SIMULTANEOUS IN-VIVO MEASUREMENTS OF HBO(2) SATURATION AND PCR KINETICS AFTER EXERCISE IN NORMAL HUMANS

Simultaneous measurements of phosphocreatine (PCr) and oxyhemoglobin ( HbO(2)) saturation were made during recovery from exercise in calf mus cles of five male subjects. PCr was measured using magnetic resonance spectroscopy in a 2.0-T 78-cm-bore magnet with a 9-cm-diam surface coi l. Relative HbO(2) saturation was measured as the difference in absorp tion of 750- and 850-nm light with use of near-infrared spectroscopy. The light source and detectors were 3 cm apart. Exercise consisted of isokinetic plantar flexion in a supine position. Two 5-min submaximal protocols were performed with PCr depletion to 60% of resting values a nd with pH values of > 7.0. Then two 1-min protocols of rapid plantar flexion were performed to deplete PCr values to 5-20% of resting value s with pH values of < 6.8. Areas of PCr peaks (every 8 s) and HbO(2) s aturation (every 1 s) were fit to a monoexponential function, and a ti me constant was calculated. The PCr time constant was larger after max imal exercise (68.3 +/- 10.5 s) than after submaximal exercise (36.0 /- 6.5 s), which is consistent with the effects of low pH on PCr recov ery. HbO(2) resaturation approximated submaximal PCr recovery and was not different between maximal (29.4 +/- 5.5 s) and submaximal (27.6 +/ - 6.0 s) exercise. We conclude that magnetic resonance spectroscopy me asurements of PCr recovery and near-infrared spectroscopy measurements of recovery of HbO(2) saturation provide similar information as long as muscle pH remains near 7.0.