title: Hyperthermia, but not muscle water deficit, increases glycogen use during intense exercise.
abstract: We determined if dehydration alone or in combination with hyperthermia accelerates muscle glycogen use during intense exercise. Seven endurance-trained cyclists (VO2max  = 54.4 ± 1.05 mL/kg/min) dehydrated 4.6% of body mass (BM) during exercise in the heat (150 min at 33 ± 1 °C, 25 ± 2% humidity). During recovery (4 h), subjects remained dehydrated (HYPO trial) or recovered all fluid losses (REH trials). Finally, subjects exercised intensely (75% VO2max ) for 40 min in a neutral (25 ± 1 °C; HYPO and REH trials) or in a hot environment (36 ± 1 °C; REHHOT ). Before the final exercise bout vastus lateralis glycogen concentration was similar in all three trials (434 ± 57 mmol/kg of dry muscle (dm)) but muscle water content was lower in the HYPO (357 ± 14 mL/100 g dm) than in REH trials (389 ± 25 and 386 ± 25 mL/100 g dm; P < 0.05). After 40 min of intense exercise, intestinal temperature was similar between the HYPO and REHHOT trials (39.2 ± 0.5 and 39.2 ± 0.4 °C, respectively) and glycogen use was similar (172 ± 86 and 185 ± 97 mmol/kg dm, respectively) despite large differences in muscle water content. In contrast, during REH, intestinal temperature (38.5 ± 0.4 °C) and glycogen use (117 ± 52 mmol/kg dm) were significantly lower than during HYPO and REHHOT . Our data suggest that hyperthermia stimulates glycogen use during intense exercise while muscle water deficit has a minor role.
authors.affiliation: Exercise Physiology Laboratory, University of Castilla - La Mancha, Toledo, Spain.
authors.forename: V E
authors.initials: VE
authors.lastname: Fernández-Elías
authors.forename: N
authors.initials: N
authors.lastname: Hamouti
authors.forename: J F
authors.initials: JF
authors.lastname: Ortega
authors.forename: R
authors.initials: R
authors.lastname: Mora-Rodríguez
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D015415:Biomarkers / Q000378:metabolism; D018592:Cross-Over Studies; D003681:Dehydration / Q000209:etiology / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005334:Fever / Q000209:etiology / Q000503:physiopathology*; D006003:Glycogen / Q000378:metabolism*; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D052097:Quadriceps Muscle / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D015415:Biomarkers; D006003:Glycogen
keywords: Muscle glycogen; hydration status; muscle water content; performance; thermoregulation