Voluntary Cooling During Exercise Is Augmented In Heat Sensitive People With Multiple Sclerosis

PURPOSE: Body cooling improves exercise tolerance in heat sensitive people with Multiple Sclerosis (MS). The effectiveness of cooling modalities in real-world settings requires appropriately engaging in cooling behavior. We tested the hypothesis that people with MS voluntarily engage in cooling behavior during exercise to a greater extent than healthy controls. METHODS: In a 27.0±0.2°C, 41±2% RH environment, 7 subjects with relapsing-remitting MS who exhibited heat sensitivity (34±7y, 167±5cm, 72±15kg, EDSS: 1.9±0.8, 1 male) and 7 healthy subjects (CON, 37±7y, 168±7cm, 71±11kg, 1 male) completed two randomized trials cycling for 40 min (EX) at a fixed rate of metabolic heat production (3.5 W/kg) followed by 30 min recovery (REC). In one trial, subjects were restricted from engaging in cooling (NONE). In the other, subjects pressed a button to receive 2 min of ~2°C water perfusing a suit top as often as desired (COOL). Mean skin (Tsk, 8 site) and core (Tcore, telemetry pill) temperatures and mean skin wettedness (Wsk, 8 site) were recorded continuously. Total voluntary time in cooling provided an index of cooling behavior. Ratings of perceived exertion (RPE), composite heat sensitivity symptom scores (HSSS, MS only) and subjective fatigue (MS only) were recorded every 10 min. RESULTS: Tcore (+0.5±0.1°C, P<0.01) and Wsk (+0.52±0.02 a.u., P<0.01) increased in EX and remained elevated in REC (P<0.01) but were not different between trials (P≥0.35) or groups (P≥0.60). Tsk decreased in MS COOL compared to MS NONE from min 20 EX to 5 REC (P≤0.02). There were no other differences in Tsk (P≥0.25). MS spent more total time in cooling in EX (MS: 13.4±3.0 min; CON: 7.4±3.6 min, P<0.01) but not REC (MS: 1.7±1.4 min; CON: 0.3±0.7 min, P=0.40). In both trials, RPE was higher in MS vs. CON (P<0.01). HSSS increased in EX (P<0.01) but was not different between trials (P=0.25). Subjective fatigue was not different between trials in EX (P≥0.97) but was lower at 10 and 20 min of REC in COOL (P<0.02). CONCLUSIONS: MS engaged in body cooling during EX to a greater extent than CON. While cooling did not affect HSSS or fatigue during EX, MS reported greater reductions in fatigue following exercise when cooling was permitted. Cooling during exercise could improve exercise participation and adherence. Supported by: ACSM Foundation Research Endowment Grant