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.)

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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.

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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.

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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.

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