Primary Muscles Worked: Rectus abdominus (your six-pack), the obliques, serratus, and the tranversus abdominus. This exercise also works your chest, shoulders, back, and even your glutes.
Why I Like It: This is a great exercise to strengthen your entire core. When done correctly it's taking the benefits of the plank and magnifying them. This exercise is great for building your serratus, which runs along the sides of your abs. When developed it really frames in your six-pack and makes you look extra fit.
How to: Start in a kneeling position. As the wheel rolls forward, you want to work toward a fully extended position. The more extended you are, the more challenging the exercise. Using your abs (not your arms) bring the wheel back to the starting position. Focus on a crunching motion, or "curling" your trunk. If you keep your back straight you will work more of your arms, lats, and shoulders. If you don't have access to an ab wheel you can use a straight bar with 10-pound plates on each side.