Biomarkers predicting the effectiveness of normobaric altitude training

Abstract Purpose The aim of the present study was to identify blood-based biomarkers that could predict individual VO 2 max improvement before the start of an artificial altitude training camp. Methods In an exploratory intervention study, 15 young highly trained athletes from the German Athletics Federation completed a 21-day Live High – Train Low program at an artificial altitude house, which simulated an altitude of 800 km·h (approximately 1.900–2.500 m) under normobaric hypoxia. V̇O₂max was measured pre- and post-intervention, and blood parameters were collected at six time points (pre, post and four times at altitude. The pre measurement functioned as baseline and was used for the predictive model. Results Altitude training led to a mean V̇O₂max increase of 2.1 mL · kg⁻¹ · min⁻¹ (+ 3.1%), with high interindividual variability (–1.7 to + 4.5 mL · kg⁻¹ · min⁻¹). Neither training load, sex, nor discipline explained these differences. Logistic regression analyses identified monocyte percentage (> 10%) and neutrophil percentage (> 50%) emerged as the strongest predictors of responder status (McFadden’s R² = 0.61 and 0.65, respectively), while neutrophil-to-lymphocyte-ratio (NLR) and hematocrit also showed significant predictive value. Threshold analyses revealed that high-responders consistently displayed lower neutrophil activity (NLR 42.5%), in contrast to low-responders. Longitudinal biomarker trajectories further supported these distinctions, with high-responders maintaining adaptive immune and iron-related profiles, whereas low-responders exhibited persistent signs of innate immune activation and suboptimal erythropoietic status. Conclusion These results highlight the relevance of functional biomarker profiles for individualized training planning in elite sports. Practically, this opens new possibilities for the targeted use of altitude training while minimizing health risks.