Low muscle oxidative capacity contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). Near-infrared spectroscopy (NIRS) allows non-invasive determination of the muscle oxygen consumption false(normalmtrueV˙normalO2false) recovery rate constant (k), which is proportional to oxidative capacity assuming two conditions are met: 1) exercise intensity is sufficient to fully-activate mitochondrial oxidative enzymes; 2) sufficient O2 availability. We aimed to determine reproducibility (coefficient of variation, CV; intraclass correlation coefficient, ICC) of NIRS k assessment in the gastrocnemius of 64 participants with (FEV1 64±23%predicted) or without COPD (FEV1 98±14%predicted). 10–15s dynamic contractions preceded 6min of intermittent arterial occlusions (5–10s each, ~250mmHg) for k measurement. k was lower (P<0.05) in COPD (1.43±0.4min−1; CV=9.8±5.9%, ICC=0.88) than controls (1.74±0.69min−1; CV=9.9±8.4%; ICC=0.93). Poor k reproducibility was more common when post-contraction normalmtrueV˙normalO2 and deoxygenation were low, suggesting insufficient exercise intensity for mitochondrial activation and/or the NIRS signal contained little light reflected from active muscle. The NIRS assessment was well tolerated and reproducible for muscle dysfunction evaluation in COPD.

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