Top 9 Fitness Myths -- Busted!

It's easy to fall into the trap: A workout buddy passes along an exercise tip, and then you pass it on to several folks you know. One day, you're at the gym, and sure enough, you hear the same tip repeated, so you figure it must be true. But experts say that in the world of fitness, myths and half-truths abound – and some of them may be keeping you from getting the workout you need.

"Some myths are just harmless half-truths, but many others can actually be harmful," says professional triathlete and personal coach Eric Harr, author of The Portable Personal Trainer. "They can cause frustration in working out and sometimes even lead to injury," he notes.

One reason myths get started, says Harr, is that we all react to exercise a little differently. So what's true for one person may not be true for another.

"In this sense you sometimes have to find your own 'exercise truths' – the things that are true for you," says Harr.

That said, experts say there are also some fitness myths that just need busting, and the sooner the better!

To help put you on the path to a healthier, safer, and more enjoyable workout, WebMD got the lowdown from several top experts on what's true and what's not when it comes to exercise tips.

Fitness Myth No. 1: Running on a treadmill puts less stress on your knees than running on asphalt or pavement.

"Running is a great workout, but it can impact the knees -- and since it's the force of your body weight on your joints that causes the stress, it's the same whether you're on a treadmill or on asphalt," says Todd Schlifstein, DO, a clinical instructor at New York University Medical Center's Rusk Institute.

The best way to reduce knee impact, says Schlifstein, is to vary your workout.

"If you mix running with other cardio activities, like an elliptical machine, or you ride a stationary bike, you will reduce impact on your knees so you'll be able to run for many more years," says Schlifstein.

Fitness Myth No. 2: Doing crunches or working on an "ab machine" will get rid of belly fat.

Don't believe everything you hear on those late-night infomercials! Harr says that while an ab-crunching device might "help strengthen the muscles around your midsection and improve your posture," being able to "see" your abdominal muscles has to do with your overall percentage of body fat.  If you don't lose the belly fat, he says, you won't see the ab muscles.

But can doing ab crunches help you to lose that belly fat? Experts say no.

"You can’t pick and choose areas where you’d like to burn fat," says Phil Tyne, director of the fitness center at the Baylor Tom Landry Health & Wellness Center in Dallas.  So crunches aren't going to target weight loss in that area.  

"In order to burn fat, you should create a workout that includes both cardiovascular and strength-training elements. This will decrease your overall body fat content," including the area around your midsection, he says.