Effect of live‐high, train‐low strategy induced by chronic low‐dose carbon monoxide exposure on haematological parameters and performance in trained individuals

Altitude training enhances haematological adaptations and endurance at sea level, typically requiring exposure to ∼2500 m altitude for 3–4 weeks. Emerging evidence suggests that low-dose carbon monoxide (CO) inhalation might mimic hypoxia and might be used by elite athletes. In this study, we examine whether periodic low-dose CO exposure can replicate the live-high, train-low model in well-trained individuals, focusing primarily on haematological and performance effects of CO exposure, with haematological markers commonly used to interpret haemoglobin mass changes discussed as exploratory. Eight well-trained individuals (four males and four females) participated in a randomized crossover study. They completed two training blocks of 4 weeks at sea level: one with CO inhalation (INCO) to simulate live-high, train-low and one with ambient air as a control (AIR), separated by a 6 month washout. Haematological variables, in vivo muscle oxidative capacity and performance metrics were assessed before and after each intervention. After INCO, haemoglobin mass (p = 0.018; +53.6 ± 10.8 g. vs. +0.8 ± 11.8 g), red blood cell volume (p = 0.032; +156.6 ± 66.7 mL vs. −65.1 ± 50.7 mL) and blood volume (p = 0.036; +240.4 ± 120.5 mL vs. −208.3 ± 167.5 mL) increased significantly compared with AIR. INCO significantly reduced immature reticulocytes (p = 0.04), but muscle oxidative capacity and performance metrics remained unchanged. These findings suggest that daily low-dose CO exposure at sea level over 4 weeks enhanced haematological adaptations more than standard training but did not affect muscle oxidative capacity or performance.