Ice Slurry Ingestion Leads to a Lower Net Heat Loss during Exercise in the Heat

Ice Slurry Ingestion Leads to a Lower Net Heat Loss during Exercise in the Heat. Med. Sci. Sports Exerc., Vol. 48, No. 1, pp. 114- 122, 2016. 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- C +/- 1.4- C; 23.7% +/- 2.6% relative humidity [ RH]). Methods: Nine men cycled at approximately 55% V. O2peak for 75 min and ingested 3.2 mLIkgj1 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 T 20 kJ greater Hfluid ( P G 0.001) with ICE ingestion was overcompensated by a 381 +/- 199- kJ lower Esk ( P < 0.001). Net heat loss ( 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 andWBSL were lower by 0.16 +/- 0.14 mgIminj1 Icmj2 ( P G 0.01) and 191 +/- 122 g ( P G 0.001), respectively, and SkBF tended to be lower ( P = 0.06) by 5.4% maxAU +/- 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 degrees C, ICE 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 ingestion during exercise in warm, dry conditions should be reconsidered.