New study finds that prolonged training at altitude may decrease athletic performance

It has been long established endurance doctrine that training at altitude increases an endurance athletes performance by boosting the number of red blood cells in the body and thus increasing the athletes ability to use oxygen.
In other words, more red blood cells in the blood steam directly increases the amount of endurance for better performance.
But a new study just published in Proceedings of the National Academy of Sciences and funded by the British Heart Foundation finds that long exposure to high altitudes can actual decrease endurance and performance.
According to HealthCanal.com:
"an extended stay at altitude can bring a loss of the muscle’s ability to use oxygen to carry out work. The number of mitochondria, the oxygen-using powerhouses of the cell, falls with a prolonged stay at high altitude," the study found.

"It is the higher capacity to deliver fuel to muscles that athletes are interested in," explains lead author Dr Federico Formenti of the Department of Physiology, Anatomy and Genetics at the University of Oxford. "However, it’s not clear how long they should train at altitude or how high up they need to be to get the optimal benefits"
It's important to note that this study was very small.
It compared the performance of only 5 people with a rare condition called Chuvash polycythemia or CP to that of 5 non CP individual or "controls" using a "an exercise bike test, in which study participants were asked to keep a constant pedal rate against a steadily increasing resistance, those with CP had to stop exercising earlier. The maximum work rate they achieved for their weight was 30% less than controls."
"There may be an optimum time for athletes to train at altitude," suggests Dr Formenti. "More work is needed to find out how long athletes should spend at low oxygen levels to get the most benefit."

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