Abstract
In this study, we aimed to test the hypothesis that the degree of heterogeneity in the matching of quadriceps microvascular O2 requirement to O2 delivery ratio (VO2/Q) would be lower after prior heavy exercise. Seven healthy male subjects (23.7 ± 5.5 years) performed repeated bouts of 6 min heavy cycle exercise (80% VO2max). Pulmonary VO2 was measured breath-by-breath and changes in deoxygenation [deoxy-(Hb+Mb)] were assessed simultaneously at ten different sites of the quadriceps using multi-channel near-infrared spectroscopy. Prior exercise had no significant effect on the time constant of the Phase II VO2 (Bout 1: 22.7 ± 3.3 vs. Bout 2: 22.2 ± 6.1 s), but reduced the amplitude of the slow component during subsequent heavy exercise. The time constant of deoxy-(Hb+Mb) primary component (τp) for bout 1 was faster than for bout 2 (8.6 ± 1.2 vs. 12.1 ± 0.5 s, p < 0.01). The time delay of deoxy-(Hb+Mb) for bout 1 was longer than for bout 2 (12.2 ± 1.2 vs. 9.6 ± 1.3 s, p < 0.01). Prior exercise resulted in a reduction in the dispersion of τp of deoxy-(Hb+Mb) (standard deviation of 10 sites, Bout 1: 1.2 vs. Bout 2: 0.5 s). These results suggest that the reduction of the amplitude of the VO2 slow component during subsequent heavy exercise might be associated with 1) less heterogeneous VO2/Q and 2) and enhanced muscle O2 delivery (presumably by the increased and/or faster capillary blood flow), which in turn might have led to decreased recruitment of type II fibers. [J Physiol Sci. 2007;57 Suppl:S187]
