Limitations to the prediction of maximum oxygen intake from cardiac frequency measurements.

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Abstract
The cardiac frequency (fH) and O2 consumption (VO2) curves of 80 healthy male subjects aged 20-50 yr. in relation to the over-all limitations of predicting maximum O2 intake (VO2max) were examined, together with the accuracy of the Astrand-Rhymlng, Mar-garia, and Maritz-Wyndham prediction nomograms. The major drawback to all extrapolation methods is the asymptotic nature of fH/VO2 curve. This introduces an error of 1,200 ml at the 95% confidence level and precludes accurate and reliable estimation of VO2max. In comparison, the error due to the intersubject variability in fH max is small and insignificantly different from that to be expected from random day-to-day variations in measurement of fH and VO2- The mean errors with 95% confidence limits using the 3 nomograms are [long dash]624 [plus or minus] 836, -529 [plus or minus] 776, and -430 [plus or minus] 708 ml, respectively. The underlying reasons which might be responsible for the asymptotic value of the fH curve and alternative formulas for predicting VO2max are discussed. If an accuracy greater than +15% is required, then there may be no alternative but to measure VO2max directly.