For training in a new way, the CoreAlign can be retrofitted with the challenge of instability through the Rotator Discs. The durable Rotator Discs are great for improving balance, alignment, core strength, joint stability and more. The discs are fitted with plugs that are inserted into the base of the CoreAlign carts to ensure the disc is held in place. Why choose rotator discs with resistance? Strengthen the end range of motion to improve joint support and stability. Light resistance is perfect for the upper body, heavy resistance for the lower body. Why choose rotator discs with resistance? Strengthen the end range of motion to improve joint support and stability. Light resistance is perfect for the upper body, heavy resistance for the lower body.