QUESTIONS: What are the effects of resistance training on muscle strength, physical function and muscle power in adults who are overweight or obese? Which factors moderate the effects? DESIGN: Systematic review of randomised controlled trials, with random effects meta-analyses and meta-regressions. PARTICIPANTS: Adults who are overweight or obese. INTERVENTION: Resistance training lasting >= 4 weeks. OUTCOME MEASURES: Muscle strength, muscle power and physical function. RESULTS: Thirty trials with 1,416 participants met the eligibility criteria. Pooled analyses indicated that resistance training has a large beneficial effect on muscle strength (SMD 1.39, 95% CI 1.05 to 1.73, I2 = 85%) and a moderate effect on physical function (SMD 0.67, 95% CI 0.25 to 1.08, I2 = 71%) in adults who are overweight or obese. However, the effect of resistance training on muscle power was unclear (SMD 0.42, 95% CI -3.3 to 4.2, I2 = 46%). The effect of resistance training on strength was greatest for the upper body (versus lower/whole body: beta 0.35, 95% CI 0.05 to 0.66) and in dynamic strength tests (versus isometric/isokinetic beta 1.20, 95% CI 0.60 to 1.81), although trials judged to have good methodological quality reported statistically smaller effects (versus poor/fair quality: beta -1.21, 95% CI -2.35 to -0.07). Concomitant calorie restriction did not modify strength gains but reduced the effect of resistance training on physical function (beta -0.79, 95% CI -1.41 to -0.17). Small study effects were evident for strength outcomes (beta 5.9, p < 0.001). Conclusions Resistance training has a large positive effect on muscle strength and a moderate effect on physical function in adults who are overweight or obese. However, the effect of resistance training on muscle power is uncertain. In addition, concomitant calorie restriction may compromise the functional adaptations to resistance training. REGISTRATION: PROSPERO CRD42019146394.

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