MUSCLES ENGAGED Abdominals The abdominal muscles (abs) provide movement and support to your core area. The deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will have, and this often contributes significantly to a healthy back. Exercise Instructions Step 1 Start on your back with your shoulders raised off the floor and both legs up at 90 degrees. Step 2 While keeping your core engaged slowly exhale as you lower one leg down to the floor without touching your heel at the bottom. Step 3 Raise your leg back up to the starting position while maintaining control through the entire range of motion.