Do male athletes with already high initial haemoglobin mass benefit from 'live high-train low' altitude training?

What is the central question of this study? It has been assumed that athletes embarking on an 'live high-train low' (LHTL) camp with already high initial haemoglobin mass (Hb_mass ) have a limited ability to increase their Hb_mass further post-intervention. Therefore, the relationship between initial Hb_mass and post-intervention increase was tested with duplicate Hb_mass measures and comparable hypoxic doses in male athletes. What is the main finding and its importance? There were trivial to moderate inverse relationships between initial Hb_mass and percentage Hb_mass increase in endurance and team-sport athletes after the LHTL camp, indicating that even athletes with higher initial Hb_mass can reasonably expect Hb_mass gains post-LHTL. It has been proposed that athletes with high initial values of haemoglobin mass (Hb_mass ) will have a smaller Hb_mass increase in response to 'live high-train low' (LHTL) altitude training. To verify this assumption, the relationship between initial absolute and relative Hb_mass values and their respective Hb_mass increase following LHTL in male endurance and team-sport athletes was investigated. Overall, 58 male athletes (35 well-trained endurance athletes and 23 elite male field hockey players) undertook an LHTL training camp with similar hypoxic doses (200-230 h). The Hb_mass was measured in duplicate pre- and post-LHTL by the carbon monoxide rebreathing method. Although there was no relationship (r = 0.02, P = 0.91) between initial absolute Hb_mass (in grams) and the percentage increase in absolute Hb_mass , a moderate relationship (r = -0.31, P = 0.02) between initial relative Hb_mass (in grams per kilogram) and the percentage increase in relative Hb_mass was detected. Mean absolute and relative Hb_mass increased to a similar extent (P ≥ 0.81) in endurance (from 916 ± 88 to 951 ± 96 g, +3.8%, P < 0.001 and from 13.1 ± 1.2 to 13.6 ± 1.1 g kg^-1 , +4.1%, P < 0.001, respectively) and team-sport athletes (from 920 ± 120 to 957 ± 127 g, +4.0%, P < 0.001 and from 11.9 ± 0.9 to 12.3 ± 0.9 g kg^-1 , +4.0%, P < 0.001, respectively) after LHTL. The direct comparison study using individual data of male endurance and team-sport athletes and strict methodological control (duplicate Hb_mass measures and matched hypoxic dose) indicated that even athletes with higher initial Hb_mass can reasonably expect Hb_mass gain post-LHTL.