Sex differences in absolute and relative changes in muscle size following resistance training in healthy adults: a systematic review with Bayesian meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review with Bayesian meta-analysis of 29 comparative resistance training studies
PubMed 40028215 · doi:10.7717/peerj.19042
What was done
A systematic review and Bayesian meta-analysis evaluated sex differences in absolute and relative muscle size changes following resistance training (RT) in healthy adults aged 18–45 years. Eligible studies involved male and female participants undergoing identical RT protocols with pre- and post-intervention muscle size assessments. From 2,720 screened records, 29 studies were included. Primary outcomes were standardized mean differences (SMD), log response ratios (lnRR) with exponentiated percentage change, and probability of direction (pd). Moderating variables analyzed included muscle size measurement tool, body region, muscle fiber type, and RT experience.
What was found
Absolute increases in muscle size slightly favored males compared to females (SMD = 0.19, 95% highest density interval [HDI]: 0.11 to 0.28; pd = 100%). In contrast, relative increases in muscle size were similar between sexes (exponentiated percentage change of lnRR = 0.69%, 95% HDI: -1.50% to 2.88%). Outcomes were minimally affected by the measurement method used and were not moderated by participant RT experience. By region, absolute hypertrophy favored males for upper-body but not lower-body musculature. Type I muscle fiber hypertrophy slightly favored males, whereas Type II muscle fiber hypertrophy was similar between sexes.
Why it matters
This review demonstrates that females achieve relative muscle hypertrophy comparable to males following resistance training, showing that sex-based differences in growth potential are primarily restricted to absolute gains.
Limits
The analysis was restricted to healthy adults aged 18–45 years, limiting generalizability to older adults or clinical groups. Total participant count was not reported in the abstract. The abstract did not report details on intervention duration, training volume, adherence, or nutritional and hormonal controls across included studies.
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