I'm not sure the strength training was such a big issue. Has it been confirmed that he gained muscle? I think it was more his confidence in his TDD and hands that he wasn't conditioned to be put on his back much. Once that happened, and happened often he lost the mental edge, and his game plan shut down. All that was left was heart and pride.
"Let them see that their words can cut you, and you'll never be free of the mockery. If they want to give you a name, take it, make it your own. Then they can't hurt you with it anymore." - Tyrion Lannister