title: Effects of hyperthermia on the metabolic responses to repeated high-intensity exercise.
abstract: In this study, we investigated the metabolic and performance responses to hyperthermia during high-intensity exercise. Seven males completed two 30-s cycle sprints (SpI and SpII) at an environmental temperature of 20.6 (0.3) degrees C [mean (SD)] with 4 min recovery between sprints. A hot or control treatment preceded the sprint exercise. For the hot trial, subjects were immersed up to the neck in hot water [43 degrees C for 16.0 (3.2) min] prior to entering an environmental chamber [44.2 (0.8) degrees C for 30.7 (7.1) min]. For the control trial, subjects were seated in an empty bath (15 min) and thereafter in a normal environment [20.2 (0.6) degrees C for 29.0 (1.9) min]. Subjects' core temperature prior to exercise was 38.1 (0.3) degrees C in the hot trial and 37.1 (0.3) degrees C in the control trial. Mean power output (MPO) was significantly higher in the hot condition for SpI [683 (130) W hot vs 646 (119) W control ( P<0.025)]. Peak power output (PPO) tended to be higher in the hot trial compared with the control trial for SpI [1057 (260) W hot vs 990 (245) W control ( P=0.03, NS)]. These differences in power output were a consequence of a faster pedal cadence in the hot trial ( P<0.025). There were no differences in sprint performance in SpII in the hot trial compared to the control trial; however, MPO was significantly reduced from SpI to SpII in the hot condition but not in the control condition ( P<0.025). Plasma ammonia was higher in the hot trial at 2 min post-SpI [169 (65) micromol l(-1 )hot vs 70 (26) micromol l(-1) control ( P<0.01)], immediately and at 2 min post-SpII [231 (76) micromol l(-1) hot vs 147 (72) micromol l(-1) control ( P<0.01)]. Blood lactate was higher in the hot trial compared with the control trial at 5 min post-SpII ( P<0.025). The results of this study suggest that an elevation in core body temperature by 1 degrees C can improve performance during an initial bout of high-intensity cycle exercise but has no further beneficial effect on subsequent power production following a 4-min recovery period.
authors.affiliation: Physiology and Sport Science, School of Science and the Environment, Coventry University, Priory Street, CV1 5FB, Coventry, UK.
authors.forename: D M
authors.initials: DM
authors.lastname: Linnane
authors.forename: R M
authors.initials: RM
authors.lastname: Bracken
authors.forename: S
authors.initials: S
authors.lastname: Brooks
authors.forename: V M
authors.initials: VM
authors.lastname: Cox
authors.forename: D
authors.initials: D
authors.lastname: Ball
mesh_terms: D000328:Adult; D000641:Ammonia / Q000097:blood*; D001831:Body Temperature; D004734:Energy Metabolism; D004735:Energy Transfer; D005334:Fever / Q000097:blood / Q000503:physiopathology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D010807:Physical Endurance; D013647:Task Performance and Analysis
chemical_list: D019344:Lactic Acid; D000641:Ammonia