Plank This straightforward but challenging movement builds core stability and strength through your shoulders, core, and hips. Lie in a pushup position with forearms resting on the floor, elbows under shoulders, and bent 90 degrees. Push up off the elbows, tucking your chin so your head is in line with your body. Keep head inline with spine and belly button drawn in. Hold for 20 seconds, rest for a minute, and repeat.