Dean Karnazes has an incredible and rare condition which means he never gets cramps or muscle burn. And this is a man who has taken on some of the toughest endurance runs in the world.
He's run a marathon to the South Pole in temperatures of -40°F, run through Death Valley in 120 degree temperatures. And he's also competed in the Marathon des Sables, known as the toughest footrace on earth it's a six day ultramarathon involving 156 miles.
But perhaps his most superhuman feat is the fact he once ran 350 continuous miles, going for three nights without sleep. "The third night of sleepless running was a bit psychotic." he's said. "I actually experienced bouts of ‘sleep running’, where I was falling asleep while in motion, and I just willed myself to keep going.”
Karnazes first realised he was physically different to other runners while preparing to run 50 marathons over 50 days across all 50 states of the US in 2006.
“I was sent to a testing center in Colorado,” he told The Guardian. “First, they performed an aerobic capacity test in which they found my results consistent with those of other highly trained athletes, but nothing extraordinary. Next, they performed a lactate threshold test. They said the test would take 15 minutes, tops. Finally, after an hour, they stopped the test. They said they’d never seen anything like this before.”
Most of us have what's known as a lactate threshold and going beyond it means your body starts producing lactic acid, the cause of cramps, at a rate where it cannot be broken down, causing exercise to become pretty much unbearable.
Karnazes' condition means he can very quickly clear lactic acid from his system, so he never reaches this threshold meaning he can effectively, with the right training, run for days—which he did.
It's believed that this is a genetic condition but was also helped by the fact that Karnazes did a lot of running from a very young age—a mix of nature and nurture.
He's basically X-Men in real life. You can learn more about how Karnaze prepares for a run in the video below.