Comparing muscle V̇o from near-infrared spectroscopy desaturation rate to pulmonary V̇o during cycling below, at, and above the maximal lactate steady state.

Muscle oxygen uptake (V̇o) 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 V̇o. However, its correspondence with pulmonary oxygen uptake (V̇o) during exercise remains unknown. This study investigated the V̇o and V̇o 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: ) ramp incremental test; and ) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); ) constant-PO exercise bouts to task failure at ) 15% below MLSS (MLSS); ) MLSS; and ) 15% above MLSS (MLSS). V̇o was estimated at baseline, at , , , , and at task failure. V̇o was continuously recorded during the constant-PO bouts. V̇o and V̇o significantly increased from to in MLSS condition (all values <0.05) and from to in MLSS condition (all < 0.05). V̇o and V̇o were correlated ( range of 0.70-0.98, all < 0.001) among exercise intensities in both females and males. In addition, both variables were also correlated when expressed as percent ( range of 0.52-0.77, all < 0.001). V̇o and V̇o responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇o and V̇o were correlated regardless the exercise intensity and sex of the participants. It was unknown if muscle oxygen uptake (V̇o) derived from near-infrared spectroscopy oxygen desaturation slope during 5-s blood flow occlusion, was similar to the pulmonary oxygen uptake (V̇o) across time and among different exercise intensities. We showed that ) V̇o and V̇o had similar responses across time and among intensities below, at, and above the maximal lactate steady state; ) both variables were strongly correlated; and ) these observations were consistent between females and males.