5 Things not to let your personal trainer talk you into

If your manicurist has to have a legit license to operate, why expect anything less from your personal trainer? After all, you are placing your heart rate in their hands. Every expert offering a service-from your dentist to your realtor-has a legit license and state-regulated credentials, but that's not the case with your fitness pro at your local gym. So we asked Women's Health fitness expert Rachel Cosgrove how we can protect ourselves from shoddy body sculptors. Here's her advice:

1. Sitting at a weight machine No seated chest presses, no seated leg extensions, no seated anything! In order to burn maximum calories and injury-proof your body, you should be standing on your feet, using your core, working multiple muscles at the same time.

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2. More than 15 to 20 reps of a core exercise If you can do that many, it's time to add weight (think holding a weight plate against your chest) or switch up the exercise (say, crunches on a Swiss ball).

3. A chest day, a back day, a bicep day, or any other body-part-specific day A full-body routine that works your muscles in a variety of ways is more efficient for achieving a lean body. You are not a body builder; you are a woman who wants to be fit.

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4. Keeping your knees behind your toes during squats You don't keep your knees behind your toes when you bend down to pick up your laundry, so why force it at the gym?

When you're working out solo, it can help you main­tain your center of gravity. But with a trainer spotting you--and making sure you don't lean too far forward and put excess pressure on your knees--it's OK to go as low as possible and, as a result, let your knees jut out a bit past your tootsies

Fitness Rules You Can Break

5. More than three days of cardio a week Thirty minutes three times a week is plenty for weight loss (assuming you're following a smart eating plan) and cardiovascular health. Anything more just puts excessive stress on your delicate joints. Of course, the exception is if you're training for a race or an endurance-­focused sport.

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TELL US: What's the best fitness advice you've ever been given?

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