Some basic characteristics of blood were analyzed as part of the previous study (3 weeks at altitude, 3 weeks of re-exposure at sea level).
In response to altitude, blood plasma decreased by approximately 20%, causing an increase in hemoglobin and hematocrit measures. The red cell count increased further because of an increase in erythropoietin (EPO) which stimulates the bone marrow to release new red blood cells (reticulocytes). The red cell count remained elevated for the duration of the altitude stay.
Upon returning to sea level changes occurred:
Implications. If altitude training is to benefit sea level performances, physiological changes associated with acclimatization should be appropriate for, retained, and present during performance. This did not occur in the course of this study. When athletes competed after three weeks of re-exposure to sea level all altitude changes had disappeared.
The exposure in this study was to moderate altitude (2,000 m). The physiological changes were similar to those evidenced when acclimatizing to high altitude (>3,000 m) but the values were lower. This suggests that there are degrees of severity of adaptation to altitude.
[One is left pondering the question that was raised in the previous study. What would be the effect on sea level performance if swimmers trained at high altitude for an extended period of time (e.g., 6 months)?
A further question is what happens to performance if swimmers are brought down from altitude to compete immediately? Since the physiology of swimming an event at altitude is different for the same event at sea level, it is unlikely that any enhancement will occur other than because of a placebo effect.]
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