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 Start with the small of your back on top of the center of the Bosu. Place one leg on the floor, the other extended out in front of your body and both hands placed to each side of your head. Step 2 Crunch up towards your knees, pull your leg in to your chest and fully contract your abs Step 3 Roll back on the Bosu and extend you leg back out to the starting position and repeat.