She wore an itsy-bitsy hot-pink bikini…

Last Thursday, Jennifer Aniston shot another scene for Just Go with It on the Hawaiian island of Kauai — wearing close to nothing.

Shooting near a tropical waterfall, the 41-year-old actress wore a barely-there, hot-pink bikini. The tan star’s super-sleek physique is no accident. “She’s obsessed with staying fit and young,” a source says in the latest Us Weekly.

And Aniston has another incentive to look good on the Just Go With It set: 23-year-old costar and Sports Illustrated cover girl Brooklyn Decker. “Jen’s intimidated,” the source says of Decker. “She’s very conscious of her body.”

To keep in fighting form, the 5-foot-6 actress spends at least an hour (sometimes more) daily at the gym at the Four Seasons in Maui — sweating it out on the treadmill and elliptical.

“I saw her on the treadmill, and it was angled all the way up,” one Four Seasons guest recalls. “I couldn’t do that for one minute!”

source: US Magazine