How does the Swiss ball work?This great Swiss Ball is awesome to use in the Gymnic Home , Office or you can even use to watch TV. The Swiss ball is Anti Burst simply place on the floor, sit on the ball and you begin exercising. The slightly unstable base improves your posture, prevents slouching and stops prolonged stress on the structures of the lower back. Birthing balls are recommended use during pregnancy to help make the process of giving birth much easier for the expectant mother. The ball is burst resistant quality. Receive ball with pump & Instruction guide. Best Size for You55cm (22") diameter Swiss Ball for people 155-167.5cm (5' 2" - 5' 6") tall.65cm (26") diameter Swiss Ball for people 167.5-175cm (5' 6" - 5' 9") tall.75cm (30") diameter Swiss Ball for people 175-192cm (5' 9" - 6' 4") tall.