title: Muscle metabolic responses during 16 hours of intermittent heavy exercise.
abstract: The alterations in muscle metabolism were investigated in response to repeated sessions of heavy intermittent exercise performed over 16 h. Tissue samples were extracted from the vastus lateralis muscle before (B) and after (A) 6 min of cycling at approximately 91% peak aerobic power at repetitions one (R1), two (R2), nine (R9), and sixteen (R16) in 13 untrained volunteers (peak aerobic power = 44.3 +/- 0.66 mL.kg-1.min-1, mean +/- SE). Metabolite content (mmol.(kg dry mass)-1) in homogenates at R1 indicated decreases (p < 0.05) in ATP (21.9 +/- 0.62 vs. 17.7 +/- 0.68) and phosphocreatine (80.3 +/- 2.0 vs. 8.56 +/- 1.5) and increases (p < 0.05) in inosine monophosphate (IMP, 0.077 +/- 0.12 vs. 3.63 +/- 0.85) and lactate (3.80 +/- 0.57 vs. 84.6 +/- 10.3). The content (micromol.(kg dry mass)-1) of calculated free ADP ([ADPf], 86.4 +/- 5.5 vs. 1014 +/- 237) and free AMP ([AMPf], 0.32 +/- 0.03 vs. 78.4 +/- 31) also increased (p < 0.05). No differences were observed between R1 and R2. By R9 and continuing to R16, pronounced reductions (p < 0.05) at A were observed in IMP (72.2%), [ADPf] (58.7%), [AMPf] (85.5%), and lactate (41.3%). The 16-hour protocol resulted in an 89.7% depletion (p < 0.05) of muscle glycogen. Repetition-dependent increases were also observed in oxygen consumption during exercise. It is concluded that repetitive heavy exercise results in less of a disturbance in phosphorylation potential, possibly as a result of increased mitochondrial respiration during the rest-to-work non-steady-state transition.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, ON N2L 3G1, Canada. green@healthy.uwaterloo.ca
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: T A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: G P
authors.initials: GP
authors.lastname: Holloway
authors.forename: J
authors.initials: J
authors.lastname: Moule
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
authors.forename: D
authors.initials: D
authors.lastname: Ranney
authors.forename: A R
authors.initials: AR
authors.lastname: Tupling
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D003401:Creatine / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D005636:Fructosephosphates / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006019:Glycolysis / Q000502:physiology; D006801:Humans; D007291:Inosine Monophosphate / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology; D011773:Pyruvates / Q000378:metabolism; D012146:Rest / Q000502:physiology; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013997:Time Factors