Most 13-year-olds, especially boys, haven't yet completed puberty, which means lifting weights won't produce big muscles. Your muscles are influenced by your hormones, and until your body matures, you can't build big muscles. Your body just don't have the capacity to buff up like adults' muscles do, and lifting heavy weights can be dangerous to your muscles and tendons. You may not be able to become a bodybuilder now, but there are steps you can take to make your muscles healthier and more efficient for the future.
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Any activity that uses your muscles also helps build and strengthen them. If you aren't physically active or play sports regularly, now is a good time to start. Try joining a team or club sport, such as baseball, soccer or hockey. Go outside and skateboard, ride your BMX bike, swim or ski. Maintaining a schedule of regular physical activity -- aim for an hour a day -- will keep you lean, fit and strong for years to come.
A Teenager's Diet
A well-rounded diet of nutritious foods helps your muscles grow and stay healthy. There's no magic food or food group that will bulk you up; instead, make sure you're getting adequate amounts of each food group. Look for healthy sources of protein such as lean meats, eggs, fish and nuts; whole-grain breads, pastas and cereals; low-fat milk, yogurt, cheese and other dairy products; and plenty of fresh fruits and vegetables. Drink milk instead of sodas or diet sodas. A multivitamin will add calcium and iron to help your bones and muscles develop as you mature.
Add resistance training to your exercise schedule three days a week. Although lifting heavy weights can be dangerous for growing muscles because your body is still growing and developing, you can use light weights or work with resistance bands. Exercises like pushups, situps and chinups also strengthen your muscles. Gymnastics is another muscle-building activity; even if you don't take lessons, you can practice somersaults and cartwheels in your backyard.
Performance-Enhancing Drugs Won't Work
Steer clear of trying any steroids or other "performance-enhancing drugs." These drugs are bad news for anyone, but especially teenagers still going through puberty. Steroid use can cause facial hair growth, male-pattern baldness and menstrual cycle changes in girls and infertility, development of breasts and increased risk of prostate cancer in boys. Both sexes are at risk of heart disease, liver damage, high blood pressure and cancer from steroid use. If you've used steroids in the past or are thinking about using them, talk to a doctor or other trusted adult.