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 on top of the Bosu with your lower back placed slightly forward on the Bosu. Make sure that your tailbone keeps contact with the Bosu. Step 2 Crunch up into half seated position breathing out and fully contracting your abs at the top of the motion. Step 3 Exhale as you open your abs back up onto the Bosu and repeat.