Assessment of exercise intensity formulas by use of ventilatory threshold

Guidelines for training heart rate (HR) during aerobic exercise are often determined by predictive formulas. Measurement of the heart rate at ventilatory threshold (VT) by expired gas analysis provides a direct index of the upper limits of conditioning intensity. We evaluated 115 nonsmoking, healthy adults with measurement of peak oxygen uptake to classify groups as low- (n=45), average- (n=45), and high (n=25) -fitness. Heart rate at VT was compared with the approximate midpoint (77 percent) of recommended training intensity as estimated by the Karvonen equation, predicted maximal (220-age), and measured maximal HR formulas. No significant difference among the various HR formulas at 77 percent and HR at VT were found for high-fitness individuals. Among the low- and average-fitness groups, the Karvonen formula at 77 percent was significantly higher (p < 0.001) than HR at ventilatory threshold. Predicted and measured maximal HR at 77 percent were not above the VT among the low- and average-fitness individuals and are appropriate for training intensity. However, the Karvonen formula appears to overestimate heart rate intensity among those of low and average fitness and may be excessive for these groups.