sitting watching the tv uses oxygen...lol. i get both points, up until a couple of yrs back, i used to do alot of running 10k, half marathon and full marathon. think marshman may have been differentiating between a full blown lung busting sprint to a slow pace setting LONG jog. to me, a 10k, tho shorter, was harder on the lungs, as you have to hit your pace fast and hold it, no need to fuel up over the distance. half marathon and above is more an endurance test and you must take on fuel (glycogen) as you go or your body will start using lean muscle and you'll hit the infamous "wall". to me, th