Thursday, April 7, 2011

Step 2: Sit Better!

The Desk Warriors Guide to Building a Healthy Back! 2/10

By reading part 1 of The Desk Warriors Guide to Building a Healthy Back, we know that sitting for prolonged periods is something to be avoided. But what are we to do when sitting can't be avoided? After all, our jobs, our livelihoods are now spent hunched over computers. We can't all earn a living on our feet like pro-athletes, dancers or even bartenders for that matter. We have to sit at a desk and work.

This begs the question, what is the most optimal seated posture?


I will first address the myth about "proper" posture. When we sit with "proper" posture, our feet flat on the floor, our knees and hips at 90', the spine long and upright; the head and chest up and our lumbar curve maintained we are actually damaging our lumbar spines. This may be aesthetic sitting posture or proper school boy/girl posture, but according to my man Stuart McGill it is only tolerable for 10 minutes max and should not be attempted further.


"Ideal" Sitting Posture Try to sit unsupported like our man with the "ideal" posture for 10 minutes...


If you take us up on the "ideal" seated posture challenge, what will happen is you will engage your core muscles to the point of fatigue. As discussed in the previous post, engaging the core muscles results in a shortening of the muscles, thus spinal compression. The hip angle of 90* with core compression results in increased compression of the spine, thus increased intradiscal pressures (pressure on your discs). Take a moment to stand up tall and feel your core muscles. Feel the muscles in your lower back and the muscles that surround your waist. You shouldn't feel a great deal of muscular tension. When standing upright, you are designed to elicit the smallest amount of muscular effort. The curvature of your lumbar spine bears the brunt of your weight and only perturbations during movement should result in greater core muscular activity.

So when engaged in prolonged sitting, we want to find ourselves in a position where like standing, the core musculature is at a minimal tone or effort. The typical seated posture or worse, the forward bending seated posture compresses the vertebrae in a manner that sends the disk posteriorly (backwards) This causes a posterior annulus strain of the disk while (center of the disk bursting through the annular layers of the disk leading to bulging and eventually herniated discs). We now know that the outer layers of the annulus fibrosus are innervated (containing nerves) This means that delamination, as occurs when the nucleus of the disc bursts through annular layers (bulging disc) causes pain without impinging on the larger sciatic nerve as previously thought. Further prolonged sitting leads to creep in the posterior passive tissues, which is essentially loosened spinal ligaments allowing for more shearing movement on the spine. This is bad. Think of the mechanism of grating cheese, that is anterior posterior shear, not something you want going on in your low-back.

Now we've deduced that sitting with "ideal" posture or a hip angle of 90* is not a good long-term seated posture.We guessed that leaning forward and increasing the hip angle is even worse because it accelerates the rate of all the above jargon happening in your spine (as viewed below or here). So let's get to the meat and potatoes. How can we sit longer and not destroy our spines and health in the process?
The above T-bone steak looking thing is an illustration of your vertebral discs. The center or nucleus migrating posteriorly as intradiscal pressures increase in various postures.

Now you smart ones out there probably took a good look at the above picture above and hypothesized that since
laying down has the least amount of intradiscal pressures via relaxed musculature, that a more reclined posture is
optimal.

You would be correct. However, a back angle of anything less than 135* can't really be considered sitting since you are closer to laying down. Assuming we have to be at a desk/work station in a seated position, the ideal posture is one in which muscle activation is lowest via support (back of chair or lumbar support), maintenance of the normal lumbar curve and one in which we can change position easily.


The reason we need to change positions easily and regularly is to not overload any one tissue. Tissue loads need to be migrated from tissue to tissue in order to minimize the accumulated microtrauma of any one tissue. Think about it, you fidget for a reason. You are spreading the microtraua from tissue to tissue. McGill recommends changing postures very often. Atleast every ten minutes.


The chair is not helping the situation. Chairs are designed by architects, not biomechanists. Ideally, you would want a chair with a great deal of lumbar support. The Nottingham chair is one that supports the lumbar spine and aims to keep a posture more congruent with standing, thus sparing the spine. Standing desk stations are also a great way to preserve the spine. But yes, the Nottingham chair is expensive and unstylish and standing desk stations have their problems as well.


So when forced to sit for long periods of time. We want a chair that supports the entire back, rather than doing all the work ourselves via the core musculature and contributing to spinal compression in a flexed posture (contributing to discogenic pain). We want to be able to mimic normal standing posture as best as possible so a chair that supports the normal lumbar curvature is essential. If your work chair does not do this, simply buy a lumbar support. Arm rests also alleviate spinal compression, so use them when you get the chance. Most importantly, we want a chair with the ability to recline. The more the better. The optimal seated position would be in a lazy boy, but as most desk warriors aren't afforded this luxury, we must aim to achieve this recumbent position via lumbar support and reclining our chairs. Again, I reiterate that any position must be changed eventually to promote circulation and to spread the microtrauma to various tissues, thus our reclined lumbar supported position must to be changed regularly.


The least compressive the posture, the longer it can be tolerated. So Desk Warriors, arm yourselves with an arsenal of appropriate desk postures. Change the angle of your back via more or less lumbar support or varying degrees of reclination. Shift your weight to your right, then your left. Sit with your legs crossed, left and right. Cross your legs with your lean on. Essentially be mindful of maintaining your neutral lumbar spine while shifting into a variety of comfortable positions.


This stance on postural shifting can also be applied to sleep. No one sleeps in any one position and they shift subconsciously. They do this because it's our way of our body spreading the stresses to different tissues as we should do when we sit, stand, lie etc…

In conclusion, the ideal posture for prolonged sitting is a reclined ~135 back angle posture where our natural lumbar, thoracic and cervical curves are preserved. However, we learned that after a certain exposure, no position is safe and that we must find a variety of Desk Warrior poses to serve our productivity needs.


Callaghan, J.P., and McGill S.M. (2001) Low back joint loading and kinematics during standing and unsupported sitting. Ergonomics, 44 (4): 373-381


And of course the books cited in Step 1: Sit Less

4 comments:

  1. That is a really interesting graph. It's interesting to note that sitting poorly puts even more pressure on your back than lifting something does! That's crazy. You've convinced me that I need to have better posture. Would sitting in big and tall office chairs help?

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  2. Gary, the more support your office chair has the better. If you can rest your head against a the back of the chair that is a good thing (especially for the cervical (neck) spine. Again, when forced to endure long seated postures, varying your posture is an effective tool at limititing the cumulative trauma to any one spinal structure.

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  3. Thanks! I was just in a car accident and have been hyper sensitive to this. Hopefully since I am young this may have been a good wakeup call to avoid irreversible damage later in life.

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  4. Thanks. For any knee pain we can use knee brace

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