Moving with good form requires the right kind of fuel. Simply look at triathletes finishing an Ironman or runners finishing a marathon. Often they are bent over, twisted, and shuffling. Their gait patterns have been broken. Their bodies have been broken.
You’d be surprised at how rapidly your gait falls apart when your gas tank is low. You may start out your run with fluid motion and with swift and efficient form. Yet after twenty or thirty minutes – or maybe at mile twenty, for you marathoners – you may look as though you ran through a minefield, dragging one leg, swinging one arm out to the other side, scuffing your heels, and drooping your head. And at the finish line, you look even worse as you’re leaning to one side or hunched over because your lower back is in agony.
Did an injury occur during your run? In a way, yes, but not so directly.