Combined intermittent hypoxic exposure at rest and continuous hypoxic training can maintain elevated hemoglobin mass after a hypoxic camp

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 (Vo(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 (HYPIHE + CHT), whereas the other 22 HYP athletes were not exposed to IHE or CHT (HYPSL). Hb(mass) increased from PRE to POST1 in both HYPIHE + CHT (4.4 +/- 0.7%, means +/- SE) and HYPSL (4.1 +/- 0.6%) (both P < 0.001). Compared with PRE, Hb(mass) at POST2 remained 4.2 +/- 0.8% higher in HYPIHE + CHT (P < 0.001) and 1.9 +/- 0.5% higher in HYPSL (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%. Vo(2max) and time to exhaustion during an incremental treadmill test (n = 35) were elevated from PRE to POST2 only in HYPIHE + 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.