Crown Seating

In 1953, an orthopedic surgeon named J.J. Keegan ran a study that should be required reading in every dental school. He took radiographs of people lying on their sides in relaxed, unsupported positions and looked at what the lumbar spine actually wanted to do. The answer: it settled at a trunk-thigh angle somewhere around 135 degrees. Not 90. Not the right angle every conventional chair has been quietly enforcing on you since the day you sat down in one.
Here's what happens at 90 degrees. Your hamstrings and glutes pull on the pelvis, rotating it posteriorly. The pelvis takes the lumbar spine with it. Your natural lordotic curve flattens, then reverses. Intradiscal pressure climbs — Nachemson's classic disc-pressure work in the 1960s and 70s, later refined by Wilke in vivo in 1999, consistently showed that sitting loads the lumbar discs more than standing, and slouched sitting loads them more still.
The saddle position opens that angle. Hips drop below the knees, the pelvis rolls into a neutral or slightly anterior tilt, and lordosis reappears without you thinking about it. That's the whole mechanism. You don't have to maintain good posture. You have to stop being forced out of it.

Your lumbar spine has a natural inward curve. A flat stool flattens it. Eight hours of that flattening is why your lower back is talking to you by 2 PM. A saddle stool opens your hip angle past 125 degrees and lets your pelvis sit in a neutral tilt, so lordosis stays where anatomy intended. You're not "bad at posture." You're sitting on the wrong thing. Learn more at crownseating.com

Your lumbar spine has a natural inward curve. A flat stool flattens it. Eight hours of that flattening is why your lower back is talking to you by 2 PM. A saddle stool opens your hip angle past 125 degrees and lets your pelvis sit in a neutral tilt, so lordosis stays where anatomy intended. You're not "bad at posture." You're sitting on the wrong thing.