The main benefit of altitude training is that when elite athletes acclimate to high altitude, they acquire more red blood cells which allows their blood to carry more oxygen. When they compete at lower altitudes, they get a natural boost to the muscles when additional oxygen is available.
This blood expanding effect can enhance performance in elite athletes by 1 to 2 percent. While that may sound like a tiny improvement, it can be the difference between missing the final cut for a competitive team and earning a medal.