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.
It has frequently been demonstrated that prior high-intensity exercise facilitates pulmonary oxygen uptake [Formula: see text] response at the onset of subsequent identical exercise. To clarify the roles of central O(2) delivery and/or peripheral O(2) extraction in determining this phenomenon, we investigated the relative contributions of cardiac output (CO) and arteriovenous O(2) content difference [Formula: see text] to the [Formula: see text] transient during repeated bouts of high-intensity knee extension (KE) exercise. Nine healthy subjects 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 6 min of rest. Throughout the protocol, continuous-wave Doppler ultrasound was used to measure beat-by-beat CO (i.e., via simultaneous measurement of stroke volume and the diameter of the arterial aorta). The phase II [Formula: see text] response was significantly faster and the slow component (phase III) was significantly attenuated during the second KE bout compared to the first. This was a result of increased CO during the first 30 s of exercise: CO contributing to 100 and 56% of the [Formula: see text] speeding at 10 and 30 s, respectively. After this, the contribution of [Formula: see text] became increasingly more predominant: being responsible to an estimated 64% of the [Formula: see text] speeding at 90 s, which rose to 100% by 180 s. This suggests that, while both CO and [Formula: see text] clearly interact to determine the [Formula: see text] response, the speeding of [Formula: see text] kinetics by prior high-intensity KE exercise is predominantly attributable to increases in [Formula: see text].
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.