Typically athletes who incorporate altitude into their training will live at high-altitude for a period of time but train at lower altitudes.  This allows the body to adapt to altitude (including an increase in red blood cells) and these adaptations confer benefits to endurance performance.  Training low, however, is important, as it allows athletes to train at maximal intensity (which is not possible at altitude).  

Dear Gherman,

The body's adaptation to high altitude helps significantly but doesn't fully compensate for the lack of oxygen. Previous research showed that there is a drop in VO2 max of 2% for every 300 m elevation above 1500 m even after allowing for full acclimatization. It's know that this is a difficult concept to believe because so many programs have touted the benefits of high altitude training.To fully appreciate this realize that there aren't any world record times at high altitudes. Think about this a moment. The air density is much lower, thus wind resistance is much lower. Wind resistance is the cyclists biggest barrier to speed. If all other factors were equal, then there must be faster times at higher altitudes. Because there aren't, means that something else must have decreased. That something is the engine -- the human engine. Furthermore, while adaptation to high altitude makes you better at high altitude it hasn't proved useful for making you faster at sea level. In addition, there is a lot of mysticism that surrounds the belief of enhanced sea-level performance after altitude training, but the current scientific evidence is lacking. The reason is that some of the adaptive responses at high altitude are actually a hindrance at lower altitude. As more research is done then perhaps a training regimen that shows definitive improvement will emerge. The best advice as of 1994 is that high-altitude training is like "magic shoes" -- If it works for you then wear them. There is some more recent evidence to suggest that a "train-low, sleep high" approach may confer some advantages. In this scenario, training is carried out at low altitude -- to push anaerobic threshold, and VO2 max --but sleeping is done at high altitude so that the hypoxic stress increases red cell mass. Certainly a creative approach and one which might yield excellent results, because it may give the athlete the "best of both worlds". In a practical sense it may be difficult to construct, but if you are lucky enough to live in a situation that allows this type of training, it is worthy of consideration.

In addition, I send to you some material which deal directly with this subject.

I hope this helps.

http://www.rice.edu/~jenky/sports/altitude.html

Hi,

Marcelo Guimarães wrote: “In addition, there is a lot of mysticism that surrounds the belief of enhanced sea-level performance after altitude training, but the current scientific evidence is lacking”. Yes, it is almost correct.

However, do not forget some additional aspects, if you consider such training as running, cycling, XC skiing, etc. The aspects:

All it helps to make your training more effective and less burdensome.

Hi Andrei

Adapting the altitude increases the hematocrit and blood viscosity and thus higher risk to form clots. Intense training promotes platelet agglutination. So I do not see as necessary, see how dangerous.

"We conclude that 4 wk of acclimatization to moderate altitude, accompanied by high-intensity training at low altitude, improves sea level endurance performance even in elite runners. Both the mechanism and magnitude of the effect appear similar to that observed in less accomplished runners, even for athletes who may have achieved near maximal oxygen transport capacity for humans"

http://m.jap.physiology.org/ content/91/3/1113.abstract? ijkey= afba69c98df58026d22385e15af041 b479a26521&keytype2=tf_ ipsecsha

"the multifactor cascade of responses induced by hypoxia includes angiogenesis, glucose transport, glycolysis, and pH regulation, each of which may partially explain improved endurance performance independent of a larger number of red blood cells. Specific beneficial nonhematological factors include improved muscle efficiency probably at a mitochondrial level, greater muscle buffering, and the ability to tolerate lactic acid production."

http://www.ncbi.nlm.nih.gov/ pubmed/17805094

"transcranial magnetic stimulations were delivered to the first dorsal interosseus motor cortex area during short-term hypoxic (HX) and normoxic (NX) condition. M waves, voluntary activation, F waves, resting motor threshold (rMT), recruitment curves (100-140% of rMT), and short-interval intracortical inhibition and intracortical facilitation were measured. These data demonstrate that acute hypoxia results in increased cortical excitability and suggest that acute hypoxia alters motor cortical ion-channel function and GABAergic transmission"

http://m.jap.physiology.org/ content/101/6/1673.long

"The altitude sojourn began 1 wk after the USA Track and Field National Championships, when the athletes were close to their season's fitness peak. Sea level 3,000-m time trial performance was significantly improved by 1.1% (95% confidence limits 0.3–1.9%). One-third of the athletes achieved personal best times for the distance after the altitude training camp. The improvement in running performance was accompanied by a 3% improvement in maximal oxygen uptake (72.1 ± 1.5 to 74.4 ± 1.5 ml · kg−1 · min−1). Circulating erythropoietin levels were near double initial sea level values 20 h after ascent (8.5 ± 0.5 to 16.2 ± 1.0 IU/ml). Soluble transferrin receptor levels were significantly elevated on the 19th day at altitude, confirming a stimulation of erythropoiesis (2.1 ± 0.7 to 2.5 ± 0.6 μg/ml). Hb concentration measured at sea level increased 1 g/dl over the course of the camp (13.3 ± 0.2 to 14.3 ± 0.2 g/dl)"

Article Nonhematological Mechanisms of Improved Sea-Level Performanc...

Article The effects of short-term hypoxia on motor cortex excitabili...

Article "Living high - training low" altitude training improves sea ...