I guess this is something where all of the many callouses on my palms came in handy. I use my freakin' hands so much I didn't even notice the exertion or pressure from pushing down on the tread of my wheels; I push my chair with the butt of my palms and I push with my wheels (not the push rims). I know I could do 15min on a good day.
I know this is off topic but I couldn't help passing a comment on your avatar ATG, well done, in time with a bit more work, that might actually look like a tricep!!