At the gym, I see a lot of people working hard to tone up, trim down and get stronger. But I also see folks making exercise choices under false assumptions -- some based on outdated advice, some because they're following the lead of other members, and some just because they don't know any better. In fact, you may be surprised at the muscles you’re actually working during your favorite exercises.

Here, some of the most commonly misunderstood moves -- and while they’re still safe and effective ways to tone up, they may not exactly be doing what you think they are:

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