A 2012 study by the University of Indiana reports that there is little difference in height, weight and strength between boys and girls through the ages of 11 to 12 years old. At the onset of puberty, males grow at a more rapid rate than females, resulting in a significant difference in strength.
The study by the University of Indiana examined the athletic performance between boys and girls, using data compiled by USA Swimming. The researchers compared performance in the 50-meter freestyle among swimmers aged 6 to 19 years old, analysing roughly 1.9 million swims in all. They selected this specific race, as performance at this distance is dictated by muscular power and function rather than training. Performance was identical between boys and girls at age 8 or younger, and little difference was found between the sexes at the ages of 11 to 12 years. Significant differences in performance were discovered between the sexes starting at the age of 13 years. This is attributed to the fact that males gain strength and height at a more rapid rate than females at the onset of puberty.
A 1993 study by McMaster University examined the differences in strength between mature males and females. The study found females to be 52 percent as strong as males in their upper bodies, and 66 percent as strong as males in their lower bodies. This is attributed to female muscles having smaller muscle fibers than male's, as well as less lean tissue in the female upper body.