title: Elevations in core and muscle temperature impairs repeated sprint performance.
abstract: OBJECTIVE
  The present study investigated the effects of hyperthermia on intermittent exercise and repeated sprint performance.
  
  
  METHODS
  Seven men completed 40 min of intermittent cycling comprising of 15 s exercise (306 +/- 22 W) and 15 s rest periods (0 W) followed by 5 x 15 s maximal sprints on a cycle ergometer in normal (approximately 20 degrees C, control) and hot (40 degrees C, hyperthermia) environments.
  
  
  RESULTS
  Completion of the intermittent protocol in the heat elevated core and muscle temperatures (39.5 +/- 0.2 degrees C; 40.2 +/- 0.4 degrees C), heart rate (178 +/- 11 beats min(-1)), rating of perceived exertion (RPE) (18 +/- 1) and noradrenaline (38.9 +/- 13.2 micromol l(-1)) (all P < 0.05). During the first sprint (n = 6), both peak and mean power output were similar across the environmental conditions. However, mean power over the last four sprints declined to a larger extent during hyperthermia compared with the control trial (P < 0.05). Consequently, average mean power output during the five sprints was lower in hyperthermia (558.0 +/- 146.9 W) compared with control (617.5 +/- 122.6 W; P < 0.05). Power output during the repeated sprints was reduced by hyperthermia despite an elevated muscle temperature that should promote sprint performance. Venous plasma potassium concentrations (H; 5.3 +/- 0.8 mmol l(-1) vs. C; 6.3 +/- 1.0 mmol l(-1), P = 0.06) and muscle lactate levels (H; 76.6 +/- 24.3 mmol kg(-1) dry weight vs. C; 108.8 +/- 20.1 mmol kg(-1) dry weight) were lower following the hyperthermic sprints compared to control.
  
  
  CONCLUSIONS
  Although an elevated muscle temperature is expected to promote sprint performance, power output during the repeated sprints was reduced by hyperthermia. The impaired performance does not seem to relate to the accumulation of recognized metabolic fatigue agents and we, therefore, suggest that it may relate to the influence of high core temperature on the function of the central nervous system.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.
authors.forename: B
authors.initials: B
authors.lastname: Drust
authors.forename: P
authors.initials: P
authors.lastname: Rasmussen
authors.forename: M
authors.initials: M
authors.lastname: Mohr
authors.forename: B
authors.initials: B
authors.lastname: Nielsen
authors.forename: L
authors.initials: L
authors.lastname: Nybo
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001831:Body Temperature / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D016552:Ergometry / Q000379:methods; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D018737:Hand Strength / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007773:Lactates / Q000032:analysis; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D011188:Potassium / Q000097:blood
chemical_list: D001786:Blood Glucose; D007773:Lactates; D006003:Glycogen; D011188:Potassium; D009638:Norepinephrine; D004837:Epinephrine