I don't think low T, or thyroid, or whatever medical reason causes some athletes to become sedentary. Personally I think they just simply get burned out, and some suffer joint pain from the years of sport activity and it pains too much to do whatever they may want to do. I remember when I was racing I got burned out, and I wasn't even a pro dedicating 8 to 12 hours a day 7 days a week to it! Anyway, that's my opinion based on no facts.