P-31 magnetic resonance spectroscopy study of phosphocreatine recovery kinetics in skeletal muscle: the issue of intersubject variability

We have analyzed by P-31 MRS the relationship between kinetic parameters of phosphocreatine (PCr) recovery and end-of-exercise status under conditions of moderate and large acidosis induced by dynamic exercise. Thirteen healt hy subjects performed muscular contractions at 0.47 Hz (low frequency, mode rate exercise) and 0.85 Hz thigh frequency, heavy exercise). The rate const ant of PCr resynthesis (kpc,) varied greatly among subjects (variation coef ficients: 43 vs. 57% for LF vs. HF exercises) and protocols (k(PCr) values: 1.3 +/- 0.5 min(-1) vs. 0.9 +/- 0.5 min(-1) for LF vs. HF exercises, P< 0. 03). The large intersubject variability can be captured into a linear relat ionship between k(PCr), the amount of PCr consumed ([PCr2]) and pH reached at the end of exercise (pH(end)) (k(PCr) = -3.3+0.7 pH(end)-0,03 [PCr2]; P= 0.0007; r=0.61). This dual relationship illustrates that mitochondrial acti vity is affected by end-of-exercise metabolic status and allows reliable co mparisons between control, diseased and trained muscles. In contrast to k(P Cr), the initial rate of PCr recovery and the maximum oxidative capacity we re always constant whatever the metabolic conditions of end-of-exercise and can then be additionally used in the identification of dysfunctions in the oxidative metabolic pathway. (C) 2000 Elsevier Science B.V. All rights res erved.