testing, rehabilitation interventions for this reduction in exercise capacity can be assessed and targeted.