Combined intermittent hypoxic exposure at rest and continuous hypoxic training can maintain elevated hemoglobin mass...

Athletes use hypoxic living and training to increase hemoglobin mass (Hb_mass), but Hb_mass declines rapidly upon return to sea level. We investigated whether intermittent hypoxic exposure (IHE) + continuous hypoxic training (CHT) after return to sea level maintained elevated Hb_mass, and if changes in Hb_mass were transferred to changes in maximal oxygen uptake (V̇o_2max) and exercise performance. Hb_mass was measured in 58 endurance athletes before (PRE), after (POST1), and 30 days after (POST2) a 27 ± 4-day training camp in hypoxia (n = 44, HYP) or at sea level (n = 14, SL). After returning to sea level, 22 athletes included IHE (2 h rest) + CHT (1 h training) in their training every third day for 1 mo (HYP_{IHE + CHT}), whereas the other 22 HYP athletes were not exposed to IHE or CHT (HYP_SL). Hb_mass increased from PRE to POST1 in both HYP_{IHE + CHT} (4.4 ± 0.7%, means ± SE) and HYP_SL (4.1 ± 0.6%) (both P < 0.001). Compared with PRE, Hb_mass at POST2 remained 4.2 ± 0.8% higher in HYP_{IHE + CHT} (P < 0.001) and 1.9 ± 0.5% higher in HYP_SL (P = 0.023), indicating a significant difference between the groups (P = 0.002). In SL, no significant changes were observed in Hb_mass with mean alterations between -0.5% and 0.4%. V̇o_2max and time to exhaustion during an incremental treadmill test (n = 35) were elevated from PRE to POST2 only in HYP_{IHE + CHT} (5.8 ± 1.2% and 5.4 ± 1.4%, respectively, both P < 0.001). IHE + CHT possesses the potential to mitigate the typical decline in Hb_mass commonly observed during the initial weeks after return to sea level.NEW & NOTEWORTHY Sets of 2-h intermittent hypoxic exposure + 1-h continuous hypoxic training, every third day, possess the potential to mitigate the typical decline in Hb_mass that is commonly observed during the initial weeks after return to sea level from an altitude camp. Inclusion of IHE + CHT in the training regimen was also accompanied by improvements in V̇o_2max and exercise performance in most but not all Tier 3-Tier 5 level endurance athletes during the training season.