Bieber's gettin' ripped!
At a backstage gym in Greenville, NC on Dec. 16 of last year, Bieber, 17, worked with trainer Dolvett Quince -- perfecting his physique with chinups, bench-presses, stretches and much more.
Turns out that when fans aren't watching, the "Baby" singer doesn't mind showing off.
The star "loves to run around with his shirt off all the time," Never Say Never director Jon Chu says in Us Weekly's Justin Bieber: My Private World.
He even showed his stomach to Rihanna earlier this year. "Justin Bieber just flashed me his abs," the "Only Girl" chanteuse Tweeted during a private dinner. "Wow! He actually had a li'l six pack!"
Another thing that helps him stay lean: Although Bieber occasionally indulges in junk food like Doritos and Fruit Roll-Ups, "He's pretty good about his diet," his voice coach Jan Smith tells Us "He eats healthy."