GymGym balls are a great way to keep your back in action, or to get fit. Used in sports, recreation, in classrooms and offices, they are a great tool for exercise and active sitting. If you're thinking of using a gym ball as a chair, take a look at our Sitness Ball Chairs
Gymnic Gym Ball
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While sitting on the ball, the knees should be lower than the pelvis; i.e. the angle between thighs and the upper body should be greater than 90 degrees. For approximate sizes, see table and sketch below.