Abstract
In the setting of “living high,” it is unclear whether high-intensity interval training (HIIT) should be performed “low” or “high” to stimulate muscular and performance adaptations. Therefore, 10 physically active males participated in a 5-week “live high-train low or high” program (TR), whilst eight subjects were not engaged in any altitude or training intervention (CON). Five days per week (~15.5 h per day), TR was exposed to normobaric hypoxia simulating progressively increasing altitude of ~2,000–3,250 m. Three times per week, TR performed HIIT, administered as unilateral knee-extension training, with one leg in normobaric hypoxia (~4,300 m; TRHYP) and with the other leg in normoxia (TRNOR). “Living high” elicited a consistent elevation in serum erythropoietin concentrations which adequately predicted the increase in hemoglobin mass (r = 0.78, P < 0.05; TR: +2.6%, P < 0.05; CON: −0.7%, P > 0.05). Muscle oxygenation during training was lower in TRHYP vs. TRNOR (P < 0.05). Muscle homogenate buffering capacity and pH-regulating protein abundance were similar between pretest and posttest. Oscillations in muscle blood volume during repeated sprints, as estimated by oscillations in NIRS-derived tHb, increased from pretest to posttest in TRHYP (~80%, P < 0.01) but not in TRNOR (~50%, P = 0.08). Muscle capillarity (~15%) as well as repeated-sprint ability (~8%) and 3-min maximal performance (~10–15%) increased similarly in both legs (P < 0.05). Maximal isometric strength increased in TRHYP (~8%, P < 0.05) but not in TRNOR (~4%, P > 0.05). In conclusion, muscular and performance adaptations were largely similar following normoxic vs. hypoxic HIIT. However, hypoxic HIIT stimulated adaptations in isometric strength and muscle perfusion during intermittent sprinting.
Highlights
Since the 1968 Olympic Games in Mexico City (2,300 m) athletes have used altitude training to prepare for endurance exercise performances at sea-level
Subjects performed high-intensity interval-training (HIIT) with one leg in hypoxia equivalent to ∼4,300 m (TRHYP, FiO2: 12.3%), whilst the contralateral leg trained in normoxia (TRNOR)
It was postulated that lower muscular oxygenation status during high-intensity interval training (HIIT) in hypoxia, via activation of hypoxia-sensing pathways, could induce unique muscular adaptations to eventually enhance exercise performance
Summary
Since the 1968 Olympic Games in Mexico City (2,300 m) athletes have used altitude training to prepare for endurance exercise performances at sea-level. Extensive research has shown “living high” while “training low” to be the better approach in altitude training, because this strategy enables athletes to spend sufficient time in hypoxia to stimulate erythropoiesis whilst maintaining high mechanical work output and oxygen fluxes during training (Stray-Gundersen and Levine, 2008; Millet et al, 2010). Live High-Train Low or High can continue living in their normal home environment, while “living high” in normobaric hypoxia, yet training at sea level. Hypobaric and normobaric hypoxic exposure recently were reported to be efficient in increasing total hemoglobin mass (Hbmass) (Hauser et al, 2016). Even within a given individual, Hbmass does not respond consistently to sequential altitude training exposures (McLean et al, 2013). Pertinent markers for individual altitude sensitivity are still lacking
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