Jennifer Lopez is more than just a beautiful face -- she's got killer legs too! The actress, singer, designer, and mom has trusted one man for more than a decade to keep her gams (and that bodacious bum) in shape: Gunnar Peterson. The A-list trainer tells Shape magazine, "If you want to enhance the shape of your butt, as well as tone and tighten, the most important exercises are squats and lunges," Peterson says. "Be sure to use weights, weights, weights, and weights… and then some weights!" In addition to the traditional squats and lunges, make sure to twist and turn as you do them to workout the side muscles and enhance the lower body. While you may not become a chart-topping pop singer, these exercises will surely get your curves under control a la J.Lo.