Preliminary vastus lateralis characterization with time domain near infrared spectroscopy during incremental cycle exercise

Functional near infrared spectroscopy (NIRS) is a widespread non-invasive technique to monitor skeletal muscle metabolism. However, only variation of oxygenated (HHb), deoxygenated (O2Hb), total (tHb) hemoglobin and saturation (SO2) are usually reported. In this study, Time Domain (TD) NIRS approach was exploited to perform a preliminary quantitative characterization of vastus lateralis muscle during incremental exercise. A population of 11 healthy young male subjects performed on a mechanical cycle ergometer an incremental exercise (initial work rate range = 60-96 W, increment = 12-18 W/min) until exhaustion. TD NIRS, heart rate, pulmonary ventilation (VE), O2 uptake (VO2), CO2 output (VCO2), blood lactate concentration ([La]b) and Borg scale were measured during the exercise. From TD NIRS, muscles absolute values of absorption and scattering coefficients were obtained with a homogeneous approach and hemoglobin concentrations and saturation levels were calculated. The time courses of HHb, O2Hb, tHb and SO2 were consistent with previous literature results. A high inter-subject variability was found for both optical properties and hemodynamic concentrations. Further statistical group analysis will be required in order to highlight significant behavior within the population and correlation with physiological parameters.