An uncomfortable chair is an uncomfortable chair regardless of fitness. Being fit helps prevent longterm injury from sitting in bad chairs, it doesn't make them magically comfortable.

This assumed truism is actually arguable.

I can see that some furniture is better than others, but I actually am rarely all that uncomfortable regardless of the furniture. I will sit on a hard stool or a cheap chair with compressed dead cushion or a sumptuous stuffed chair almost equally fine all day long doing something engaging. As a kid I spent all day every day on rock hard absolutely non customizable chairs, and was fine. Because I was a kid.

The argument that you are the major ingredient in the equation of your comfort, not the chair, holds up.