Abstract des Autors

This study evaluated the time courses of intracellular pH and the metabolism of phosphocreatine (PCr) and inorganic phosphate (Pi) at the onset of four exercise intensities and recoveries. During a series of rest-exercise-recovery procedures, 31P-MRS were accumulated using 32 scans/spectrum requiring 12.8 s each. At the onset of exercise, PCr decreased expondentially with a time constant of 27-32 s regardless of the exercise intensity. The time constant PCr resynthesis during recovery was about 27-40 s. The PCr kinetics were independent of exercise intensity. There were similar Pi kinetics at the onset of all types of exercise, while those of Pi recovery became significantly longer at the higher exercise intensities. Furthermore, the intracellular pH indicated temporary alkalosis just at the onset of exercise, probably due to absorption of hydrogen ions by PCr hydrolysis, and then decrease at a point about 40-50 of the preexercise PCr. The pH recovery time was longer than that for the Pi or PCr kinetics. By using a more efficient resolution system it was possible to obtain the phosphorus kinetics during exercise and to follow PCr resynthesis within the first few minutes of recovery. From our results it was concluded that in general the time course of PCr and Pi metabolism were unaffected by the exercise intensity, both at the onset of exercise and during recovery, with the exception of Pi recovery.