Cold Water Ingestion Improves Exercise Tolerance of Heat-Sensitive People with MS

Purpose
Heat intolerance commonly affects the exercise capacity of people with multiple sclerosis (MS) during bouts of hot weather. Cold water ingestion is a simple cooling strategy, but its efficacy for prolonging exercise capacity with MS remains undetermined. We sought to identify whether cold water ingestion blunts exercise-induced rises in body temperature and improves exercise tolerance in heat-sensitive individuals with MS.

Methods
On two separate occasions, 20 participants (10 relapsing–remitting MS (expanded disability status scale, 2–4.5); 10 age-matched healthy controls) cycled at ∼40% V˙O2max at 30°C and 30% relative humidity until volitional exhaustion (or a maximum of 60 min). Every 15 min, participants ingested 3.2 mL·kg−1 of either 1.5°C (CLD) or 37°C (NEU) water. Rectal (Tre) temperature, mean skin (Tsk) temperature, and heart rate (HR) were measured throughout.

Results
All 10 controls but only 3 of 10 MS participants completed 60 min of exercise in NEU trial. The remaining 7 MS participants all cycled longer (P = 0.006) in CLD (46.4 ± 14.2 min) compared with NEU (32.7 ± 11.5 min), despite a similar absolute Tre (NEU: 37.32°C ± 0.34°C; CLD: 37.28°C ± 0.26°C; P = 0.44), change in Tre (NEU: 0.38°C ± 0.21°C; CLD: 0.34°C ± 0.24°C), absolute Tsk (NEU: 34.48°C ± 0.47°C; CLD: 34.44°C ± 0.54°C; P = 0.82), and HR (NEU: 114 ± 20 bpm; CLD: 113 ± 18 bpm; P = 0.38) for the same exercise volume.

Conclusions
Cold water ingestion enhanced exercise tolerance of MS participants in the heat by ∼30% despite no differences in Tre, Tsk or HR. These findings support the use of a simple cooling strategy for mitigating heat intolerance with MS and lend insight into the potential role of cold-afferent thermoreceptors that reside in the abdomen and oral cavity in the modulation of exercise tolerance with MS in the heat.