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 Lie on your back with both feet extended and your arms over your head. Step 2 Lift your arms, head and shoulders up off of the floor and crunch up towards a single leg. Step 3 Lower your single leg and body back down to the floor, alternate legs and repeat.