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 by lying on your back with your arms and legs fully extended. Step 2 Pull your shoulder and legs off the floor by fully contracting your abs. Make sure your lower back stays pressed to the floor. Step 3 Relax and lower your body back to the starting position and repeat the action.