Factors Affecting the Rate of Phosphocreatine Resynthesis Following Intense Exercise
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Sports Med 2002; 32 (12): 761-784 0112-1642/02/0012-0761/$25.00/0 © Adis International Limited. All rights reserved.
Factors Affecting the Rate of Phosphocreatine Resynthesis Following Intense Exercise Shaun McMahon and David Jenkins School of Human Movement Studies, University of Queensland, Brisbane, Queensland, Australia
Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Energy Production at the Onset of Muscular Contraction . . . . . . . . 2. Metabolic Consequences of Intense Contraction and Muscle Fatigue 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Depletion of Phosphocreatine (PCr) . . . . . . . . . . . . . . . . . . 2.3 Decline in Intracellular pH (pHi) . . . . . . . . . . . . . . . . . . . . . 3. Phosphorus Nuclear Magnetic Resonance Spectroscopy (31P-NMR) . . 4. Relative Versus Absolute Concentrations of ATP and PCr . . . . . . . . 5. PCr and the Nature of its Resynthesis . . . . . . . . . . . . . . . . . . . . 6. The Effect of pHi on PCr Recovery . . . . . . . . . . . . . . . . . . . . . . 7. The Importance of O2 for PCr Resynthesis . . . . . . . . . . . . . . . . . . 8. The Role of ADP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Relationship Between PCr Resynthesis and Maximal Aerobic Power . . 9.1 Results from Previous Work . . . . . . . . . . . . . . . . . . . . . . . . 10.Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Within the skeletal muscle cell at the onset of muscular contraction, phosphocreatine (PCr) represents the most immediate reserve for the rephosphorylation of adenosine triphosphate (ATP). As a result, its concentration can be reduced to less than 30% of resting levels during intense exercise. As a fall in the level of PCr appears to adversely affect muscle contraction, and therefore power output in a subsequent bout, maximising the rate of PCr resynthesis during a brief recovery period will be of benefit to an athlete involved in activities which demand intermittent exercise. Although this resynthesis process simply involves the rephosphorylation of creatine by aerobically produced ATP (with the release of protons), it has both a fast and slow component, each proceeding at a rate that is controlled by different components of the creatine kinase equilibrium. The initial fast phase appears to proceed at a rate independent of muscle pH. Instead, its rate appears to be controlled by adenosine diphosphate (ADP) levels; either
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