Response Variation, Resistance Training, and Fat Mass in Older Adults with Overweight/obesity: A Meta-analysis

It is unknown whether true inter-individual response differences (IIRD) exist with respect to changes in fat mass as a result of resistance training in older adults with overweight and obesity. PURPOSE: Determine whether true IIRD exist with respect to changes in fat mass as a result of resistance training in older adults with overweight and obesity. METHODS: Meta-analysis of randomized controlled trials in adults >60 years of age. Change outcome standard deviations (resistance training minus control) treated as point estimates for fat mass were used to calculate true IIRD from each study. In addition, treatment effect data (resistance training minus control) were also extracted and pooled for analysis. The inverse variance heterogeneity (IVhet) model was used to pool all results. RESULTS: Twelve resistance training studies lasting 8 to 24 weeks (median = 12) and representing 433 participants (242 resistance training, 191 control) were pooled for analysis. Statistically significant treatment effect reductions in fat mass were observed (mean, -1.3 kg, 95% confidence interval, -1.8 to -0.8 kg), with changes equivalent to a relative reduction of 4.5%. However, no statistically significant IIRD were observed (mean, 0.7 kg, 95% confidence interval, -1.1 to 1.4 kg). The 95% prediction interval for true IIRD in a future study was -1.8 to 2.0 kg. The percent chance, i.e., probability, of a clinically meaningful difference in variability, i.e., IIRD, was 45.6% (only possibly clinically important). CONCLUSIONS: While resistance training is associated with statistically significant reductions in fat mass among older adults with overweight and obesity, there is currently a lack of convincing evidence to support the notion that true resistance training associated IIRD exist. Therefore, a search for potential mediators and moderators, including genetic interactions, associated with resistance training and changes in fat mass among older adults with overweight and obesity may not be warranted. However, additional research is needed before any true level of certainty can be established.