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Excerpt
PURPOSE: To investigate the effects of repeated bouts of heavy intermittent exercise on substrate and metabolic changes in working skeletal muscle. METHODS: Ten untrained volunteers (VO2peak 44 ± 2.7 ml/kg/min, 0±SE) performed 6 min of cycle exercise at approximately 90% VO2peak each hour for 16 hours. Tissue was extracted from the vastus lateralis both prior to (PRE) and following (POST) exercise at 1 (R1), 2 (R2), 9 (R9) and 16 (R16) repetitions and analysed for high energy phosphagens (ATP, PCr), lactate (La) and Glycogen (Glyc). RESULTS: At R1, the concentrations (mmol/kg dry wt) of ATP (22.6±0.99 vs 18.4±1.1) and PCr (77.4±2.3 vs 17.2±3.7) decreased (P<0.05) with exercise by 19% and 78%, respectively. These changes were not affected by the number of repetitions. The 20–25 fold increase (P<0.05) observed in La (mmol/kg dry wt) at R1 (3.19±0.51 vs 81.2±15) and R2 (5.53±0.82 vs 110±16) was blunted (P<0.05) at R9 (4.06±0.87 vs 47.9±7.5) and R16 (6.25±1.0 vs 56.5±5.8). Similar decreases (P<0.05) in muscle glycogen (mmol glucosyl units/kg dry wt) were observed at R1 (432±34 vs 353±30), R2 (334±29 vs 267±32), R9 (152±21 vs 89±18) and R16 (131±13 vs 56±7.0). CONCLUSION: The results suggest that muscle phosphorylation potential is protected during repetitive heavy exercise with decreasing Glyc levels while production/removal of La is altered.
