"The devil sent into him a grave temptation to luxuria. So the holy Father, seeing it right away, took off his clothes and beat himself with cords saying, 'So, Brother Ass, thus should you remain, under the whip! The habit is of religion and you can't steal it; if you want to go away, go!'" (Thomas of Celano's second Life, chapter 82)
We often quote St. Francis's nickname for his body, Brother Ass, in the sense that the body is stubborn and often unwilling to cooperate with our spiritual aims. But as I've thought about it over the years, I think there is a positive side as well. Like an ass, the body is capable of bearing tremendous burdens and getting a lot of work done when trained properly. We have all seen this in hard-working Christians.