title: Ice Slurry Ingestion Leads to a Lower Net Heat Loss during Exercise in the Heat.
abstract: OBJECTIVE
  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% VO2peak for 75 min and ingested 3.2 mL · kg(-1) 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). 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 and WBSL were lower by 0.16 ± 0.14 mg · min(-1) · cm(-2) (P < 0.01) and 191 ± 122 g (P < 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 °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.
authors.affiliation: 1School of Human Kinetics, University of Ottawa, Ottawa, ON, CANADA; and 2Thermal Ergonomics Laboratory, Exercise and Sports Science, Faculty of Health Sciences, University of Sydney, NSW, AUSTRALIA.
authors.forename: Nathan B
authors.initials: NB
authors.lastname: Morris
authors.forename: Geoff
authors.initials: G
authors.lastname: Coombs
authors.forename: Ollie
authors.initials: O
authors.lastname: Jay
mesh_terms: D000328:Adult; D001628:Beverages; D001642:Bicycling / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D002151:Calorimetry; D004326:Drinking; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D007053:Ice; D008297:Male; D012039:Regional Blood Flow; D012867:Skin / Q000098:blood supply; D012881:Skin Temperature / Q000502:physiology; D013546:Sweating / Q000502:physiology; D055815:Young Adult
chemical_list: D007053:Ice