Swapping your office chair for an exercise ball gives you an excuse to sneak a few calorie-burning exercises, like wall squats and ball passes, into your day. But just the act of sitting on the exercise ball burns calories, too.
Sitting vs. Standing
Working while sitting on an exercise ball burns about 6 percent more calories than working on a normal office chair, according to a 2008 University of Buffalo study published in the "European Journal of Applied Physiology." Study subjects burned a similar number of calories by standing while working, but reported that they liked working on the ball better than working while standing.
How many calories you actually burn while sitting on the ball depends on what you're doing. According to Harvard Health Publications, desk work burns about 106 calories per hour if you weigh 135 pounds, and about 156 calories per hour if you weigh 185 pounds. Apply the 6-percent increase for sitting on an exercise ball and you can expect to burn about 112 to 165 calories per hour during office work on the ball.
The exercise ball's instability forces your core muscles to work constantly at keeping you stable. This might account for the extra calorie burn and offers you a chance to develop some abdominal tone with no extra effort.