Effect of individual characteristics and aerobic training on the %HRR-%V˙O2R relationship

This study aimed to assess if, during incremental exercise, considering individual characteristics can make the relationship between the percentages of heart rate (HRR) and oxygen uptake (VO2R) reserve either 1:1 or more accurate. Cycle ergometer data of the maximal incremental exercise tests performed by 450 healthy and sedentary participants (17-66 years) of the HERITAGE Family Study, grouped for sex, ethnicity, age, body fat, resting HR, and VO2max, were used to calculate the individual linear regressions between %HRR and %VO2R. The mean slope and intercept of the individual linear regressions of each subgroup were compared with 1 and 0 (identity line), respectively, using Hotelling tests followed by post-hoc one-sample t-tests. Two multiple linear regressions were also performed, using either the slopes or intercepts of the individual linear regressions as dependent variables and sex, age, resting HR, and VO2max as independent variables. The mean %HRR-%VO2R relationships of all subgroups differed from the identity line. Moreover, individual linear regression intercepts (8.9±16.0) and slopes (0.971±0.190) changed (p<0.001) after 20 weeks of aerobic training (13.1±11.1 and 0.891±0.122). The multiple linear regressions could explain only 3.8% and 1.3% of the variance in the intercepts and slopes, whose variability remained high (standard error of estimate of 15.8 and 0.189). In conclusion, the %HRR-%VO2R relationship differs from the identity line regardless of individual characteristics and their difference increased after aerobic training. Moreover, due to the high interindividual variability, using a single equation for the whole population seems not suitable for representing the %HRR-%VO2R relationship of a given subject, even when several individual characteristics are considered.