HRR and VO2R Fractions Are Not Equivalent: Is It Time to Rethink Aerobic Exercise Prescription Methods?

Introduction According to current guidelines, the intensity of health-enhancing aerobic exercise should be prescribed using a percentage of heart rate reserve (%HRR), which is considered to be more closely associated (showing a 1:1 relation) with the percentage of oxygen uptake reserve (%VO2R) rather than with the percentage of maximal oxygen uptake (%VO2max) during incremental exercise. However, the associations between %HRR and %VO2R and between %HRR and %VO2max are under debate; hence, their actual relationships were investigated in this study. Methods Data from each stage of a maximal incremental exercise test performed by 737 healthy and physically inactive participants of the HERITAGE Family Study were screened and filtered then used to calculate the individual linear regressions between %HRR and either %VO2R or %VO2max. For each relationship, the mean slope and intercept of the individual linear regression were compared with 1 and 0 (i.e., the identity line), respectively, using one-sample t-tests. The individual root mean square errors of the actual versus the 1:1 predicted %HRR were calculated for both relationships and compared using a paired-sample t-test. Results The mean slopes (%HRR-%VO2R, 0.972 +/- 0.189; %HRR-%VO2max, 1.096 +/- 0.216) and intercepts (%HRR-%VO2R, 8.855 +/- 16.022; %HRR-%VO2max, -3.616 +/- 18.993) of both relationships were significantly different from 1 and 0, respectively, with high interindividual variability. The average root mean square errors were high and revealed that the %HRR-%VO2max relationship was more similar to the identity line (P < 0.001) than the %HRR-%VO2R relationship (7.78% +/- 4.49% vs 9.25% +/- 5.54%). Conclusions Because both relationships are different from the identity line and using a single equation may not be appropriate to predict exercise intensity at the individual level, a rethinking of the relationships between the intensity variables may be necessary to ensure that the most suitable health-enhancing aerobic exercise intensity is prescribed.

Automated summary

This study investigated the relationships between %HRR and %VO2R, as well as %HRR and %VO2max, in 737 healthy and physically inactive participants. Results showed high interindividual variability in both relationships, suggesting a need to rethink the relationships between intensity variables to ensure appropriate prescription of health-enhancing aerobic exercise.