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 stretched out and your hands laid out above your head. Step 2 Without using momentum, fully sit-up and reach for your toes. Step 3 Roll back down into the starting position with full control.