Sit on It: Exercise Ball vs. Office Chair
After years of searching for the most ergonomic desk chair,
many are opting to ditch the chair altogether and spend their
workdays sitting on an exercise ball instead. Advocates call it
"active sitting" and see it as an easy and effective way to not
only improve posture, but also work the core muscles
throughout the day. In addition, the instability of the ball
requires individuals to frequently change position, which may
help alleviate the discomfort of prolonged sitting, particularly
in those with low-back pain.
If you've tried it, however, you know firsthand that it isn't
easy. In fact, sitting for prolonged periods on an exercise ball
can be downright tiring as numerous muscles throughout the
body, both large and small, must be engaged to keep you
balanced and upright.

But is sitting on a ball really a better alternative to your standard desk chair? Researchers at the
University of Waterloo, Ontario, Canada, set out to answer this question by examining the
effects of prolonged ball sitting. The study, sponsored in part by the American Council on
Exercise, consisted of two parts:

An assessment of torso muscle activation, spine load and stability while sitting on an exercise
ball and on a stool

An assessment of the pressure distribution over the buttocks and thighs while sitting on a
stool, an office chair and an exercise ball
Eight healthy men in their 20s, all without any history of low-back pain, were recruited to
participate in the study. Each subject sat for 30 minutes on an exercise ball and 30 minutes on
a wooden stool while watching a movie. The men were instructed to maintain an upright sitting
posture while various measurements were taken. These included muscle surface
electromyography to determine muscle activation of the rectus abdominis, internal and
external obliques, latissimus dorsi and erector spinae; and electromagnetic tracking to measure
lumbar spine kinematics. Stability and compression values were also calculated.
Researchers concluded that there was no difference in the degree of muscle activation of the
muscles between the stool and the ball. Therefore, prolonged sitting on an unstable surface
such as an exercise ball is not significantly different than sitting on a harder surface such as a
regular desk chair in terms of muscle activation, spine posture, spine loads or overall spine
stability. However, subjects tended to shift and change body position more often while sitting
on the ball, which some believe is better for you than sitting in one position for long periods of

Even so, researchers remain skeptical of the benefits of ball sitting at work. "While it appears
that sitting on an exercise ball accommodates increased movement, there is little effect on
spine loads and muscle activity and the resulting spine stability," explains study author Stuart
McGill, Ph.D., a leading expert in spinal biomechanics.

McGill acknowledges that more research is needed to determine if sitting on a ball has an effect
on the smaller, deeper muscles. Additionally, the amount of air pressure in the ball, and thus
the level of instability, could also have an effect on muscle activation levels.

But if your muscles are being activated equally while on a ball or on a chair, why does sitting on
a ball feel so uncomfortable after a while? Researchers explain that sitting on a ball
significantly expands the contact area (more of the individual's lower body makes contact with
the ball than with the chair), which could result in uncomfortable soft-tissue compression.

In other words, don't ditch that office chair just yet. If you find sitting on a ball tiring, don't
force yourself to do it just because you think it's good for you. If you enjoy sitting on a ball,
however, limit your sessions to 30 minutes or less. Simply switch back to your chair if you
start to feel uncomfortable.

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