Altitude training is commonly used by competitive athletes to improve sea level performance. Especially when interspersed with normoxic training sessions using the "living high - training low" model, it results in an expanded hemoglobin mass and blood volume, and 1-3% improvements in endurance performance in most (though not all) athletes. However the robustness and duration of this improvement remain uncertain and the deacclimatization process has been little studied. Coaching "lore" dictates a period of prolonged sea level recovery before competition, though this concept has not been proven rigorously. Moreover, there is some Suggestion that low altitude training may mitigate some of the negative aspects of performing all training at higher altitudes, and allow competition soon after exposure. Three major processes need to be considered in examining the "off response" after a period of altitude training: 1) the basic biology of the hypoxia response pathway which results in rapid hydroxylation of HIF under normoxic conditions and ubiquitinization/proteosome destruction of the HIF-vHL complex; 2) the suppression of erythropoietin below baseline levels with restoration of normoxia leading to the withdrawal of EPO's stimulatory effect on the EPO receptor as well as its protective effect on young erythrocytes resulting in destruction of early red cell forms, so called "neocytolysis"; and 3} the dynamic process of ventilatory acclimatization/de-acclimatization which may increase ventilatory work in the first few days at sea level leading to an obligate increase in oxygen utilization by the respiratory rnuscles, especially in elite athletes who may already be flow limited at high levels of ventilation. Like the acclimatization process, there may be substantial individual variability in the timing and magnitude of these processes. Therefore the timing of competition or intensification of training may have to be individualized for each athlete. Finally, there may be strategies that can be employed by the competitive athlete to maintain acclimatization while at sea level, and this topic may be a fruitful area for future research.
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