Dean Karnazes: The Man Who Doesn’t Tire of Running

Most runners have to stop when they reach their lactate threshold, but Dean Karnazes’ muscles never tire: he can run for three days and nights without stopping. What’s his secret? The answer: he doesn’t have a lactate threshold.

When running, you break down glucose for energy, producing lactate as a byproduct and an additional source of fuel that can also be converted back into energy. However, when you exceed your lactate threshold, your body is no longer able to convert the lactate as rapidly as it is being produced, leading to a buildup of acidity in the muscles. It is your body’s way of telling you when to stop – but Karnazes never receives such signals.

“To be honest, what eventually happens is that I get sleepy. I’ve run through three nights without sleep and the third night of sleepless running was a bit psychotic. I actually experienced bouts of ‘sleep running’, where I was falling asleep while in motion, and I just willed myself to keep going.”

A brief explainer on the lactate process:

Your body clears lactate from the blood via a series of chemical reactions driven by the mitochondria in your muscle cells. These reactions transform lactate back to glucose again and they are enhanced by specific enzymes. The clearance process also works more efficiently if your mitochondria have a larger capacity, increasing their ability to use lactate as a fuel.

Years of training will improve both your enzymes and mitochondria and so improve your clearance, but there is a limit to how much you can improve your lactate threshold by training alone. If you inherit these enzymes and a larger mass of mitochondria genetically, your personal limits will be far higher.

In this 2006 interview with Outside Magazine, Dean offered his thoughts on pursuing his passion:

Outside: I know you just ran a marathon and want to get back to the bus to relax, so I’ll jump right in. The theme of our story is how to take your life from a seven to a ten. How did you decide to do that for yourself? 

Dean Karnazes: I made the commitment to turn my passion into my vocation. I’d always thought if I start making my life what I love, I might hate it. I might not enjoy it as much for some reason. I think that was an excuse more than anything else, because now that I’ve decided to do exactly what I love to do, it’s been the most rewarding, fulfilling experience of my life.

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