title: Muscle metabolites and performance during high-intensity, intermittent exercise.
abstract: Six men were studied during four 30-s "all-out" exercise bouts on an air-braked cycle ergometer. The first three exercise bouts were separated by 4 min of passive recovery; after the third bout, subjects rested for 4 min, exercised for 30 min at 30-35% peak O2 consumption, and rested for a further 60 min before completing the fourth exercise bout. Peak power and total work were reduced (P < 0. 05) during bout 3 [765 +/- 60 (SE) W; 15.8 +/- 1.0 kJ] compared with bout 1 (1,168 +/- 55 W, 23.8 +/- 1.2 kJ), but no difference in exercise performance was observed between bouts 1 and 4 (1,094 +/- 64 W, 23.2 +/- 1.4 kJ). Before bout 3, muscle ATP, creatine phosphate (CP), glycogen, pH, and sarcoplasmic reticulum (SR) Ca2+ uptake were reduced, while muscle lactate and inosine 5'-monophosphate were increased. Muscle ATP and glycogen before bout 4 remained lower than values before bout 1 (P < 0.05), but there were no differences in muscle inosine 5'-monophosphate, lactate, pH, and SR Ca2+ uptake. Muscle CP levels before bout 4 had increased above resting levels. Consistent with the decline in muscle ATP were increases in hypoxanthine and inosine before bouts 3 and 4. The decline in exercise performance does not appear to be related to a reduction in muscle glycogen. Instead, it may be caused by reduced CP availability, increased H+ concentration, impairment in SR function, or some other fatigue-inducing agent.
authors.affiliation: Department of Physiology, The University of Melbourne, Parkville, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Hargreaves
authors.forename: M J
authors.initials: MJ
authors.lastname: McKenna
authors.forename: D G
authors.initials: DG
authors.lastname: Jenkins
authors.forename: S A
authors.initials: SA
authors.lastname: Warmington
authors.forename: J L
authors.initials: JL
authors.lastname: Li
authors.forename: R J
authors.initials: RJ
authors.lastname: Snow
authors.forename: M A
authors.initials: MA
authors.lastname: Febbraio
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis / Q000378:metabolism; D000328:Adult; D001706:Biopsy; D002118:Calcium / Q000378:metabolism; D016552:Ergometry; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019271:Hypoxanthine / Q000378:metabolism; D007291:Inosine Monophosphate / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology
chemical_list: D010725:Phosphocreatine; D007291:Inosine Monophosphate; D019271:Hypoxanthine; D019344:Lactic Acid; D000255:Adenosine Triphosphate; D006003:Glycogen; D002118:Calcium