The ability to walk all day without pain. I've an Arthritic knee that's not ready to be replaced at the moment but a couple of miles walking, using a stick is about my limit these days.
The good news is I can still ride. I this was taken on Monday, having ridden from Reeth.
(OK not that far, but still a reasonable ride, for me.)
I was last there in 2007 on my QNT for a ride to Northallerton and before that in 1966 hiking from Barnard Castle to Reeth.How I'd love to do that walk again.
The day before I did Durham big ride.