Is long-term exercise intervention effective to improve cardiac autonomic control during exercise in subjects with multiple sclerosis? A randomized controlled trial

Background. Patients with multiple sclerosis (MS) suffer from a disturbed cardiac autonomic control during exercise (based on heart rate (HR) changes during exercise), which affects exercise tolerance. Whether long-term exercise intervention improves HR changes during exercise in patients with MS remains unknown. Aim. To examine whether long-term exercise intervention improves HR changes during exercise, and correlates with improvements in exercise tolerance, in patients with MS. Design. Randomized controlled trial. Setting. University rehabilitation facility. Population. Twenty-three patients with MS were randomly assigned to six months of follow-up (n=9) or six months of exercise training (n=14, 54-60 training sessions). Methods. At baseline and after three and six months of follow-up, exercise-onset (first 20 and 60 seconds) and -offset (1-minute recovery) heart rate (HR) change was determined during a constant-load exercise test: these data reflect the (re)activation of the (para)sympathetic nervous system at initiation and/or cessation of exercise. Blood lactate, HR, oxygen uptake, expiratory volume and ratings of perceived exertion (RPE) were assessed during exercise as indicators for exercise tolerance. Results. Exercise-onset and -offset HR and exercise tolerance did not change during follow-up in the control group (P>0.05). In the exercise intervention group, blood lactate content and RPE during exercise decreased significantly (group/time interaction effect P<0.05), but exercise-onset and -offset HR did not change (P>0.05). No correlations were found between changes in exercise tolerance and changes in exercise-onset and -offset HR (P>0.05). Conclusion. In patients with MS, long-term exercise intervention does not improve HR changes during exercise, despite improvements in exercise tolerance, indicating that cardiac autonomic control during exercise is not easily improved by exercise intervention in patients with MS. Clinical Rehabilitation Impact. This study indicates that patients with MS suffer from a disturbed cardiac autonomic control during exercise, based on heart rate changes, which is not easily remediated by exercise intervention. Because a disturbed cardiac autonomic control is related to exercise intolerance in MS, it should further be explored how to remediate this anomaly through exercise intervention or other approaches.