Date of Award

2001

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Paul Sacco

Abstract

The use of V02MAX as a measure of cardiorespiratory fitness is widespread throughout the fields of exercise physiology, physiology and medicine. VO2MAX is described as the maximal rate of oxygen consumption during increasing exercise intensities and is defined by a plateau or levelling off of oxygen consumption (VO2). Taylor et al. (1955) derived the primary criterion for a levelling off (plateau) of VO2 at the end of an incremental exercise test to exhaustion to be a change in VO2 (ΔVO2) <150mL or 2.1 mL/kg/min during the final minute. This primary criterion has been widely accepted and utilised since 1955. Secondary criteria have also been introduced due to the difficulty in obtaining a VO2 plateau in all subjects. The secondary criteria used to verify that VO2MAX has been attained include I) blood lactate (La) >8mmol/L, a respiratory exchange ratio (RER) >1.15, a rating of perceived exertion (RPE) > 17, and an age-predicted maximal heart rate (APMHR) ±10 beats/min from predicted using 220-age. Despite the use of such secondary criteria, none of these items have been adequately assessed for their sensitivity or specificity for coinciding with a VO2 plateau at VO2MAX. 64 male and female subjects drawn from university sports science students and local triathalon and running clubs, between 18 and 55 years of age, performed two randomly assigned tests held on separate days. All participants completed a VO2MAX test for each of cycle ergometry (CE) and treadmill (TM) running. During each test, breath-by-breath indirect calorimetry was performed to derive data of minute ventilation (VE), oxygen consumption (VO2), carbon dioxide production (VCO2), and RER. Heart rate (HR) captured data was acquired by telemetry, ratings of perceived exertion (RPE) were obtained at peak exercise intensity, and finger-prick blood lactate (La) samples were taken at 30 seconds and 120 seconds post-exercise. All VO2 data was processed using a 3 breath smoothing function. Limitations of time restricted the enzymatic analysis of La samples and therefore these results were not included in this study. Multiple regression found that there were no correlations in bivariate or multivariate conditions and that no secondary criteria could explain the variance in the presence or absence of a VO2 plateau. None of the secondary criteria could discriminate between those subjects that attained a VO2 plateau and those that did not. Sensitivity was very low, but specificity generally good for both modes of exercise (TM RER and CE RPE >90%). However only TM RER could positively predict the occurrence of a VO2 plateau, where all other secondary criteria were poor positive and negative predictors using Bayes theorem. Secondary criteria such as APMHR, RER and RPE should not be used to verify VO2MAX in the absence of a VO2 plateau as they are neither sensitive, specific nor able to predict the absence or presence of a VO2 plateau. The only valid criterion is the V02 plateau and researchers and clinicians should consider validating alternative measures to determine V02MAX in the absence of a VO2 plateau.

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