title: Noninvasive measurement of phosphocreatine recovery kinetics in single human muscles.
abstract: The rate at which phosphocreatine (PCr) is resynthesized after exercise is related to muscle oxidative capacity (Vmax). With the use of a one-dimensional image-guided, localized nuclear magnetic resonance spectroscopy technique, PCr kinetics were monitored in the medial gastrocnemius of eight healthy subjects after voluntary, short duration, maximal rate exercise. Localized spectra were obtained every 6 s with <5% contamination from nonselected regions. Maximal rate exercise elicited near-maximal to maximal muscle activation, as indicated by the high-PCr hydrolysis rate (2.26 +/- 0.07 mM/s) and extensive PCr depletion. At the end of 9 s of maximal rate exercise, PCr was depleted by 61.4 +/- 2.4% and intracellular pH was 7.04 +/- 0.03. After 9 s of maximal rate exercise, PCr recovered with a rate constant (kPCr) of 1.87 +/- 0.15 min(-1) and a Vmax of 67.2 +/- 6.0 mM/min. Independent of prior activity, aerobic ATP synthesis rates reached 48.6 +/- 4.9 mM/min within 9 s. Extending maximal rate exercise to 30 s resulted in 92.0 +/- 1.2% PCr depletion and an intracellular pH of 6.45 +/- 0.07. The intracellular acidosis separated the direct relationship between kPCr and muscle Vmax but did not affect the initial PCr resynthesis rate.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: G
authors.initials: G
authors.lastname: Walter
authors.forename: K
authors.initials: K
authors.lastname: Vandenborne
authors.forename: K K
authors.initials: KK
authors.lastname: McCully
authors.forename: J S
authors.initials: JS
authors.lastname: Leigh
mesh_terms: D000328:Adult; D015444:Exercise; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010725:Phosphocreatine / Q000096:biosynthesis*; D015203:Reproducibility of Results; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D010725:Phosphocreatine