High-Altitude Acclimatization Improves Recovery from Muscle Fatigue

Purpose: We investigated the effect of high-altitude acclimatization on peripheral fatigue compared to sea level and acute hypoxia. Methods: At sea level (350 m), acute hypoxia (environmental chamber), and chronic hypoxia (5050 m, 5-9 days) (partial pressure of inspired oxygen = 140, 74 and 76 mmHg, respectively), 12 participants (11 in chronic hypoxia) had the quadriceps of their dominant leg fatigued by 3 bouts of 75 intermittent electrically-evoked contractions (12 pulses at 15 Hz, 1.6 s between train onsets, and 15 s between bouts). The initial peak force was ~30% of maximal voluntary force. Recovery was assessed by single trains at 1, 2, and 3 min post-protocol. Tissue oxygenation of rectus femoris was recorded by near-infrared spectroscopy. Results: At the end of the fatigue protocol, the impairments of peak force and peak rates of force development and relaxation were greater (all P < 0.05) in acute hypoxia (~51, 53 and 64%, respectively) than sea level (~43, 43 and 52%) and chronic hypoxia (~38, 35 and 48%). Peak force and rate of force development recovered faster (P < 0.05) in chronic hypoxia (pooled data for 1-3 min: ~84 and 74% baseline, respectively) compared to sea level (~73 and 63% baseline) and acute hypoxia (~70 and 55% baseline). Tissue oxygenation did not differ among conditions for fatigue or recovery ( ACCEPTED P > 0.05). Conclusion: Muscle adaptations occurring with chronic hypoxia, independent of other adaptations, positively influence muscle contractility during and after repeated contractions at high altitude.