Port de Bras 2 on the BoSU is a variation of the Classical Pilates Arc Barrel exercise of the same name. This version adds arm circles when moving through flexion and etension to increase the challenge and increase the stretch. YouâÂÂll strengthen your abdominal muscles, increase spinal flexibility and open the front of the shoulders. Please visit www.PilatesOnFifth.com (for more info), www.UltimatePilatesWorkouts.com (for more videos) and www.Shop.PilatesOnFifth.com (for store).