If you're just starting out in the weight room, most fitness experts recommend you begin by training three sessions a week, ranging from 20 minutes to an hour, allowing at least one day off between sessions. It's best to work only two or three muscle groups during each session, for example, legs and arms one session and chest and back the next. Before you head for the weight bench, you should warm up by spending 10 minutes pedaling on a stationary bicycle or by taking a brisk walk around the gym. Perform two to three different exercises for each body part to make sure you work each muscle in the group effectively. If you're pressed for time, you can schedule a short jog or bicycle ride either before or after a strength-training session.
Strength training is a great way for teens to improve their strength, endurance, and muscle tone.
For specific medical advice, diagnoses, and treatment, consult your doctor.