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 raised and your ankles crossed. Step 2 With your hands placed by your side, crunch up and contract your abs. As you crunch, breath out and press your lower back against the floor. Step 3 Lower your shoulder blades back down to the mat and repeat.