Comparing muscle V^_ O₂ from near-infrared spectroscopy desaturation rate to pulmonary V^_ O₂ during cycling below, at, and above the maximal lactate steady state

Muscle oxygen uptake (V^_ O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V^_ O_2m. However, its correspondence with pulmonary oxygen uptake (V^_ O_2p) during exercise remains unknown. This study investigated the V^_ O_2m and V^_ O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities. Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2 and 3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4–6) constant-PO exercise bouts to task failure at i) 15% below MLSS (MLSS_-15%); ii) MLSS; and iii) 15% above MLSS (MLSS_{þ 15%}). V^_ O_2m was estimated at baseline, at min 5, min 10, min 20, min 30, and at task failure. V^_ O_2p was continuously recorded during the constant-PO bouts. V^_ O_2p and V^_ O_2m significantly increased from min 5 to min 30 in MLSS condition (all P values <0.05) and from min 5 to min 10 in MLSS_{þ 15%} condition (all P < 0.05). V^_ O_2p and V^_ O_2m were correlated (r² adj range of 0.70–0.98, all P < 0.001) among exercise intensities in both females and males. In addition, both variables were also correlated when expressed as percent (r² adj range of 0.52–0.77, all P < 0.001). V^_ O_2p and V^_ O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V^_ O_2p and V^_ O_2m were correlated regardless the exercise intensity and sex of the participants. NEW & NOTEWORTHY It was unknown if muscle oxygen uptake (V^_ O_2m) derived from near-infrared spectroscopy oxygen desaturation slope during 5-s blood flow occlusion, was similar to the pulmonary oxygen uptake (V^_ O_2p) across time and among different exercise intensities. We showed that 1) V^_ O_2m and V^_ O_2p had similar responses across time and among intensities below, at, and above the maximal lactate steady state; 2) both variables were strongly correlated; and 3) these observations were consistent between females and males.