Last Word on Point:Counterpoint: The kinetics of oxygen uptake during muscular exercise do/do not manifest time-delayed phases

Abstract

TO THE EDITOR: Not one of the proposed physiological mechanisms support the existence of time-delayed instantaneous stepwise increments in oxygen demand that mark the beginning of each time-delayed phase and are the very foundation of the time-delayed three-phase exponential model. The chance of finding physiological mechanisms to support such behavior is nonexistent, due mainly to the instantaneous nature of the increment. Not one of the proposed physiological mechanisms contradicts the model (2, 3), as even without time-delayed phases it produces features that only become apparent after a period of time. As shown in (5), this model can incorporate a far more realistic oxygen demand (i.e., one that changes smoothly with intensity and time to account for inertia and changing underlying physiological processes) than the obviously erroneous instantaneous increments of the three-phase model.