Schena, F., Cuzzolin, L., Rossi, L., Pasetto, M. & Benoni, G. (2002). Plasma nitrite/nitrate and erythropoietin levels in cross-country skiers during altitude training. Journal of Sports medicine and Physical Fitness, 42, 129-134.

Trained male cross country skiers (N = 9) who normally lived at 800-1,200 m altitude, spent two days in altitude acclimatization and then underwent six days of intensive training at moderate altitude (3,100 m). Untrained males (N = 6) served as controls.

Hematocrit increased significantly in controls after eight days at altitude. Erythropoietin (EPO) increased significantly only after intensive training. Although controls increased, the values were not significant. Nitrite/nitrate baseline levels were significantly higher in the skiers than in the controls. After acclimatization, the nitrite/nitrate levels in controls rose to be similar to those of the athletes. Other hematological factors did not change. Altered factors returned to lower-altitude baseline levels within seven days after returning from altitude. It was concluded:

". . . the athletes entered in this study remained at moderate altitude for a too short period to influence haematological parameters; a continuous period of at least some weeks is probably needed for optimal haematological adaptation in athletes training at altitude" (p. 133).

Implication. When trained athletes experience short exposures (e.g., one week) to altitude, blood factors other than EPO are not altered significantly.

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