Chest. Shoulders. Arms. Abs. Guys tend to focus on all of those "mirror muscles" when training. Today, we're going to focus on the muscles you can't see in the mirror. Then, we'll learn how to train and get the benefits that come with these important but oft-neglected muscles.

1. Posterior deltoid -Often called the rear delt, this muscle is responsible for moving your arm back and moving it away from the center of your body. Shoulder instability and injuries are often the result of a weakness in the posterior deltoid.

A traditional McDonald's burger with a 16-ounce coke and a small order of fries carries 627 calories and 19 grams of fat.

Upgrade to a Big Xtra! with cheese, and "super size" the drink and fries. Now your lunch packs a whopping 1,805 calories and 84 grams of fat.

Q:Is there a single muscle group that can be considered "king"?

A:This one's up for grabs, but in my estimation there's no question--it's your wheels, better known as your legs.