Woman jogging

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Your Growling Stomach Is Interrupting Your A.M. Jog
If you're going to get your heart pumping for at least 30 minutes in the morning, have a snack first, says Christine Rosenbloom, PhD, the sports dietician for Georgia State University athletics. You've been fasting all night, so you need some carbohydrates to top off your depleted glycogen stores. The ideal snack will be low in fat and protein, which take longer to digest, and have about 30 grams of carbohydrates. Rosenbloom recommends a tube of energy gel, a packet of instant oatmeal made with water, one cup of dry cereal or a plain mini-bagel. Wash your choice down with a four-ounce glass of water. She says your body will be able to convert these carbs into energy if you eat 15 to 30 minutes before your workout.

Read more: The best things to eat before working out
Women chat between exercise

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You're Over-Resting Between Sets
This is one of the most common mistakes fitness guru Bob Greene sees at his boot camps and the gym. To increase strength, you need to do your second and third sets of eight to ten reps with slightly fatigued muscles. If you have enough time to vent to your workout partner, then your muscles have enough time to recover. Instead of taking a break, Bob suggests, take a brief "pause" that lasts for just 15 to 30 seconds. "Any more than that and you'll lose the benefit you gained from the previous set," he says.

Read more: More workout mistakes
Bikram yoga

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You've Devoted Yourself Exclusively to Bikram Yoga
Bikram alone can't provide the perfect workout—and neither can running, cycling, swimming or any other activity you do exclusively. In his book 20 Years Younger, Bob Greene found that the people in the absolute best shape were those who switched between three to five different exercises each week. That's the optimum way to work as many muscles as possible and avoid injuries from overuse, he says.

Read more: Bob Greene reveals the other ways you may be sabotaging your workouts
Woman doing crunches

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Your Core Moves Are Flawed
Reality-TV shows like MTV's Jersey Shore show how crunches can ripple the abs, but it wasn't until the last decade or so that we've fully understood what these intense sit-ups do to our spines. "They're really hard on the discs," says Dr. Michael R. Bracko, an exercise physiologist and certified strength and conditioning specialist in Alberta, Canada. "Imagine that the discs are like jelly doughnuts stacked in between each vertebra," he says. "If you repeatedly flex the spine by doing crunches, it could cause the disks to rupture." (That's a situation we'd like to avoid.) The best way to work the core is to keep the spine in a neutral position, Bracko says. He recommends planks, which work the rectus abdominis as well as the obliques.

Read more: Exercises you think you need—but don't
Woman watching tv on treadmill

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You're More Focused on Friday Night Lights Reruns Than on Running
Watching Coach Taylor try to inspire the Panthers can make your treadmill miles fly by, but that's just the problem: When you get too caught up in a TV show or magazine, you stop focusing on pushing yourself. This doesn't mean you need to sweat in bored silence. "Using music is the most efficient way to keep up intensity, especially if you can program your own," says Michael Olajide Jr., fitness expert and cofounder of Aerospace High Performance Center in New York City. A fast beat can motivate us to sweat off a few more calories. So leave the book at home, turn off the TV (or, if you don't want everyone in the gym to hate you, choose a cardio machine that's not in front of the screen) and crank up your favorite mix.

Read more: 4 workout mistakes and how to fix them
Bob Harper

You're Working Your Arm Joints, Not Your Arm Muscles
When you lock your arms during push-ups, you not only put unnecessary stress on your elbow and shoulder joints, but you also take some of the load off your muscles, giving them a chance to rest. In this video, celebrity trainer Joel Harper shows you how to do a proper push-up that will keep your biceps, triceps and chest muscles pumping and burning (that's a good thing, trust us).

Video: Fixes for 8 common exercise mistakes
Woman balancing on a bosu

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You Lift Weights So Quickly That You Lose Count of Your Reps
Speeding through your sets could be a sign you're depending on momentum, doing the exercise incorrectly or using too much or too little weight. With any strength move, go at a slow, controlled pace: two seconds up, two seconds down. "There should be no point at which you pick up speed," says California trainer Jay Blahnik, the author of Full-Body Flexibility. He recommends this slow-down trick: While doing lunges, place your front foot on a Bosu Balance Trainer. The instability forces most people to focus more intently to avoid slipping.

Read more: Rework your workout