Thermoregulatory responses to ice slurry ingestion during low and moderate intensity exercises with restrictive heat loss

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ObjectivesWe investigated the thermoregulatory responses to ice slurry ingestion during low- and moderate-intensity exercises with restrictive heat loss. DesignRandomised, counterbalanced, cross-over design. MethodsFollowing a familiarisation trial, ten physically active males exercised on a motorised treadmill at low-intensity (L; 40% VO2max) or moderate-intensity (M; 70% VO2max) for 75-min, in four randomised, counterbalanced trials. Throughout the exercise bout, participants donned a raincoat to restrict heat loss. Participants ingested 2gkg−1 body mass of ambient water (L+AMB and M+AMB trials) or ice slurry (L+ICE and M+ICE trials) at 15-min intervals during exercise in environmental conditions of Tdb, 25.1±0.6°C and RH, 63±5%. Heart rate (HR), gastrointestinal temperature (Tgi), mean weighted skin temperature (Tsk), estimated sweat loss, ratings of perceived exertion (RPE) and thermal sensation (RTS) were recorded. ResultsCompared to L+AMB, participants completed L+ICE trials with lower ΔTgi (0.8±0.3°C vs 0.6±0.2°C; p=0.03), mean RPE (10±1 vs 9±1; p=0.03) and estimated sweat loss (0.91±0.2L vs 0.78±0.27L; p=0.04). Contrastingly, Tgi (p=0.22), Tsk (p=0.37), HR (p=0.31), RPE (p=0.38) and sweat loss (p=0.17) were similar between M+AMB and M+ICE trials. RTS was similar during both low-intensity (4.9±0.5 vs 4.7±0.3; p=0.10) and moderate-intensity exercise (5.3±0.47 vs 5.0±0.4; p=0.09). ConclusionsPer-cooling using ice slurry ingestion marginally reduced thermal strain during low-intensity but not during moderate-intensity exercise. Ice slurry may be an effective and practical heat mitigation strategy during low-intensity exercise such as in occupational and military settings, but a greater volume should be considered to ensure its efficacy.