Comparing muscle V̇o 2 from near-infrared spectroscopy desaturation rate to pulmonary V̇o 2 during cycling below, at, and above the maximal lactate steady state.

Muscle oxygen uptake (V̇o 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 V̇o 2m . However, its correspondence with pulmonary oxygen uptake (V̇o 2p ) during exercise remains unknown. This study investigated the V̇o 2m and V̇o 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 +15% ). V̇o 2m was estimated at baseline, at min 5 , min 10 , min 20 , min 30 , and at task failure. V̇o 2p was continuously recorded during the constant-PO bouts. V̇o 2p and V̇o 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 +15% condition (all P < 0.05). V̇o 2p and V̇o 2m were correlated ( r 2 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 ( r 2 adj range of 0.52-0.77, all P < 0.001). V̇o 2p and V̇o 2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇o 2p and V̇o 2m were correlated regardless the exercise intensity and sex of the participants. NEW & NOTEWORTHY It was unknown if muscle oxygen uptake (V̇o 2m ) derived from near-infrared spectroscopy oxygen desaturation slope during 5-s blood flow occlusion, was similar to the pulmonary oxygen uptake (V̇o 2p ) across time and among different exercise intensities. We showed that 1 ) V̇o 2m and V̇o 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.