![image](belsky4e_fig08_03.jpg)
Changes in blood hemoglobin and red blood cells during puberty in males and females: At puberty, increases in the amount of hemoglobin in the blood and in the number of red blood cells cause children of both sexes to get far stronger. But notice that these changes are more pronounced in boys than in girls.
Data from: Tanner, 1955, p. 103.