An organism tends to behave differently when exposed to higher altitudes. Training at altitude presents an effective means to enhance performance especially in endurance athletes.
The high altitude environment may be divided into three zones according to its altitude (Máček, Radvanský, 2011):
- medium altitude 1.500-2.500 m above sea level
- higher altitude 2.500-5.300 m above sea level
- extreme altitude over 5.300 m above sea level
In this environment (Fig. 29) both the atmospheric pressure and partial oxygen pressure (PO2) tend to drop with rising altitude. With rising altitude the air temperature is reduced by 1°C for every 150 m of altitude irrespective of latitude. Latitude, however, tends to affect seasonal and daily temperature fluctuations (differences in the sun and in the shade).
Figure 29 External conditions in various altitudes
Alpine fresh air shows a reduced pressure of water vapours, the absolute humidity is likely to be extremely low in high altitudes. The combination of low relative humidity may be perceived as very uncomfortable. The air tends to be drier and thinner. The intensity of sunshine, especially its UV element rises, however. The intensity of UV radiation expands by 20-30% for every 1.000 m, these effects are multiplied by snow reflection. Also the intensity of cosmic rays grows (generation of oxygen radicals whose amount grows in proportion with a rising oxygen pressure). In higher altitudes lower gravitation and air flow may be observed.
The reduced partial pressure unfavourably affects both the transfer of oxygen from alveoli into capillaries of a small blood circulation (through diffusion) and the transport of oxygen to tissues. This results in the situation where the tissues are deprived of the adequate oxygen supply, hypoxia (Jančík et al., 2007) The high altitude environment causes the reduced haemoglobin affinity for oxygen which affects a sports performance.
Response of an organism to the high altitude environment
In the altitude of 2.500 m above sea level a decline in the supply of oxygen to tissues is not significant. Only 15% of those entering this level my show signs of acute altitude disease. (Máček, Radvanský, 2011)
Hypoxic conditions of the high altitude environment affect physiological responses of the organism. A diffusive gradient which plays an indispensable role in the exchange of oxygen between the blood and tissues is significantly disturbed. The percentage of haemoglobin saturated with oxygen is reduced. The organism is trying to avert these negative influences through activation of regulatory mechanisms and thus increase the oxygen supply. As a result hyperventilation occurs both under resting conditions and under workload, and deeper (enlargement of tidal, i.e. breathing volume- VT) and faster breathing (increase in breathing frequency -BF) appears. Regarding circulatory parameters both the heart rate (HR) and the cardiac output (Q) tend to increase. Openings of vascular capillaries increase dramatically preventing acute hypoxia. There follows a gradual decrease of the blood plasma volume resulting in the increased concentration of erythrocytes which in turn allows greater oxygen transfer and thus compensates for the reduced oxygen supply (Jančík et al., 2007)
The decline in bodily performance may well be connected to the reduction of VO2 max which drops in a linear manner with rising altitude, about 10% for 100 m (Máček, Radvanský, 2011, according to Wilmore, Costill).
Adaptation (acclimatization)
Adaptation of an organism to the high altitude environment is a long-term matter. It is a complex process spanning a few weeks, the speed of which depends on the altitude. There is a gradual increase in the capacity of the oxygen transporting system. More erythropoietin is released (EPO) which increases the generation of erythrocytes in the bone marrow. Thanks to this the level of haemoglobin which transports oxygen in the blood, is rising. In an organism there occurs a continual increase of mitochondria, myoglobin and enzyme activity. Vascularisation (growth of blood vessels into a tissue with the result that the oxygen and nutrient supply is improved) is strengthened. (Jančík et al., 2007, according to Havlíčková, 2004)
Recent studies do not confirm a significant improvement in performance in the lowlands following altitude training. Conditions in the medium and higher altitudes lead to dehydration and muscle atrophy.
To achieve overall improvement of performance current studies recommend training at lower altitudes alternated with stays at medium altitudes (to achieve an increase in erythrocytes).
Acclimatization
The duration of acclimatization varies depending on an individual in question and other factors such as the climbing speed, absolute height reached, relative height difference surpassed and the momentary health condition.
Medium altitude 1.500-2.500 m above sea level
The saturation of arterial blood with oxygen (SaO2) exceeds 90%, tissue oxygenation is not constrained. In the first days of the stay resting ventilation increases.
High altitude 2.500-5.300 m above sea level
2.500 m above sea level is the threshold altitude to trigger acclimatisation processes. SaO2 drops significantly under 90%. At this altitude complete and long-term acclimatization may be achieved. La Rinconada, Peru, a mining village is currently the highest permanent human habitation at an altitude of up to 5.100 m above sea level.
Extreme altitude over 5.300 m above sea level
Humans are not able to adjust to these altitudes and during longer stays the organism starts to waste away. Oxygenation is secured only by significant ventilation. Starting at an altitude of 6.000 anaerobic glycolysis and generation of lactate are inhibited. The oxygen saturation value on the peak of Mount Everest reaches about 50%.
Acclimatization progression
Acclimatization is divided into stages. Complete acclimatization to a certain altitude is indicated by the resumed (i.e. identical with original values) resting heart frequency measured on awakening in the morning. The duration of acclimatization varies depending on an individual in question and other factors such as the climbing speed, absolute height reached, relative height difference surpassed and the momentary health condition.
The following information shows approximate duration of acclimatization needed at different altitudes:
3.000 m – 2-3 days
4.000 m – 3-6 days
5.000 m – 2-3 weeks
Humans are not able to adjust to altitudes over 5.500 m (over this limit the decline of health and performance is inevitable despite maximum physical preservation). Adaptation mechanisms enable the organism to survive only a few days at such altitude. Adaptation to hypoxia includes changes in oxygen transportation into tissues and changes in its utilization in cells. Accommodation, i.e. the initial response in untrained individuals, takes effect in a few seconds to hours. The terms acclimatization and acclimation refer to changes taking effect in the course of days or months of the stay in a hypoxic environment (phenotypic adaptations which become reversible after return to normoxic conditions).
Acclimatization stages:
- Latent phase – takes place during the first six hours after reaching a particular altitude, without symptoms of acute altitude disease (AAD)
- Acclimatization – period of acclimatization acquisition accompanied by a substantial risk of acclimatization disorders (AAD)
- Acclimatization – a period spanning 2-3 weeks during which a human becomes optimally adapted to an altitude and is capable to produce his/her maximum physical performance
- Degradation (altitude deterioration) – accompanied by a decline in physical and mental functions
General rules of acclimatization
- To stay overnight at the lowest possible altitude, climb in stages and stay overnight at an altitude lower than the one reached.
- Every 500 m of covered altitude should be compensated by two nights spent at the same altitude. It is not advisable to stay overnight in a camp higher by more than 1.000 m during a single week.
- To sleep with the upper part of the body slightly elevated, acclimatization may not be accelerated by any medicine.