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), ΔT_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 ΔT_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.