Running the Tor des Geants is not for the faint of heart. Widely regarded as one of the world's toughest endurance events, the 210-mile (336-kilometer) foot race climbs through some of the steepest and wildest terrain in the Italian Alps, taking runners up and over some 25 major mountain passes and involving a total of more than 80,000 feet (24,000 meters) of vertical elevation gain.

The rules are simple. This is not a stage race. Whoever gets to the finish line first is the winner, simple as that. From the moment the starter's gun goes off in the mountain village of Courmeyeur, in Italy's Aosta Valley, competitors have 150 hours to complete the course. How, when, where, even if they get any sleep during the race is completely up to them. The focus is solely on getting to the finish.

Only the fittest and most tenacious can see it through. Last year's winner completed the course in just under 76 hours, running day and night along a tough mountain track, pausing along the way for a mere three hours or so of catnapping.

So how can it be that the finishers of this gruelling race end up experiencing less muscle soreness and fatigue than similarly fit athletes who compete in races less than half the length?

It appears that sleep deprivation and pacing strategies play key roles in protecting an athlete's muscle tissue in extreme endurance events, according to a new study by researchers at the Institute of Sports Science at the University of Lausanne, in Switzerland, which appears this week in the open-access journal Plos One.

Is This Super Endurance Finding New?

"Very new," said the report's lead author Jonas Saugy. "This is the first physiological study of athletes who are competing in a mountainous ultra-marathon more than 50 hours long," he said.

Saugy and his colleagues monitored the performances of 25 top competitors at last year's Tor des Geants, athletes who finished in the top third of the rankings. They tested the effects of sleep deprivation and checked various blood and muscle markers for inflammation and muscle fatigue.

Then they compared these results with an earlier study done on similarly fit athletes who had run the 103-mile (166-kilometer) Ultra-Trail du Mont-Blanc—an equally tough but much shorter race. "And when we did that, we found that inflammation and muscle damage were much lower in the athletes who had completed the Tor des Geants than in those who had done the shorter event," said Saugy.

The molecular-level research done by Saugy and colleagues dovetails nicely with the firsthand experiences of world-class ultra-marathoner Dean Karnazes, who over the course of his career has run dozens of extreme endurance events all over the globe, from the Gobi to the South Pole, sometimes covering distances of up to 350 miles (560 kilometers) nonstop.

"This is fascinating research," said Karnazes. "I have done a good many runs over 200 miles (320 kilometers) and been surprised to find myself feeling surprisingly good the next day—often better than when I have run much shorter races. My support crews have also noticed much better than expected recuperation after really long runs."

Karnazes added, "It'll be interesting to see where they go with this."

A Tired Body's Response

In a nutshell, the reason behind that surprising level of endurance may come down to shrewd pacing and the body's response to the cumulative weariness brought about by many hours of sleep deprivation, explained Saugy. "During the first part of the race, runners adopted an anticipatory pacing strategy," he said.

"They didn't sleep much, if at all, simply trying to run as far as they could in the shortest amount of time. As the race progressed, though, the cumulative effects of sleep deprivation forced them to decrease their speed and intensity, helping to preserve muscle tissue.

"Moreover, in the latter stages of the race they tended to sleep more—the sleep periods again helping them to preserve their muscle tissue," said Saugy.

Why Is This Important?

If you're an elite athlete competing in one of these extreme mountain-running endurance events, this kind of research can be very important in understanding how to manage your reserves, and what role sleep deprivation will play in your performance, Saugy suggests. "Pacing is really paramount in these competitions," he said.