Validity of criteria for establishing maximal O₂ uptake during ramp exercise tests

The incremental or ramp exercise test to the limit of tolerance has become a popular test for determination of maximal O₂ uptake \((\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}).\) However, many subjects do not evidence a definitive plateau of the \(\dot{V}{\hbox{O}}_{{{2}}} \) -work rate relationship on this test and secondary criteria based upon respiratory exchange ratio (RER), maximal heart rate (HR_max) or blood [lactate] have been adopted to provide confidence in the measured \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}.\) We hypothesized that verification of \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}\) using these variables is fundamentally flawed in that their use could either allow underestimation of \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}\) (if, for any reason, a test were ended at a sub-maximal \(\dot{V}{\hbox{O}}_{{{2}}}\)), or alternatively preclude subjects from recording a valid \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}.\) Eight healthy male subjects completed a ramp exercise test (at 20 W/min) to the limit of tolerance on an electrically braked cycle ergometer during which pulmonary gas exchange was measured breath-by-breath and blood [lactate] was determined every 90 s. Using the most widely used criterion values of RER (1.10 and 1.15), \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}\) as determined during the ramp test (4.03 ± 0.10 l/min) could be undermeasured by 27% (2.97 ± 0.24 l/min) and 16% (3.41 ± 0.15 l/min), respectively (both P < 0.05). The criteria of HR_max (age predicted HR_max ± 10 b/min) and blood [lactate] (≥8 mM) were untenable because they resulted in rejection of 3/8 and 6/8 of the subjects, most of whom (5/8) had demonstrated a plateau of \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}\) at \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}.\) These findings provide a clear mandate for rejecting these secondary criteria as a means of validating \(\dot{V}{\hbox{O}}_{{{{\rm 2max}}}}\) on ramp exercise tests.