This is another of Chao’s favorites for building the gluteus medius, a butt muscle that rarely gets love but is crucial for building strong running mechanics, since it stabilizes the pelvis. Start with your feet shoulder-width apart. Wrap a band around your ankles and sit back into a slight squat. Keeping your core tight, step left with your left leg. Then follow with your right leg, but try to avoid bringing your feet together—you want to keep some tension on the band. Continue walking left, one foot at a time. Go 20 feet, then return the other direction.