Armstrong, a six-time winner of the Tour de France bicycle race who next month will try for his seventh straight victory, can cover 32 miles, or 50 kilometers, in one hour of riding. In contrast, the average cyclist covers 16 miles; a top marathon runner can cover 21 miles on a bike.
Armstrong can ride up the mountains in France generating about 500 watts of power for 20 minutes, something a typical 25-year-old could do for only 30 seconds. A professional hockey player might last three minutes and then throw up.
How does he do it?
So how does he do it? According to a scientist who studied Armstrong at regular intervals from 1992 to 1999, his prowess can be explained by a set of physiological changes that took place in his body over those seven years and that, in all probability, are continuing.
The changes are described in an article entitled "Improved Muscular Efficiency Displayed as Tour de France Champion Matures" in the June issue of The Journal of Applied Physiology.
The scientist, Edward Coyle, director of the Human Performance Laboratory at the University of Texas, has studied cyclists for 25 years. He says they need large hearts and low levels of lactic acid the byproduct of intense exercise in their blood. Their efficiency, measured as how many watts of cycling power are generated for a given cycling input, needs to be high.
"Lance came to us when he was 20 years old, very early in his career," Coyle said. "He wanted to know what he could do to improve himself."
Armstrong, Coyle said, indeed had an exceptionally large heart and low lactic acid. "But his muscle efficiency was not very good," he said. "It came in at 21 percent. That first year two other athletes we studied were better."
Armstrong showed subsequent improvements until his career was stopped short in 1996 with a diagnosis of testicular cancer. Eight months after his treatment ended, he was back in the Austin, Texas, laboratory.
"He wanted to know if anything was permanently wrong," Coyle said.
They took measurements and found nothing to stop him, except his own willingness to compete.
Armstrong did compete.
Improved efficiency: Increased slow-twitch muscles
"In the next two years his heart got even better, his lactic acid dropped further and, amazingly, his efficiency increased to 23 percent," Coyle said.
That may not sound like much, but it means that for the same level of oxygen consumption, Armstrong gets more power to the pedals. By taking off body weight, he was delivering 18 percent more power to his muscles.
There is only one way such efficiency could improve, Coyle said: more slow-twitch muscles, the type that do not burn out quickly and that are used in standing or walking. Fast-twitch muscles, which burn out fast, are used for sprinting and heavy lifting.
Rodent studies show that chronic stimulation to muscle tissue increases the amount of slow-twitch fibers, Coyle said. Armstrong appears to have increased the proportion of his slow-twitch muscles from 60 percent to 80 percent.
In bicycle races, slow-twitch fibers are up to twice as efficient as fast twitch.