Sherpas are among the most unfathomably fit athletes around.

Even the most experienced climbers require additional oxygen when they trek 8,848m (that's 29,029 feet) above sea level to Mount Everest's peak. But Sherpas, an ethnic group of people from the mountain regions of Nepal, are an exception—they live at high altitude without seeming to suffer any health consequences, according to University of Cambridge researchers.

At that altitude, Sherpa bodies seem to run on premium while everyone else is burning on fumes, struggling to ascend behemoth peaks amid low levels of oxygen and barometric pressure. That's because Sherpas are working at a higher caliber than the rest of us.

Now, thanks to fascinating new research published in the Proceedings of the National Academy of Sciences, we know exactly how Sherpas' bodies have adapted over time to make them high-functioning mountain trekkers.

First: Why high altitudes really screw with people

If you live at sea level, then cart your ass up to the Mount Everest Base Camp in Nepal, you'll be ascending to a nauseating 5,300m (about 17,400ft). When you go beyond 9-10,000m, you enter the stratosphere, which has about half the oxygen you're used to, making it increasingly difficult to breathe—and exercise, per the British Medical Journal

Because of this, your body is forced to work harder to get oxygen to your brain and muscles. One of the ways it does this is by cranking out more red blood cells, which transport oxygen around the body to your organs. Problem is, this thickens your blood, slowing its flow, and increasing the odds of blood vessel blockages.

At this point, it's not uncommon to suffer from hypoxia, a condition where your body's tissues aren't getting enough oxygen. The consequences are grave. Without oxygen, your cells begin to die, damaging organs like your liver and brain. Symptoms include confusion, racing heart rate, and shortness of breath. Getting oxygen into your body is the most crucial step to get a handle on hypoxia. Typically, climbers take time to let their bodies acclimate to major altitude changes in order to prevent this. But the researchers believe their findings—how and why Sherpas are so efficient at producing energy in scarce oxygen conditions—can lead to new treatment options that'll help more than just mountaineers.

5 ways Sherpas are biologically superior mountain climbers

Cambridge University researchers studied the metabolic adaptations Sherpas (and Tibetan populations) possess, then compared them to that of lowlanders. The scientists followed two groups of climbers as they made a gradual ascent up to Everest Base Camp. The lowlanders group was made of 10 investigators who worked the Everest Base Camp laboratory, and the Sherpas group comprised 15 climbers living in low-lying areas. 

The scientists took blood samples and muscle biopsies of the lowlanders group in London for a baseline measurement and in Kathmandu, Nepal for the Sherpas, then again at Everest Base Camp, and a third time two months post-trek. For the Sherpas, measurements taken at altitude rarely changed from baseline, suggesting they were born with their metabolic differences. But, for lowlanders, the measurements changed over time at altitude, suggesting that their bodies started adapting and mimicking the Sherpas'. Here's where Sherpas surpass your average climber:

  1. Fewer red blood cells but higher amounts of nitric oxide. Sherpas' bodies don't produce a surplus of red blood cells in response to low oxygen like we see in lowlanders. However, their bodies do pump out more nitric oxide, a chemical that opens blood vessels to promote stronger blood flow. This keeps them alert and energized. 
  2. More efficient use of oxygen. Mitochondria, as you probably remember from fifth grade biology, are the powerhouses of the cell. Researchers found the Sherpas' mitochondria were more efficient at using oxygen to produce ATP, the energy that powers our bodies.
  3. Better fat-burning capacity. Your muscles can get energy from sugar or by burning fat, which is called fat oxidation. Most of the time, our bodies pull energy from fat. When you exercise or you're under physical strain, your body generates energy from sugars, since the process is chemically simpler. Interestingly enough, Sherpas have lower levels of fat oxidation, suggesting they're more efficient at generating energy from fat.
  4. Steady phosphocreatine levels. Phosphocreatine is an energy reserve that acts as a safeguard to help muscles contract when ATP is depleted. In lowlanders, after two months at high altitude, phosphocreatine levels crashed, but in Sherpas, the levels actually increased.
  5. Low amounts of free radicals. When the body suffers a lack of oxygen, it can form harmful free radicals that can damage cells and tissues. For lowlanders, levels of free radicals rapidly increased at high altitude in the beginning, while levels in Sherpas remained very low.  

"Sherpas have spent thousands of years living at high altitudes, so it should be unsurprising that they have adapted to become more efficient at using oxygen and generating energy," lead study author Andrew Murray said in a press release. "When those of us from lower-lying countries spend time at high altitude, our bodies adapt to some extent to become more 'Sherpa-like', but we are no match for their efficiency."

 Still, it couldn't hurt to plan a high-altitude trip. Research shows your body's performance-boosting metabolic changes stick around for at least a week or two. There's a reason endurance athletes train at high altitude.

Think you have what it takes to survive a mammoth climb? These are the fitness requirements for conquering a climb like Everest.

*This study is part of Xtreme Everest, a project aimed at improving outcomes for critically ill patients (not necessarily in relation to altitude sickness) in intensive care by understanding how our bodies respond to the extreme altitude on the world's highest mountain. It's partially funded by the British Heart Foundation.