title: Phosphocreatine hydrolysis by 31P-NMR at the onset of constant-load exercise in humans.
abstract: The kinetics of phosphocreatine (PC) breakdown in human plantar flexors at the onset of constant-load aerobic exercise was determined by high-resolution 31P-nuclear magnetic resonance spectroscopy (NMRS). The half time of the process (t1/2PC) was obtained by fitting curves (n = 13) from five subjects at various aerobic work loads for which muscle pH was not different from that at rest. Steady-state PC concentration ([PC]) was not < 70% of the resting value and was linearly related to the work load (w) ([PC] = -3.01 +/- 0.08 w + 1 (r = 0.48, 2P < 0.1)). The average t1/2PC was 16.2 s and was independent of work load. Because the half time of the muscle PC kinetics reflects the half time of the O2 uptake (MO2) kinetics (t1/2MO2), the latter is equal to that found earlier in the isolated perfused dog gastrocnemius. Whereas in the dog the above t1/2MO2 compares well with the homologous half time of the O2 uptake at the alveolar level, in humans such equivalence is found only at extremely low work loads, when the transient contribution by anaerobic glycolysis is negligible.
authors.affiliation: Department of Physiology, Centre Médical Universitaire, Geneva, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Binzoni
authors.forename: G
authors.initials: G
authors.lastname: Ferretti
authors.forename: K
authors.initials: K
authors.lastname: Schenker
authors.forename: P
authors.initials: P
authors.lastname: Cerretelli
mesh_terms: D000328:Adult; D000332:Aerobiosis; D015444:Exercise / Q000502:physiology*; D006207:Half-Life; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007866:Leg / Q000033:anatomy & histology / Q000502:physiology; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D010477:Perfusion; D010725:Phosphocreatine / Q000378:metabolism*
chemical_list: D010725:Phosphocreatine