Recent studies have demonstrated that brief daily IAE (intermittent altitude exposure) was equally as effective as continuous altitude residence in inducing physiological adaptations consistent with altitude acclimatization. Although the positive benefits of IAE have been clearly defined, the potential negative consequences of IAE on health, specifically the immune system, remain undefined. The present study determined the effects of IAE on WBC (white blood cell) and hormonal responses during rest and exercise at 4300 m altitude. Six lowlanders (age, 23±2 years; body weight, 77±6 kg; values are means±S.E.M.) completed a V̇O2max (maximal O2 uptake) and submaximal cycle ergometer test during a 30-h SL (sea level) exposure and during a 30 h exposure to 4300 m altitude-equivalent once before (PreIAE) and once after (PostIAE) a 3-week period of IAE (4 h·day−1, 5 days·week−1, 4300 m). The submaximal cycle ergometer test consisted of two consecutive 15-min work bouts at 40% and 70% of altitude-specific V̇O2max. Blood samples were obtained at rest and during both exercise work bouts for measurements of WBC count, leucocyte subset counts, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine). WBC, neutrophil and lymphocyte counts increased significantly (P<0.05) during rest and exercise from SL to PreIAE and decreased (P<0.05) during rest and exercise from PreIAE to PostIAE. Monocyte counts decreased (P<0.05) during rest and exercise from PreIAE to PostIAE, but eosinophil and basophil counts did not change. Cortisol, adrenaline and noradrenaline did not change during rest or exercise from SL to PreIAE or PostIAE, but all increased significantly (P<0.05) from rest during the two work bouts. In conclusion, this type of IAE stimulus did not induce a hormonal stress response and did no harm in terms of activation of the immune system at altitude, as measured by WBC and leucocyte subset counts. This method of pre-acclimatization can therefore be highly recommended for inducing altitude acclimatization without the ‘altitude residency’ requirement.

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