Effect of prior exercise on pulmonary O2 uptake and estimated muscle capillary blood flow kinetics during moderate-intensity field running in men.

The effect of prior exercise on pulmonary O2 uptake (VO2p) and estimated muscle capillary blood flow (Qm) kinetics during moderate-intensity, field-based running was examined in 14 young adult men, presenting with either moderately fast (16 s<tauVO2p<30 s; MFK) or very fast VO2p kinetics (tauVO2p<16 s; VFK) (i.e., primary time constant, tauVO2p). On four occasions, participants completed a square-wave protocol involving two bouts of running at 90-95% of estimated lactate threshold (Mod1 and Mod2), separated by 2 min of repeated supramaximal sprinting. VO2p was measured breath by breath, heart rate (HR) beat to beat, and vastus lateralis oxygenation {deoxy-hemoglobin/myoglobin concentration (deoxy-[Hb+Mb])} using near-infrared spectroscopy. Mean response time of Qm (Qm MRT) was estimated by rearranging the Fick equation, using VO2p and deoxy-[Hb+Mb] as proxies of muscle O2 uptake (VO2) and arteriovenous difference, respectively. HR, blood lactate concentration, total hemoglobin, and Qm were elevated before Mod2 compared with Mod1 (all P<0.05). tauVO2p was shorter in VFK compared with MFK during Mod1 (13.1+/-1.8 vs. 21.0+/-2.5 s, P<0.01), but not in Mod2 (12.9+/-1.5 vs. 13.7+/-3.8 s, P=1.0). Qm MRT was shorter in VFK compared with MFK in Mod1 (8.8+/-1.9 vs. 17.0+/-3.4 s, P<0.01), but not in Mod2 (10.1+/-1.8 vs. 10.5+/-3.5 s, P=1.0). During Mod2, HR kinetics were slowed, whereas mean deoxy-[Hb+Mb] response time was unchanged. The difference in tauVO2p between Mod1 and Mod2 was related to Qm MRT measured at Mod1 (r=0.71, P<0.01). Present results suggest that local O2 delivery (i.e., Qm) may be a factor contributing to the VO2 kinetic during the onset of moderate-intensity, field-based running exercise, at least in subjects exhibiting moderately fast VO2 kinetics.