Gabe Mirkin, M.D.
The best time for future Olympic athletes to start training is before they reach puberty. Having large strong muscles makes you a better athlete, and starting training before puberty enlarges bones. Muscles growth is limited by the size of the bones on which they attach. The larger the bone, the stronger the muscle. The larger and stronger your muscles, the harder you can hit a ball. Children who start to play tennis before they go into puberty have larger bones in the arm that holds the racquet.
Lifting weights during growth does not prevent children from growing to their full potential heights. Children who lift weights with good supervision do not suffer more injuries than adults. We used to worry that large muscles would make you musclebound and interfere with coordination, but with increased strength comes increased speed and increased coordination. The best time for future Olympians to start training is while their bones are still growing.