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.