title: Fluid Replacement Attenuates Physiological Strain Resulting From Mild Hypohydration Without Impacting Cognitive Performance.
abstract: OBJECTIVE
  The impact of mild hypohydration on physiological responses and cognitive performance following exercise-heat stress (EHS) were examined compared with conditions when fluids were ingested ad libitum (AL) or replaced to match sweat losses (FR).
  
  
  METHODS
  Twelve unacclimatized, recreationally-active men (22.2 ± 2.4 y) completed 50 min cycling (60%VO2peak) in the heat (32°C; 65% RH) under three conditions: no fluid (NF), AL, and FR. Before and after EHS, a cognitive battery was completed: Trail making, perceptual vigilance, pattern comparison, match-to-sample, and letter-digit recognition tests.
  
  
  RESULTS
  Hypohydration during NF was greater compared with AL and FR (NF: -1.5 ± 0.6; AL: -0.3 ± 0.8; FR: -0.1 ± 0.3% body mass loss) resulting in higher core temperature (by 0.4, 0.5 °C), heart rate (by 13 and 15 b·min-1), and physiological strain (by 1.3, 1.5) at the end of EHS compared with AL and FR, respectively. Cognitive performance (response time and accuracy) was not altered by fluid condition; however, mean response time improved (p < .05) for letter-digit recognition (by 56.7 ± 85.8 ms or 3.8%; p < .05) and pattern comparison (by 80.6 ± 57.4 ms or 7.1%; p < .001), but mean accuracy decreased in trail making (by 1.2 ± 1.4%; p = .01) after EHS (across all conditions).
  
  
  CONCLUSIONS
  For recreational athletes, fluid intake effectively mitigated physiological strain induced by mild hypohydration; however, mild hypohydration resulting from EHS elicited no adverse changes in cognitive performance.
authors: Western Michigan University, Kalamazoo, Michigan.
authors: Matthew T
authors: MT
authors: Wittbrodt
authors: Mindy
authors: M
authors: Millard-Stafford
authors: Ross A
authors: RA
authors: Sherman
authors: Christopher C
authors: CC
authors: Cheatham
mesh_terms: D000328:Adult; D001642:Bicycling; D003071:Cognition / Q000502:physiology*; D018592:Cross-Over Studies; D003681:Dehydration / Q000209:etiology / Q000503:physiopathology / Q000523:psychology / Q000628:therapy*; D015444:Exercise / Q000502:physiology*; D005440:Fluid Therapy / Q000379:methods; D006339:Heart Rate; D018869:Heat-Shock Response; D006358:Hot Temperature; D006801:Humans; D008297:Male; D064133:Sports Nutritional Physiological Phenomena / Q000502:physiology*; D013546:Sweating; D055815:Young Adult