Travis Mayer, the silver medalist in the moguls event at the Salt Lake City Olympics, estimates that about 30 to 50 percent of his daily training is spent on balance. His favorite piece of equipment is the standard exercise ball. "Probably the most beneficial exercise is sitting on your butt with it," he says. Sit on top of the ball with your knees and waist each bent at 90 degrees and your feet touching the floor. Have a partner toss a medicine ball to you at different angles for several minutes. With your hands occupied, keeping an even keel becomes surprisingly difficult. For an advanced workout, try the drill while kneeling. "By tossing the medicine ball," Mayer says, "you're doing something that doesn't have a set pattern, which forces you to make adjustments."