Moderators of Resistance Training Effects in Overweight and Obese Adults: A Systematic Review and Meta-analysis

Purpose This study aimed to analyze whether the effects of resistance exercise on whole-body fat and lean mass are moderated by exercise dosage (i.e., duration, volume, and intensity), age, body mass index, baseline values, assessment methods, and prescription of aerobic exercise and caloric restriction in overweight/obese adults. Methods A systematic search was undertaken in 11 databases from inception to December 2020, with an updated search undertaken in April 2022. Eligible randomized controlled trials examined the effects of resistance-based exercise programs on whole-body fat mass and lean mass in adults who were overweight or obese. Meta-analysis was undertaken with a random-effects model. Associations between mean differences and potential moderators were tested by meta-regression models. Results Sixty-seven articles describing 65 trials (n = 2537) were included. Resistance-based exercise programs resulted in a significant change of -1.6 kg (95% confidence interval [CI] = -1.9 to -1.3 kg, P < 0.001) in whole-body fat mass and +0.8 kg (95% CI = 0.6 to 0.9 kg, P < 0.001) in lean mass. Male participants experienced greater effects than females (P < 0.001), whereas those presenting with higher levels of fat mass at baseline experienced greater reductions in this outcome (P = 0.084). For lean mass, younger adults experienced greater improvements compared with older participants (P = 0.009), whereas programs comprising resistance exercise and caloric restriction resulted in significant reductions in lean mass (P = 0.035). Resistance exercise dosage or prescription of aerobic exercise was not associated with change in these outcomes. Conclusions Resistance-based programs improve body composition regardless of the resistance exercise dosage or aerobic component prescribed in adults who are overweight or obese. In addition, subgroups based on demographic characteristics, baseline levels, and presence of caloric restriction may present with more favorable responses in body composition.