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Ergonomic Design Features
for Office Chairs



With more than 40 years of experience as Australia and NZ’s largest specialised ergonomic product provider we are often asked what makes a great ergonomically designed chair. The answer is that the chair has been designed to suit both people and a particular function.

We would say that all our chairs, including fixed height and conference chairs and even school chairs are designed with ergonomic considerations at top-of-mind, but of course they perform different functions.

In fact we would say that there is no such thing as an “ergonomic chair”, only chairs which are fit for a particular purpose and have human factors in design as the paramount design objective. What may be ergonomic in one application can be totally inappropriate in another application or for another user.

Today we are looking only at Office Task Chairs, those chairs typically parked behind a desk and which are the primary working seat. Health professionals and users rightly put an emphasis on these chairs as they are the ones that have a big workload with users spending many (too many) sedentary hours sitting in these chairs.

It is impossible to describe an ergonomically designed task chair without also describing how to correctly sit in the chair, so let’s start from the ground up:

Your feet need to be flat on the floor, with your bottom level with or below the knees. Unless you get really lucky that your lower leg length (popliteal) matches the seat height that means that your chair needs to have an:

1. Adjustable Seat Height

All good office task chairs come with a handle activated gas cylinder which uses your body weight to compress the gas downwards, but when the handle is released, the compressed gas is released and the chair rises. The other function of this mechanism is to provide swivel, allowing the user to easily turn away from the desk to get up and down and to pivot from one task to the next.

Gas cylinders come in a variety of dimensional ranges. If a chair goes a long way up it cannot come a long way down. Sometimes if you have inherited a chair and desk it may be impossible to place your feet flat on the floor. If this is the case an adjustable footrest can be a simple fix.

During the working day you will find that you adopt several postures on the chair, perhaps leaning forward to type or write and leaning backwards to read and talk on the phone. This is normal, as you rest various muscle groups, and there is no prescriptive single posture which is “ergonomic”. You need to move and the ideal chair supports those different postures, which means your seat needs the below other features.

2. Seat tilt

When you lean your body weight forward to type or write the seat needs to tilt forwards as well to support you and not have the front edge of the seat cutting in to the back of the thighs. Some people perch on the edge of the seat, sitting quite upright. There is nothing wrong with that posture for brief periods of time, the important thing is to change posture regularly.

Some standards recommend up to 5 degrees of forward tilt. Leaning back puts your back in contact with the backrest and seat tilt should slope backwards, again supporting that posture. Of course if the backrest does not move as well then you can end up “bunched up” so backwards seat tilt should always be used in combination with backrest tilt.

As we have already said regular changes in posture are critical to relieve pressure on different muscle groups. If a chair does not have backrest tilt then people are going to slouch in the chair and be unsupported, rounding out the lower back and failing to maintain the natural S shaped curve of the back (the lordosis). We would always recommend backrest tilt in a high usage Office Task Chair.

3. Backrest Tilt

Most standards call for back tilt of 10 degrees, but most modern office chairs easily surpass that recommendation. How far the chair tilts is a question of balance. The chair needs to remain secure and not be at risk of toppling backwards and here you need to try before you buy.

Men and women have different body shapes. Men are top heavy and generally taller so their weight is higher up the chair, making it easier to tilt the backrest but also putting users at risk of leaning too far backwards. Very tall people should not be using a chair with a high degree of backwards tilt.

You drive the amount of seat tilt and backrest tilt by pressing back against the chair, but you cannot do that unless your feet are flat on the ground that is why the next adjustment is so important.

4. Seat Pivot Point

Basic Office Task Chairs have a central pivot point, they tilt close to the gas lift connection point, but in doing so that raises the front edge of the chair, for people of smaller stature that lifts their feet off the ground and they are no longer in control of the chair. In more sophisticated chairs the pivot point is towards the front edge of the chair.

When the chair seat tilts feet remain in the same position. This style of tilt is called “knee tilt” and is highly desirable for women and people with a light frame.

Have you ever plonked into an office chair and experienced that “whoopsie” feeling when you feel the chair is going to tip over backwards? That’s because the resistance of the chair is inadequate to control your weight. Conversely some people with a lighter frame may find it difficult to budge the chair, that’s why you may need the next adjustment. -->

5. Tension adjustment

A tension adjustment knob or wheel controls the amount of resistance that the chair offers to push back against tilt by slightly changing the geometry of the gas strut or spring.

That means you feel more in control of the chair. It lets you balance the resistance to your own body weight and to move freely and with support throughout the working day.

Being in contact with the backrest can help to support the musculo-skeletal system, but it is important that the backrest be the right shape to offer that support. Ideally the chair should have a pronounced lumbar support.

6. Lumbar support

The lumbar support should be quite low on the backrest, somewhere around the L4/L5 vertebrae. Many lumbar supports are too high to be effective in retaining the natural lordosis of the spine. In a seated posture there is surprisingly little variance between humans of where this falls so height adjustment of a lumbar support while preferable is not critical.

It is important however to be able to vary the amount of resistance the lumbar support offers. Many of the best chairs on the market, especially mesh backed chairs do allow people to dial up the shape of the lumbar support.

