Make the Most of the Weight Machines at Your Gym

Targets: Butt, quads, and hamstrings

Why it's key: The leg press involves more muscle fibers than the other leg-isolating machines -- the seated leg extension machine (on which you extend your legs until they are parallel to the floor) and the donkey-kick-like machine dubbed the butt blaster. It also requires a powerful multijoint movement that carries over into everyday activities, like climbing stairs and riding a bike, Porcari says.

How to use it: "To target your butt, position your feet higher on the plate and adjust the seat so that you can bring your knees very close to your chest," Schoenfeld says. To target your quads, put your feet lower on the plate. And avoid rising onto your tiptoes unless you want to tone your calves at the expense of eking out more reps: "You'll end up fatiguing your calves, reducing results to the target muscles," Schoenfeld says.