Credit: Flynet

She's known for her killer legs and million-dollar smile, but Cameron Diaz is suddenly taking after her beefy baseball beau -- she's got amazing guns!

After working out with her man Alex Rodriguez at a Venice, Calif. gym on Thursday, Diaz, 38, showed off her super-buff, muscular arms. (Another superstar who's flaunted her own ripped biceps? Rodriguez's ex girlfriend Madonna.)

Diaz and Yankees slugger Rodriguez, 35, made a splash in front of millions of fans at the Super Bowl in Texas Feb. 6 -- when the hot and heavy couple were photographed feeding one another popcorn.

But how does the Green Hornet actress stay in such fighting shape? She hits the gym (often with pro Teddy Bass) five times a week. Her usual routine: a two-mile run, 30 minutes of Pilates and strength-training moves like squats and lunges.

As for her diet, she'll ban white carbs and alcohol if she needs to slim-down quick for a red carpet event -- but Diaz doesn't count calories, and allows herself the occasional french fry splurge.