Key result
NIRS during arterial occlusions successfully tracks mVO2, showing greater uptake at 50% versus 25% MVC.
Why the study?
The slow component of oxygen uptake has customarily been measured via pulmonary gas exchange, which includes contributions from respiratory, cardiac, and postural muscles rather than isolated muscle.
NIRS during brief arterial occlusions can assess the slow component of muscular oxygen uptake during intermittent isometric contractions and discriminate between different contraction intensities.
Enables noninvasive mVO2 slow-component assessment during isometric exercise; leaves open validation in clinical populations and dynamic settings.
When exercising in the severe‐intensity domain, oxygen uptake (V̇O 2 ) does not reach a steady state since it slowly and continuously drifts due to the appearance of the slow component of V̇O 2 (V̇O 2sc ). V̇O 2sc has been customarily evaluated by measuring V̇O 2 using pulmonary gas exchanges, including the contribution of the metabolic expenditure of the respiratory muscles, heart, and muscles recruited for stabilizing the posture, etc. We assessed the muscular oxygen uptake (mV̇O 2 , in μM·s −1 ) of flexor digitorum superficialis by using near‐infrared spectroscopy (NIRS) during brief arterial occlusions imposed over repeated, cyclic isometric hand grips performed at two different percentages (25%; 50%) of maximal voluntary contraction (MVC). mV̇O 2 was significantly larger at 50% MVC than at 25% MVC at all the time points ( p < 0.05) as expected, apart from the values at the 3rd minute. Secondly, mV̇O 2 increased linearly at 25% of MVC (mV̇O 2 = 1.73 + 0.108 × min; r 2 = 0.993; p < 0.0033) and at 50% of MVC (mV̇O 2 = 2.41 + 0.240 × min; r 2 = 0.956; p < 0.0223) from the 3rd minute of exercise onwards; the slopes of the two linear regressions were significantly different ( p < 0.0232). We suggest that the V̇O 2sc of mV̇O 2 occurring during intermittent isometric contractions can be assessed with NIRS during brief complete arterial occlusions regularly interspersed in the series of contractions. In addition, the technique can discriminate the rates of increase of mV̇O 2 corresponding to different percentages of MVC.
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Tam et al. (2025) studied this question. Repeated, cyclic isometric hand grips at 50% MVC vs. 25% MVC was evaluated on Muscular oxygen uptake (mVO2) measured by NIRS (p=<0.05). Near-infrared spectroscopy during brief arterial occlusions successfully assessed the slow component of muscular oxygen uptake, showing significantly larger mVO2 at 50% vs 25% MVC (p<0.05).
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