Activity-Induced Changes in Skeletal Muscle Metabolism Measured with Optical Spectroscopy

Abstract

Purpose Previous studies have used near-infrared spectroscopy (NIRS) to measure skeletal muscle mitochondrial capacity. This study tested the hypothesis that NIRS measured mitochondrial capacity would improve with endurance exercise training and decline with detraining. Methods Nine, young, participants performed four weeks of progressively increasing endurance exercise training of the wrist flexor muscles followed by approximately five weeks of inactivity. The rate of recovery of muscle oxygen consumption (mVO2) was measured with NIRS every 3-7 days, indicating mitochondrial oxidative capacity. Results A linear increase in mitochondrial capacity (NIRS rate constant) was found with a group average of 64 ± 37% improvement after four weeks of exercise training (p < 0.05). Mitochondrial capacity declined exponentially upon cessation of exercise training, with a mean half-time of ~7.7 days. Conclusion Both the magnitude and time course of mitochondrial adaptations to exercise training and detraining measured with NIRS was consistent with previous studies using both in vitro and in vivo techniques. These findings show that NIRS based measurements can detect meaningful changes in mitochondrial capacity.

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