Men's Health/Peter Hapak Justin Bieber

Justin Bieber Flexes for Men’s Health

Justin Bieber stripped down to his Calvins, and now he’s showing off his tatted body for the April “Reinvention” issue of Men’s Health. The pop sensation, who turned 21 over the weekend, gives his Beliebers an eyeful in the steamy images, which were not Photoshopped.

Biebs has been spending time in the gym working on his physique (his workout plan consists of lifting weights five times a week), and is also giving his reputation a makeover.

“This has been a really big year for me, as far as figuring stuff out,” he tells the magazine. “A year from yesterday, I was in jail.”

Justin Bieber

Justin Bieber Covers Men’s Health

In the interview, he reveals that he can solve a Rubik’s Cube “in less than a minute,” loves legs on a woman (“I really like jean shorts and like a tank top. Or spandex”), and relates to Michael Jackson.

“I’m a perfectionist, too,” he says. “I’ve always been different, and I haven’t been afraid to be different.”

And don’t let his small frame fool you. He’s been beating up bullies (and paparazzi) since the sixth grade. “I was a pitbull,” says Bieber. “I was small but I could hold my own.”

The singer will poke fun at himself during Comedy Central’s “Roast of Justin Bieber,” which airs March 30.