Dean Karnazes, a 53 year old ultrarunner from California has completed some of the toughest endurance events on the planet, from the legendary Marathon des Sables to completing a marathon to the South Pole in temperatures of -25C. Amazingly, he has never experienced any form of cramping or muscle burn.

Karnazes he first realized he was different from other runners while training for the next stunt, running 50 marathons across 50 states in 50 days. Along with other runners, he was sent for an aerobic capacity test as well as 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," he revealed.
Under normal circumstances, the body uses oxygen to break down glucose to produce energy. During intense exercise however, there is insufficient oxygen available to produce the required amount of energy, which results in the production of lactate, or lactic acid.

Lactate can be further converted to energy without oxygen, but prolonged exercise causes it to build up faster than it can get burned off. The point when lactic acid starts to build up is called the "lactate threshold."

The lactic acid build-up is what causes the burning feeling in muscles, leading to aches, cramps and weakness. It is the body’s way of telling you to slow down or stop – but Karnazes never receives this signal. “No matter how hard I push, my muscles never seize up. That's kind of a nice thing if I plan to run a long way," he says.

As Laurent Messonnier from the University of Savoie explains, lactate is cleared via a series of chemical reactions driven by the mitochondria in muscle cells. And such reactions transform lactate back to glucose again and they are enhanced by specific enzymes.

Years of training will improve both the enzymes and mitochondria and result in improved clearance. However, there is a limit to how much lactate threshold can be improved by training alone. Those who inherit these enzymes and a larger mass of mitochondria genetically have far higher personal limits.

While genetics can give the propensity for a natural advantage, genes are still expressed differently depending on your environment and your lifestyle. Karnazes believes that his lactate clearance abilities might be caused or enhanced by his low body fat, low sweat rate, a high alkaline diet and low exposure to environmental toxins.

An interesting experiment could be to repeat the lactate threshold test with Karnazes' brother, who plays competitive volleyball but no extensive amount of running.

"I would be curious if he exhibits some of those same abilities to clear lactic acid from his system." Karnazes says.

This might shed some light on the genetic and environmental influences on his own lactate clearance abilities. MIMS