Quantitative Evaluation of Oxygenation and Metabolism in the Human Skeletal Muscle

The forearm muscles of five healthy males were monitored for changes in microvessel hemoglobin saturation (SO2-TRS) by near infrared time-resolved spectroscopy (NIRTRS) and changes in phosphorus metabolites by magnetic resonance spectroscopy (31P-MRS) during 12 min of resting arterial occlusion. Muscle oxygenation and phosphorus metabolites were also measured during grip exercises at varying intensities. Upon the initiation of occlusion, SO2-TRS fell progressively until it reached a plateau in the latter half of the occlusion. Phosphocreatine (PCr) began to decrease around 6 min after the initiation of arterial occlusion. The resting O2 store and O2 consumption were 295 μM and 0.95 μM/sec, respectively-values which reasonably agree with the reported results. A significant correlation was observed between the changes in SO2-TRS and PCr during exercise (r2 = 0.80, p < 0.001). These results indicate that NIRTRS is able to provide reliable information about resting metabolism and oxidative rate during exercise. NIRTRS and MRS are useful to monitor oxygenation and energetics noninvasively in the human muscle.