title: Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia.
abstract: OBJECTIVE
  We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI).
  
  
  METHODS
  Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (T re) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until T re reached 38.1 °C or for a maximum of 15 min. T re, heart rate (HR), skin blood flux (SBF) and mean skin temperature (T sk) were monitored continuously during cooling.
  
  
  RESULTS
  Pre-cooling body mass was decreased in the HY trial (-2.66 ± 1.23 % body mass) and maintained in the EU trial (-0.66 ± 0.44 %) compared to baseline mass (P < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min, P = 0.046). HR, SBF, and T sk were not different between EU and HY trials (P > 0.05), however, all variables significantly decreased with immersion independent of hydration status (P < 0.001).
  
  
  CONCLUSIONS
  The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA. clbutts@uark.edu.
authors.forename: Cory L
authors.identifier: http://orcid.org/0000-0002-8720-5206
authors.initials: CL
authors.lastname: Butts
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Luhring
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Cody R
authors.initials: CR
authors.lastname: Smith
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Tucker
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Moyen
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Ganio
authors.affiliation: University of Arkansas, 155 Stadium Dr HPER 321, Fayetteville, AR, 72701, USA.
authors.forename: Brendon P
authors.initials: BP
authors.lastname: McDermott
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000502:physiology*; D003080:Cold Temperature; D015444:Exercise; D005260:Female; D006801:Humans; D006979:Hyperthermia, Induced; D007036:Hypothermia, Induced; D007053:Ice; D007101:Immersion; D008297:Male; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D007053:Ice
keywords: Cold-water immersion; Dehydration; Exertional heat illness treatment; Exertional hyperthermia; Hypohydration