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Affiliation
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School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada. Thermal Ergonomics Laboratory, Exercise and Sports Science, Faculty of Health Sciences, University of Sydney, NSW, Australia. |
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Abstract
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PURPOSE: To compare the reductions in evaporative heat loss from the skin (Esk) to internal heat loss (Hfluid) induced by ice slurry (ICE) ingestion relative to 37°C fluid and the accompanying body temperature and local thermoeffector responses during exercise in warm, dry conditions (33.5±1.4°C, 23.7±2.6% RH).
METHODS: Nine men cycled at ∼55% VO2peak for 75 min and ingested 3.2 ml/kg aliquots of 37°C fluid or ICE after 15, 30, and 45 min of exercise. Metabolic heat production (M-W), rectal temperature (Tre), mean skin temperature (Tsk), whole-body sweat loss (WBSL), local sweat rate (LSR) and skin blood flow (SkBF) were measured throughout. Net heat loss (HLnet) and heat storage (S) were estimated using partitional calorimetry.
RESULTS: Relative to the 37°C trial, M-W was similar (P=0.81) with ICE ingestion, however, the 200±20 kJ greater Hfluid (P<0.001) with ICE ingestion was overcompensated by a 381±199 kJ lower Esk (P<0.001). HLnet was consequently 131±120 kJ lower (P=0.01) and S was greater (P=0.05) with ICE ingestion compared with 37°C fluid ingestion. Concurrently, LSR and WBSL were lower by 0.16±0.14 mg·min·cm (P<0.01) and 191±122 g (P<0.001) respectively, and SkBF tended to be lower (P=0.06) by 5.4±13.4%maxAU in the ICE trial. Changes in Tre and Tsk were similar throughout exercise with ICE compared to 37°C fluid ingestion.
CONCLUSIONS: Relative to 37°C, ice slurry ingestion caused disproportionately greater reductions in Esk relative to Hfluid, resulting in a lower HLnet and greater S. Mechanistically, LSR and possibly SkBF were suppressed independently of Tre or Tsk, reaffirming the concept of human abdominal thermoreception. From a heat balance perspective, recommendations for ice slurry ingestion during exercise in warm, dry conditions should be reconsidered.
Language: en |