V02 'overshoot' during moderate-intensity exercise in endurance-trained athletes: the influence of exercise modality.
ABSTRACT The purpose of this study was to investigate the influence of exercise modality on the 'overshoot' in V(O2) that has been reported following the onset of moderate-intensity (below the gas exchange threshold, GET) exercise in endurance athletes. Seven trained endurance cyclists and seven trained endurance runners completed six square-wave transitions to a work-rate or running speed requiring 80% of mode-specific GET during both cycle and treadmill running exercise. The kinetics of V(O2) was assessed using non-linear regression and any overshoot in V(O2) was quantified as the integrated volume (IV) of O(2) consumed above the steady-state requirement. During cycling, an overshoot in V(O2) was evident in all seven cyclists (IV = 136 +/- 41 ml) and in four runners (IV = 81 +/- 94 ml). During running, an overshoot in V(O2) was evident in four runners (IV = 72 +/- 61 ml) but no cyclists. These data challenge the notion that V(O2) always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the V(O2) overshoot during cycling (11/14 subjects) compared to running (4/14 subjects) indicates that the overshoot phenomenon is related to an interaction between high levels of aerobic fitness and exercise modality. We speculate that a transient loss in muscle efficiency as a consequence of a non-constant ATP requirement following the onset of constant-work-rate exercise or an initially excessive recruitment of motor units (relative to the work-rate) might contribute to the overshoot phenomenon.
SourceAvailable from: David Poole
Article: Oxygen Uptake Kinetics[Show abstract] [Hide abstract]
ABSTRACT: Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population. © 2012 American Physiological Society. Compr Physiol 2:933-996, 2012.04/2012; 2(2):933-996. DOI:10.1002/cphy.c100072
Article: Response[Show abstract] [Hide abstract]
ABSTRACT: An abstract is unavailable. This article is available as HTML full text and PDF.Medicine & Science in Sports & Exercise 06/2010; 42(7):1428. DOI:10.1249/MSS.0b013e3181df44ee · 4.46 Impact Factor
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ABSTRACT: An incremental ramp exercise is a protocol that is frequently used in the domain of exercise testing to get an insight into the exercise tolerance of both healthy active populations (including athletes) and patients, due to the specific characteristics of the protocol. The continuous and linear increase in work rate is not only less strenuous for populations with a very low exercise capacity but it requires the aerobic metabolism to adapt to the continuously changing conditions. Therefore, this protocol can provide important information on the adaptive capacity of individuals to exercise in non-steady-state conditions. The ramp exercise has also been used in the past two decades to get an insight into the underlying mechanisms of the oxygen uptake (·VO₂) response (and kinetics) to exercise. Against the expectations, it has been shown that the parameters that quantify the ·VO₂ response to ramp exercise do not completely correspond to those obtained from constant work-rate transitions and incremental step exercise. For that reason, it could be concluded that the ·VO₂ response is specific to ramp exercise, and thus is determined by other mechanisms than those which determine other protocols. Although the ·VO₂ response to ramp exercise has a high level of reproducibility and a uniform pattern can be observed, especially for the ·VO₂ response below the gas exchange threshold (GET) [above the GET, the ·VO₂ response is less clear], some prudence is necessary when interpreting potential differences in the ·VO₂ response between populations. Several methodological issues (e.g. baseline work rate, ramp slope) exert an important impact on the ·VO₂ response to ramp exercise. The main purpose of this review is to provide an overview of the methodological and physiological factors that have an impact on the ·VO₂ response to ramp exercise. It is of importance that exercise physiologists take these factors into consideration, not only prior to the conductance of the ramp exercise in a variety of subjects, but also when interpreting the obtained results.Sports Medicine 05/2012; 42(6):511-26. DOI:10.2165/11599690-000000000-00000 · 5.32 Impact Factor