While on the 3ft one a nice thing to try is, lay on the top of it a lift your arms and feet of the floor and stomach on the Ball and Balance while slightly Rocking side to side. Its a good little Corr number, you can spread the Arms and Legs to balance good for the Psossa and upper Abs and does wonders for the Hamstrings . make sure you stretch them after. Theres one thats even better with 4 balls but it takes a lot of Corr strength to even try it its one of them