Characterizing cerebral and locomotor muscle oxygenation to incremental ramp exercise in healthy children: relationship with pulmonary gas exchange

To characterize the oxygenation responses at cerebral and locomotor muscle level to incremental exercise in children and to assess the interrelationship with the pulmonary gas exchange responses. Eighteen children (9 boys, 9 girls) (mean age 10.9 +/- 1.0 years) performed incremental cycle ramp exercise to exhaustion. The concentration of cerebral and muscle oxygenated (O(2)Hb) and deoxygenated (HHb) hemoglobin (by means of near-infrared spectroscopy) and pulmonary gas exchange was recorded. Cerebral and muscle O(2)Hb and HHb values were expressed as functions of oxygen uptake (VO2) and breakpoints were detected by means of double linear model analysis. The respiratory compensation point (RCP) was determined. The breakpoints in cerebral and muscle O(2)Hb and HHb were compared and correlated to RCP. The subjects reached peak power output of 105 +/- 18 W and VO2peak of 43.5 +/- 7.0 ml min(-1) kg(-1). Cerebral O(2)Hb increased to an intensity of 89.4 +/- 5.5 %VO2peak, where a breakpoint occurred at which cerebral O(2)Hb started to decrease. Cerebral HHb increased slightly to 88.1 +/- 4.8 %VO2peak, at which the increase was accelerated. Muscle HHb increased to 90.5 +/- 4.8 %VO2peak where a leveling-off occurred. RCP occurred at 89.3 +/- 4.3 %VO2peak. The breakpoints and RCP did not differ significantly (P = 0.13) and were strongly correlated (r > 0.70, P < 0.05). There were no differences between boys and girls (P = 0.43) and there was no significant correlation with VO2peak (P > 0.05). It was shown that cerebral and muscle oxygenation responses undergo significant changes as work rate increases and show breakpoints in the ongoing response at high intensity (85-95 %VO2peak). These breakpoints are strongly interrelated and associated with changes in pulmonary gas exchange.