Physiological Adaptations to Hypoxic vs. Normoxic Training during Intermittent Living High

Figures

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  Figure 1. Schematic presentation of the study protocol. The study involved two experimental groups, o which one group was enrolled in a “live high” intervention using normobaric hypoxia (TR, n = 10), whilst the other group lived at sea level (CON, n = 8). In TR one leg was trained in 12.3% FiO2 (TRHYP, ~4,300 m), whilst the other leg was trained in 20.9% FiO2 (TRNOR). The week before (pretest) and the week after (posttest) the intervention period a series of measurements were performed. During the intervention period venous blood samples were taken on a weekly basis. MVC, maximal voluntary contraction; RSA, repeated-sprint ability; Hbmass, total blood hemoglobin mass; sFer, serum ferritin; MAX3′, 3-min maximal performance test (MAX3′); VO2max, maximal oxygen uptake rate.

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  Figure 2. Effect of incremental altitude on arterial oxygen saturation during “living high.” %SpO2, Arterial oxygen saturation. §, P < 0.05 compared to week 1 at altitude.

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  Figure 3. Effect of “living high” on serum erythropoietin concentration. Data are means ± SEM (n = 10) and individual data (dotted lines) for serum erythropoietin concentration (sEPO) in subjects living in normobaric hypoxia with simulated altitude gradually increasing from 2,000 m in week 1 to 3,250 m in week 5. See Methods for further details. §, P < 0.05 compared to sea level.

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  Figure 4. Effect of living high on blood hemoglobin mass and serum ferritin concentration. Data represent means ±SEM (n = 10) and individual values (lines) for hemoglobin mass (Hbmass, A) and serum ferritin concentrations (sFer, B) before (Pretest) and after (Posttest) living 5 weeks in normoxia (CON) or in normobaric hypoxia (TR) with simulated altitude gradually increasing from 2,000 to 3,250 m. Iron supplementation was provided in subjects with sFer below 100 μg·L−1 (dotted lines), but not in subjects with sFer above 100 μg·L−1 (solid lines). See Methods for further details. *P < 0.05 compared to the pretest.

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  Figure 5. Relationship between changes in serum erythropoietin concentration and changes in hemoglobin mass during “living high.” ΔHbmass, change in total blood hemoglobin mass; ΔsEPO, mean increase in serum erythropoietin concentration during 5 weeks of normobaric hypoxia with simulated altitude gradually increasing from 2,000 to 3,250 m of simulated altitude.

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  Figure 6. Effect of knee-extension training in normoxia vs. hypoxia on muscle oxygenation status. Curves represent mean values (n = 10) for tissue oxygenation index (TOI, A,B) and muscle total hemoglobin (tHb, C,D) measured by NIRS in subjects living for 5 weeks in normobaric hypoxia with simulated altitude gradually increasing from 2,000 to 3,250 m. Meanwhile one leg was trained in 12.3% FiO2 (TRHYP, ~4,300 m, full lines), whilst the other leg was trained in 20.9% FiO2 (TRNOR, dotted lines). The training sessions consisted of two times 4 series of 30 knee-extensions at 20% 1RM in week 1, increasing to two times 6 series of 30 knee-extensions at 25% of 1RM in week 5. Mean values ± SEM are given at the right side of each graph (TRNOR, □; TRHYP, ■). Values were measured in week 1 (A,C) and week 5 (B,D) of the training period. See Methods for further details. *P < 0.05 compared to week 1; # P < 0.05 compared to training in normoxic conditions.

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  Figure 7. Effect of knee-extension training in normoxia vs. hypoxia during “living high” on muscle total hemoglobin content during the repeated-sprint ability test. (A) represents the typical signal of muscle total hemoglobin (tHb) measured by NIRS during the repeated-sprint ability test (n = 1), with tHb decreasing during consecutive knee extensions and increasing during recovery intervals. (B,C) represent means ± SEM for the change in tHb (ΔtHb) and HHb (ΔHHb), respectively, during the consecutive knee extensions and during the recovery intervals of the repeated-sprint ability test before (open bars) and after (solid bars) subjects living for 5 weeks in normobaric hypoxia with simulated altitude gradually increasing from 2,000 to 3,250 m. One leg was trained in 12.3% FiO2 (TRHYP, ~4,300 m), whilst the other leg was trained in 20.9% FiO2 (TRNOR). See Methods for further details. *P < 0.05 compared to the pretest.