MUSCLES ENGAGED Chest Strengthening the chest muscles will help you push things easily and effortlessly. The muscles in your chest help stabilize your shoulder joint, which reduces your vulnerability shoulder joint injuries. Working your chest muscles also has an aesthetic factor (body contouring). 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 Stability Ball A stability or exercise ball is a ball constructed of soft elastic and filled with air until firm.Most stability balls range from a diameter of approximately 35 to 85 centimeters (14 to 34 inches). 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 in a push-up position on the underside of the Bosu with both legs on top of a stability ball. Step 2 Making sure your core is engaged, first perform a push-up on the Bosu followed by a double knee tuck. Step 3 Return both legs back to the starting position, re-stabilize our body and repeat.