Sportswoman doing plank exercises with assistance of her personal trainer.
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Are you undermining your workout? Fitness experts weigh in on common exercise infractions—and how to correct them easily.

1. You Need to Switch Up Your Workouts

“After doing the same cardio or strength routine three to six times, your body adapts and you burn fewer calories,” says Michael Sokol, the owner of One-on-One Fitness Personal Training Services, in Chicago and Scottsdale, Arizona. Eventually your results—weight loss, muscle definition—will slow down. Also, repeatedly placing stress on the same muscles and joints could lead to an overuse injury.

Action plan: Once a month, change one thing about your cardio and weight-training regimens: Take a Zumba class in lieu of your Saturday walk, for instance, or use a resistance band instead of dumbbells. Bonus: Mixing things up may help you stick with exercise. A 2001 study conducted at the University of Florida, in Gainesville, found that people who varied their routines enjoyed their workouts more—and exercised more regularly—than did people who went with the same thing every day.

2. Cardio Isn’t the Magic Bullet for Weight Loss

While biking, running, and walking are great for your heart, “research suggests that it’s difficult to lose fat when you do only cardiovascular activity,” says Jeff Halevy, a celebrity trainer and the CEO of Halevy Life, a health and fitness service company in New York City. Although aerobic exercise will burn calories, it doesn’t really change your metabolism. What does: lean muscle mass. “Muscle helps you burn more calories even after your workout is over,” says Halevy. The more lean muscle mass you have, the higher your resting metabolic rate (the baseline amount of calories you burn in a day), says Wayne Westcott, Ph.D., the director of fitness research at Quincy College, in Quincy, Massachusetts. Women tend to lose five to seven pounds of muscle in each decade of adulthood—one reason why the pounds creep on as we get older. Westcott’s research has found that if you do strength training three times a week, you can add an average of three pounds of muscle in about three months, increasing your metabolism by 6 to 7 percent.

Action plan: Keep doing cardio three times a week, but add two or three strength-training workouts. Aim to work all the major muscles over the week; complete one to two sets of 8 to 12 repetitions of each exercise. To get started, check out the website of the American Council on Exercise for an extensive library of weight-training moves.

3. Wimpy Weights Will Get You Nowhere

According to the “overload principle,” for muscles to become stronger, they have to be challenged with a load that’s heavier than what they’re used to. (Think about the weight of your handbag—dinky three-pound dumbbells just don’t compare.) Without challenging your muscles, “you can’t substantially strengthen or tone them,” says Halevy.

Action plan: Choose a weight that you can lift for only 10 to 15 repetitions before losing good form—trainers call this “working to failure.” (That doesn’t mean your arms should feel like noodles when you’re done, or that you can’t bang out a second set after a minute or two of rest.) Don’t worry: You won’t bulk up. “Women’s bodies have a biological limit on how much muscle mass they can build,” says Halevy. “It’s hard for women to get big without using steroids.”

4. Muscles Come in Pairs; Train Them that Way

Most of us focus on what trainers call the mirror muscles—the ones you see when you look in the mirror (biceps, quadriceps). But just as every action has an equal and opposite reaction, every muscle has a mate that works in the opposite way. For example, you use your triceps to extend your arm and your biceps to bend it. To avoid imbalances that can lead to injury, it’s essential to train both equally.

Action plan: Consider doing weight training in what’s known as a split. Work, say, your biceps and hamstrings one day, then your triceps and quadriceps the next. This way, you’ll hit every muscle pair over the course of a week. One exception: the back muscles. “Many women have weak back muscles from working at a computer all day,” says Carly Pizzani, a New York City–based personal trainer. If you’re deskbound from nine to five, follow a two-to-one ratio when working your back and chest. That is, for every exercise you do for the chest, do two for the back.

5. Crunches Aren’t Crucial for Strong Abdominals

“They’re not the best exercise choice, because they strengthen only a few of the muscles in your core,” says Pizzani. What’s more, if your abs are weak, doing crunches could cause a strain on your neck, since you’ll probably be pulling on it in an effort to lift your torso.

