When and Why Do Sex Differences in Handgrip Strength Emerge? Age-Varying Effects of Testosterone From Childhood to...

On average, males are stronger than females, with hormonal changes during puberty often cited as a contributing factor to this advantage. However, not all evidence consistently supports this explanation. The purpose of this study was to determine (1) when sex differences in handgrip strength and testosterone emerge, and (2) whether testosterone mediates the sex difference in handgrip strength and if this effect varies across age.

Time-varying effect modeling (TVEM) was used to examine age-specific trajectories of handgrip strength and testosterone, and to assess whether these trajectories differed by sex. A moderated mediation analysis was conducted to test whether the sex difference in handgrip strength was mediated by testosterone level, and whether this effect varied across age. Data were drawn from the 2011-2012 and 2013-2014 cycles (N = 11,035) of the National Health and Nutrition Examination Survey.

TVEM indicated that the sex difference in handgrip strength emerged at age 8, whereas the sex difference in testosterone level became evident at age 10. A moderated mediation analysis revealed that testosterone mediated the association between sex and handgrip strength, and this effect decreased with age (IMM = -0.18, 95% CI: -0.20, -0.16).

Sex difference in handgrip strength appears to be driven, in part, by the testosterone levels. However, this difference can be observed even before the onset of puberty, which suggests that testosterone alone does not fully explain the sex difference in muscle strength. This finding may have important implications for decisions regarding inclusivity and fairness in sports that emphasize strength.