Who taught you how to sit? I'm guessing nobody, you probably just figured out how to do it by trial and error when you were a baby. You learned how to stay upright and eventually not fall over while resting on your butt; that was a major milestone when you were 8 months old, but you haven't been given much credit for it later in life, have you? Unfortunately, it's later in life that you are going to need to be good at it, because chances are you are going to be spending multiple hours a day staring at a computer screen. It is time you learned how to sit properly.
*Movements and postures demonstrated well in the video at the end of this post
Our bodies are built to deal with the vertical load of gravity, but at the same time are inherently lazy when it comes to holding everything up properly. We have a tendency to get engrossed in what is visually in front of us with little regard to how we have positioned our bodies to allow our eyes to see what we want to see. Your brain has a head righting reflex that tries to keep your head looking straight forward in the easiest way possible; unfortunately this usually comes at the expense of your neck and back.
The goal of sitting properly is to effectively vertically stack your torso and head on top of your pelvis and hips in a nice gentle S-curve. The odds of you doing this properly are stacked against you for a few reasons. First, most people have one, two or three of the following: forward head posture, an overly braced lower torso, and/or really flexible or really stiff hips. Second, most chairs are not designed very ergonomically and promote slouching more than support. Finally, life just gets in the way of your awareness of gravity and proper posture and you sit the way your body takes you. If you create a little body awareness, learn how to use your chair properly and have someone help you with your physical restrictions, sitting properly can significantly diminish the chronic tension and pain that can come from working at a desk all day.
The first place to start is to learn how to get your pelvis on top of your hips, not behind them or in front of them. Some people sit on their tail bone all day, while others tend to sit on their upper legs. It requires a balance of your hip flexors, abdominals and back muscles to stack everything and have you sit on your SITS bones properly (these are the deep bones in your butt). The SITS bones should be back on the chair and spread wide apart to create a stable base, not tucked underneath you and together. This position of your pelvis is very important because it sets the foundation of the natural S-curve of your spine above. When your pelvis is rolled backward and your SITS bones are together, it will make your back muscles have to work way harder to try and sit up straight….
so Step 1 is get your butt underneath you!
Good stacking Sits bones apart Pelvis behind hips
Step 2 is to get your torso over top of your pelvis without lurching it forward, leaning it backwards or slouching it downward. Those that tend to sit on their tailbones will have a tendency to let their whole body collapse into a big slouch, while those that sit on their upper legs will tend to perch on the edge of the chair and hold their torso in front of their hips. Very hypermobile people tend to do both, they will perch on the edge until they get tired, then collapse into a slouch. Very stiff people will immediately start with their hips in front of them, lean their torso back and push their heads forward. We all have our own strategies, but the one position that allows us to sit efficiently is the one that stacks the spine and lets the skeleton do most of the work instead of the muscles and ligaments.
Creating awareness of your torso position is typically the hardest for most people because you rarely think about what your mid, lower back is doing, but learning not to overly brace your back and instead use your diaphragm and abs for support are important steps to help you sit well. Use a mirror and look at your side profile to try and create a vertical line down the midline of your torso through your hip socket. You will likely find that your torso either wants to be tipped forward or tipped backward and that if you achieve straight, your head might be pushed well forward; here is where you learn how much your trunk and pelvis have been accommodating your neck. The upper part of your back is relatively the stiffest part and if it gets rounded it will push your head forward. Your body will compensate for this by tipping your head up and chin forward, by overly extending your lower torso and/or just sliding your butt forward on the chair to get your body under your head the easy way. These practices are immediately the most comfortable when you sit, but are the exact things that lead to pain and your posture getting worse over time.
Butt & Head forward Well Stacked Don't Perch!
Your upper back doesn't move that much, so when you try to lift your head and chest up, it should be a subtle, gentle movement that elongates your upper spine instead of leans you backward. It should be a movement that doesn't negatively alter the positions you have found with your torso and pelvis below. When you effectively get your pelvis on your hips, your torso on your pelvis and your head on your torso, it will look great, but might feel challenging to hold. The muscles you feel working are the ones your need to strengthen and just sitting properly can strengthen them. People that tend to sit back on their tail bones will have to learn to use their hip flexors and low abs to hold the pelvis forward over the hips. People that sit on their upper legs have to learn to let their back go and draw their ribcage backward over their hips and use their back together with their abs instead of in place of. Many people have to learn to do both.
Your hip flexors attach from the front of your lower spine and the inside bowl part of your pelvis down into your groin. To use them effectively for sitting it will feel like you are using your lower stomach muscles. Once you have shimmied your butt underneath you, gently try to pull your pubic bone down to the floor. This should create a tension in your lower stomach and act to slightly tip your pelvis over top of your hips, if this forces your whole torso forward you are using your back muscles not your hip flexors. If your lower torso is forward, place your two hands on your lower ribcage and try to gently slouch it backwards while maintaining your hip flexors. The tendency is to be all or nothing; a big C-curve instead of a gentle S-curve. You need to be able to hold your pelvis forward and your ribcage back. (Demonstrated well in the video below)
Pelvis on top of hip Front view Hip flexor holds pelvis forward
Chairs can either make sitting well easier or harder. If you are really tall or really short, chairs are not made for you so learning how to use them is that much more important. Ideally a chair is high enough for you that your knees end up slightly below your hips, or a hip angle of about 90 degrees. It should also be small enough that your feet rest flat on the floor and that you can sit back against the back rest without the seat pan pressing into your upper calves. If your thighs are quite short, you should buy a small chair or place an additional back support on the backrest behind you. On adjustable desk chairs there are typically two levers on the side, one adjusts the height of the chair and the other affects the angle of the seat pan and the back rest. You want to have the back rest angled forward enough that when you sit back on it, it supports your torso in a position that is relatively over top of your hips, not well behind it.
If you have a significant head forward posture, sitting with your torso more vertical will feel like you are leaning forwards, but it is just your head that is forward so use a mirror, if you can, to see that what you feel and reality might be two different things. Your body will naturally slide your hips forward on the chair and want your torso to lean backward to accommodate your head; don't let it. Keep your butt underneath you, your torso supported vertically by the chair and focus on elongating your neck and head upwards, not backwards.
If you set up your chair well, it will allow the lumbar support and the back rest to support your torso for you so you can make sitting a relatively passive process for your back. Sitting poorly for eight hours a day can be harder on your body than a contact sport, so learn to sit back in your chair and let it do most of the work. Your job is simply to maintain some awareness of gravity and to reposition yourself every 15 minutes or so.