ORIGINAL RESEARCH article
Front. Physiol.
Sec. Exercise Physiology
This article is part of the Research TopicExercise and the Oxygen Cascade: From the Lungs to the MuscleView all 4 articles
VO2max and the kinetics of VO2, muscle oxygen delivery and muscle deoxygenation
Provisionally accepted
- University of Alberta, Edmonton, Canada
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Aerobic fitness and oxygen uptake kinetics (τV̇ O2) at the onset of exercise appear to be inversely correlated, however, the mechanisms underlying changes in τV̇ O2 across different aerobic fitness have not been elucidated. The purpose of this study was to investigate the relationship between maximal V̇ O2 (V̇ O2max) and τV̇ O2 and determine whether the capacity to deliver or to utilize O2 limits τV̇ O2 in an aerobic fitness dependent manner. Twenty-three healthy, young males (25±4 years) with a V̇ O2max classified as superior (S; V̇ O2max > 60 mL·kg-1·min-1, n=7), good (G; V̇ O2max = 45-55 mL·kg-1·min-1, n=8) or poor (P; V̇ O2max < 40 mL·kg-1·min-1, n=8) performed two moderate-intensity knee-extension (KE) exercise transitions (80% of gas exchange threshold) on a custom-built KE ergometer. V̇ O2 was measured breath-by-breath. Leg blood flow (BF) was measured by doppler ultrasound at the femoral artery, and leg vascular conductance (LVC) was calculated as LBF·mean arterial pressure (MAP)-1. Near-infrared spectroscopy derived-[HHb] was measured on the vastus lateralis muscle. τV̇ O2, τLVC, and τ[HHb] data were averaged and fit with a mono-exponential function. τV̇ O2 were faster in the S (P < 0.01) and G (P < 0.05) than the P fitness group. τ[HHb] was faster in the S (P < 0.05) than the P fitness group. V̇ O2max was inversely related to τV̇ O2 (r = -0.71; P < 0.001) and τ[HHb] (r = -0.55; P < 0.01), but not with τLVC (r = -0.12; P > 0.05). τV̇ O2 was positively correlated with τ[HHb] (r = -0.57; P < 0.01), but not with τLVC (r = -0.25; P > 0.05). V̇ O2max and τV̇ O2 were inversely related across three fitness levels. Furthermore, these findings indicate that O2 delivery is not rate-limiting for τV̇ O2 across fitness levels and suggest that the intracellular capacity to utilize O2 may be the primary limiting factor for τV̇ O2 in healthy young adults regardless of aerobic fitness.
Keywords: maximal oxygen uptake, aerobic fitness, Oxygen uptake kinetics, blood flow kinetics, deoxyhemoglobin kinetics, Oxidative Phosphorylation, oxygen delivery
Received: 30 Jun 2025; Accepted: 28 Oct 2025.
Copyright: © 2025 Marinari and DeLorey. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Darren DeLorey, darren.delorey@ualberta.ca
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