THE OXYGEN COST OF VENTILATION AND ITS EFFECT ON THE VO2 PLATEAU

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Because the respiratory muscles demand a significant portion of VO2 during maximal exercise, whole-body VO2 (wb-VO2) models may not accurately represent the VO2 of the exercising muscles, which could affect the ability to detect a VO2 plateau. A VO2 model that adjusts for the VO2 required to ventilate the lungs (VEVO2) during exercise would provide a more accurate means for detecting the VO2 plateau. PURPOSE The purposes of this study were to: a) determine the VEVO2 across a range of ventilations (VE) representing incremental exercise to exhaustion, b) to adjust wb-VO2 data by subtracting out the VEVO2 data in order to more accurately assess whether a VO2 plateau occurred in the exercising muscles and, c) develop a regression equation to predict the VEVO2 based on exercise VE data alone. METHODS 13 men and 9 women performed an incremental exercise test to exhaustion on a cycle ergometer. The VEVO2 was measured at 9 different VE, which spanned the range of VE experienced during the exercise test. The VEVO2 mimicking trials were performed at rest on the ergometer with the specific breathing rate and coinciding VE obtained from the exercise test. Between 3–5% carbon dioxide was added to the inspirate to maintain PETCO2 levels. After the determination of the VEVO2, it was subtracted from the wb-VO2. The resulting data represented the VE-adjusted VO2 (VO2-VE), which was analyzed along with the wb-VO2 data for the presence of a VO2 plateau. RESULTS/CONCLUSIONS The maximal VEVO2 expressed as a percent of wb-VO2max equaled 18.1% + 4.4%. There was an exponential relationship between VEVO2 and increasing VE. The regression equation using all 184 VEVO2 data points to predict the VEVO2 produced an R2 of 0.911 with a standard error of estimate of 73.0 mlO2/min., indicating that the VEVO2 can be predicted accurately from exercise VE data alone. It was determined that the magnitude of the increase in wb-VO2 during maximal exercise was greater than VO2-VE (p < 0.05). The VO2 plateau occurred in 1 of 22 subjects using wb-VO2 and in 15 of 22 subjects using the VO2-VE data.