People do different jobs in offices, but increasingly those tasks are keyboard based. Many users report that an armrest helps to support the elbows and unload the shoulders from having to keep arms suspended over a keyboard.

For older and less mobile workers armrests are an essential part of getting into and out of an Office Task Chair, helping to lower the worker into position or providing extra leverage in exiting the chair. Fixed armrests are generally frowned upon for keyboard based tasks as they can impede pulling the chair up close to the desk leaving the user too far away and reaching to make keystrokes.

7. Adjustable Armrests

Adjustable armrests strike a balance between support and getting close enough to the desk. The top of the armrest can be adjusted to below (or in some cases above) desk height, thereby avoiding collisions.

The most flexible armrests adjust for height, width and pivot and the better chairs have a soft armrest which is comfortable throughout the working day.

The “feel”, sometimes called the “bum test” of chair is often what sells the chair, people like to sink into a plush upholstered chair and have that “snug” feel, but this can be a trap. It will not feel the same after hours of use and may break down and lose shape over prolonged use.

8. Foam or Mesh Quality

That soft foam or mesh feel can be an indicator of a sloppy mesh fitting or too light a foam density. A certain degree of foam density and thickness is required to help a chair maintain its shape and resilience over many years of use. Generally a thinner seat profile needs a higher foam density.

Some good chairs have a dual foam, firm underneath and softer on top. Generally foam densities need to be higher on seats than backrests as the seat bears most of the load.

Often in offices with staff changes people inherit chairs which were really chosen for someone else, or increasingly the same chair is used by multiple users. For many people of smaller stature this can present a particular problem, the seat depth is too large and projects past the knees when the back is in contact with the backrest.

This leads to poor posture and slouching as the user struggles to get their feet on the ground. In such cases seat depth adjustment can be a solution.

9. Seat Depth Adjustment

Some superior chairs offer seat depth adjustment where the seat pan is mounted to a rail which can track backwards and forwards, typically that adjustment is around 150mm. This adjustment is usually only made once per user but in shared situations is a critical adjustment.

It is quite unnecessary if a chair is only going to have one user and the user has tried the chair before purchase.

Because people come is different shapes and sizes so do chairs, but there is no evidence that a high back chair is more or less ergonomic than a mid or low back chair. That choice is often one of appearance or status.

The accepted wisdom is that a higher back chair denotes a higher rank in an organisation. If people feel the need for support at chest and shoulder level then a sensible alternative can be a chair with an adjustable backrest.

10. Adjustable Backrest

Moving the lumbar support from the lower back is not a good idea, that’s where it is designed to go, so chairs which adjust backrest height without being able to adjust lumbar position are sub-optimal. If you elect to have an adjustable backrest research shows that the adjustment needs to be simple and intuitive or people will just not bother.

A simple ratchet mechanism is a sound solution, by simply lifting the backrest it clicks into place. Such adjustments are infrequent and in some views unnecessary after the chair has been initially set-up for a particular user.

Being able to wheel around the desk space has been a boon to productivity, extending the close hand reach of your working space quickly and simply, all good office chairs should be on castors, but there are some things you need to know.

11. Castors

Which castor depends on which floor. A soft-tyred castor is generally suitable on both a hard floor and most office carpets, however a hard castor is only designed for use on thicker carpets. If in doubt a soft tyred castor is generally a safer choice. Another option is a brake castor which stops the chair running away when you stand up…take your weight off the chair and a friction brake prevents the chair escaping too far.

Soft-tyred castors are usually identified by having two tones, a black body vs a cream or grey tyre.

12. Finally a word on mechanisms

The ANZ standard (AS/NZS 4438) was written many years ago ( Sylex Ergonomics sat on the committee that wrote that standard) when most chair mechanisms were activated by two or three handles. A two handle chair activated a gas lift and a backrest tilt, a three handle chair added seat tilt to the repertoire, so some lazy language crept into the office furniture business.

For those that knew no better a 2 handle chair became “semi-ergonomic” and a three handle chair was “fully ergonomic”. This verbal short hand never captured the full story of how to correctly fit a chair to a user and a task. If anyone describes their chair to you as “fully ergonomic”, run.

Further as time has moved on and improvements in components and mechanisms continued, the number of handles became completely irrelevant as it became possible to combine functions and even eliminate functions by having the chair do the adjustments automatically.

An example of this is the Syncron action. Synchron combines both seat and back tilt into one function. If the seat moves the backrest moves in a set ratio, usually 2 or 2.1 to 1. That means it is impossible to make an inappropriate combination of seat and back tilt. It’s like the difference between a manual gearbox in a car and an automatic gearbox, (you can’t make a bad gear change in an auto). It is a vastly superior product to manual/individual adjustments, but the myth persists that more handles are better.

Most people have little or no idea how to adjust their chair so it is no surprise that research from the Ergonomics Dept at Cornell University has found that the more handles knobs and adjustments a chair has the less likely users are to be able to set their chair up correctly. Except for the gas lift, less than half of all people are even aware that their chair has other adjustments.

Most buyers of office chairs are doing it for the first time, so speak to people who actually know chairs, not just someone trying to flog you their product.

At Sylex Ergonomics all of our people are actually trained and certified in ergonomics and we take pride in supplying the right product for the right application and always with an understanding of human needs.
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