Reliability of NIRS portable device for measuring intercostal muscles oxygenation during exercise

This study assessed the intra-individual reliability of oxygen saturation in intercostal muscles (SmO2-m.intercostales) during an incremental maximal treadmill exercise by using portable NIRS devices in a test-retest study. Fifteen marathon runners (age, 24.9 +/- 2.0 years; body mass index, 21.6 +/- 2.3 kg center dot m(-2); V?O-2-peak, 63.7 +/- 5.9 mL center dot kg(-1)center dot min(-1)) were tested on two separate days, with a 7-day interval between the two measurements. Oxygen consumption (V?O-2) was assessed using the breath-by-breath method during the V?O-2-test, while SmO2 was determined using a portable commercial device, based in the near-infrared spectroscopy (NIRS) principle. The minute ventilation (VE), respiratory rate (RR), and tidal volume (Vt) were also monitored during the cardiopulmonary exercise test. For the SmO2-m.intercostales, the intraclass correlation coefficient (ICC) at rest, first (VT1) and second ventilatory (VT2) thresholds, and maximal stages were 0.90, 0.84, 0.92, and 0.93, respectively; the confidence intervals ranged from -10.8% - +9.5% to -15.3% - +12.5%. The reliability was good at low intensity (rest and VT1) and excellent at high intensity (VT2 and max). The Spearman correlation test revealed (p <= 0.001) an inverse association of SmO2-m.intercostales with V?O-2 (rho = -0.64), VE (rho = -0.73), RR (rho = -0.70), and Vt (rho = -0.63). The relationship with the ventilatory variables showed that increased breathing effort during exercise could be registered adequately using a NIRS portable device.