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What is the best sitting posture?

I teach people how to sit properly every day in my clinical work. The principle is simple, the shape of your spine when you sit should mimic the shape of your spine when you stand. However, it's not always so easy to achieve.

Morfit Standing Morfit Sitting

 

The bit that many people get wrong is the fine tuning of the pelvis. We must sit on our ‘sit bones’. 

Sit bone

It is very easy for us to roll off our ‘sit bones’ and on to our buttocks and indeed this is often perceived to be comfortable. This rotates the pelvis too far backwards and effectively puts the lower spine in a permanent position of forward bending. 

Sit tall vs sit slumped demonstrationMost low back pain originates in the lower half of the lumbar spine and so this action is important.
To be able to sit well, with your thighs at 90° to your torso, most of us must use the back of the chair to control the pelvis and hold it in the right position.
The pressure that is exerted onto the back of the seat can be considerable. I have measured this myself. For a 55Kg person this can be 7-8Kgs and for a 90 Kg person this can be over 20 Kgs.

Pulling pelvis with scales

To sit like this using your muscles alone for any length of time is an impossible ask, our muscles fatigue and we slowly slump. So, it is important that you use the back of the chair, not only to support your lower back but more importantly to stop your pelvis from rolling backwards.

Having an office chair with a shorter back is easier to set up to fit you well. They don’t look as ‘sumptuous’ as high-backed chairs, but it is easier to get the correct support in the low back and pelvis region.

Office chair with a shorter back

A chair with a higher back, needs to have an adjustable lumbar support to have any chance of getting the support in the right spot.

Office chair with longer back support

 MAIN POINTS

  • Sit on sit bones to mimic your standing spinal posture.
  • When the hip angle is at 90°, use the back of the chair to hold the pelvis and low back.
  • Perching at the front of the chair can be a good variation if you increase the hip angle to greater than 90°.

 

Another sitting option is perching on the front of the chair. This allows us to drop our knees lower than our hips which opens up the hip angle.

Studies have shown that if we increase the hip angle to greater than 90° it is easier to sit up on our ‘sit bones’.

Hip angles 90 110 degrees

For this to be practical, we must perch on the front of the chair. This is best done if we raise the chair a little and allow us to drop our knees below our hips.

This obviously means that your muscles are working to hold you upright, but their activity is no different from standing still. 

Finally, there is no substitute for getting out of your chair frequently and getting your muscles working, i.e. walking.