Oxygen uptake kinetic response to exercise in children.

The oxygen uptake (.VO2) kinetic response to exercise assesses the integrated response of the cardiovascular system and the metabolic requirements of the exercising muscle. The response differs both qualitatively and quantitatively according to the exercise intensity domain (moderate, heavy, very heavy and severe) in which it lies. In each domain, a rapid cardiodynamic phase 1 response is followed by an exponential rise in .VO2 toward a projected steady state (for which the inverse of the rate constant is represented as the time constant [tau]). The achievement of the new steady state may be delayed and elevated due to a slow component of .VO2 in the heavy intensity domain, or above this exercise intensity, the achievement of peak .VO2 truncates the exercise period. For each of these domains, specific mathematical models have been identified and may be applied to appropriate breath-by-breath response data in order to allow quantification of the response. Much of our understanding of the .VO2 kinetic response and the methodologies required to obtain meaningful assessment are derived from adult studies. Although pioneering, early studies with young people were lacking in suitable equipment and the methodologies used may consequently have clouded the true interpretation of the kinetic response. More recently, with the advent of online breath-by-breath analysis systems, studies using mathematical modelling procedures have been hindered by the low signal-to-noise ratio which is inherent to children's response profiles. This has the effect of widening the confidence intervals for estimated parameters, and therefore questions the validity in making inter- and intra-study comparisons. In addition, the difficulty in accurately assessing domain demarcators, especially critical power, often confounds the interpretation of age and sex effects on the exercise response.This review therefore analyses the literature to date on the .VO2 kinetic response during childhood and adolescence, and specifically highlights concerns with technical rigour in its determination. Rigorously determined data indicate that the exponential rise in .VO2 is more rapid in children than adults and that at exercise intensities above the anaerobic threshold, the slow component of .VO2 may be attenuated in the young. Sex differences have not been found in the response to moderate intensity exercise, and there does not appear to be a consistent correlation between peak .VO2 and tau in children. However, sex differences in the response to exercise intensities above the anaerobic threshold are identified and discussed.