I think endurance sports (and many other sports, like rock climbing, which I enjoy), are a mix of type 1 and type 2 fun (https://www.rei.com/blog/climb/fun-scale). There may be some suffering while you do it, but the overall experience is positive when you look back at it. This is quite different from surgery without anesthesia, which would definitely not be fun in the end, at least for most people.