A 2006 study by a different group of researchers from the same university was even more damning. That group had volunteers sit for 30 minutes each on an exercise ball and a wooden stool.

The trouble is, the ball only works if you sit up straight—which most people don't. Dr. Nick Shamie, an associate professor of spine surgery at the University of California, Los Angeles ...

Whether students or adults are sitting on traditional chairs or using core strength to balance on exercise balls, she said, everyone needs to stand and move around after 20 to 30 minutes of sitting.

THE BOTTOM LINE Sitting on an exercise ball burns more energy than sitting on an office chair, but the evidence that it improves posture is lacking. scitimes@nytimes.com ...

After a couple more days of this, you may find yourself sitting on the exercise ball chair for much longer periods of time. (A week later, I spend the majority of my day on the exercise ball chair ...

“For one, people tend to slouch and use poor posture, and sitting in a chair puts your abs on ‘slack’ and decreases core strength. Using an exercise ball counteracts both of these things.” ...

Most people with rheumatoid arthritis need to improve stability, balance, and core strength. An exercise ball can help you work on all three aspects. Learn how to get started.