Step 1: Lie face-up. Bring both knees to your chest and curl your head and shoulders off the floor. Step 2: Clasp your hands over your left knee and extend the right leg; don’t let it touch the floor, as you turn toward your bent knee. Switch sides: Bring your right knee in and extend your left leg. Runner’s Secret Weapon: Turning your sternum toward the bent knee mimics how your body turns toward your forward leg when you run.