Sex Differences in Strength During Development: Implications for Inclusivity and Fairness in Sport

Males, on average, are bigger and stronger than females. Hormonal differences during puberty are one reason given for this performance advantage. However, not all evidence supports that thesis. Our aim was to further this discussion by measuring early life changes between sexes (when hormones would be similar) in components of muscle function.

Fifty-one children (29 boys, 22 girls) completed this study. Forearm muscle size and strength were assessed three times with each time point being separated by approximately a year (2021-2023).

There was no sex*time interaction for handgrip strength (p = 0.637). There was, however, a time (p < 0.001) and sex (p < 0.001) effect. Strength increased each year and boys were stronger than girls (difference of 1.5 [95% 0.7, 2.3] kg). There was no sex*time interaction for ulnar muscle thickness (p = 0.714) but there was a time (p < 0.001) effect. Muscle size increased each year but there was no evidence of a sex effect (p = 0.12; difference of 0.81 [95% -0.21, 1.8] mm). A strong positive within-participant correlation between muscle size and strength (r = 0.803 95% CI: [0.72, 0.86], p < 0.0001) was found across time.

Muscle size and strength increased together but this increase did not differ based on sex and boys were stronger than girls. Future work is needed to determine the reason for this difference in maximal strength. Any effect was seemingly present at the initial measurement (at the age of 4 years), since muscle size and strength did not change differently between boys and girls over time.