This is good advice, if it doesn't become idolatry. If a person would sacrifice her soul for physical gain, then that physical gain is idolatry. By the way, this world always will try taking a soul, leading the weak to do wrong or to go too far. Gender "change" is a fair example of that. And I think extreme bodybuilding can lead the weak to try recreating themselves as a means not to be weak anymore, not realizing they're sacrificing the spiritual self that has true strength (2 Cor 12:9).