They look like fun… those big, brightly colored exercise balls that can improve stability and flexibility and strengthen the back. Now they’ve made their way from the gym to the office. And in the quest for the most ergonomic desk chair, many office workers prefer the “active sitting” these balls offer.

But there’s a catch. It’s harder to sit on an exercise ball than it looks. In fact, it’s tiring because it requires so many muscles to stay balanced and upright. Is the balancing act worth it? And is it better than your trusty desk chair? Probably not, says the American Council on Exercise, a sponsor of a recent Canadian study.

The study group included eight healthy men in their twenties with no history of low-back pain. Each watched a movie while sitting upright for thirty minutes on an exercise ball and on a wooden stool. Researchers measured muscle activation in the large muscles used while sitting and tracked the kinematics… or study of motion… of the lower back or lumbar spine.

So which provided the best workout… the stool or the ball? Neither, say researchers, who found no difference between the two in muscle activation, spine posture or overall spine stability.

So hold on to your office chair. If you get tired sitting on an exercise ball, don’t force yourself to use one. If you like sitting on it, limit sessions to thirty minutes or less, and switch to your desk chair as soon as you feel uncomfortable.