08/18/2011 12:28 am ET Updated Oct 17, 2011

How To Build That Strong (And Sexy!) Muscle Mass

Last week I discussed that our muscle mass and strength have a large impact on how well our bodies' age. This week I'll continue by describing ways to measure (and build!) your muscle.

Although aerobic exercise -- things like running, bicycling, swimming, and dancing -- are good workouts for your heart and lungs and help you lose weight, these aren't going to help you maintain your strength. "The only type of exercise that prevents sarcopenia is resistance exercise," says William Evans, Ph.D, a professor of geriatrics, physiology, and nutrition at the University of Arkansas in Fayetteville who has studied how older people can address their muscle declines. (Sarcopenia, by the way, is the medical term for muscle loss.) Studies looking at athletes who have been running all their lives found that, though they're leaner and have lower risk of chronic diseases, their strength is similar to sedentary people of the same age.

You have to use resistance exercise to maintain and build your muscle. Some people refer to this type of activity as lifting weights, and pumping dumbbells and barbells certainly works. But you can also use strength-training machines at the gym or stretchy elastic bands. For some exercises, such as abdominal crunches, you simply use your own body weight. But what all these activities have in common is that they require you to push your muscles against a form of resistance.

To appreciably increase your muscle size and strength, Dr. Evans says, you can't use weights that feel extremely light. Rather, you need to do exercises that incorporate at least 60 percent of the weight you can lift one time. In his studies, Dr. Evans typically has subjects lifting 80 percent of their maximum. Also, the weight you use should tire you out within eight to 12 repetitions. For example, if you can curl a 30-pound dumbbell once, you should aim for curling a 20-pound dumbbell up to 12 times. Curling a 10-pound dumbbell 20 times, by contrast, won't build your muscle strength. Likewise, if you can curl a 20-pound dumbbell once, you'll want to work on curling a 12-pound dumbbell up to 12 times.

If you're worried about building bulk, well, don't be. Few women actually gain significant muscle mass doing strength exercises, unless they're genetically predisposed to it. Do check with a trainer or someone at your gym if you're not certain of a safe starting weight.

Early in your resistance training, you'll notice quick improvements, Dr. Evans says. In even just 2 months, your strength may double. This isn't simply a matter of your muscles getting bigger --your brain learns how to use your muscles more efficiently, too.

But, as you stick with it, your strength-training plan must be progressive. You have to add repetitions and use heavier weights (or thicker elastic bands). That's because your muscles get stronger, so they can adapt to lifting a certain weight. After you curl that 12-pound dumbbell 12 times for several sessions, it ceases to be a challenge, and you stop gaining strength. So once you can lift a weight 12 times, it's time to use a heavier weight and strive to lift it at least eight times.

Doing two sets of each exercise is a sufficient workout for your muscles, Dr. Evans says. That means you'd lift the weight -- or stretch the band -- a "set" of eight to 12 repetitions, then take a rest or do a different exercise, and then do another set.

Just two strength-training workouts a week, with exercises that work all your major muscle groups during each session, are adequate for building and maintaining your muscles. Your full-body workout would include exercises that focus on the fronts of your arms (biceps), backs of your arms (triceps), chest, shoulders, upper back, the fronts and backs of your thighs, your abdomen, and your lower back.

It's beyond the scope of this blog to tell you everything you need to know about strength training. But here are some tips to keep in mind.

■ Talk to your doctor before beginning any new type of exercise program. Lifting weights may not be appropriate for people with certain conditions, such as high blood pressure or joint problems.
■ Strive for two strength-training workouts, each containing 10 or so exercises that give you a full-body workout. Do two sets of eight to 12 repetitions of each exercise.
■ Consider working at least one session with a qualified fitness professional. A certified personal trainer can help you design a program, teach you how to do exercises, and observe your form to ensure it's correct.
■ Warm up for five to 10 minutes before a strength-training session and cool down afterward. Walking briskly and pumping your arms is a good warm-up.
■ You have a lot of options for how to train. According to Dr. Evans, a simple and economical approach is to use elastic bands or tubes. You can do many exercises by standing on one end and tugging on the other, standing in the middle and pulling both ends, or holding each end and pulling them apart. Free weights, like dumbbells and barbells, also improve balance and coordination, but you need a spotter to help you with some exercises. Weight machines tend to be a little safer and easier to use, he says.
■ When you increase the amount of weight you lift or the difficulty of the elastic band you stretch, make the challenge only five to 10 percent harder. This will limit your risk of injury.
■ Don't do strength-training sessions for the same muscle groups on back-to-back days. Your muscles need more time to recover.
■ Work opposing muscles proportionally. That means working muscles on the fronts and backs of your upper arms, your upper back and chest, and your lower back and abdomen. Ignoring muscle groups throws your body out of balance.
■ Get plenty of protein. As you read earlier, the recommended daily allowance of protein for adults may not be enough to encourage sufficient muscle maintenance as you get older. Researchers haven't pinned down exactly how much you should strive to get. If you aim for getting 30 percent of your calories from protein, however, you should get enough to support muscle maintenance and growth. Get most of your protein from low-fat sources, Dr. Evans recommends. Protein will be much more efficient at building muscle when you eat it within 30 minutes after a workout, he says. Have a turkey sandwich, some low-fat yogurt or cottage cheese, or nibble on some steamed edamame. Half a cup of these green immature soybeans contains a whopping 14 grams of protein!

Cheryl Forberg RD is a James Beard award-winning chef, Nutritionist for NBC's The Biggest Loser and NYT bestselling author. Her latest book is Flavor First (Rodale). She lives on a farm in Napa, California. For more nutrition and cooking tips, visit Cheryl's website