Shoulder Bridge One Leg Circle is a variation of the original Pilates exercise Shoulder Bridge. Circling the extended leg challenges the core as deep muscles of the spine stabilize against the circular movement of the leg. YouâÂÂll also tone the gluteal muscles and flatten the abdominals while you strengthen your core. If you are having trouble keeping the pelvis still, spread your arms wider on the mat to create a larger base of support, find the place where you can stabilize, and then challenge yourself by bringing the arms closer to your sides. Please visit www.PilatesOnFifth.com (for more info), www.UltimatePilatesWorkouts.com (for more videos) and www.Shop.PilatesOnFifth.com (for store).