A 13-year-old can get buff by improving muscular strength, fortifying the tendons and ligaments that surround his bones and muscles and improving self-esteem through strength training. Bodybuilding, weightlifting and powerlifting are not recommended for children and teenagers, because these disciplines place too much stress on developing cartilage, tendons and bones. However, it is safe to improve muscle tone through dietary adjustments and exercise.
Strength-train for 30 minutes two or three times per week. Use your body weight, rather than weight machines or free weights, to perform exercises such as lunges, pushups, chinups, squats and pullups. Once you can complete 15 repetitions of each exercise easily, you can add a 1- to 2-pound dumbball to your workout routine.
Add resistance bands to your workout. Resistance bands are like giant rubber bands, which you use in your exercise routines. Use resistance bands in a variety of exercises that target every part of your body, such as bicep curls, tricep extensions, crunches, standing twists and seated rows.
Participate in a physical activity for 60 minutes a day to help build muscle mass and improve strength. You can do anything that you like, including dancing, bike riding, running or playing basketball with friends.
Join an organized sport, such as baseball, basketball, football, hockey, soccer or swimming. Training for a sport with a qualified coach provides a routine of drills and practices that increase your stamina, skills and knowledge of your favorite sport activity. It also gradually builds up your muscles as your body matures.
Eat a variety of foods from each food group every day. Include foods such as eggs, which are full of protein, omega-3 fatty acids and fiber, and protein-rich legumes and whole grains, which slowly release carbohydrates into the body, helping you to rebuild muscle and increase your exercise endurance.