Here's a rare example of a metal ergonomic chair designed circa 1920, when wooden furniture was common, and concerns for workers' spinal health was not.
Called the Do More Chair, it was designed by the now-defunct Tan-Sad Chair Co. in England. The series of holes in the structural components show where the adjustability is for the seat and backrest. I wish there was a close-up photo of the pins or bolts, which the ad below says can be adjusted without the use of tools. Additionally, you can see that the height is adjustable as the central shaft is threaded.
The chair was also distributed in the Netherlands by Dutch furniture brand Ahrend (hence the ads shown below are in Dutch).
As vintage furniture retailer Ztijl explains of the chair:
"In 1920 comfort was seen as a luxury, workers at factories often worked in factories on backless benches. The 'Do More Chair' was therefore far ahead of its time. It can swivel, has wheels and both the sitting position and the backrest are adjustable."
Here's an English machine-translation of the Dutch ads:
"The Do More Chair [vs.] an ordinary office chair.
"Our Do More anti-fatigue chairs promote health through their ideal seating style: Back supported - chest relaxed.
"The unparalleled adjustability meets individual requirements. The adjustment is done without any tools. Our Do More Chairs fit in any environment."
"The Do More Chair. The ideal chair for the working person. For use in offices, drawing offices*, laboratories, for operating office machines and telephones, etc. Back support for your work."
*Dutch speakers: A little help here? Does "Teekenbureaux" mean drafting pool?