Mario Lopez – Shirtless Celebrity Studs

Mario Lopez went from being hunk A.C. Slater on 'Saved by the Bell' to the hunk who hosts the 'X Factor' and 'Extra.'

When the occasion calls for it, he also takes off all his clothes to decorate Christmas trees. And whenever he loses a bet.

If you want to look like him, you're in luck -- his own series of fitness videos is on YouTube. They use circuit training to give you six-pack abs. In theory, anyway.

He trains a whopping six days a week, and here's his tip for wannabee fit-dudes: "Find something you love to do and fight to improve each day. If you love to play at it, you'll work hard at it."