An interesting article in the New York Times yesterday examines Why Joggers Labor and Olympians Fly. Apparently elite atheletes (like we know from cyclist Lance Armstrong) possess physiological traits that "normal" people don't have, such as larger hearts.
Exercise physiologists say there are three components to great running: A high VO2 max, the volume of oxygen an athlete can consume at maximum exertion; great running efficiency, a measurement of the energy used to run at a particular pace; and an ability to keep going at a high level of exertion for a long time, expressed as the percentage of VO2 max that can be sustained during a run.
Some day I'd like to get my VO2 max measured. Meanwhile, my marathon training has been progressing quite well, or it was until yesterday when I was running in the woods, took my mind off the trail, and started thinking about the interval training I was going to do after I warmed up. Then I tripped on a root and went non-Olympian flying through the air, bonking my knee as I skidded along the pine needled floor of the forest. No interval training after that, just a slow jog back home and a day of icing the knee. I guess I'm still in the "Joggers Labor" phase of my running career.