Final answer:
Around age 11, males generally see increased development of muscles and bones, particularly in the upper body, while females develop more body fat and secondary sexual characteristics like breast and hip growth.
Step-by-step explanation:
Beginning around age 11, males tend to develop more muscles and bones, especially in the upper body, resulting in broader shoulders and chests relative to their hips. At the same time, females typically develop more body fat, particularly in the breasts and hips, leading to a widening of the pelvis and hips relative to their shoulders and chests. This sex difference in growth during puberty accounts for the sexual dimorphism in adult human body composition and shape.
Male muscles may continue to grow and gain strength even after height growth has ceased, resulting in significant muscle development. In contrast, females not only experience increased body fat for reproductive purposes but also undergo significant development of secondary sexual characteristics, such as breasts and pubic hair. The adolescent growth spurt contributes to these changes, with girls typically beginning their growth spurt earlier than boys and developing primary and secondary sexual characteristics during this time.