Plonking ourselves down

We are plonkers – most of us. We plonk ourselves down in chairs and don’t think too much about whether we need to make adjustments or whether the chair suits our body dimensions.

One aspect of chair use that in my experience people are often less familiar with, and possibly don’t always recognise the importance of, is the of seat pan depth – the front to back distance of the seat pan.

The ideal situation, is that when you are tucked up nicely against the backrest, there should still be a small horizontal gap between the front edge of the seat pan, and the back of your knees (the area known as your popliteal).

Why the gap?

If there is no gap, one of two things will most likely happen.

You will either slump down in your chair which means that your lower back is not properly supported and loses its natural healthy inward curve in the lumbar area. Over time this is likely to lead to back-ache and stiffness.

Alternatively – to avoid this happening, some people will sit forward away from the backrest. This is fine for a short period, but unless you happen to be a Jedi master of core strength and postural awareness, you will fairly quickly find that your lumbar area once again loses its natural curve, and bends outward, putting strain on the lower back.

So it’s a lose-lose scenario. If there is no gap, your seat pan is too long for you – simple as that.– which is why the popliteal-seat pan gap is really important.

How to fix it?

You should aim to have about 3 finger horizontal width’s of gap between the back of your knees and the front of the seat pan, when you are tucked firmly against your backrest.

Check whether your chair has adjustable seat pan depth. Control designs for this function do vary quite a lot between chair types and manufacturers, so you may need to do a bit of exploring – check online if you have to – a lot of chair manufacturers put user instructions online. The seat pan depth control can take the form of a simple lever, a button, or even a rotary dial or two.

Often you need to stand up to adjust this setting because your weight on the seat can stop slide mechanisms etc.

If your chair does not have adjustable seat pan depth and you don’t have ‘the gap’, in the first instance you should look to use a back support pad which will move you forward on the seat, at the same time providing you with lumbar support. There are various pads available, from a rolled up towel all the way to the more fancy mesh supports. The main thing is that when using one, your back is supported in the lumbar area particularly, and it has effectively created the gap you need behind your knees.

If this doesn’t work – if you can’t find a comfortable back pad or you feel uncomfortable because by using one you have lost support higher up the back as a result of using one, you may need to look at replacing your chair. A thorough face-to-face DSE assessment may be useful to confirm this and to make sure there are no other issues that need resolving.

Also worth bearing in mind: This is one of the key reasons why we ergonomists nag people about working on their laptops on the sofa etc. (don’t do it!!) It’s not just about neck posture, sofas tend to have long seat pans, so unless people make special adjustments – using cushions etc. their backs won’t be well supported.

Hopefully those are some useful tips. The key message is – Stop plonking, start adjusting! Get to know your chair and don’t be worried about taking control of it and making changes. If you try something and it doesn’t feel comfortable, just change it again until it does.