Resistance training and inter-interindividual response differences on cardiorespiratory fitness in older adults: An ancillary meta-analysis of randomized controlled trials

Examine true inter-individual response differences (IIRD) as a result of resistance training on cardiorespiratory fitness in older adults. Data from a recent meta-analysis of 22 randomized controlled trials representing 552 men and women (292 resistance training, 260 control) ≥ 60 years of age were included. The primary outcome was cardiorespiratory fitness (VO_2max) in ml^.kg^-1.min^-1. Using the inverse variance heterogeneity (IVhet) model, statistically significant treatment effect (resistance training minus control) increases in VO_2max in ml^.kg^-1.min^-1 were found (mean, 1.8, 95% CI, 0.4 to 3.3 ml^.kg^-1.min^-1, p = 0.01; Q = 82.8, p < 0.001; I²= 74.6%, 95% CI, 61.6 to 83.3%; ${\tau }^2$ =1.1). The 95% prediction interval (PI) was -0.8 to 4.5 ml^.kg^-1.min^-1. However, no statistically significant IIRD was observed (mean, 0.6, 95% CI, -1.1 to 1.4 ml^.kg^-1.min^-1; ${\tau }^2$ =1.5). The 95% PI was -1.8 to 2.0 ml^.kg^-1.min^-1. In conclusion, while progressive resistance training may increase VO_2max in ml^.kg^-1.min^-1, a lack of true resistance-training-associated IIRD exist.