Abstract

Low cardiorespiratory fitness (VO_2max) is an important risk factor for diabetes, cardiovascular disease and some cancers, making lifestyle interventions especially relevant. There is purported to be substantial inter-individual differences in how VO_2max responds to lifestyle/exercise interventions. Recently, we described the appropriate approach for quantifying these inter-individual differences. Therefore, we aimed to apply this approach to quantify inter-individual differences in the responses of VO_2max. We re-analysed data from the influential ‘Activity Counselling Trial’ (ACT), which was designed to determine the effects of general lifestyle assistance as well as formal counselling on physical activity and VO_2max in 479 men and 395 women. Importantly, an appropriate comparator group was also present in order to quantify ‘true’ inter-individual differences in VO_2max response. For women, the ‘true’ inter-individual responses in VO_2max (expressed as a SD) were found to be±129 (95% Confidence interval: −40 to 187) ml/min in the general lifestyle assistance group and±93 (−91 to 160) ml/min in the formal lifestyle counselling group. For men, true individual differences in response were±116 (95%CI: −130 to 210) ml/min and±148 (−105 to 234) ml/min in the assistance and counselling groups, respectively.

Although the mean increase in VO_2max was greater in women, this increase corresponded to a trivial effect size. This application of the appropriate analyses to the ACT dataset indicate that, on average, the effects of activity counselling on VO_2max were small, although there were moderate ‘true’ inter-individual differences in the VO_2max response in women (0.34 SD) and small ‘true’ inter-individual differences in men (0.27 SD). Further genotype investigation may therefore be warranted in order to determine the mediators of this observed heterogeneity in response.