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Excerpt
Measurements of the muscle oxidative rate by near infrared spectroscopy(NIRS) require repeated arterial occlusions. Therefore, disadvantages, such as a poor time resolution, occur. If muscle oxygenation level is an indicator of the muscle oxidative rate, oxidative metabolism can be continuously monitored. The purpose of this study was to determine the relationship between oxygenation levels and oxidative rates. Muscle oxygenation and energetics in the finger flexors (N=10) were measured by NIRS and magnetic resonance spectroscopy, respectively. The resting metabolic rate was measured from the phosphocreatine (PCr) breakdown rate during a 15 min arterial occlusion. Muscle oxygenation was monitored during submaximal dynamic grip exercises at varying intensities (10-40% of maximum voluntary contraction). The oxidative rate was measured from the initial deoxygenation rate during a brief arterial occlusion at the end of the exercise and at 3, 5, 10, 15, 20, and 30 min during recovery. The resting metabolic rate was 7.0 μM ATP/sec on average. The end-exercise oxygenation levels varied, ranging from 89 to 68% on average, when the resting oxygenation level was defined as 100%, while the minimum oxygenation level was 0%. Oxidative rates during exercise increased 4.2 to 9.7 fold of the resting value on average, while oxidative rates during recovery gradually decreased with time - 3.6 to 1.2 fold of the resting value on average. Muscle oxygenation levels and the oxidative rates showed a linear relationship during exercise and showed a sigmoidal relationship during recovery. These results indicate that muscle oxygenation level is an indicator of oxidative rate during exercise and recovery.
