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

Area of Science:

• Sports Science and Physiology
• Altitude Training
• High-Intensity Interval Training (HIIT)

Background:

• The optimal training environment (hypoxia vs. normoxia) for high-intensity interval training (HIIT) during "live high" altitude exposure remains unclear.
• Understanding these adaptations is crucial for optimizing training protocols in sports and for physiological research.

Purpose of the Study:

• To investigate the effects of performing HIIT in normobaric hypoxia versus normoxia on muscular and performance adaptations in physically active males.
• To compare the efficacy of "live high-train low or high" protocols for enhancing physiological markers and physical performance.

Main Methods:

• A 5-week "live high-train low or high" program involving normobaric hypoxia exposure (simulating 2,000-3,250m) for 5 days/week.
• Participants performed unilateral knee-extension HIIT 3 times/week, with one leg in hypoxia (TR_HYP, ~4,300m) and the other in normoxia (TR_NOR).
• Measurements included serum erythropoietin, hemoglobin mass, muscle oxygenation, buffering capacity, pH-regulating proteins, muscle blood volume oscillations, muscle capillarity, repeated-sprint ability, maximal performance, and maximal isometric strength.

Main Results:

• "Living high" increased hemoglobin mass (+2.6%) and serum erythropoietin.
• Hypoxic HIIT (TR_HYP) showed lower muscle oxygenation but increased muscle blood volume oscillations during sprints (~80%) compared to normoxic HIIT (TR_NOR).
• Both TR_HYP and TR_NOR similarly improved muscle capillarity (~15%), repeated-sprint ability (~8%), and 3-min maximal performance (~10-15%).
• Maximal isometric strength increased significantly in TR_HYP (~8%) but not in TR_NOR.

Conclusions:

• Muscular and performance adaptations to HIIT during "live high" are largely similar whether training is performed in normoxia or hypoxia.
• Hypoxic HIIT specifically enhanced maximal isometric strength and improved muscle perfusion during intermittent sprinting.
• These findings suggest that incorporating hypoxic HIIT may offer specific advantages for strength and vascular adaptations within an altitude training paradigm.