REA BLAKEY, CNN MEDICAL CORRESPONDENT (voice-over): When it comes to fighting flab, genetics make a big difference.</s>UNIDENTIFIED FEMALE: There are three basic body types for men and for women. There are ectomorph, mesomorph and an endomorph.</s>BLAKEY: Dr. Peak says it's important to know which one you are. Are you the small-boned, slender ectomorph with a high metabolism and lots of energy?</s>UNIDENTIFIED FEMALE: One of the things that would be really good for you to do is to build up a little bit more muscle mass.</s>BLAKEY: Consistent strength training builds muscle and strengthens bones. Or maybe you're more muscular with limited flexibility, medium to large bone structure, a mesomorph.</s>UNIDENTIFIED FEMALE: Those people have to be careful. They really need to concentrate on aerobic because just because they look muscular, doesn't mean necessarily that they're fit.</s>BLAKEY: Thirty to 60 minutes of running, biking or aerobics three to five times a week is the best prescription for this body type. If you're an endomorph, large boned with a high percentage of body fat and a slow metabolism, you gain weight easily.</s>UNIDENTIFIED FEMALE: Here's where you really want to be able to both build up some good old lean-body mass, and that's muscle mass with your weight lifting, but also to really get into your aerobic training.</s>BLAKEY: Stick to low-impact aerobics, brisk walking, biking or skating. Dr. Peak recommends strength training three days a week focusing on upper body with light weights, 15 to 20 repetitions each. You can't control your body type; you can control your fitness level. For "Feeling Fit," I'm Rea Blakey.
Feeling Fit: The Right Exercise for Your Body Type