Body composition and body shape remain relatively constant during middle childhood. During preadolescence and early adolescence (9 to 11 years in girls; 10 to 12 years in boys), the percentage of body fat increases in preparation for the growth spurt that occurs during adolescence. This body fat increase occurs earlier in girls than in boys, and the amount of increase is greater in girls. Preadolescents, especially girls, may appear to be “chunky,” but this is part of normal growth and development. During middle childhood, boys have more lean body mass per inch of height than girls. These differences in body composition become more significant during adolescence.

Growth

During middle childhood, children grow at a slow consistent rate before reaching a large growth spurt during adolescence.

Skeletal and Muscular

The average weight increase during middle childhood is 5 to 7 pounds a year. The average height increase is 2 to 3 inches a year. By the age of 11 years, the average girl is 4 feet, 10 inches tall, and the average boy 4 feet, 9 1/2 inches tall.

Muscle mass increases as baby fat decreases, while the legs become longer, and the body trunk becomes slimmer. Strength gradually increases due to heredity and exercise, doubling their strength, during these years. Because of a greater number of muscle cells boys are usually stronger than girls.