Does Aerobic Training Promote the Same Skeletal Muscle Hypertrophy as Resistance Training? A Systematic Review and Meta-Analysis

Background Currently, there are inconsistencies in the body of evidence for the effects of resistance and aerobic training on skeletal muscle hypertrophy. Objective We aimed to systematically review and meta-analyze current evidence on the differences in hypertrophic adaptation to aerobic and resistance training, and to discuss potential reasons for the disparities noted in the literature. Methods The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed for this review. The Downs and Black checklist was used for the assessment of methodological quality of the included studies. A random-effects meta- analysis was employed. In total, three analyses were performed: (1) for whole-muscle knee extensor data ; (2) for type I fiber cross- sectional area ; and (3) for type II fiber cross-sectional area. Results The final number of included studies in the present review is 21. All studies were of good or moderate methodological quality. The meta-analysis for whole-muscle hypertrophy resulted in a significant pooled difference (p < 0.001) in responses between the aerobic training and resistance training interventions. The pooled Hedge’s g, favoring resistance over aerobic training, was 0.66 (95% confidence interval 0.41–90 ; I2 = 0%). The meta-analysis for type I fiber cross-sectional area data resulted in a significant pooled difference (p < 0.001) between the aerobic training and resistance training groups. The pooled Hedge’s g, favoring resistance training over aerobic training, was 0.99 (95% confidence interval 0.44–1.54 ; I2 = 24%). The meta-analysis of type II fiber cross- sectional area data resulted in a significant pooled difference (p < 0.001) between the aerobic training and resistance training groups. The pooled Hedge’s g, favoring resistance training over aerobic training, was 1.44 (95% confidence interval 0.93–1.95 ; I2 = 8%). Conclusions The results of this systematic review and meta-analysis suggest that single- mode aerobic training does not promote the same skeletal muscle hypertrophy as resistance training. This finding was consistent with measurements of muscle hypertrophy both at the whole-muscle and myofiber levels. While these results are specific to the knee extensor musculature, it can be hypothesized that similar results would be seen for other muscle groups as well.