He played heavier than his weight or body could handle.
There is no telling how many players have lingering injuries that they just play through for the rest of their career.
I remember I had some weird cartilage damage in my chest for years from working out. You literally hear it click and it was a permanent pain. I have a very high tolerance for pain so I just accepted it.
Then one day I just took some over the counter supplements and two days later is was good as new. Blew me away. The body is the greatest invention but there is so much we don't understand about it