The aim of the current study was to investigate the effects of prolonged exposure to moderate altitude as well as of the contribution of training at altitude on hematological parameters. Eight young male and three female skiers (15.4 +/- 0.2 (SE) years) were exposed to 5 weeks of physical training 4-5 hours a day at an elevation of 2,700 m or 3,700 m (for only 3 days) in summer. Living quarters were at 2,100 m for 2 weeks and at 2,700 m for the following 3 weeks. Their blood samples were collected 3-4 days before and after the training. As was anticipated, the values of red blood cells (+13%), hemoglobin (+11%), and hematocrit (+15%) increased significantly after descent, indicating erythropoiesis. Unexpectedly, however, serum erythropoietin (EPO) concentration decreased significantly (-25%). Meanwhile, moderate-altitude training resulted in a significant rise in red blood cell 2,3-diphosphoglycerate (DPG) level (+18%), which suggests the shift of the oxygen dissociation curve to the right, and there was clearly an inverse relation between EPO and 2,3-DPG levels after descent (r = -0.870), although the precise physiological meaning remains vague. After training, serum creatine kinase isoenzyme (MB) activity increased significantly (+31%) and a-hydroxybutyrate dehydrogenase activity appeared to rise (+18%), possibly implying the elevated synthesis of cardiac enzymes. On the other hand, the finding that serum alanine aminotransferase activity increased definitely after descent (+52%), might foretell hepatic insufficiency, when such altitude training were continued. Thus the results obtained suggest that the combined effects of moderate-altitude hypoxia and endurance training may be rather double-edged in juveniles.
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