Stop sabotaging your workout with these surprisingly common mistakes and you'll see the pounds disappear in no time.

By Kelly James-Enger

Common Slip-ups

Wondering why after all those hours you've spent sweating on the treadmill, the scale still hasn't budged? Unfortunately, small fitness mistakes can make getting and staying in shape much more difficult. Here are some common slipups that even the most seasoned exercisers are guilty of. Try the following quick fixes and, rest assured, you'll completely transform your fitness routine. Soon you'll be gazing at a trimmer image in your full-length mirror.

Zoning Out Instead of Honing In

So you climb on the exercise bike and lose yourself in a magazine? You may battle boredom, but you won't burn as many calories or challenge your muscles as much as when you focus your mind solely on exercising, says Michael Meyers, PhD, director of the human performance research laboratory at West Texas A&M University in Canyon, Texas.

The Right Way

  • To set the seat height, put your heel on the pedal. When your foot is at the lowest point, your leg should be almost, but not completely, straight.
  • Your upper body should be relaxed, with your elbows just slightly bent. Your arms should in no way interfere with the motion of your knees.
  • Place your hands lightly on top of the handlebars instead of gripping them tightly.

The Wrong Way

  • Flipping through a book or magazine while pedaling.
  • Positioning the seat too low so that your legs are cramped, or setting it so high that you have to pedal on your tiptoes.
  • Crouching over the handlebars like Lance Armstrong.

Using Your Hands, Not Your Feet

Climb on the StairMaster or treadmill and you'll burn calories — but only if you use the machine the right way. Focus on moving your legs, and leave your arms out of the picture as much as possible.

The Right Way

  • Hold the bars lightly or just touch them briefly when you need to balance.
  • Face straight ahead, shoulders back and abs tight.
  • On the StairMaster, keep your entire foot flat on the pedal as much as possible.

The Wrong Way

  • Leaning on the side rails and supporting your body weight with your hands.
  • Going so fast you have to hold on to keep up.
  • Standing on your toes, which can aggravate your Achilles tendon.

Letting Gravity Do the Work

"Yanking"and "dropping" are terms that shouldn't be used when working with weights. To get the most out of strength-training and stretching, movements should be smooth and controlled.

The Right Way

  • Maintain an upright posture with head up, shoulders back, ab muscles engaged, and feet shoulder-width apart.
  • Raise and lower the weights slowly and smoothly, pausing slightly after each repetition.
  • Keep your palms facing up. Don't rotate your wrists as you lift or lower the weights.

The Wrong Way

  • Leaning back as you yank up the weights when performing biceps curls with handheld weights.
  • Using momentum to raise and lower the weights.
  • Letting your elbows drift away from the sides of your body.

Rushing to Finish

If you hurry to get through your workout, you're not doing your body any favors. Many people rush through things they don't like, such as crunches.

The Right Way

  • Lift and lower your head and chest together in a slow and controlled movement.
  • Keep your fingers lightly on the sides of your head, with your elbows directly out to the sides, or cross your arms over your chest.
  • Keep your feet flat on the ground the whole time, with your knees slightly bent.

The Wrong Way

  • Lacing your fingers behind your head and pulling your neck forward with your hands.
  • Going too fast.
  • Not bending your knees (which helps support your back).

Guessing at Technique

At the gym, do you jump on the leg-extension machine (or any weight machine) as soon as the woman ahead of you climbs off? Your intentions may be good, but using the wrong settings increases your risk of injury and compromises your workout. Take the time to set the equipment properly; if you don't know how to use it, ask a gym employee or a personal trainer for advice.

The Right Way

  • Keep the axis of rotation through the knee joint. Machines often have a dot indicating where to line up your knee.
  • Press your back against the back pad throughout the entire exercise.
  • Don't look down. Instead, keep your shoulders back and head facing forward.

The Wrong Way

  • On the leg-extension machine, keeping your seat pulled too far forward or pushed too far back.
  • Going at a rapid pace and not controlling movement.
  • Grasping the hand grips and using your upper body to help lift and lower the weight.

Other Common Pitfalls

Pitfall #1: You Consume More Calories Than You Burn.

Your regular workout probably burns far fewer calories than you might think. Chances are, it doesn't give you license to treat yourself to a postworkout doughnut. The metabolism-boosting benefits of exercise have been exaggerated, says Meyers. Don't expect to burn off more than about 300 calories in even an intense 45-minute workout. If you're exercising to lose weight, you have to use more calories than you take in to see a difference on the scale.

Pitfall #2: You Never Pick Up the Weights.

Strength-training won't "pump you up." One study found that women who lifted weights for 24 weeks increased their muscle size by only 3 to 11 percent while they boosted their strength by 12 to 24 percent. "Getting big, bulky muscles is impossible for women, as they don't have enough of the male hormone testosterone," says study author William Kraemer, PhD, professor of kinesiology at the University of Connecticut in Storrs. "Women who lift heavy weights actually gain lean tissue mass and lose fat mass, leading to leaner and smaller dimensions."

Pitfall #3: You Don't Have a Fitness Plan.

It's not enough to simply show up at the gym. A study conducted at the YMCA in Atlanta found that exercisers who didn't set goals were more than twice as likely to quit their programs as those who did. "You wouldn't go on a long road trip without a map," says certified personal trainer Lori Incledon, author of Strength Training for Women (Human Kinetics). "Your workout program is exactly the same."

In other words, don't just say, "I'll exercise more." Instead, commit to swimming with a friend before work Monday, Wednesday, and Friday, or to a postdinner walk every night. Specific goals will help guide you to your fitness destination.

Pitfall #4: You've Allowed Your Routine to Become Routine.

You've overcome the biggest hurdle: committing to a regular workout routine. Unfortunately, doing the same thing workout after workout not only leads to boredom, but repetitive activities like jogging, biking, and even walking can cause injury. A recent study conducted at the University of Virginia found that about half of all sports injuries are due to overuse of certain muscles.

Bust out of your rut by switching between aerobic activities that use different muscle groups — mix walking with swimming or biking with rowing. When you strength-train, try different moves (like push-ups instead of chest presses) every six weeks to continually challenge yourself.