Does sitting on a stability ball increase fall risk during ergonomic reaching tasks?

Although sitting on a stability ball has become an alternative to using an office chair, little is known about the increased potential for a fall on the deformable seat. This study examined differences in stability between sitting on a seat pan of a backless office chair and a stability ball during reaching tasks. Sixteen participants performed forward and lateral reaching tasks on a backless and armless office chair and stability ball while whole-body motion and force data under the seat were recorded. Even with participants placing their feet 16.5 cm wider when seated on the ball, the perceived fall risk was significantly greater. Centre of pressure displacement tended to be smaller under the ball for lateral reach directions, but larger during far anterior reaches. While not statistically significant, the medial-lateral margin of stability was on average 3.4 cm smaller on the ball. Despite attempts to increase stability by widening their stance, stability ball fall risk remained higher.