Children begin to develop muscles as they go through adolescence and begin to mature. Muscle development depends on a variety of factors, such as sex, heredity, age and exercise. Participating in resistance exercise before the age of puberty may help develop a child's strength, but it is unlikely to lead to larger muscles.
Puberty
Signs of secondary sexual characteristics signal the beginning of puberty, the time when hormone production can lead to muscle development. This stage occurs when male voices begin to deepen, and boys develop pubic and underarm hair. Puberty for girls involves the beginning of breast development and the onset of menstruation.
Muscle Mass
Although children who lift weights before puberty can increase their strength, developing muscle mass requires waiting for puberty. Creating resistance makes muscles work harder, helping to create additional muscle fibers that lead to an increase in muscle size and volume. Although free weights and resistance bands are common tools for building muscles, a teen can simply use the weight of her own body while doing pushups, sit-ups, lunges and squats. Low androgen levels in girls result in less muscle mass, compared with teenage boys, although strength training can augment natural muscle development in teenage girls, as well as create a more toned appearance. Muscle toning is a common reason many girls do resistance exercises.
Routine
The American Academy of Pediatrics recommends that teens begin with low-resistance exercises. After a teen can do 15 repetitions with good form and proper technique, he should add weight in small increments. To build strength and develop muscles, the teen should work out for at least 20 minutes two to three times each week. Training more than four times a week fails to produce additional benefits. The teen should spend about 10 minutes warming up and cooling down before and after each lifting routine.
Precautions
Any teen who wants to lift weights to develop larger muscles should get a physical first. The teen should avoid maximum lifts that require all her strength. The teen should wait until she develops physical and skeletal maturity before bodybuilding, warns the American Academy of Pediatrics. She should learn the proper way to do weight-training exercises and have a spotter standing by when she does exercises that involve lifting weights above her body or head.
