Back on the big screen again this summer, Cameron Diaz holds her own as an action star alongside Tom Cruise in the movie Knight and Day. How does the actress stay trim and agile? Diaz claims it's as simple as "just exercise a healthy diet, lots of water, lots of laughter, (and) lots of sex," she tells Life & Style magazine. Also helping her is a combination of plank exercises that work the abs, back, and legs as well as squats with shoulder presses. Get Cameron's workout on her trainer Teddy Bass' Web site and you'll be in butt-kicking shape in no time.