Comparing muscle (V)over dotO₂ from near-infrared spectroscopy desaturation rate to pulmonary (V)over dotO₂ during cycling below, at, and above the maximal lactate steady state

Muscle oxygen uptake ((V)over dotO(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)over dotO(2m). However, its correspondence with pulmonary oxygen uptake ((V)over dotO(2p)) during exercise remains unknown. This study investigated the (V)over dotO(2m) and (V)over dotO(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%). (V)over dotO(2m) was estimated at baseline, at min 5, min 10, min 20, min 30, and at task failure. V_O2p was continuously recorded during the constant-PO bouts. (V)over dotO(2p) and (V)over dotO(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). (V)over dotO(2p) and (V)over dotO(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). (V)over dotO(2p) and (V)over dotO(2m) responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, (V)over dotO(2p) and (V)over dotO(2m) were correlated regardless the exercise intensity and sex of the participants.