I'm almost ready to say that "ergonomic keyboard" is an oxymoron.
Thinking outside the box: Some musical instruments have a small number of keys for a large number of notes. Playing for long time periods without injury is now part of the basic training that all musicians receive.
Maybe a model for an ergonomic keyboard would be something like a saxophone.
You want to look up 'chording keyboards' - They're one of the few things from Engelbart's 'Mother Of All Demos' that's not now a standard part of computing.
Unfortunately, designers these days seem to hate modal interfaces because they detract from "walkup usability", so I doubt we'll see these making a comeback.
Then again, maybe Apple's multi-touch gestures are close enough to chording that they'll be rediscovered and become cool again.
I don't see the advantage of chording based input, it actually requires more effort to press two or three keys at once. I guess I'm thinking of the use of modifier keys. Anecdotally speaking, it increases tension as well because of the need to maintain more complex finger/hand positions under stress and high repetitions.
All things considered it's only a different kind of effort. You have to learn how to distribute smoothly the tension in all limbs, it's abstract at first, but that's how musicians can play anything. Also maybe chorded keyboard would fit or need a better set of commands. More abstract ones thus less many.
Thinking outside the box: Some musical instruments have a small number of keys for a large number of notes. Playing for long time periods without injury is now part of the basic training that all musicians receive.
Maybe a model for an ergonomic keyboard would be something like a saxophone.