It's great to be on the ball at work; just don't sit on one
One of the trends in the past 10 years that tries to tackle the poor posture epidemic at work is the exercise or balance ball chair. We have been told countless times that the chair increases the activity of core muscles and provides a workout while sitting at work.
Even with the small amount of truth behind unstable surface training to increase muscle activity, transferring that philosophy to a sedentary position at work just doesn’t ... work. When we exercise, it is for a specific amount of time ranging from 30 minutes to an hour of varying positions and movements. Our workouts do not consist of a static position on an unstable surface for more than a few minutes.
Studies have found that there is an increase in muscle activity when using a balance ball chair for the first 10 to 12 minutes. After that, the potential benefit of activity abates. In fact, after about 15 minutes your posture begins to suffer as the central core muscles responsible for assisting with sitting up straight become fatigued. When these muscles stop functioning, the loads that the spine has to deal with start to increase and the position of the pelvis begins to shift. This results in an increase to the lumbar spine due to the loss of the lordotic curve.
Another concern with sitting for a prolonged period of time on an exercise ball is an increase in compression of soft tissue, which results in discomfort. An exercise ball does not provide adequate surface area and support, resulting in increased compression and disturbances of sensation. A chair has more surface area that does not change based on positioning.
A workout program involves reps and hold times that are designed to take you to the edge of your endurance and strength level without pushing you to the point of substitution or breaking form. Not only does breaking form reduce the effectiveness of the exercise, but it also exposes the body to a higher chance of injury as the supporting musculature no longer has the ability to limit excessive motion. The inability to redistribute the force over multiple structures results in an overload or injury.
There are studies that show an increase in core activation for a short period of time when using a balance ball. However, these types of chairs are not designed to sit on for long periods of time. The longer a person sits on the ball, the more strain on the core muscular supports. This results in overuse or overload of the muscles of the lumbar spine, which increases unneeded load to the joints of the spine.