Oxygen Uptake Kinetics During Exercise

The characteristics of oxygen uptake (V̇O2) kinetics differ with exercise intensity. When exercise is performed at a given work rate which is below lactate threshold (LT), V̇O2 increases exponentially to a steady-state level. Neither the slope of the increase in V̇O2 with respect to work rate nor the time constant of V̇O2 responses has been found to be a function of work rate within this domain, indicating a linear dynamic relationship between the V̇O2 and the work rate. However, some factors, such as physical training, age and pathological conditions can alter the V̇O2 kinetic responses at the onset of exercise. Regarding the control mechanism for exercise V̇O2 kinetics, 2 opposing hypotheses have been proposed. One of them suggests that the rate of the increase in V̇O2 at the onset of exercise is limited by the capacity of oxygen delivery to active muscle. The other suggests that the ability of the oxygen utilisation in exercising muscle acts as the rate-limiting step. This issue is still being debated.