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


Medicine & Science in Sports & Exercise: December 2013 - Volume 45 - Issue 12 - p 2346–2352
doi: 10.1249/MSS.0b013e31829a726a
Applied Sciences

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 4 wk of progressively increasing endurance exercise training of the wrist flexor muscles followed by approximately 5 wk of inactivity. The rate of recovery of muscle oxygen consumption (mV˙O2) was measured with NIRS every 3–7 d, 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 4 wk of exercise training (P < 0.05). Mitochondrial capacity declined exponentially upon cessation of exercise training, with a mean half-time of approximately 7.7 d.

Conclusions Both the magnitude and the 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.

Department of Kinesiology, University of Georgia, Athens, GA

Address for correspondence: Terence Edward Ryan, PhD, University of Georgia, 330 River Rd., Athens, GA. 30602; E-mail:

Submitted for publication March 2013.

Accepted for publication May 2013.

© 2013 American College of Sports Medicine