We've Been Conned: Ergonomic Chairs By and Large Aren't Ergonomic
Cynical click-bait headline aside, I'll cut to the chase: they don't work.
There are three main reasons why that is:
You'll think it's supposed to take responsibility for you. This is a commonly held view, and the more expensive the chair is, the more likely you will fall into this trap. A chair is an inanimate object: it is incapable of "doing" anything, let alone taking responsibility for you. For sure, a good ergonomic chair will provide what we call in the Alexander Technique a "mechanical advantage," but it won't be providing any guarantees. You need to provide your own guarantees.
There's a strong chance you will adjust it to your current conception of comfort or habitual use, i.e. to support your current levels of collapse and effectively ingraining them further.
This is probably the most pernicious of the three; you'll bring your old habits to it. Even if the chair is set up perfectly to offer you the greatest mechanical advantage, the habitual way you use yourself will fight against this advantage. Have you ever felt that a well-set-up ergonomic chair leaves you feeling more tired than a regular chair?
Frankly, a piano stool is as ergonomic as a chair needs to be. You don't see piano players on stage, or at home, with fancy ergonomic chairs. In fact, I'm sitting on a piano stool as I write this! Yes, piano players tends to be more dynamic in their movement, but it's their mental engagement rather than the physicality you could learn a little something from.
If you redefine sitting as standing on your bottom then you can see why a firm flat surface is all that is required.
When you consider the cost of ergonomic chairs, and they don't come cheap, it seems strange to me to want to spend all that money when an Alexander Technique teacher can teach you to sit well in any chair, freeing you to sit anywhere with ease and poise, for less. But that's just me. I guess it's usually employers who are forking out for expensive furniture, but given my points above, if you are an employer, it might be more cost-effective to educate your staff rather than the furniture.
I was talking to a client the other day who has back pain issues, and she was telling me a story of how when a friend had offered her a chair and asked which one she'd like. She replied, "It's not the chair, but how you sit in it." Couldn't have put it better myself!
Getting slightly away from my above points, have you noticed that schools don't have ergonomic chairs? Well, this is actually a very sorry state of affairs, because children are not at "work," and are not covered by Occupational Health and Safety rules. School chairs are frequently designed to slope backward so they stack more easily. What's so bad about this? If the surface you are sitting on slopes backward, your pelvis will naturally want to tilt back, causing your lower back to round, resulting in slouching. I'll leave the rest to your imagination. It's actually an anti-ergonomic chair — so much so that teachers, who are at work, are advised not to sit on them by OSHA. (Alexander Technique teacher Richard Brennan has started a petition to ban backward-sloping chairs.)