This move works your glutes, so it's the perfect antidote to sitting on your butt from nine to five. Lie on your back with your heels on the chair, knees bent, arms at your sides. Using your glutes and without pushing up with your arms, lift your butt off the ground until your body forms a straight line. Hold, then return to start. Do three sets of 25, suggests personal trainer Amie Hoff, founder of Hoff Fitness in New York City.