There is little fact-based evidence on the positives and negatives specific to exercise balls for chairs. But the most important thing to remember while sitting is to maintain the ideal position. If you are sitting on an exercise ball your back remains unsupported for an extended period of time. This requires muscle endurance to maintain the correct body posture. When your postural muscles begin to fatigue, you will begin to slouch; similar to sitting poorly in a regular chair. Sitting on an exercise ball requires your arms to remain unsupported while you type or use a computer mouse. This unsupported arm position at a computer workstation for an extended period requires muscle endurance in the upper back. When the upper back muscles begin to fatigue, you compensate by assuming a position with either an increased arch or flexed position in the low back, which can lead to back pain.