Lie on your back with your arms at your sides; press your heels into the ball side of the BOSU, and lift your pelvis up until your knees, pelvis, and shoulders form a straight line.
Hold your bridge while you lift your right knee toward your chest, until your hip is at a 90-degree angle. Return the heel to the ball, and lift the left knee. Do not let your pelvis sag or your back overarch while lifting and lowering your knees. This completes one rep.