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  • Writer's pictureDr. Donald Littlewood

The 4-90 Rule for setting up your desk chair

It’s been four months since sh*t hit the fan and we all went into quarantine. All of a sudden, the masses were working from home in setups that were not ideal. Cut to July 2020 and we are still here, working from home with no real sense as to when we will be going back to the office. If you haven’t already, it is time to really set up that workstation so that it works best for you.

In this blog post, you will learn how to properly set up your chair so that you are able to work from home with less pain & discomfort. And it can be done in under 5 minutes. This is going to be done through my 4-90 Rule, which highlights four areas of the body that should be at 90˚, or as close to it as possible. So let’s get to it.

01 :: Elbows

I personally think that this is the most important of the four body part angles. When your elbows are at 90˚, it allows for proper shoulder placement and easier and more effective use of the mouse & keyboard.

Why is this important?

Let’s start with your mouse & keyboard. Keeping your elbows as close to 90˚ as possible while you are working forces you to keep the things you use most at a close distance. And why do you care about this?

Well if your elbow is too extended (an angle bigger than 90˚) is going to also force your shoulder to move forward which can cause the muscles in the neck and shoulder to elongate. This elongation of the muscles worsens our posture, creates neck & shoulder pain, and can also have a traction effect on the nerves, which can cause numbness & tingling in the arm.

Having your mouse & keyboard close to you may not seem like a big deal, but when you are sitting with it at a distance from you for 8h a day, it makes a difference.

The second reason you want to keep your elbows as close to 90˚ is to make sure that your shoulders don’t rise up as you are working. When the angle of your elbows is less than 90˚, it automatically causes you to wear your shoulders like earrings.

Wearing your shoulders like earrings is just bad news bears all around:

  • It really tightens the upper trapezius and levator scapulae muscles which are likely not happy to begin with. Along with the neck pain & upper back pain that this brings, headaches are not common here either.

  • It further perpetuates the stress response. When we have muscles that are contracted for a prolonged period for no reason, your body’s stress response slowly gets worse.

So what to do about your elbow angle?

If you are in a computer chair, adjust the seat height to get the right angle. If you are in a dining chair, sitting on a throw pillow should do the trick.

02 :: Hips

The hips don’t lie when it comes to low back pain. And prolonged sitting is one of the major causes of low back pain, so it is crucial that we nip this one in the bud!

Our spine has natural curves, a lordosis (or concave) curve in the neck & low back, and a kyphosis (or convex) curve in the upper/mid back. These curves are really important for maintaining the structure & function of the spine & spinal column as well as supporting the hips & shoulders. On top of this, when we are standing, a proper lumbar lordosis is really important for shock absorption & weight distribution.

But when we sit, our lumbar lordosis naturally flattens and it is our goal to maintain as much of the lumbar lordosis we possibly can. How do we do this? Well honestly, it comes down to using the back of your chair.

It sounds like a no-brainer, but you’d be surprised how many people naturally sit on the edge of their chair. While it does force us to sit taller, it actually flattens that lumbar lordosis which makes our bodies more susceptible to low back pain. If you find that you can’t use the back of your chair, then stick a throw pillow in between you and the chair. You’ll probably find it helps.

Now I know I said in the intro to this blog that we would be talking about 4 90˚ angles. And I haven’t said anything about the 90˚ angle of the hips, so let’s talk about why that angle is so important.

When the angle of your hips is around 90˚, your lumbar lordosis curve is as close to the standing curve as possible. When that angle is too big or too small, it increases & decreases the lumbar lordosis curve, respectively. So, by supporting your low back, you are inherently supporting your hips & keeping that angle at 90˚.

One thing to look out for as you are modifying your chair, or looking for a new one, is the seat depth. You need to make sure that while you are sitting with your back against the chair (or the support pillow) that your knees are ~2 inches longer than the seat. This is going to be most comfortable for you & help you out with angle no. 03.

03 :: Knees

Okay, gearing up for angle number 03 … your knees. Why is this so important?

You need your knees to be at a 90˚ angle to help with your hip angle and to help with your foot angle. But the good thing is, you don’t actually have to do much here. If your hips are set & what I tell you in no. 04 is set, then your knees should naturally fall into place.

Moving on!

04 :: Ankles/feet

The fourth & final joint that needs to be at 90˚ is your ankles. And it is one that is often overlooked.

You want your feet to be flat on the floor.

The main reason for this is because it supports your low back. When people cross their legs, it automatically causes you to have unequal weight on each hip and therefore causes uneven load transfer into your low back.

Crossing your legs also automatically twists one hip and rotates the low back ever so slightly. But when those slight movements are maintained for a long period of time over many weeks/months, cumulative damage definitely occurs.

Modification: even the best of desk chairs aren’t made for everyone, so you may need a little bit of help to get those feet flat on the floor. It’s time to break out that old textbook or shoebox to rest your feet on if you can’t get them flat on the floor. Just remember that your knees should be at 90˚ too!

Final thoughts

How you sit in your chair is important as is what you should be looking for when you are adjusting or making modifications to a chair you already have. Remember to keep your elbows, hips, knees & ankles as close to 90˚ as you can.

If you need more tips and tricks on posture, I have created a great free resource that contains three really easy posture exercises that you can do to help get you started on your journey. Head on over to to get your copy today!

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