Acute Normobaric Hypoxia at 2000 and 3000 m Significantly Lowers the Maximal Lactate Steady State (MLSS) in Trained...

The reduced availability of oxygen under hypoxic conditions makes it necessary to adjust training intensity by reducing the workload and modifying exercise zones. The aim of this study was to evaluate the effects of normobaric hypoxia of varying severity (H2000: FiO₂ = 16.5%, ~2000 m; H3000: FiO₂ = 14.5%, ~3000 m) on physiological variables associated with the maximal lactate steady state (MLSS) in trained cyclists, including the work rate (WRMLSS), oxygen uptake (VO₂MLSS), minute ventilation (V̇EMLSS), and the heart rate (HRMLSS). Sixteen trained male cyclists (age: 30 ± 5 years; body height: 180.5 ± 8.0 cm; body mass: 75.2 ± 9.0 kg; body fat content: 10.2 ± 2.0%; VO_{2 max}: 57.0 ± 6.0 ml/kg/min) performed incremental and constant-load exercise tests under normoxic (N) and hypoxic (H2000 and H3000) conditions to determine the MLSS. Exposure to H2000 and H3000 significantly reduced the WRMLSS by 9.3% and 18.5%, respectively, as well as VO₂MLSS by 7.2% and 17% compared with normoxia (p < 0.05), while the HRMLSS remained unchanged. SpO₂ showed a statistically significant (p < 0.05) drop between N and H2000 (-10.61%), as well as N and H3000 (-16.43%). Blood lactate concentration at the 30^th min of MLSS exercise was significantly (p < 0.05) higher under both H2000 (+36%) and H3000 (+34%) conditions compared to N. These findings indicate that acute normobaric hypoxia equivalent to 2000 and 3000 m significantly impairs the ability to sustain exercise at MLSS intensity. It is recommended that MLSS power be reduced by ~10% at 2000 m and by ~20% at 3000 m, while HR values remain unchanged under both conditions.