The trend of swapping your office chair for an exercise ball seems to be fading a bit. However, many patients still ask me if it is beneficial to sit on an exercise ball rather than a chair. The exercise ball is an unstable surface that in theory should lead to increased trunk movement which aids in the nutrition of your muscles and vertebral discs and increases the activity of your core musculature. There are other proposed benefits as well, but let’s find out if they outweigh the negative side effects.
A 2009 study published in the journal Applied Ergonomics, researchers compared an adjustable office chair with armrests to an exercise ball while the participants did a one hour typing task. The chair and the ball were fit to the subject’s body size so when sitting their knee angle was 90 degrees. As hypothesized by the authors they found 33% more global trunk motion when sitting on the exercise ball (not found to be significant). They also found the average rate of change of lumbar EMG and amplitude of lumbar spine muscles to be 66% and 38% higher when on the ball. Although increased spinal movement and muscle activation are good for spine health, they also increase forces on the spine, which can have detrimental effects on the intervertebral discs. To test this, the authors looked at the compressive forces on the spine and found that spinal shrinkage was significantly greater when sitting on an exercise ball than the office chair. Another implication of increased muscle activity is that it can lead to muscle fatigue which can increase your susceptibility of low back injury.
Another study by McGill published in 2006 in Applied Biomechanics, looked at pressure distribution. Comparing an exercise ball, an office chair, and a stool they found that the surface contact area was significantly greater with the exercise ball. The increased contact area actually increases the level of discomfort when sitting on the ball. This is because the soft tissue is now absorbing the pressure of sitting, when it should be on the boney part of your butt!
In conclusion, although there seem to be benefits of sitting on an exercise ball, the benefits are outweighed by the significant negative effects to your spine. For this reason use a traditional office chair at work or utilize an exercise ball for short periods at a time to limit the shrinkage of your spine!
Stay healthy my friends,
Dr. Adam