Endurance Training: Is Fatigue Just In Our Heads?

According to this article at National Geographic Adventure a new study seems to indicate that fatigue may all just be in our head. The study says that it is a side effect brought on by our neverous system in order to prevent us from overdoing it while we exercise. They even offer a few ways of fighting off fatigue and getting your body to go even further. Interesting study to say the least, but when I'm six miles into a run, on a very hot day, I'm not sure all that fatigue is in my head. :)