CanDo Donut Exercise, Workout, Core Training, Swiss Stability Ball for Yoga, Pilates and Balance Training in Gym, Office… $13.00 – $28.06 Make sure this fits by entering your model number. IMPROVE BALANCE AND STRENGTH: Can Do Inflatable Donut Balls improve core strength, balance, coordination, and flexibility. USE BY ANYONE ANYWHERE: Flat side provides stability while sitting on the exercise ball, but while exercising it adds instability to engage stabilizing muscles to increase fitness effectiveness.