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

This study examined the ability of the HR(index) model to accurately predict maximal oxygen uptake ([Image: see text]O(2max)) 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 HR(index) prediction equation (METs = 6 × HR(index) − 5, where HR(index) = HR(max)/HR(rest)) was used to generate estimates of energy expenditure, which were converted to body mass-specific estimates of [Image: see text]O(2max). Estimated [Image: see text]O(2max) was compared with measured [Image: see text]O(2max). Across all protocols, the HR(index) model significantly underestimated [Image: see text]O(2max) 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 [Image: see text]O(2max) significantly underestimated for the Bruce and WFI protocols but not the UCLA, Cycle, or Shuttle protocols. Although no significant differences in [Image: see text]O(2max) 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 [Image: see text]O(2max) 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 HR(index) model significantly underestimated [Image: see text]O(2max) in a group of aerobically fit young men. Estimates generated using the model did not differ from measured [Image: see text]O(2max) 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 HR(index) model; however, further investigation to establish the model's predictive accuracy is warranted.