I have ignored computer ergonomic professionals my entire computing life, but this winter, a pain in my lower back would not go away. Instead of listening to "experts" I followed the advice of ancient swordsmen.
Samurai guards used to sit in a kneeling position, with one knee up and one knee on the ground. The instability of the position, which required an active rebalancing, along with the slight tinge of pain on the lowered knee cap on the ground, made it ideal for long uneventful shifts. The position kept people awake, which kept them sharp and engaged so they'd be ready when the sonofabitch ninjas finally showed their facemasks. It's like a single replacement for a chair, and coffee.
I find that physiologically it also makes a great alternative to the sitting position, where one's back and gluts and neck are constantly stretched while the hip flexors and abs are constantly compressed but unused. This way, I stretch one leg at a time. The kneeling also keeps my eyes level with the screen of a laptop, and the desk too relatively high to lean on (which causes me to slouch). I don't get too tired, as I can rest my chest against the desk when I need to.
Through the day, I sit on an exercise ball, too, but I never feel better than when I am in the sitting stance. Swordsmen were also able to draw swords from this stance, to address attackers in front and behind them. I just change knees every few emails. Just in case the ninjas show. [Iaido, image from]
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*This stance works for me, but I am not an ergonomic expert. Obviously.
UPDATE: Yeah, this shit makes my knees feel like shit. Don't listen to me.