2023

Peltonen, Juha E.; Leppävuori, Antti; Lehtonen, Elias; Mikkonen, Ritva; Kettunen, Oona; Nummela, Ari; Ohtonen, Olli; Gagnon, Dominique D.; Wehrlin, Jon P.; Wilber, Randall L.; Linnamo, Vesa

In response to altitude/hypoxic living and training, an increase in hemoglobin mass (Hb-mass) is believed to be the most important factor behind any improvement in maximal oxygen uptake (VO2max). Following return to sea level, Hb-mass decreases rapidly, reaching a pre-hypoxia level within approximately 30 days. PURPOSE: To examine i) if intermittent hypoxic exposure at rest (IHE) + intermittent hypoxic training (IHT) maintains Hb-mass after return to sea level and ii) whether the expected response in Hb-mass is reflected in changes in VO2max. METHODS: 48 national and international level endurance athletes (19 women, 29 men, age 23 ± 4 years) participated the study during their off-season. 33 athletes completed a 27 ± 2-day hypoxic camp at 2347 ± 110 m either living high-training high and low (n = 27) or living high-training high (n = 6). After returning to sea level, 17 athletes (G1) carried out a combination of IHE + IHT (2 h rest +1 h exercise) every third day for one month while 16 athletes (G2) were not exposed to hypoxia. A control group (n = 15) lived and trained at sea level (G3). Hb-mass (optimized CO-rebreathing technique) and VO2max were measured before (PRE), after (POST1), and 30 days after (POST2) the hypoxic camp. Statistical methods included: two-way repeated measures ANOVA, paired t-test, and Pearson correlation. Values are mean ± SD. RESULTS: At PRE, Hb-mass (11.8 ± 1.5, 12.7 ± 2.3, 12.2 ± 2.2 g/kg) and VO2max (63 ± 8, 64 ± 9, 65 ± 5 ml/kg/min) did not differ between G1, G2, and G3. Following a hypoxic camp, Hb-mass increased in both G1 and G2 (5.6 ± 4.3% and 5.2 ± 3.3%, both p < 0.001) but not at sea level in G3 (-0.1 ± 2.2%). At POST2, Hb-mass was maintained in G1 (-0.2 ± 4.8%) but decreased towards pre-hypoxia levels in G2 (-3.1 ± 3.7%, p < 0.01) with no change in G3 (-0.3 ± 2.7%). VO2max increased 4.0 ± 4.2%, 2.9 ± 4.1%, and 1.9 ± 2.8% at POST1 in G1, G2, and G3, respectively (all p < 0.05). At POST2, difference to POST1 was 1.7 ± 4.3%, -1.1 ± 4.1% and -2.1 ± 6.6% in G1, G2, and G3, respectively (all n.s.). No correlation existed between changes in Hb-mass and VO2max. CONCLUSIONS: Acknowledging individual variation, IHE + IHT is potentially effective for maintaining Hb-mass after return to sea level in endurance athletes. Changes in Hb-mass and VO2max, however, do not necessarily occur in parallel.