Debunked: Sitting on a yoga ball is no better than sitting in a chair

"To be quite frank, I cannot see any advantage or reason for a person to be using an exercise ball as an office chair," says Jack P. Callaghan, who holds the Canada Research Chair in Spine Biomechanics and Injury Prevention at the University of Waterloo in Ontario.

http://www.poormojo.org/pmjadaily/archives/039740.php