With you knees bent behind your body, lie sideways with one elbow ont the top of the BOSU.

Slowly raise your hips off the floor until your body, from your knees to the top of your head, is straight as a plank. Contract your abdominals to maintain the plank position. Do not let upper body sag into your shoulder. Hold the position as long as you can without sagging. Switch to the opposite side.

Repeat.