title: Separate and combined effects of exposure to heat stress and mental fatigue on endurance exercise capacity in the heat.
abstract: OBJECTIVE
  This study investigated the effects of exposure to pre-exercise heat stress and mental fatigue on endurance exercise capacity in a hot environment.
  
  
  METHODS
  Eight volunteers completed four cycle exercise trials at 80% maximum oxygen uptake until exhaustion in an environmental chamber maintained at 30 °C and 50% relative humidity. The four trials required them to complete a 90 min pre-exercise routine of either a seated rest (CON), a prolonged demanding cognitive task to induce mental fatigue (MF), warm water immersion at 40 °C during the last 30 min to induce increasing core temperature (WI), or a prolonged demanding cognitive task and warm water immersion at 40 °C during the last 30 min (MF + WI).
  
  
  RESULTS
  Core temperature when starting exercise was higher following warm water immersion (~38 °C; WI and MF + WI) than with no water immersion (~36.8 °C; CON and MF, P < 0.001). Self-reported mental fatigue when commencing exercise was higher following cognitive task (MF and MF + WI) than with no cognitive task (CON and WI; P < 0.05). Exercise time to exhaustion was reduced by warm water immersion (P < 0.001) and cognitive task (P < 0.05). Compared with CON (18 ± 7 min), exercise duration reduced 0.8, 26.6 and 46.3% in MF (17 ± 7 min), WI (12 ± 5 min) and MF + WI (9 ± 3 min), respectively.
  
  
  CONCLUSIONS
  This study demonstrates that endurance exercise capacity in a hot environment is impaired by either exposure to pre-exercise heat stress or mental fatigue, and this response is synergistically increased during combined exposure to them.
authors.affiliation: Faculty of Health Care Sciences, Himeji Dokkyo University, 7-2-1 Kamiono, Himeji, Hyogo, 670-8524, Japan. hotani@himeji-du.ac.jp.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Otani
authors.affiliation: Hyogo University of Health Sciences, Kobe, Hyogo, Japan.
authors.forename: Mitsuharu
authors.initials: M
authors.lastname: Kaya
authors.affiliation: Hyogo University of Health Sciences, Kobe, Hyogo, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Tamaki
authors.affiliation: Department of Human Physiology, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Phillip
authors.initials: P
authors.lastname: Watson
mesh_terms: D001831:Body Temperature; D003071:Cognition; D015444:Exercise / Q000502:physiology; D017079:Exercise Tolerance; D018869:Heat-Shock Response; D006358:Hot Temperature; D006801:Humans; D008297:Male; D005222:Mental Fatigue; D011897:Random Allocation; D055815:Young Adult
keywords: Cognitive function; Core temperature; Fatigue; Heat stress; Skin temperature; Thermoregulation