High-intensity interval training in hypoxia does not affect muscle HIF responses to acute hypoxia in humans

Purpose The myocellular response to hypoxia is primarily regulated by hypoxia-inducible factors (HIFs). HIFs thus conceivably are implicated in muscular adaptation to altitude training. Therefore, we investigated the effect of hypoxic versus normoxic training during a period of prolonged hypoxia (‘living high’) on muscle HIF activation during acute ischaemia. Methods Ten young male volunteers lived in normobaric hypoxia for 5 weeks (5 days per week, ~ 15.5 h per day, F i O 2 : 16.4–14.0%). One leg was trained in hypoxia (TR HYP , 12.3% F i O 2 ) whilst the other leg was trained in normoxia (TR NOR , 20.9% F i O 2 ). Training sessions (3 per week) consisted of intermittent unilateral knee extensions at 20–25% of the 1-repetition maximum. Before and after the intervention, a 10-min arterial occlusion and reperfusion of the leg was performed. Muscle oxygenation status was continuously measured by near-infrared spectroscopy. Biopsies were taken from m. vastus lateralis before and at the end of the occlusion. Results Irrespective of training, occlusion elevated the fraction of HIF-1α expressing myonuclei from ~ 54 to ~ 64% ( P < 0.05). However, neither muscle HIF-1α or HIF-2α protein abundance, nor the expression of HIF-1α or downstream targets selected increased in any experimental condition. Training in both TR NOR and TR HYP raised muscular oxygen extraction rate upon occlusion by ~ 30%, whilst muscle hyperperfusion immediately following the occlusion increased by ~ 25% in either group ( P < 0.05). Conclusion Ten minutes of arterial occlusion increased HIF-1α-expressing myonuclei. However, neither normoxic nor hypoxic training during ‘living high’ altered muscle HIF translocation, stabilisation, or transcription in response to acute hypoxia induced by arterial occlusion.