Not so fast, Lance Armstrong. Those high-elevation bike rides may not be doing you any favors after all.

Prolonged exposure to low-oxygen levels can actually be detrimental to physical performance, according to new research by a team of Oxford University researchers.

Athletic training high in the mountains is thought to enrich the blood with a higher amount of red blood cells. This happens when our bodies respond to the thin air’s low-oxygen levels by overproducing a particular protein, which then stimulates a hormone called erythropoietin (EPO).

EPO encourages bone marrow to make more red blood cells, meaning the body can carry more oxygen for a period of time, thereby possibly improving performance when athletes descend from a high altitude. It’s the reason why so many soccer teams trained at altitude for the World Cup.

In recent years, EPO has become famous for its genetically engineered counterpart, which several athletes have admitted to taking in a prohibited practice known as “blood doping.”

But the researchers found that metabolisms changed at altitude, becoming so much less efficient that the effects could counteract the benefits of altitude training.

“This change is counterproductive for physical performance. Its magnitude can overcome the positive effect of the elevated number of red blood cells, and it can be disadvantageous for athletes,” Federico Formenti, one of the lead scientists, said in a press release.

Patients with genetically high levels of the EPO-inducing protein were recruited for the experiment. Their exercise abilities and muscle metabolisms were tested through cycling exercises.

Results showed that chronically elevated levels of the EPO-inducing protein are associated with very limited exercise capacity.

“Only a limited exposure to altitude can be beneficial for athletic performance, and future research needs to quantify a prescribed amount of exposure to low oxygen levels,” Formenti said.

The study appears today in the journal Proceedings of the National Academy of Sciences.

Image courtesy of Flickr.