Puberty Triggers 50% Surge in Male Upper-Limb Strength, Widening Early Childhood Gap

New research reinforces that sex differences in physical strength, initially modest in childhood, dramatically increase with the onset of puberty, particularly in males. This "explosion" in strength is largely attributed to hormonal changes, notably a significant rise in testosterone in boys. The findings underscore the biological underpinnings of these disparities, challenging notions that they are solely environmentally induced.

According to a recent meta-analysis by J.L. Nuzzo, boys exhibit greater grip strength from birth, a difference that becomes substantial by age 16, with girls' grip strength averaging approximately 65% of boys'. Another meta-analysis by Nuzzo, focusing on upper- and lower-limb strength, reveals that between ages 5 and 10, boys possess 17-18% greater upper-limb strength and 8-10% greater lower-limb strength than girls. This gap significantly widens in adolescence.

"Sex differences in strength are small in childhood, then suddenly explode at puberty," noted Steve Stewart-Williams, a prominent researcher in evolutionary psychology, in a recent social media post. This observation is supported by scientific consensus, which points to male puberty as a critical inflection point. During this period, boys experience a 20- to 30-fold increase in testosterone, a potent anabolic hormone that drives muscle growth.

The surge in strength observed in adolescent males is primarily due to increased muscle mass, influenced by higher testosterone levels and changes in body composition, including greater fat-free mass. By ages 14-17, boys demonstrate approximately 50% greater upper-limb strength and 30% greater lower-limb strength compared to girls. This contrasts with girls, whose strength gains are more influenced by estrogen and typically plateau earlier.

While environmental factors like physical activity and training play a role, research indicates that biological differences are the primary drivers of these strength disparities. Studies have shown that even when pre-pubertal boys and girls are matched for time spent practicing sports, boys retain a significant strength advantage, largely due to differences in muscle and fat mass. This biological divergence continues to inform discussions across various fields, including sports policy.