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Muscle O2 diffusion capacity by NIRS: A new approach in the air

We read with great interest the recent original study on non-invasive estimation of skeletal muscle oxidative capacity and O2 diffusion capacity (Pilotto et al. 2022). We congratulate the authors for their excellent, pioneering and meticulous work on the use of non-invasive techniques for assessing the functional limitations to exercise capacity in the final stage of the oxygen cascade. This study aimed to non-invasively investigate skeletal muscle O2 diffusion capacity (DmO2) by combining the near-infrared spectroscopy (NIRS) technique and a known vascular occlusion protocol (Zuccarelli et al. 2020) under two different levels of tissueO2 availability in the vastus lateralis muscle. By modulating the occlusion and recovery times, Pilotto et al. (2022) estimated DmO2 as the difference of the recovery rate constant ( k) of skeletal muscle O2 uptake obtained under high and low tissue O2 availability, respectively (Pilotto et al. 2022). Although we acknowledge merit to Pilotto et al. (2022) for this novel approach, in the present letter, we aim to comment on the following two important points: (i) the use of hypoxia to modulate O2 supply to working muscle and (ii) the potential benefit of this methodological ‘hypoxic’ improvement for the standardization (and potentially the reliability) of the protocol.