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, flex your abs and form a hollow position. Step 2 Without breaking the hollow, rock back and forth. Step 3 Complete the recommended number of reps or until you can no longer maintain the hollow position.