Have you ever wondered if women can really build muscle as fast as men? Traditional wisdom often points to testosterone as the secret sauce for muscle growth, but a groundbreaking 2025 meta-analysis challenges that notion. This study shows that although men start with more muscle, the relative muscle gains in women are just as impressive. In this literature review I break down the author’s findings and explore what they mean for anyone interested in strength training and fitness.

This 2025 systematic review and Bayesian meta-analysis by Refalo et al. examined sex-based differences in muscle hypertrophy following resistance training (RT) in healthy adults aged 18–45. Analyzing 29 studies, the authors found that while absolute increases in muscle size slightly favored males, relative gains were comparable between sexes. The study also explored moderating factors such as muscle region, fiber type, and training experience, concluding that females possess a similar relative potential for hypertrophy as males.

A review by James Shmagranoff

Sex differences in absolute and relative changes in muscle size following resistance training in healthy adults: A systematic review with Bayesian meta-analysis. PeerJ, Refalo, M. et al. (2025)

Introduction:

Resistance training is widely recognized for its role in promoting skeletal muscle hypertrophy, yet the extent to which biological sex influences training outcomes remains a topic of ongoing investigation. In recent years, the fitness and rehabilitation communities have increasingly emphasized the importance of evidence-based approaches to training across diverse populations. The 2025 meta-analysis by Refalo et al. offers a comprehensive synthesis of current research on sex differences in muscle growth, employing Bayesian statistical methods to evaluate both absolute and relative changes in muscle size among healthy adults. By integrating data from nearly 30 studies, this review provides critical insights into how sex-related physiological factors may—or may not—affect hypertrophic adaptations to resistance training. These findings have important implications for exercise prescription, athletic programming, and future research on individualized training responses.

Methods

1. Study Selection and Inclusion Criteria

The researchers began with a systematic literature search across multiple databases, identifying an initial pool of 2,720 studies. To ensure that the findings were both robust and relevant, stringent inclusion criteria were applied. Specifically, they included studies that met the following conditions:

- Population: Healthy male and female adults aged 18–45 years.

- Intervention: A standardized resistance training (RT) program delivered identically to both sexes.

- Outcome: Quantitative measures of muscle size recorded both before and after the intervention.

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