Control of Oxygen Uptake during Exercise

Abstract

Other than during sleep and contrived laboratory testing protocols, humans rarely exist in prolonged metabolic steady states; rather, they transition among different metabolic rates (V O2). The dynamic transition of V O2 (V O2 kinetics), initiated, for example, at exercise onset, provides a unique window into understanding metabolic control. This brief review presents the state-of-the art regarding control of V O2 kinetics within the context of a simple model that helps explain the work rate dependence of V O2 kinetics as well as the effects of environmental perturbations and disease. Insights emerging from application of novel approaches and technologies are integrated into established concepts to assess in what circumstances O2 supply might exert a commanding role over V O2 kinetics, and where it probably does not. The common presumption that capillary blood flow dynamics can be extrapolated accurately from upstream arterial measurements is challenged. From this challenge, new complexities emerge with respect to the relationships between O2 supply and flux across the capillary-myocyte interface and the marked dependence of these processes on muscle fiber type. Indeed, because of interfiber type differences in O2 supply relative to V O2, the presence of much lower O2 levels in the microcirculation supplying fast-twitch muscle fibers, and the demonstrated metabolic sensitivity of muscle to O2, it is possible that fiber type recruitment profiles (and changes thereof) might help explain the slowing of V O2 kinetics at higher work rates and in chronic diseases such as heart failure and diabetes.

Maximal aerobic power and anaerobic capacity in cycling across the age spectrum in male master athletes

“…intensity exercise (Poole et al 2008). Therefore, the assumed value of 10 s may substantially overestimate the speed of case we deal with supra-maximal or maximal exercise conditions.…”

Mechanism and implications of hyperpnea exaggeration at the onset of exercise in mechanical hyperalgesia after eccentric exercise

“…1b). V ・ O2 kinetics at the onset of exercise, evaluated at the pulmonary level, might serve as an index of overall efficiency and conditioning of the integrated systems, providing information on the mechanisms regulating O2 delivery and O2 utilization in active skeletal muscles 68) . Pulmonary V ・ O2 at phase I is assumed to reflect circulatory transit time from active muscles to lungs 69) .…”

Metabolic Mechanisms of Vocal Fatigue

“…Oxygen uptake increases exponentially at the onset of exercise and continues to increase until a steady state in oxygen uptake is reached. The dynamic behavior of oxygen uptake in the transition from rest to exercise is termed oxygen kinetics (Poole, Barstow, McDonough, & Jones, 2008). To investigate oxygen kinetics, the data were visually inspected for the rise time from baseline to the plateau in oxygen uptake during the reading task.…”

“…These are defined as the dynamic behavior of oxygen uptake in the transition from rest to exercise (Poole et al, 2008). Such kinetics are dependent on two main mechanisms: (a) central circulation to deliver oxygen to working muscles, and (b) the ability of working muscles to extract oxygen from blood flow arriving to the muscles.…”

“…In that case, recovery time following a task increases. Of interest for exercise physiology in general and the 34 present setting in particular, therapeutic implications differ for fatigue induced by poor efficiency during a task versus fatigue induced by poor recovery following a task (Poole, Barstow, McDonough, & Jones, 2008). In the former case, an individual might receive training in task efficiency.…”