But as ergonomic professionals, how can we ensure that we’re recommending the best chair for our clients? In this post, I’ll be sharing the general principles of seat design. Find out why lumbar lordosis should be one of your main priorities when recommending chairs to clients, why minimizing disc pressure and reducing the static loading of the back muscles is vital.
A lot has been written about seat design. There are new types of design available nowadays, including "dynamic" chairs, kneeling chairs, and the stability ball chairs. I'm sure you've seen them before. There are just so many options out there. However, my purpose here is not to look at the specific makes and models of the chairs but to provide some basic information that’s been foundational for the ergonomics profession for years.
If you ask me what the best chair in the market today is, my answer is: it really depends.
It depends on the chair that your client finds the most comfortable sitting in after trying it out. Here’s the thing: different people find different chairs suitable for them, so there's never "one type of office chair" that’s necessarily the best. As the ergonomic consultant, the best approach when recommending a chair is to provide two or three good designs from which your clients can choose from.
There’s no such thing as one best chair for everyone, but there are some considerations to include when recommending an ergonomic office chair to make sure that your client can really enjoy its full benefits. Find out what they are below.
When we shift from a standing position to a sitting position, anatomical changes happen. What this means is that when you're standing straight, the lumbar portion of the back is naturally curved inwards. However, when someone is sitting with the thighs at 90 degrees, the lumbar region of the back flattens out the natural curve and can even assume a convex curve (outward bend). This posture is considered to be unhealthy if maintained for a long time. However, most people end up sitting in this position throughout their day. This is why research about sedentary workers, like office workers, often reported high levels of postural discomfort.
Under normal circumstances, we don’t want to recommend that posture to our clients because it increases the pressure on the discs located between the vertebrae of the spine. What we want to recommend to them is to sit and sustain the lumbar spine in a posture called lordosis. Accordingly, one of the biggest factors to consider when looking for a good chair for your client is that it should promote lumbar lordosis.
Why is this so important?
Well, the discs between the vertebrae can be damaged by excessive pressure. Sitting without any back support increases disc pressure considerably over that experienced while standing.
Unsupported sitting in a forward slumped posture increases pressure by 90% compared to standing. However, if the chair provides sufficient support in the user’s spine and the surrounding tissues while they sit, it can take plenty of load off their back, neck, and other joints.
Break-taking strategies and habits often can't be overlooked because even if the client is using the best possible chair with the most support, they still need to limit the total amount of sitting in their day.
Another matter of concern on the design is that the chair should permit movement and provide ways to frequently shift your client's position throughout their workday. I’m going to dive into the types of chairs that try to replicate standing and movement in the office below. However, many ergonomic standards around the world suggest that getting up and moving is still ideal compared to relying on these chairs.
Aside from standing and moving our bodies, we can't leave out the engineering controls when it comes to chair design. According to some research, one way to reduce the disc pressure is to use a reclined backrest. This is because using a reclined backrest takes some of the weight from the user’s upper body, which in turn reduces pressure build up on the spinal discs.
Using armrests can also reduce disc pressure. Studies have also shown that armrests can decrease the weight on the spine by about 10% of body weight. Of course, proper adjustment of the armrests is vital to provide support to the user in a neutral optimal posture and avoid musculoskeletal discomfort.
Note: The use of a lumbar support reduces disc pressure, as does the use of armrests. However, with a reclined backrest, the effect of the armrest is insignificant.
There are ways to relax the muscles of the back without sacrificing the health of the discs. For instance, one researcher found a reduction in muscular activity in the back when the backrest was reclined up to 110 degrees. Beyond that point, there was little additional relaxation in those muscles of the back. Interestingly enough, the effects of lumbar support on muscle activity have been mixed.
So what does this information mean for you as an ergonomics consultant?
Is sitting upright at a 90-degree angle the best posture, or is it sitting with a backrest reclined at 110-degree angle?
Personally, what I recommend to my clients is to keep their backrest reclined between 95 and about 113 to 115 degrees. Of course, that includes having that lumbar support in an optimal position and this is supported by Ergonomics Standards (aka I'm not pulling this out of thin air).
The human body is simply not designed to sit in one position over a sustained period of time. The discs between the vertebrae depend on changes in pressure to receive nutrients and remove waste products. This discs also doesn't have a blood supply, so fluids are exchanged by osmotic pressure.
What this fact implies is that staying in one posture, even if it appears comfortable in the beginning, will result in reduced nutritional transport and contribute to advancing the degenerative processes in the long-term!
Dynamic sitting helps decrease static load and improve blood flow. When dynamic chairs were introduced, office chair design was transformed. Dynamic chairs have been marketed as the silver bullet to optimize spinal health. The chair design can reduce the static posture positions by allowing that user to rock in the chair and assume a variety of postures.
What I like to recommend to my clients to encourage dynamic sitting is to use a free-float position, when appropriate. This is when the chair is in a synchro tilt, and it's not locked in position. This allows the user to adjust the angles of the seat and backrest to fit their sitting posture. In this position, the chair is dynamic, and the backrest offers continual back support as it moves with the user. So it's almost like a rocking chair.
Whatever ergonomic office chair we recommend to our clients in an assessment, they’re likely not going to adjust that chair. So as a final thought, I would love you to consider and put into action some ways that would be valuable for your clients and easy for them to know how they can make chair adjustments themselves, ensure that it’s set up according to their needs, and will continue to do it for the long term. If you have any ideas, I would love to hear them in the comment section below.
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