Cerebral and Muscle Tissue Oxygenation During Incremental Cycling in Male Adolescents Measured by Time-Resolved Near-Infrared Spectroscopy

<jats:p>Near-infrared spectroscopy has long been used to measure tissue-specific O<jats:sub>2</jats:sub> dynamics in exercise, but most published data have used continuous wave devices incapable of quantifying absolute Hemoglobin (Hb) concentrations. We used time-resolved near-infrared spectroscopy to study exercising muscle (Vastus Lateralis, VL) and prefrontal cortex (PFC) Hb oxygenation in 11 young males (15.3 ± 2.1 yrs) performing incremental cycling until exhaustion (peak VO2 = 42.7 ± 6.1 ml/min/kg, mean peak power = 181 ± 38 W). Time-resolved near-infrared spectroscopy measurements of reduced scattering (µ<jats:sub>s</jats:sub>´) and absorption (µ<jats:sub>a</jats:sub>) at three wavelengths (759, 796, and 833 nm) were used to calculate concentrations of oxyHb ([HbO<jats:sub>2</jats:sub>]), deoxy Hb ([HbR]), total Hb ([THb]), and O<jats:sub>2</jats:sub> saturation (stO<jats:sub>2</jats:sub>). In PFC, significant increases were observed in both [HbO<jats:sub>2</jats:sub>] and [HbR] during intense exercise. PFC stO<jats:sub>2</jats:sub>% remained stable until 80% of total exercise time, then dropped (−2.95%, <jats:italic>p</jats:italic> = .0064). In VL, stO<jats:sub>2</jats:sub>% decreased until peak time (−6.8%, <jats:italic>p</jats:italic> = .01). Segmented linear regression identified thresholds for PFC [HbO<jats:sub>2</jats:sub>], [HbR], VL [THb]. There was a strong correlation between timing of second ventilatory threshold and decline in PFC [HbO<jats:sub>2</jats:sub>] (<jats:italic>r</jats:italic> = .84). These findings show that time-resolved near-infrared spectroscopy can be used to study physiological threshold phenomena in children during maximal exercise, providing insight into tissue specific hemodynamics and metabolism.</jats:p>