Oxygen deficits and oxygen delivery kinetics during submaximal intensity exercise in humans after 14 days of head-down tilt-bed rest

none5Beat-by-beat Q'aO2 and breath-by-breath V'O2 were assessed in ten male subjects (24 ± 3.5 years; 78 ± 7.7 kg; 182 ± 5.6 cm) during cycling exercise at 50 W before and after a 14-day period of head-down tiltbed rest (HDTBR). O2 deficit (DefO2) was calculated as the difference between the volume of O2 that would have been consumed if a steady state had been immediately attained minus that actually taken up during exercise. Q'aO2 kinetics was described fitting the data with a non-linear mono-exponential model with time delay. Mean response times (MRT) of V'O2 and Q'aO2 kinetics were then calculated. DefO2 and MRT of V'O2 response did not change after HDTBR, whereas MRT of Q'aO2 kinetics increased. The invariance of V'O2 kinetics after HDTBR suggests that, although Q'aO2 response became slower after HDTBR, it did not affect the kinetics of peripheral gas exchange, which probably remained under the control of local muscular mechanisms.mixedC. Capelli; A. Adami; G. Antonutto; M. Cautero; E. Tam;C. Capelli; A. Adami; G. Antonutto; M. Cautero; E. Tam