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

Buchheit M, Laursen PB, Ahmaidi S. Effect of prior exercise on pulmonary O-2 uptake and estimated muscle capillary blood flow kinetics during moderate-intensity field running in men. J Appl Physiol 107: 460-470, 2009. First published June 4, 2009; doi:10.1152/japplphysiol.91625.2008.-The effect of prior exercise on pulmonary O-2 uptake ((V) over dotO(2) (p)) and estimated muscle capillary blood flow ((Q) over dot(m)) kinetics during moderate-intensity, field-based running was examined in 14 young adult men, presenting with either moderately fast (16 s < tau(V) over dotO(2) (p) < 30 s; MFK) or very fast (V) over dotO(2) (p) kinetics (tau(V) over dotO(2) (p) < 16 s; VFK) (i.e., primary time constant, tau(V) over dotO(2) p). On four occasions, participants completed a square-wave protocol involving two bouts of running at 90-95% of estimated lactate threshold (Mod(1) and Mod(2)), separated by 2 min of repeated supramaximal sprinting. (V) over dot (2) (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 (Q) over dot(m) ((Q) over dot(m) MRT) was estimated by rearranging the Fick equation, using (V) over dotO(2) (p) and deoxy-[Hb + Mb] as proxies of muscle O-2 uptake ((V) over dotO(2)) and arteriovenous difference, respectively. HR, blood lactate concentration, total hemoglobin, and (Q) over dot(m) were elevated before Mod(2) compared with Mod(1) (all P < 0.05). tau(V) over dotO(2) (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 Mod(2) (12.9 +/- 1.5 vs. 13.7 +/- 3.8 s, P = 1.0). (Q) over dot(m) 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 Mod(2), HR kinetics were slowed, whereas mean deoxy-[Hb + Mb] response time was unchanged. The difference in tau(V) over dotO(2) (p) between Mod(1) and Mod(2) was related to (Q) over dot(m) MRT measured at Mod(1) (r = 0.71, P < 0.01). Present results suggest that local O-2 delivery (i.e., (Q) over dot(m)) may be a factor contributing to the (V) over dotO(2) kinetic during the onset of moderate-intensity, field-based running exercise, at least in subjects exhibiting moderately fast (V) over dotO(2) kinetics.