Blunted sweating does not alter the rise in core temperature in people with multiple sclerosis exercising in the heat

Purpose: To determine whether thermoregulatory capacity is altered by MS during exercise in the heat. Methods: Sixteen MS (EDSS: 2.9±0.9; 47±8 y; 77.6±14.0 kg) and 14 healthy (CON) control participants (43±11 y; 78.6±17.0 kg) cycled at a heat production of 4 W.kg-1 for 60 minutes at 30˚C, 30%RH (WARM). A subset of 8 MS (EDSS: 2.6±0.5; 44±8 y; 82.3±18.2 kg) and 8 CON (44±12 y; 81.2±21.1 kg) also exercised at 35°C, 30%RH (HOT). Rectal (Tre), mean skin (Tsk) temperature, and local sweat rate on the upper-back (LSRback) and forearm (LSRarm), were measured. Results: All CON, yet only 9 of 16, and 7 of 8 MS participants completed 60 min of exercise in WARM and HOT trials, respectively. All MS participants unable to complete exercise stopped with ∆Tre between 0.2-0.5˚C. The time to reach a ∆Tre of 0.2˚C was similar (MS:28±15 min, CON: 32±18 min; P=0.51). For MS participants completing 60-min of exercise in WARM, ∆Tre (P=0.13), ∆Tsk (P=0.45), LSRback (P=0.69) and LSRarm (P=0.54) were similar to CON, but ΔTb (MS:0.16±0.13˚C, CON:0.07±0.06˚C; P=0.02) and onset time (MS:16±10 min, CON:8±5 min; P=0.02) for sweating were greater. Similarly, in HOT, ∆Tre (P=0.52), ∆Tsk (P=0.06), LSRback (P=0.59) and LSRarm (P=0.08) were similar, but ΔTb (MS: 0.19±0.16˚C, CON: 0.06±0.04˚C; P=0.04) and onset time (MS:13±7 min, CON:6±3 min; P=0.02) for sweating were greater with MS. Conclusion: Even at 35˚C, a delayed sweating onset didn't alter heat loss to sufficiently affect exercise-induced rises in core temperature. Heat intolerance with MS does not seem attributable to thermoregulatory impairments.