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. Equipment Used Bosu The BOSU balance trainer stands for "Both Sides Utilized" and is most often used for balance training, various athletic drills and aerobic activities. Exercise Instructions Step 1 Lengthen your body across the Bosu with the small of your back placed on the center. Step 2 Crunch-up and and raise your leg at the same time. Fully contract your abs at the top of the motion. Step 3 Open yourself back up, stretch out your abdominal wall and repeat.