Human muscles are made up of two types of fibers - called slow twitch (Type I, and fast twitch (Type II) muscle fibers. Both set of fibers work exactly as they sound. Slow twitch fibers are slow - but they can work for long periods. They do this by burning fuel aerobically, with enough oxygen. Since the process is inherently slow, it is not nice to expect slow twitch fibers to be quick.
The exact opposite are fast twitch fibers. Fast twitch fibers deliver speed, by quickly burning whatever fuel it can find even without oxygen - anaerobically. The problem is anaerobic fuel burning is not sustainable. So the fast twitchies, they a good to get you going but do not last long.
I had known this instinctively for a while because I had, for all intents, no slow twitch fibers in my muscles. I had always been able to do the sprint - the 100m. I was second fastest in school. But increase the length to 200m, I was fourth fastest. Anything beyond that, I was not interested.
So, I had resigned myself to never being able to pound the treadmill. Then I came across that pink image up top (click to expand). This is a version of the couch to 5k program. And the best part is it works! I am currently in week 6, having run continuously for 21 minutes last week. Which for someone who can barely do 400m is unbelievable.
TED, of course, takes it to a new level. Apparently what I am doing is not unbelievable, merely something that all of us are inherently capable of. A friend sent across this timely TED video. Enjoy.