Technologic advances have greatly improved the precision with which gas exchange measurements are used to evaluate the physiologic response to exercise testing. These advances, however, have raised a number of uncertainties concerning the interpretation of data. For example, disagreement exists regarding the recognition of maximal cardiorespiratory limits. It is often assumed that this limit has been attained when oxygen uptake no longer increases concomitantly with increasing work (oxygen uptake plateau). However, automated systems that have become common allow variations in data sampling that can greatly affect the interpretation of maximal exercise. this
The plateau concept presented by Taylor and coworkers has been widely applied for more than 30 years. These investigators suggested that a 2.5 percent increase in treadmill grade not accompanied by more than 150 ml (Vmin increase in oxygen uptake reflected an individuals cardiopulmonary limit. However, a discontinuous protocol was employed to study healthy individuals, circumstances greatly differing from those used for clinical testing today. In addition, the plateau concept has been subjected to many different interpretations, and some question or dismiss the concept entirely.
We recently observed a remarkable degree of variability in the slope of the change in oxygen uptake relative to the change in work load among healthy subjects during ramp treadmill testing. By individualizing ramp work rates and varying the gas exchange sampling interval, we were able to observe the effect of these variables on the plateau phenomenon. We defined a plateau as a slope in oxygen uptake vs time at peak exercise that did not differ significantly from zero (ie, a slope that was flat). The present report addresses these observations further and evaluates the extent to which a given slope, variability in slope, or plateau could be reproduced on different days within the same individual.