It probably has much more to do with feeling. Big on some small on others, the ever popular butt is fascinating to me. Well, maybe you did it when you were a kid. The only time we really acknowledge our butt is when it hurts. All that sitting leads to one thing.
Nothing is more uncomfortable.
The more you sit the more your back hurts too. It's a pretty important thing too. Houses all those nerves and fibers and such. The neck too. What a fragile piece of work.