In part it is about control. I can't control your body, but I can control mine. Control is good. Power is good. Physical culture is the gaining and maintaining of power over that part of the physical world that is one's physical self.
Self-mastery, as the highest mastery, must include mastery of the vehicle of one's subjectivity. Control of one's vehicle is a clear desideratum. So stretch, run, hike, bike, swim, put the shot, lift the weight.
In short: rouse your sorry ass from the couch of sloth and attend to your vehicle. 'Ass' here refers to Frate Asino, Brother Jackass, St Francis' name for his body. Keep him in good shape and he will carry you and many a prodigious load over many a pons asinorum.
(It is interesting that the German Arsch, when it crossed the English Channel became 'arse,' but in the trans-Atlantic trip it transmogrified into the polyvalent 'ass.' Whatever you call it, get it off the couch.)