Determination of the Respiratory Compensation Point by Detecting Changes in Intercostal Muscles Oxygenation by Using Near-Infrared Spectroscopy

This study aimed to evaluate if the changes in oxygen saturation levels at intercostal muscles (SmO(2)-m.intercostales) assessed by near-infrared spectroscopy (NIRS) using a wearable device could determine the respiratory compensation point (RCP) during exercise. Fifteen healthy competitive triathletes (eight males; 29 ± 6 years; height 167.6 ± 25.6 cm; weight 69.2 ± 9.4 kg; [Formula: see text] O(2)-máx 58.4 ± 8.1 mL·kg(−1)·min(−1)) were evaluated in a cycle ergometer during the maximal oxygen-uptake test ([Formula: see text] O(2)-máx), while lung ventilation ([Formula: see text] E), power output (watts, W) and SmO(2)-m.intercostales were measured. RCP was determined by visual method (RCP(visual): changes at ventilatory equivalents ([Formula: see text] E· [Formula: see text] CO(2)(−1), [Formula: see text] E· [Formula: see text] O(2)(−1)) and end-tidal respiratory pressure (PetO(2), PetCO(2)) and NIRS method (RCP(NIRS): breakpoint of fall in SmO(2)-m.intercostales). During exercise, SmO(2)-m.intercostales decreased continuously showing a higher decrease when [Formula: see text] E increased abruptly. A good agreement between methods used to determine RCP was found (visual vs NIRS) at % [Formula: see text] O(2)-máx, [Formula: see text] O(2), [Formula: see text] E, and W (Bland-Altman test). Correlations were found to each parameters analyzed (r = 0.854; r = 0.865; r = 0.981; and r = 0,968; respectively. p < 0.001 in all variables, Pearson test), with no differences (p < 0.001 in all variables, Student’s t-test) between methods used (RCP(visual) and RCP(NIRS)). We concluded that changes at SmO(2)-m.intercostales measured by NIRS could adequately determine RCP in triathletes.