Use of the HR index to predict maximal oxygen uptake during different exercise protocols

This study examined the ability of the HRindex model to accurately predict maximal oxygen uptake (V˙O2max) across a variety of incremental exercise protocols. Ten men completed five incremental protocols to volitional exhaustion. Protocols included three treadmill (Bruce, UCLA running, Wellness Fitness Initiative [WFI]), one cycle, and one field (shuttle) test. The HRindex prediction equation (METs = 6 × HRindex − 5, where HRindex = HRmax/HRrest) was used to generate estimates of energy expenditure, which were converted to body mass‐specific estimates of V˙O2max. Estimated V˙O2max was compared with measured V˙O2max. Across all protocols, the HRindex model significantly underestimated V˙O2max by 5.1 mL·kg−1·min−1 (95% CI: −7.4, −2.7) and the standard error of the estimate (SEE) was 6.7 mL·kg−1·min−1. Accuracy of the model was protocol‐dependent, with V˙O2max significantly underestimated for the Bruce and WFI protocols but not the UCLA, Cycle, or Shuttle protocols. Although no significant differences in V˙O2max estimates were identified for these three protocols, predictive accuracy among them was not high, with root mean squared errors and SEEs ranging from 7.6 to 10.3 mL·kg−1·min−1 and from 4.5 to 8.0 mL·kg−1·min−1, respectively. Correlations between measured and predicted V˙O2max were between 0.27 and 0.53. Individual prediction errors indicated that prediction accuracy varied considerably within protocols and among participants. In conclusion, across various protocols the HRindex model significantly underestimated V˙O2max in a group of aerobically fit young men. Estimates generated using the model did not differ from measured V˙O2max for three of the five protocols studied; nevertheless, some individual prediction errors were large. The lack of precision among estimates may limit the utility of the HRindex model; however, further investigation to establish the model's predictive accuracy is warranted. e00124 A method to predict oxygen uptake using the ratio of heart rate to resting heart rate (HRindex) was developed and reported to be independent of testing mode and to account for factors known to contribute to intersubject variability in maximal oxygen uptake (e.g., age, sex, fitness). This study found that the HRindex prediction equation significantly underestimated maximal oxygen uptake across five protocols in young, fit men. Although small mean differences between measured and predicted maximal oxygen uptake for several protocols suggested those pre