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 in a plank position on top of the Bosu making sure that shoulders line up over top of your elbows, your hips are tucked and your back flat. Step 2 Keeping your core engaged and your back flat, softly open up both legs to slightly wider than shoulder width and back. Step 3 Complete the recommended number of repetitions and repeat if necessary.