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 your hands to the side of your head and your feet on the floor. Step 2 Crunch up until your shoulder blades are raised off the floor. Fully contract your abs at the top. Step 3 Lower yourself back to the starting position and repeat the action.