A practical indicator of muscle oxidative capacity determined by recovery of muscle O 2 consumption using NIR spectroscopy

We examined the relationship between the time constant (Tc) for muscle oxygen consumption (VO 2mus) recovery after exercise, as measured by near-infrared continuous wave spectroscopy (NIRcws), and the Tc for phosphocreatine (PCr) recovery as an index of muscle oxidative capacity. Eight healthy male subjects performed a dynamic handgrip exercise, and the VO 2mus recovery after exercise was measured with NIRcws by repeated arterial occlusion. VO 2mus was determined from the rate of deoxygenation during arterial occlusion, and muscle oxidative capacity was calculated from the Tc for PCr recovery using 31 phosphorus-magnetic resonance spectroscopy. VO 2mus increased 8.9 ± 4.9 (mean ± SD) fold of resting after exercise and thereafter decreased exponentially. The Tc for VO 2mus recovery and the Tc for PCr recovery were 33.1 ± 9.0 and 35.0 ± 8.5 s, respectively. The Tc for VO 2mus recovery was significantly correlated to the Tc for PCr recovery (r = 0.92, p < .01).