Simplified indices of exercise tolerance in patients with multiple sclerosis and healthy subjects: A case-control...

Among patients with multiple sclerosis (MS), the impairment of exercise tolerance is closely related to disability. Maximal oxygen uptake (VO_2max ) is the gold standard to assess exercise tolerance in healthy subjects (HS). Among patients with MS, the accuracy of VO_2max measurement is often impaired because the patients are unable to reach the maximal exercise intensity due to interdependent factors linked to the disease (such as pathological fatigue, pain, lack of exercise habit, and lack of mobility). This study assesses the accuracy of simplified indices for assessing exercise tolerance, which are more suitable in patients with MS. They are simple in the way they are either measurable during submaximal exercise (oxygen uptake efficiency slopes (OUES), physical working capacity at 75% of maximal heart rate (PWC_75% ), oxygen consumption at a respiratory exchange ratio of 1 (VO₂ @RER1)) or not based on gas exchange analysis (peak work rate (PWR)-based predictive equation and PWC_75% ). All indices were significantly lower in the MS group compared to the HS group (P < .001). OUES appeared highly correlated (r > .70, P < .001) with VO_2peak , in both groups, without difference between groups. PWR-based prediction of VO_2peak showed a standard error of the estimate of 315 mL min^-1 in HS and 176 mL min^-1 in MS. PWC_75% did not correlate to VO_2peak in neither group. These findings suggest an impairment of exercise tolerance functions in mildly disabled persons with MS, independently from other factors. Submaximal indices involving gas exchange analysis or peakWR-based estimation of VO_2peak are usable to accurately assess exercise tolerance.