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; V˙O 2 -máx 58.4 ± 8.1 mL·kg -1 ·min -1 ) were evaluated in a cycle ergometer during the maximal oxygen-uptake test (V˙O 2 -máx), while lung ventilation (V˙E), power output (watts, W) and SmO 2 - m.intercostales were measured. RCP was determined by visual method (RCP visual : changes at ventilatory equivalents (V˙E·V˙CO 2 -1 , V˙E·V˙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 V˙E increased abruptly. A good agreement between methods used to determine RCP was found (visual vs NIRS) at %V˙O 2 -máx, V˙O 2 , V˙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.