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 in a push-up position with one knee pulled up towards your chest. Step 2 Alternate between legs and quickly pull your knees to your chest. Step 3 make sure to keep your butt down and your core engaged.