Oxygen Uptake Dynamics: From Muscle to Mouth—An Introduction to the Symposium

Abstract

The purpose of this paper is to provide an introduction to the study of oxygen uptake (VO(2)) dynamics or kinetics. Following the onset of exercise, both muscle and pulmonary VO(2) rise in a near-exponential fashion towards the anticipated "steady-state" VO(2) demand. However, it can take 2-4 min, or even longer at higher work rates, before this steady state is attained. Slow VO(2) kinetics increase the so-called O(2) deficit and obligate a greater contribution from anaerobic mechanisms of ATP production (involving the breakdown of muscle high energy phosphates and lactate production from glycogen) to meet the ATP requirement of the exercise task. A primary goal in this area of research is therefore to elucidate the physiological mechanisms which control and/or limit the rate at which muscle VO(2) increases following the onset of exercise. At higher intensities of exercise, a continued increase in both muscle and pulmonary VO(2) is observed with time despite the external work rate remaining constant. This continued rise in VO(2), beyond the anticipated steady-state requirement for the work rate, has been termed the VO(2) "slow component," and establishing the mechanistic basis for this phenomenon is another important goal of research in this field. This paper provides an overview of some of the factors which might contribute to both the fundamental and slow phases of the VO(2) kinetics and, in so doing, provides general background material for the more specific papers that follow.

Effects of short-term dietary nitrate supplementation on blood pressure, O2uptake kinetics, and muscle and cognitive function in older adults

“…In a recent placebocontrolled study, we reported that beetroot juice supplementation significantly reduced the O 2 cost of treadmill walking and improved exercise tolerance in healthy young adults (47). These results are remarkable because the V O 2 -work rate relationship has traditionally been considered to be independent of age, health status, and aerobic fitness (36). The reduction in the O 2 cost of moderate-intensity exercise following dietary NO 3 Ϫ supplementation may be a result of a reduced ATP cost of muscle force production (5) and/or enhanced mitochondrial efficiency (51).…”

“…Faster V O 2 kinetics would be expected to reduce the reliance on nonoxidative metabolic processes across the transition from a lower to a higher metabolic rate and, therefore, to reduce muscle metabolic perturbation (i.e., changes in substrates or metabolites that have been associated with fatigue development; Ref. 36,82). In the present study, the O 2 deficit was reduced by 15% following NO 3 Ϫ supplementation, as a function of the faster V O 2 kinetics.…”

Effects of prior very-heavy intensity exercise on indices of aerobic function and high-intensity exercise tolerance

“…24,55). For heavy-intensity work rates that lie between L and critical power [CP; i.e., the power asymptote of the power-duration (P-t) relationship], the emergence of an additional delayed "slow component" (V O 2 sc) results in V O 2 attaining an eventual steady-state value greater than that predicted from the sub-L V O 2 -work rate relationship (reviewed in Refs.…”

“…For heavy-intensity work rates that lie between L and critical power [CP; i.e., the power asymptote of the power-duration (P-t) relationship], the emergence of an additional delayed "slow component" (V O 2 sc) results in V O 2 attaining an eventual steady-state value greater than that predicted from the sub-L V O 2 -work rate relationship (reviewed in Refs. 24,55), and whose origin has been demonstrated to reside predominantly within the working musculature (39,43,46). CP is thought to be equivalent to the highest work rate for which a steady-state of V O 2 , [L Ϫ ]a, and acidic pHa can be achieved [22,40,55; although see Housh et al (23) for an alternative view] and may, therefore, be regarded as reflecting a rate of aerobic energy pool reconstitution that dictates the maximum power that can be sustained without a progressively increasing anaerobic contribution (35,40,56).…”

“…Supra-CP work rates that manifest a clearly discernible V O 2sc have been termed very-heavy intensity, while even higher work rates for which the fundamental V O 2 requirement exceeds V O 2max without manifesting a slow component have been described as being of severe intensity (reviewed in Refs. 24,55).…”