The effect of prior exercise on pulmonary O2 uptake (V̇O2 p) and estimated muscle capillary blood flow (Q̇m) kinetics during moderate-intensity, field-based running was examined in 14 young adult men, presenting with either moderately fast (16 s < $τ$V̇O2 p < 30 s; MFK) or very fast V̇O 2 p kinetics ($τ$V̇O2 p < 16 s; VFK) (i.e., primary time constant, $τ$V̇O2 p). 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. V̇O2 p 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 Q̇m (Q̇m MRT) was estimated by rearranging the Fick equation, using V̇O2 p and deoxy-[Hb+Mb] as proxies of muscle O2 uptake (V̇O2) and arteriovenous difference, respectively. HR, blood lactate concentration, total hemoglobin, and Q̇m were elevated before Mod2 compared with Mod1 (all P < 0.05). $τ$V̇O2 p was shorter in VFK compared with MFK during Mod 1 (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). Q̇m 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 Mod 2 (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 $τ$V̇O2 p between Mod1 and Mod2 was related to Q̇m MRT measured at Mod1 (r = 0.71, P < 0.01). Present results suggest that local O2 delivery (i.e., Q̇m) may be a factor contributing to the V̇O2 kinetic during the onset of moderate-intensity, field-based running exercise, at least in subjects exhibiting moderately fast V̇O 2 kinetics. Copyright © 2009 the American Physiological Society.