The effect of cold-water mouth swilling on thermal perceptions and heat-related symptoms for people with multiple sclerosis exercising in a hot environment

Abstract

Purpose Cold-water ingestion improves exercise capacity in the heat for people with multiple sclerosis (MS). Whether cold-water ingestion also mitigates heat-related MS symptoms is unknown. Ingesting fluid is also limiting for people with MS with impaired bladder function. Therefore, we tested the hypothesis that swilling or ingesting cold-water (7°C) compared to ingesting thermoneutral water (37°C) would mitigate the onset of perceived MS heat-related symptoms and thermal sensation in heat-sensitive people with MS during exercise in the heat. Methods On three occasions, 13 heat-sensitive participants with MS (41 ± 12 y; 67 ± 12 kg; 1.7 ± 0.1 m; 33.3 ± 9.4 ml·kg −1 ·min −1 ) cycled at 40% VO 2max at 35 ± 1°C; 30 ± 2% RH until volitional exhaustion (maximum of 60 min). Every 15 min, participants ingested (7 IN ) or swilled (7 SW ) 7°C, or ingested 37°C (37 IN ) water. Thermal sensation, heat-related MS symptoms, rectal ( T re ), and mean skin ( T sk ) temperature were recorded throughout. Results Thermal sensation was cooler in the 7 SW ( P < 0.01) and 7 IN ( P = 0.04) compared to the 37 IN trial, but heat-related symptoms ( P = 0.57), fatigue ( P = 0.90), Δ T re (37 IN : 0.74 ± 0.37°C; 7 IN : 0.65 ± 0.38°C; 7 SW : 0.67 ± 0.34°C; P = 0.38) and Δ T sk (37 IN : 1.61 ± 0.82°C; 7 IN : 1.67 ± 0.78°C; 7 SW : 1.64 ± 0.69°C; P = 0.91), were not different between trials. Nine participants completed 60 min of exercise in the 37 IN trial whereas 10 participants completed 60 min of exercise in the 7 IN and 7 SW trials. Conclusion Swilling and ingesting 7°C water induces a cooler thermal sensation in heat-sensitive people with MS exercising in the heat but does not mitigate heat-related MS symptoms. The capacity to complete 60 min of exercise with cold-water ingestion and swilling were comparable.

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