What the biochemical tests on the muscle showed was that the Sherpas' tissue was able to make much better use of oxygen by limiting the amount of body fat burned and maximising the glucose consumption.
"Fat is a great fuel, but the problem is that it's more oxygen hungry ( = NOT AS EFFICIENT) than glucose," Prof Murray explained.
In other words, by preferentially burning body sugar rather than body fat, the Sherpas can produce MORE ENERGY PER UNIT OF OXYGEN.
(This is not good news for stupid people who think that increasing fat burning by eating a high-fat diet is the key to running faster marathons.)
A genetic variation altering the way fats are burned was established.
While all of the Sherpas carried the variant of the metabolic gene that favors burning glucose, almost none of the lowland volunteers did.
Sherpas are a specific population amongst the Nepalese ("the Ferraris of the Himalayans", Formenti calls them) who migrated to the country 500 years ago from Tibet, which has been occupied by humans for at least 6,000 years. That is plenty of time for a beneficial gene to become embedded, Prof Murray argues.
"It's not down to one gene, of course. We see better blood flow through the capillaries; and they appear to have a richer capillary network as well so that the oxygen can be delivered better to the tissues. But this gene would also have given them some advantage."
They used parallel molecular, biochemical, physiological, and genetic approaches to the study of Sherpas and native Lowlanders, studied before and during exposure to hypobaric hypoxia on a gradual ascent to Mount Everest Base Camp (5,300 m).
Compared with Lowlanders, Sherpas demonstrated a LOWER capacity for fatty acid oxidation in skeletal muscle biopsies, along with enhanced efficiency of oxygen utilization, improved muscle energetics, and protection against oxidative stress.
This adaptation appeared to be related, in part, to a putatively advantageous allele for the peroxisome proliferator-activated receptor A (PPARA) gene, which was enriched in the Sherpas compared with the Lowlanders. The findings suggest that metabolic adaptations underpin human evolution to life at high altitude, and could have an impact upon the understanding of human diseases in which hypoxia is a feature.
http://www.pnas.org/content/114/24/6382
It is not a big surprise:
http://news.bbc.co.uk/2/hi/south_asia/2937734.stm
http://news.bbc.co.uk/2/hi/south_asia/3734931.stm