Lift weights three times a week. It's the fastest way to build muscle and get results when the scale is stuck. "Research shows that regular strength-training can increase your resting metabolic rate by up to 8%," says Wayne Westcott, PhD, fitness researcher in Quincy, MA, and author of Get Stronger, Feel Younger. In one 8-week study, women and men who did only cardio exercise lost 4 pounds but gained no muscle, while those who did half the amount of cardio and an equal amount of strength-training shed 10 pounds of fat and added 2 pounds of muscle.
Rest less: If you already strength-train, shorten the time you linger between sets. "Taking a brief, 20-second break after each set burns extra calories and accelerates metabolism more than waiting the standard 60 to 90 seconds, studies show," says Westcott.
Do double-duty moves: Trade exercises that isolate a single muscle, such as biceps curls, for multi-joint, multi-muscle moves like chest presses and squats. "The more muscles you engage at once, the more calories you'll burn," he says.
It's a common scenario: The first 10 or 20 pounds come off easily, but then the scale won't budge. Plateaus can happen in as little as 3 weeks, find Drexel University researchers. As you drop weight, your body doesn't have to work as hard simply because there's less of you to move around, says Michele Kettles, MD, medical director of the Cooper Clinic in Dallas. That means your workouts produce a smaller calorie burn. For example, if you weigh 180 pounds and lose 35, you'll melt about 100 fewer calories in an hour-long cardio class—which can slow down further weight loss. And as you get older, injuries or arthritis can make it difficult to do vigorous, high-impact activities that help compensate for this calorie deficit.
Diversify: The more comfortable you become with a routine, exercise class, or fitness DVD, the less effective it gets. To continue to lose weight, you need to challenge your body in new ways. "Even replacing one exercise can create enough of a surprise to keep results coming," says Kettles. Try this: The first week of every month, do a new upper-body exercise; the second week, a new lower-body one; the third, a new abs move; and the fourth, a different type of cardio (cycling instead of walking, for example).
It may happen subconsciously, but studies show that some people move less after they begin an exercise regimen. The reason for the slowdown, experts speculate, may be post workout fatigue or the perception that if you exercise, you can afford to skimp on the small stuff. Wrong! Little activities such as standing instead of sitting, and walking more throughout the day can add up to an extra 350 calories burned per day, according to Mayo Clinic studies.
Track non-exercise activity: Record your daily step counts a couple of days when you don't work out. Then calculate your average (add up your daily totals and divide by the number of days tracked). If you don't maintain at least this level of activity every day, your fat-burning ability will decline. For instance, if you normally log 5,000 steps a day but skip half of them on days you work out, it could slow weight loss by up to 50%—even though you're exercising.
Post reminders: One study showed that signs encouraging people to take the stairs increased usage by 200%. To motivate yourself, stick notes on your bathroom mirror, microwave, TV remote, steering wheel, and computer that simply say: Move more!
Set up weekly physical outings: You'll be less likely to blow it off if you make a commitment to someone else. Plan a hike or bike ride with your family, help clean out a friend's garage, or volunteer to walk your neighbor's dog.