Use Of Hr Index To Predict Oxygen Uptake: A Validation Study

Abstract

Heart rate index (HRindex), expressed as an activity HR divided by resting HR (HR/HRrest), has been proposed to estimate oxygen uptake (VO2) of physical activity and aerobic capacity (VO2max). Recently, a prediction equation (e.g., METs=6×HRindex–5) that used HRindex to predict VO2 in MET was developed retrospectively from aggregate data of 60 published studies. However, it is unclear whether this predictive model is accurate when applied among individuals. PURPOSE: To examine the predictive validity of the HRindex equation by comparing submaximal and maximal VO2 predicted by the HRindex equation (VO2-Pred) with that measured by indirect calorimetry (VO2-Meas). METHODS: 60 healthy adults (21±2 yrs.; 28 males and 32 females) participated in this study. Each subject underwent a VO2max test and an experimental session on two separate days. The experimental session consisted of a 15-min resting period and three successive 10-min treadmill exercise bouts performed at 40%, 60% and 80% of VO2max. VO2 and HR were recorded continuously during both the VO2max test and the experimental session and these data were used to obtain VO2-Pred and VO2-Meas for each level of intensity and for VO2max. Validation was carried out by Pearson product-moment correlation analysis, paired t-test, Bland-Altman plots, and by assessment of mean absolute errors. RESULTS: A significant (p<0.05) correlation coefficient was found between VO2-Pred and VO2-Meas at 40% (r=0.56), 60% (r=0.60), and 80% of VO2max (r=0.55) and at VO2max (r=0.51). VO2-Pred differed significantly (p<0.05) from VO2-Meas at 40% (5.7±1.4 vs. 4.9±1.0 METs), 60% (8.5±2.0 vs. 7.5±1.4 METs), and 80% of VO2max (10.5±2.4 vs. 9.6±1.8 METs) and at VO2max (11.8±2.7 vs. 12.6±2.3 METs). Prediction biases were +0.74, +1.06, +0.82, and -0.83 METs, while mean absolute errors of prediction were 22.1%, 21.6%, 19.1% and 16.1% at 40%, 60%, and 80% of VO2max and at VO2max, respectively. CONCLUSION: It appears that the prediction equation involving HRindex overestimates VO2 at submaximal intensities and underestimates VO2max in healthy adults. These results suggest that further investigation aimed to establish the accuracy of using HRindex to predict VO2 is warranted.