Mega celebrities have their picks of nutritionists, chefs, assistants and personal trainers. So it says a lot that Hollywood’s elite consistently call on one trainer, Gunnar Peterson, when they want to get in shape or maintain their buff bods. In fact, Gunnar — whose client roster includes A-listers such as Jennifer Lopez, Penelope Cruz, Ben Affleck and Debra Messing — is the go-to trainer in Tinseltown. Lucky for you, we got him to offer up a few of his favorite fitness moves just for OK! readers. Grab some dumbbells and a stability ball (available at most gyms, sporting-goods stores and coresecrets.com) and get the body you’ve always wanted.