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

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% VO2max at 35 ± 1°C; 30 ± 2% RH until volitional exhaustion (maximum of 60 min). Every 15 min, participants ingested (7IN) or swilled (7SW) 7°C, or ingested 37°C (37IN) 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 7SW (P < 0.01) and 7IN (P = 0.04) compared to the 37IN trial, but heat-related symptoms (P = 0.57), fatigue (P = 0.90), ΔT re (37IN: 0.74 ± 0.37°C; 7IN: 0.65 ± 0.38°C; 7SW: 0.67 ± 0.34°C; P = 0.38) and ΔT sk (37IN: 1.61 ± 0.82°C; 7IN: 1.67 ± 0.78°C; 7SW: 1.64 ± 0.69°C; P = 0.91), were not different between trials. Nine participants completed 60 min of exercise in the 37IN trial whereas 10 participants completed 60 min of exercise in the 7IN and 7SW 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.