Kinetics of oxygenation in inactive forearm muscle during ramp leg cycling

This study was carried out to determine whether hemodynamics in inactive forearm muscle during ramp leg cycling is affected from the ventilatory threshold (VT) and respiratory compensation point (RCP), at which the rate of increase in ventilation (VE) against power output begins to increase abruptly. Change in hemodynamics was evaluated by change in oxygenation index (difference between concentrations of oxygenated hemoglobin and deoxygenated hemoglobin, HbD) measured using near-infrared spectrometry (NIRS). Each subject (n=9) performed 4-min constant-work-rate leg cycling and subsequent ramp leg cycling at an increasing rate of 10 watts.min(-1) in power output. The work rates at VT, RCP and peak oxygen uptake (VO(2 peak)) were 107 +/- 11, 172 +/- 21 and 206 +/- 20 watts, respectively. The rates of increase in VE between 10-watt leg cycling, VT, RCP and VO(2 peak) were 0.19 +/- 0.03, 0.44 +/- 0.07 and 1.32 +/- 0.47 l.min(-1).watts(-1), respectively. In one subject, HbD started to decrease during ramp exercise from the VT, and the rate of decrease increased at a high intensity of exercise. In eight subjects, although no decrease in HbD from the VT was observed, HbD showed a sudden drop at a high intensity of exercise. The work rate at which HbD began to decrease at a high intensity of exercise was 174 +/- 23 watts. This work rate was not significantly different from that at the RCP and was significantly correlated with that at the RCP (r=0.72, P<0.05). The results suggest that the abrupt increase in VE from the RCP affects hemodynamics, resulting in a decrease in HbD in inactive forearm muscle.