An important observation made from the present data was the variability in the slope of the change in oxygen uptake throughout progressive exercise, despite a constant, consistent change in external work and the use of large, averaged samples. A slope, in the present context, is defined as the change in oxygen uptake for a given sample associated with a unit change in external work. Thus, a slope not different from zero at peak exercise suggests that oxygen uptake was not increasing concomitantly with external work. The degree of variability observed would appear to preclude the determination of a plateau by common definitions. It should also be noted that a plateau was not a consistent finding with repeated testing, even though maximal heart rate, perceived exertion, and maximal gas exchange parameters did not differ between days. The variability demonstrated during each test and the lack of consistency of the slopes on different days suggests that the occurrence of a plateau may be random. Reading here

The plateau concept has been defined in many different ways, and its criteria has depended on population, protocol, and by the method in which the data are sampled. For example, the work increment near peak exercise would presumably have a marked effect on gas exchange kinetics. In addition, we have previously observed that the method of sampling data significantly affects the slope, plateau, and variability in oxygen uptake. Thus, an optimal method with which to study this phenomenon would require the ability to consistently increase work, an automated system allowing continuous gas exchange acquisition, variations in the method of sampling data, and the ability to average breaths or intervals. Although the ramp bicycle protocol has recently been studied, we believed that the ramp treadmill would be advantageous, as maximal oxygen uptake is approximately 10 percent higher on the treadmill in comparison to the bicycle ergometer. Naturally, this difference could be critical when evaluating the limits of the cardiopulmonary system. The large sampling intervals were chosen to reduce variability as much as possible and to give the subjects the best chance to plateau, if this phenomenon were to occur.