"Holding this position strengthens your core, quadriceps, and glutes, which in turn helps prevent pain in your low back, knees, and hips," says Vonda Wright, MD, an orthopedic surgeon and author of Fitness After 40. Stand with your back against the wall, feet shoulder-width apart, and squat down until your knees are at about 60 degrees; hold for 30 seconds—about the length of one commercial.