Action plan: Although you don’t have to eliminate crunches from your repertoire, you’ll get more bang for your buck with moves that work the entire core area. The plank is a good one: Lie facedown on the floor with palms down and forearms under your shoulders. Tuck your toes under and tighten your abs to lift your torso. Keep your body in one line from head to feet. Hold for 30 seconds.

6. A Workout Doesn’t Merit a Post-Gym Pig-Out

When you’re feeling virtuous after you’ve exercised, it’s easy to eat back all the calories you just burned (and then some). If you’re looking to lose weight, that won’t help you toward your goal, says Molly Morgan, a registered dietitian and a board-certified sports nutritionist in Vestal, New York. (It’s not OK to collapse on the couch afterward, either: In a 2009 study published in Medicine & Science in Sports & Exercise, long periods of sitting were associated with an increased risk of death, even for exercisers.)

Action plan: To stave off grazing after exercising, have a healthy snack an hour or two after your workout. And stay mobile as much as possible. Take the stairs, do a loop around the office, or pace while you’re on a conference call.

7. Bad Form Is Bad News When You’re Strength-Training

“When I see someone lifting weights with improper form, I get concerned,” says Sokol. “Not only can it diminish results but it can also lead to injury.”

Action plan: Even if you’ve been weight-training for a while, it’s a good idea to brush up on form. You can find videos that illustrate good lifting form on Or, even better, invest in a session with a personal trainer. A few general tips: Count “one one-thousand, two one-thousand” as you lift the weight, says Sokol, and “one one-thousand, two one-thousand” as you lower it. “If you lift too fast, you let momentum, not your muscles, do the work,” he says. When doing upper-body exercises, keep your wrists straight; when doing squats and lunges, align your knees and ankles; and when bending over for an exercise (like a dumbbell row), keep your back flat. Always keep your neck aligned with the rest of your body.

8. Working Out on an Empty Stomach Won’t Burn More Fat

A common belief is that if you exercise before you eat, your body will turn to its fat reserves for energy instead of the food in your stomach. In fact, it’s just the opposite: In a 2011 study published in the International Journal of Sport Nutrition and Exercise Metabolism, people experienced a bigger boost in metabolism—meaning, burned more fat—when they exercised after eating breakfast than when they did the same workout on an empty stomach. The authors of the study theorize that when you eat before exercising, your body uses more oxygen, resulting in a metabolism spike and an improvement in fat burning.

Action plan: Eat already! Even a small snack with carbohydrates, protein, and a little fat, eaten a half hour before, will power your workout, says Morgan. Good choices: low-fat yogurt and a banana, whole-grain cereal and low-fat milk, or oatmeal and fruit. Or make it really easy and choose a fruit-and-nut bar, such as a Lärabar ($28 for 16,

9. A Death Grip on the Cardio Machine Strains Your Body and Burns Fewer Calories

When you hold the treadmill or stair-climber handles so tightly that your knuckles turn white (because you can’t keep up with the speed, perhaps), your body is forced into an uncomfortable position, which can put strain on your muscles. And “because your legs don’t have to work as hard when you lean on the machine, the number of calories you burn plummets,” says Deborah McConnell Plitt, a trainer for the Life Fitness Academy, in Myrtle Beach, South Carolina.

Action plan: Maintain proper form. On the treadmill, you should be able to stand tall and pump your arms. On the stair-climber, keep your body centered over the pedals, with your head up and shoulders relaxed. It’s OK to hold the handrails lightly, as long as your posture is correct.

10. The Fat-Burning Zone Isn’t Really a Fat-Burning Zone

If you’ve ever played around with the controls on a cardio machine, you may have experienced the “fat burning” program, in which you exercise at a low, steady intensity. The idea is that low intensity is better for weight loss than more vigorous effort, because you can sustain it longer. But studies show that even in a shorter workout, boosting your intensity can burn as many, if not more, calories than long, steady-state cardio. And “when it comes to losing or maintaining weight, it’s the total number of calories that counts,” says Halevy. Plus, by working harder, you can get out of the gym faster.

Action plan: Slow, steady workouts are a good place to begin if you’re just starting a cardio routine. But as you get more fit, bump up the intensity. Try interval training once or twice a week on nonconsecutive days: Work at a high intensity for a short spurt (say, 30 seconds), lower the intensity to recover (for 90 seconds), and repeat for 20 to 30 minutes.