SEX DIFFERENCES IN MUSCLE STRENGTH RELATIVE TO BODY MASS: A META-ANALYSIS
James Nuzzo & Matheus Pinto in pre-print March 2026
https://sportrxiv.org/index.php/server/preprint/view/777/version/970
pdf version: https://sportrxiv.org/index.php/server/preprint/view/777/1674
ABSTRACT
On average, human males have greater body masses and generate more muscle force than human females, and body mass and muscle strength correlate. Normalizing muscle strength to body mass (strength-to-body mass ratio) might mathematically eliminate the sex difference in strength, but this has not been examined on a large scale. Here, we conducted a meta-analysis to determine if a sex difference exists in the strength-to-body mass ratio. We identified 78 studies that reported a total 352 effects comparing mean strength-to-body mass ratios in males and females. The total sample was 122,434 (61,042 males, 61,392 females). Grip strength was the most common test (21.9% of effects). The strength-to-body mass ratio was 25% greater in males than females (response ratio = 1.25 (95% prediction intervals (PI) [0.93, 1.67]). The strength-to-body mass ratio was 17% greater in males than females for lower-limb muscles (response ratio = 1.17 (95% PI [0.87, 1.59]) and 35% greater for upper-limb muscles (response ratio = 1.35 (95% PI [0.87, 1.60]). The strength-to-body mass ratio was 3% greater in males than females when 3-10 years old (95% PI [0.84, 1.27]), 9% greater when 11-13 years old (95% PI [0.89, 1.34]), 25% greater when 14-17 years old (95% PI [1.02, 1.54]), 35% greaterwhen 18-64 years old (95% PI [1.10, 1.66]), and 33% greater when ≥65 years old (95% PI [1.08, 1.65]). Thus, males generally have greater muscle strength than females even when strength is normalized to body mass. Factors other than body mass contribute to sex differences in strength.
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Already at 14 years old, a male person on average has a greater strength to body mass ratio compared to female people of the same age. Therefore, it is highly likely that a boy taking estrogen from 15 years old, has already had a body that has developed strength advantages than a female person.
There is also evidence that muscle memory formed from being male contributes to physical advantages and this has come from the studies of children and their strength differences. Grip strength is known to have started to develop from an age that is earlier than male puberty.
There is no evidence that I can find that a male person who started estrogen at 15 has zero physical advantages over a female person. I can find studies that show that suppressing testosterone does not negate male pubertal advantages.
And the Olympic medical committee, with all the evidence available, has also made a very clear policy that not even male people who have had their puberty blocked from pre puberty are included in the female sports categories. If there was even a convincing modelling study done that showed that a male person with their testosterone fully suppressed from puberty and given estrogen instead lost their physical advantages over female people, they would have made exemptions for that in their sex testing policy.