That’s right, the only way. For years, however, women were sold the same bill of goods: If you want to burn fat, be fit, and achieve body Nirvana, aerobics is the answer. And each year, millions of leotard-clad women poured into aerobic dance classes hoping to look like the babes in the health club ads, only to come out with bodies that looked startlingly similar to the ones they started with. I saw this happen time and again among women in the classes I taught, and I saw it in myself, too.  Don’t get me wrong: We were a whole lot healthier from the workouts. All that cardiovascular activity blasts stress and builds healthier hearts and lungs. And it definitely burns extra calories. But when you’re looking for total body toning, aerobics alone just doesn’t do the job. But strength training does because it doesn’t just burn calories while you are exercising, it increases your muscle mass, which helps you burn more calories all day. What’s more, strength training gives you great curves, super posture, better bones, and even provides a lot of the same benefits as aerobic exercise.  A woman I’ve trained with, marathon runner and editor Alisa Bauman, age 30, says it best: “I run, cycle, do yoga, swim, play sports, and eat well, but all the dieting and aerobic exercise in the world doesn’t give me the type of body I can get from lifting weights.”

Metabolism Magic

Strength training works because making muscles fires up your metabolism and keeps your body running at its fat-burning best. (This is why many men can toss down a bucket of wings and a pitcher of beer without a worry about weight gain–they naturally have more muscle.) Every pound of muscle on your body burns between 30 and 50 calories a day—even when you’re sleeping. Every pound of fat burns only two to five calories. Women often blame their weight problems on sluggish metabolisms when what’s really to blame is their lack of muscle. Unless you start strength training, the problem only gets worse. As we get older, we naturally lose some of our muscle mass. Starting somewhere after age 35, women start losing about a half-pound of muscle a year. By age 50, that can jump to up to a pound loss each year. That’s why women in their late 30s and 40s often complain that even though they are not eating or exercising differently, they are still gaining weight—they are literally losing metabolism-revving muscle.The good news is that you can stop early midlife fat spread in its tracks just by adding a little muscle. Researchers at Tufts University in Massachusetts found that people who strength trained for 12 weeks and increased their muscle mass by just 3 pounds could eat 15 percent more calories—that’s about 300 calories (the amount in two slices of cheese pizza!) a day for an average woman—without gaining an ounce. Even better, they also lost fat pounds in the process.  Over time, these muscle-metabolism gains can add up to major fat losses. Consider this: If you gain 3 pounds of muscle and burn 40 additional calories per pound, you’ll burn 120 additional calories per day, or 3,600 calories per month. At that rate, those 3 pounds of muscle will burn off 12 pounds over the course of a year. “When I started weight training, I saw results within 3 weeks. My pants became loose around the waist. I could see my arms toning up. I just looked better in the same clothes, even though I was technically gaining weight,” recalls editor Bridget Doherty, 29. “That never happened with any other exercise before.”

Compact Powerhouse

The easiest way to understand the dynamics of strength training is to remember these two cardinal rules. One: Muscle tissue takes up considerably less space (and is much more aesthetically pleasing) than fat tissue. Two: Muscle tissue weighs more than fat tissue. Too often, women who are having fabulous success with their fitness programs step on a scale and get discouraged because they haven’t lost as much weight as they hoped to. Their clothes fit better. They feel better. They look great. But they’re still sweating the numbers on the scale. Your better bet is to pay attention to your measurements. Is your waistline getting trimmer? Are your legs firmer? Do your clothes hang better? You can also get your body composition tested at your local health club. Or test it yourself with a home monitoring device—Tanita and Body Logic both make good home-testing models.  Body composition testing gives you a better picture of what’s actually happening as you lose body fat and gain strength, because it breaks your weight into lean tissue and fat tissue. And it’s highly motivating to see those numbers change.By monitoring your clothes, appearance, and body composition, you also can ditch any fears you might have about “bulking up.” Some women still worry that strength training will make them bigger instead of trimmer. While it may give you more noticeable muscles in certain areas, like shapely, round shoulders and beautiful, curvy biceps, it will help you tighten, tone, and get more lean overall. Plus, women simply don’t have the hormones necessary to bulk up like Sly Stallone through simple strength training. It takes hours of lifting, and usually a little outside stimulus, for females to build real bulk. In fact, exercise scientists have found that women can build lean tissue and improve their upper-body strength by 40% without seeing real changes in body size. Through moderate weight training–that’s two or three times a week—you can expect to increase your strength by 30 to 50%. Get the picture?

Play More and Better

If you play sports, strength training will make you play better. If you don’t play sports, strength training will make you want to go out and play.  When your muscles are strong, you can run faster, cycle better, throw farther, and swing a racket with more power. You’re less likely to get hurt because strong muscles support your joints while you play, helping you avoid sprains and strains. You have better balance, making you more sure on your feet. Even better, you can recover from tough exertion more quickly. “I’ve seen a remarkable improvement on the bike since I started strength training,” says Liz Reap, 31, a photographer and Fuji team-sponsored cyclist. “I have more muscle endurance and pure power. I don’t fatigue as quickly. And I recover better, so I don’t have lingering soreness for days after a tough race.” Even women who tend to shy away from sports find themselves becoming more physically active once they pick up weight training. “Because I saw such a difference in myself with strength training, I was encouraged to try more,” says Doherty. “Without planning on it, I noticed that I started to walk more and try activities that I wouldn’t have tried before. “These benefits are especially pronounced for women who are currently out of shape or overweight. The fact is, even though physical activity is what they need most, many overweight women avoid exercise like oral surgery—and not unreasonably so. Frankly, exercise can really suck when you’re out of shape. It’s no fun feeling winded and sore doing something that’s supposed to make you feel so spectacular. Weight training is less intimidating and more accessible than running or even walking when you’re out of shape or overweight. Then, once those muscles get a little stronger, walking around the block isn’t such a big deal. You start becoming more spontaneously active simply because you feel more capable and confident. “The exercises were so simple, I wasn’t sure they would make any difference when I started,” says Jodya Wasilko, 57, a client of mine who, frustrated by many years of feeling unfit, started strength training 2 years ago. “But soon, daily activities became so much easier. I was redecorating my house and moving furniture like it was nothing. I even signed up for my first charity walk. It was a great accomplishment.”

Live Longer and Happier

Maybe best of all, strength training can make you happy. For one, strength training is a great way to blow off the stress, anxiety, and tension of the day. You’ll sleep like a stone at night, as your body demands high-quality sleep to recover from your workouts. Studies show that you’ll be less likely to suffer from depression, an ailment that clouds women’s lives more often than men’s. And you’ll simply feel good about yourself. Strong, toned muscles make women ooze confidence and live comfortably in their bodies like nothing else I’ve seen. “My strength training has helped me look and feel stronger, which I equate with feeling more beautiful, capable, and confident,” says Reap, 31. “My posture has improved, my attitude about myself has improved; I feel more balanced.” Can you ask for anything more? More from Prevention: 16 Highly Effective Toning Moves

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