Use of Heart Rate Index to Predict Oxygen Uptake - A Validation Study.

An equation that uses heart rate index (HRI) defined as HR/HRrest to predict oxygen uptake (VO) in METs (e.g., METs = 6 × HRI - 5) has been developed retrospectively from aggregate data of 60 published studies. However, the prediction error of this model as used by an individual has not been established. Therefore, the purpose of this study was to examine the predictive validity of the HRI equation by comparing submaximal and maximal VO predicted by the equation (VO-Pred) with that measured by indirect calorimetry (VO-Meas). Sixty healthy adults (age 20.5 ± 2.4 yr., body mass 69.4 ± 13.4 kg, height 1.7 ± 0.1 m) underwent a VOmax test and an experimental trial consisting of a 15-min resting measurement and three successive 10-min treadmill exercise bouts performed at 40%, 60% and 80% of VOmax. VO and HR were recorded during both the submaximal and maximal exercises and used to obtain VO-Pred and VO-Meas for each intensity and for VOmax. Validation was carried out by paired t-test, regression analysis, and Bland-Altman plots. A modest but significant ( < 0.05) correlation was observed between VO-Meas and VO-Pred at 40% ( = 0.58), 60% ( = 0.53), and 80% of VOmax ( = 0.56) and at VOmax ( = 0.50). No differences between VO-Pred and VO-Meas were found at 40% (5.53 ± 1.21 vs. 5.28 ± 0.98 METs, respectively) of VOmax, but VO-Pred was higher ( < 0.05) than VO-Meas at 60% (8.42 ± 1.77 vs. 7.96 ± 1.39 METs, respectively) and 80% (10.79 ± 2.13 vs. 10.29 ± 1.81 METs, respectively) of VOmax. In contrast, VO-Pred was lower ( < 0.05) than VO-Meas at VOmax (12.32 ± 2.30 vs. 13.38 ± 2.24 METs, respectively). Standard errors of the estimate were 0.81, 1.20, 1.54, and 1.97 METs at 40%, 60%, 80% of VOmax and at VOmax, respectively. These results suggest that further investigation aimed to establish the accuracy of using HRI to predict VO is warranted.