Sex differences in skeletal muscle fiber types: A meta-analysis.
Level 1 - systematic review of randomized trials
Meta-analysis of cross-sectional observational studies (by design analogy, not clinical CEBM)
PubMed 37424380 · doi:10.1002/ca.24091
What was done
A meta-analysis of 110 studies evaluated sex differences in skeletal muscle fiber cross-sectional area, fiber type distribution percentage, and fiber area percentage in 2,875 men and 2,452 women. Muscle fiber typing was performed via myofibrillar ATPase histochemistry (71.8% of studies) and/or immunohistochemistry, immunofluorescence, or SDS-PAGE for myosin heavy chain (MHC) isoforms (35.4% of studies). Biopsies were predominantly sampled from the vastus lateralis (79.1%) in healthy individuals (92.7%) aged 18 to 59 years (80.9%).
What was found
Men showed larger muscle fiber cross-sectional areas across all fiber types (g = 0.40 to 1.68), higher distribution percentages of Type II, MHC II, IIA, and IIX fibers (g = 0.26 to 0.34), higher area percentages of Type II, IIA, MHC IIA, and IIX fibers (g = 0.39 to 0.93), and larger Type II/I and Type IIA/I fiber area ratios (g = 0.63 and 0.94). Women showed higher Type I and MHC I distribution percentages (g = -0.13 and -0.44), higher Type I and MHC I area percentages (g = -0.53 and -0.69), and larger Type I/II fiber area ratios (g = -1.24).
Why it matters
This meta-analysis quantifies baseline sex differences in human skeletal muscle composition, confirming that men have larger fibers and greater Type II fast-twitch proportions while women have higher Type I slow-twitch proportions. These structural differences provide an anatomical foundation for observed sex differences in muscle strength, fatigue resistance, and metabolic function.
Limits
Data were heavily skewed toward a single muscle group, with 79.1% of biopsies taken from the vastus lateralis, limiting generalizability to other muscle groups. Most participants were healthy adults aged 18 to 59 years (80.9%), with limited representation of older adults or clinical populations. Fiber typing methods also varied across studies between histochemistry and protein electrophoresis.
Cited by
- supports The male biological form is characterized by greater bone density, more fast-twitch muscle fibers, and higher levels of testosterone compared to females.