For more than 3 decades, endurance athletes around the world have engaged in altitude training. 

In the field of athletics, runners from Kenya, Ethiopia or Morocco have dominated their disciplines for several years: these are athletes who live at altitude or who at least spend protracted periods in high altitude areas. 

Western and Asian athletes have taken to periodic training sojourns at altitude too. 

There are at least three principal effects of altitude training on the organism: 

- Increases in haemoglobin (Hb) and thus in the blood’s ability to carry oxygen 
- Higher efficiency in the respiratory gas transfer in the lungs 
- Increases in peripheral use of oxygen in the muscles. 

This article will deal only with the effects of altitude training on the blood, in particular with the variations in Hb, hemocrit levels 5HCT) and plasmatic volume (PV). 

The common finding when a person goes to moderate altitude (1800-3000 m above sea level) is a transient increase in haemoglobin and hematocrit concentrations because of a rapid decrease in plasma volume, after which haemoglobin levels and hematocrit usually fall when the plasma volume increases. 
Within 6 to 10 days, with the normalisation of plasma volume, the increase in erythropoiesis per se induces a concomitant increase in haemoglobin, hematocrit and total haemoglobin. 

Both elite athletes and non-athletes have maximal reticulocytosis (reticulocytes are the young red cells) after about 8 to 10 days at moderate altitude and continue to have elevated reticulocytes throughout an altitude training camp of 3 weeks, with a total increase of haemoglobin of about 1 to 4%. 

A more accentuated increase in red blood cell mass can be obtained with longer sojourns at moderate altitude; in fact, 4 training sojourns (3 to 4 weeks) with intervals of about 1 week may produce individual increases in haemoglobin concentrations of 10 to 15 g/L (or 1.0-1.5 gr %) 
The increase in haemoglobin level may seem small, but the total haemoglobin volume of the blood in endurance athletes is about 50% greater than in non-athletes; thus, a given increase in total haemoglobin reflects a smaller increase in athletes than non-athletes. 

The increase in blood volume found after physical training at sea level consists not only of increased red blood cell mass, but also of increased plasma volume. This is the reason for haemoglobin concentration being within the normal range even in endurance athletes with a very high total haemoglobin volume. 

When training in altitude, it is very much advisable to increase the daily protein intake up to 1.5-2.5 g/Kg: only a single day of protein deprivation can decrease erythropoietin (EPO) production after hypoxia. The most important “erythropoiesis specific” nutrition factor is, however, iron availability. 
At high altitude, as well as during severe anaemia at sea level, there is a need for rapid mobilisation of iron and even if the iron stores might be large enough (expressed as calculated serum ferritin), they may not be mobilised fast enough.

 

What about the haematological adaptation time at moderate altitudes? Data from healthy athletes suggest a true increase in haemoglobin of about 1% every week. Complete adaptation occurs when sea level residents have similar haemoglobin levels to the residents at moderate altitude. 

The normal difference in haemoglobin levels between permanent residents at sea level and at 2500 m above sea level can be estimated to be about 18gr/l, i.e. about 12%. 
Therefore, the difference in haemoglobin levels between permanent residents at sea level and at 2500 m above sea level indicates a necessary adaptation time of about 12 weeks. 
A continuous period of at least 10 weeks, with adequate iron supplementation, is probably needed for optimal haematological adaptation in athletes training at moderate altitudes. If the training period at moderate altitude must be shorter, several sojourns at short intervals are recommended. 

Can the haematological adaptation time at moderate altitudes be speeded up? Transient increase in EPO concentrations, and probably also of erythropoiesis, may be achieved during repeated short terms stays (without training) at higher altitudes during a training camp at moderate altitudes. 

- Practical Advice - 

Start iron oral supplementation at least 2 to 3 weeks before the ascent. 
Continue iron supplementation at moderate altitude at least during the first 2 to 4 weeks. If serum ferritin is below 40 ng/l, parental iron treatment (100 mg/w) is also recommended. 

 

Combine iron supplementation with vitamin C (0.5 to 1 gr/day) to increase gastrointestinal iron uptake and with tocopherol (vitamin E, 100 to 500 mg, three times daily PO) to minimize free oxygen radical formation. Ensure an adequate daily intake of protein and polyunsaturated fatty acids. 

Avoid maximal exercise especially during the first few days at high altitude to minimize any exercise-induced decrease in erythropoietin production, increase in haemolysis and acute inflammatory reactions. 

I also suggest having a complete rest on the 3rd or 4th day of your stay in moderate altitude, and another very easy training the 8th day, in order to help the adaptation to such elevations.