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

¹Laboratory of Exercise Physiology and Rehabilitation, EA 3300, Faculty of Sport Sciences, University of Picardie, Jules Verne, Amiens, France; and ²School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia

Submitted 19 December 2008 ; accepted in final form 2 June 2009

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

oxygen uptake dynamics; near-infrared spectroscopy; muscle deoxygenation; repeated sprint exercise; warm-up