Don't start bench-pressing yet. First, you need to know what you're doing.
Consider hiring a trainer to get you started. Look for a trainer who is certified by a reputable group, such as the American College of Sports Medicine or the National Strength and Conditioning Association, says Avery Faigenbaum, a professor in the College of New Jersey's health and exercise science department.
Pick a trainer who is knowledgeable and fun to work with, Yuam says. He recommends splitting the cost with a few buddies.
Yuam's fitness video, The Werewolf Workout, features people of different heights and builds doing the same exercises to underscore that machine settings must fit your body size to prevent straining.
Pediatric sports medicine expert Andrea Stracciolini, MD, of Children's Hospital Boston, says poor technique and poor supervision are top causes of injury for teens who strength train.