In high altitudes blood contain less or more hemoglobin

Question

In high altitudes is it compulsory for the blood to contain less or more hemoglobin?

Answer 1

In high altitudes, the air is rarefied and oxygen concentration is much lower than in low altitudes. In this condition the effectiveness of respiratory system should be greater and therefore the organism synthesizes more hemoglobin (and additional red blood cells) trying to acquire more oxygen. This phenomenon is termed as compensatory hyperglobulinemia. The compensatory hyperglobulinemia is the cause why athletes which will compete in high altitudes require arriving in the place some days prior to the event therefore there is time for their body to build more red blood cells and they will be less affected by the consequences of the low atmospheric oxygen concentration (that is, fatigue, reduced muscular strength).