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 legs extended and your arms up over your head. Have your legs together and your toes pointed. Step 2 Pull your shoulder and legs off the floor by fully contracting your abs and shortening the distance between your sternum and crotch. Step 3 Lower yourself back down to the floor by relaxing your abs.