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Muscle metabolic responses during 16 hours of intermittent heavy exercise

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The alterations in muscle metabolism were investigated in response to repeated sessions of heavy intermittent exercise performed over 16h. Tissue samples were extracted from the vastus lateralis muscle before (B) and after (A) 6min 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± 0.66mL·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 (μmol·(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.

On a examiné les modifications du métabolisme musculaire en réponse à des séances répétées d’un exercice intermittent intense effectué sur une période de 16 h. On a prélevé des échantillons de tissus dans le muscle vaste externe du membre inférieur avant (B) et après (A) un effort sur bicyclette de 6 min, à approximativement 91 % de la capacité aérobique maximale aux répétitions 1 (R1), 2 (R2), 9 (R9) et 16 (R16) chez 13 volontaires non entraînés (la capacité aérobique maximale = 44,3 ± 0,66 mL·kg–1·min–1, (moyenne ± é.t.). La concentration de métabolites (mmol·kg–1 p.s.) dans les homogénats à R1 a indiqué des diminutions (p < 0,05) d’ATP (21,9 ± 0,62 vs. 17,7 ± 0,68) et de phosphocréatine (80,3 ± 2,0 vs. 8,56 ± 1,5), et des augmentations (p < 0,05) d’inosine monophosphate (IMP, 0,077 ± 0,12 vs. 3,63 ± 0,85) et de lactate (3,80 ± 0,57 vs. 84,6 ± 10,3). Les concentrations (µmol·kg–1 p.s.) d’ADP libre ([ADPf], 86,4 ± 5,5 vs. 1014 ± 237) et d’AMP libre ([AMPf], 0,32 ± 0,03 vs. 78,4 ± 31) calculées ont aussi augmenté (p < 0,05). Il n’y a eu aucune différence entre R1 et R2. De R9 à R16, des diminutions marquées (p < 0,05) d’IMP (72,2 %), d’[ADPf] (58,7 %), d’[AMPf] (85,5 %) et de lactate (41,3 %) ont été observées à (A). Le protocole de 16 h a entraîné une déplétion de 89,7 % (p < 0,05) du glycogène musculaire. Des augmentations dépendantes des répétitions ont aussi été notées durant l’exercice la capacité aérobique. On conclut qu’un exercice intense répété perturbe moins le potentiel de phosphorylation, probablement en raison d’une augmentation de la respiration mitochondriale durant la transition repos-effort à l’état non stationnaire.
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Document Type: Research Article

Publication date: June 1, 2007

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