Dissociation between the time courses of femoral artery blood flow and pulmonary V̇O₂ during repeated bouts of heavy knee extension exercise in humans

Abstract

It has frequently been demonstrated that prior heavy cycling exercise facilitates pulmonarẏ VO 2 kinetics at the onset of subsequent heavy exercise. This might be due to improved muscle perfusion via acidosis-induced vasodilating effects. However, it is difficult to measure the blood flow (BF) to the working muscles (via the femoral artery) during cycling exercise. We therefore selected supine knee extension (KE) exercise as an alternative, and investigated whether the fasterVO 2 kinetics in the 2nd bout was matched by proportionally faster BF kinetics to the exercising muscle. Nine healthy subjects (aged 21-44 years) volunteered to participate in this study. The protocol consisted of two consecutive 6-min KE exercise bouts in a supine position (work rate: 70-75% of peak power) separated by a 6-min baseline rest (EX1 to EX2). During the protocol, a pulsed Doppler ultrasound technique was utilized to continuously measure the BF in the right femoral artery. The protocol was repeated at least 6 times to characterize the precise kinetics. In agreement with previous studies using cycling exercise, theVO 2 kinetics in the 2nd bout were facilitated compared with that in the 1st bout [mean ± S.D. of the 'effective' time constant (τ ): EX1, 68.6 ± 15.9, versus EX2, 58.0 ± 14.4 s. Phase II-τ : EX1, 48.7 ± 9.0, versus EX2, 41.2 ± 13.3 s. Empirical index of the slow component (∆VO 2(6-3) ): EX1, 78 ± 44, versus EX2, 57 ± 36 ml min −1 (P < 0.05)]. However, no substantial difference was observed for the facilitation of the femoral artery BF response to the 1st and 2nd exercise bouts [i.e. the 'effective' τ of the femoral artery BF: EX1, 40.8 ± 16.9, versus EX2, 39.0 ± 17.1 s (P > 0.05)]. It was concluded that the faster pulmonaryVO 2 kinetics during heavy KE exercise following prior heavy exercise was not associated with a similar modulation in the BF to the working muscles.

Prior heavy exercise elevates pyruvate dehydrogenase activity and muscle oxygenation and speeds O2uptake kinetics during moderate exercise in older adults

“…These findings are consistent with previous studies examining prior exercise in both young and older adults and suggest a greater muscle perfusion prior to and throughout Mod 2 (12,22,24). A greater muscle oxygenation is consistent with previous demonstrations of elevated HR in older adults (12,51) and greater limb conduit artery blood flow in young adults (16,17,41) during baseline exercise following heavy-intensity exercise and very early in the transition to a subsequent bout of exercise. There is evidence that O 2 availability is impaired during the transition to exercise in muscle from older animals and human subjects (3,11,12,14,39,43,44,49), and thus prior exercise in older adults likely improves O 2 availability in Mod 2 compared with Mod 1 .…”

Effects of prior heavy exercise on heterogeneity of muscle deoxygenation kinetics during subsequent heavy exercise

“…On the other hand, a rapid appearance of phase II of mQ would occur in regions where the early increase in mQ closely matches the dynamics of mV O 2 (i.e., constant deoxy-[HbϩMb]), and thereby a short TD would be followed by a slower (20). The results in the present study support the latter scenario, thus suggesting that the performance of prior heavy exercise would promote the convective delivery of O 2 (phase II mQ ) to multiple sites of the muscles, improving the adequacy of mV O 2 /mQ O 2 matching at the onset of the subsequent bout of exercise (7,9,15,16,22,23,44).…”

Muscle capillary blood flow kinetics estimated from pulmonary O2 uptake and near-infrared spectroscopy

“…For heavy exercise, comparison of MRT or P of blood flow with previous investigations in humans is not straightforward because we chose to truncate the MRT so as to reflect the primary component of the response, whereas others have included the blood flow increase associated with the V O 2 slow component (1,11,37). The rationale for limiting the calculation of the heavy exercise MRT was that we were interested in determining the relationship between the primary components of the estimated Q cap and V O 2m kinetics.…”

“…The resulting overall Q cap kinetics appeared to be tightly coupled to the temporal profile of V O2m. exercise; skeletal muscle; oxygenation INSIGHTS ON THE CONTROL OF exercising muscle blood flow (Q m ) can be gained from the investigation of its response in the transitional phase (i.e., kinetics) (21, 27), but because of methodological constraints the kinetics of Q m in humans have been studied primarily in larger vessels (1,16,22,31,37,42,44).The difficulty in obtaining measurements with a time resolution that allows reliable kinetic analysis during large muscle mass exercise (e.g., cycling or running) has led to a predominant use of knee extensor or forearm exercise with measurements of blood flow made by Doppler ultrasound (11,22,31,37,42,44). These investigations have shown that the Q m response is biphasic with an initial fast phase determined by the combined effects of muscle contraction (muscle pump) (41) and possibly rapid vasodilation (48) followed by a second slower phase that appears to match O 2 delivery and utilization (43).…”

“…The difficulty in obtaining measurements with a time resolution that allows reliable kinetic analysis during large muscle mass exercise (e.g., cycling or running) has led to a predominant use of knee extensor or forearm exercise with measurements of blood flow made by Doppler ultrasound (11,22,31,37,42,44). These investigations have shown that the Q m response is biphasic with an initial fast phase determined by the combined effects of muscle contraction (muscle pump) (41) and possibly rapid vasodilation (48) followed by a second slower phase that appears to match O 2 delivery and utilization (43).…”