Effects of exercise intensity on VO2max in studies comparing two or more exercise intensities: a meta-analysis

Purpose A strong inverse relationship exists between aerobic capacity and all-cause mortality, and survival improves when unfit subjects become fit. Clear recommendations of exercise intensity are important to ensure optimal effects of endurance training. The aim for conducting this study was to improve our understanding regarding the effects of training intensity on aerobic capacity, with the intention of giving individuals a good basis for determining exercise intensity. Methods This meta-analysis included studies comparing two or more groups exercising at different levels of intensity. Studies were identified from PubMed, and 19 studies met the inclusion criteria. A meta-analysis compared the mean difference from pre-intervention versus post-intervention maximal oxygen consumption ( V O 2max ) at various levels of intensity, initial levels of fitness and in studies with training groups equated for total work. Effect size was calculated within groups, within study, between groups and between different categories of intensity. The values of the effect sizes can be compared to Cohen’s reference values of 0.2, 0.5 and 0.8. Thus, an effect size of 0.2 classifies as small, 0.5 as medium and 0.8 as large. Results This meta-analysis shows that endurance training with high intensity is more time-efficient and preferred in terms of improving V O 2max , independent of the individual’s initial level of fitness. Conclusion The effect of different exercise intensity levels, from low to high intensity, is relatively predictable in that the effect increases with increased intensity. To make the effect of training clear to the recipient of training guidelines, this meta-analysis suggests that effect size should be incorporated in future exercise guidelines.