Author(s): NOVÁKOVÁ, M., WORONYCZOVÁ, J., CÍSAROVÁ, K., COKRTOVÁ, K., BOLEK, E., Institution: CASRI - SPORTS RESEARCH INSTITUTE OF THE CZECH ARMED FORCES, Country: CZECH REPUBLIC, Abstract-ID: 1698

INTRODUCTION:
The regulation of acid-base balance during the early stages of acclimatization at high altitudes is well studied. During the first 12 hours of acclimatization, arterial pH increases due to hyperventilation and carbon dioxide washout. This respiratory alkalosis is subsequently compensated by renal elimination of bicarbonate ions (HCO₃⁻), gradually restoring arterial pH to normal levels. Metabolic compensation is typically completed within 24 hours at low to moderate altitudes. However, data on acid-base status beyond this initial period remain scarce. Moreover, most studies have been conducted in simulated conditions or at higher altitudes, often with non-elite athletes. In this study, we aimed to monitor the acid-base balance of nine top elite biathletes on the third day after arrival at two different moderate natural altitudes and compare it to their acid-base status at low altitude.
METHODS:
A group of elite biathletes (5 males, age = 27.4 ± 4.0 years, VO2max = 69.7 ± 3.6 ml/kg/min; 4 females, age = 27.3± 3.8 years, VO2max = 59.2 ± 3.8 ml/kg/min) underwent morning arterial blood sampling to assess acid-base balance at low altitude (600 m) and on the third day after arrival at training camps at 1700 m and 2000 m. Additionally, plasma erythropoietin (EPO) concentration was measured 24 hours after ascent.
RESULTS:
On the third acclimatization day, no significant differences in acid-base balance were detected between the two altitudes. Although arterial pH remained similar to that at low altitude, other parameters showed significant changes at moderate altitudes. The arterial partial pressure of oxygen (pO₂) was significantly lower at 1700 m (8.62 ± 0.17 kPa, p < 0.01) and 2000 m (9.07 ± 0.15 kPa, p < 0.01) compared to 600 m (9.95 ± 0.16 kPa). The arterial partial pressure of carbon dioxide (pCO₂) was significantly reduced at 1700 m (3.91 ± 0.08 kPa, p < 0.01) and 2000 m (3.96 ± 0.07 kPa, p < 0.01) in comparison to 600 m (4.76 ± 0.05 kPa). Blood bicarbonate ion concentration decreased by approximately 15%. Although the available data are limited, a significant negative correlation was found between plasma EPO concentration 24 hours after ascent and the decrease in blood bicarbonate ion concentration on the third day (r = −0.64; p < 0.05).
CONCLUSION:
To our knowledge, this is the first study to monitor acid-base balance at a later stage of acclimatization in elite athletes at training camp venues under natural conditions. No significant differences in acid-base balance were observed between 1700 m and 2000 m. By day three, metabolic compensation was ongoing but insufficient to restore arterial oxygen levels to low-altitude values. Persistently low bicarbonate, a key blood buffer, could impair anaerobic performance in the subsequent days. The correlation between the 24-hour EPO response and the magnitude of metabolic compensation suggests an interconnection between erythropoiesis and acid-base regulation of the hypoxic stress.