Neuromuscular and Muscle Tissue Hemodynamic Responses When Exposed to Normobaric Hypoxia during Lower-Body Fatiguing Muscle Actions

OBJECTIVES: This study examined effects of acute hypoxia on the neuromuscular responses (electromyographic (EMG) amplitude and EMG frequency) and localized muscle tissue oxygenated hemoglobin (oxygenated hemoglobin (Oxy(Hb)), deoxygenated hemoglobin (Deoxy(Hb)), total hemoglobin (Total(Hb)), and muscle tissue oxygenation saturation (StO(2)) during the process of fatigue. METHODS: Fifteen male participants (21.4±2.8yr) performed leg extension repetitions to failure at 70% 1-repetition maximum until volitional exhaustion under Normoxic (FiO(2):21%) and Hypoxic (FiO(2):12.9%) conditions. Electromyographic amplitude, EMG frequency, Oxy(Hb), Deoxy(Hb), Total(Hb), and StO(2) were measured from the vastus lateralis at Initial, 20, 40, 60, 80, and 100% of the repetitions to failure. RESULTS: There was no significant difference in the patterns of responses for EMG amplitude, Oxy(Hb), or Deoxy(Hb) between Normoxia and Hypoxia. For EMG frequency, Hypoxia was greater than Normoxia and decreased with fatigue. Total(Hb) and StO(2) were greater under Normoxia compared to Hypoxia. The patterns of responses for EMG amplitude, Deoxy(Hb), and Total(Hb) increased throughout the repetitions to failure. Oxy(Hb) and StO(2) exhibited decreases throughout the repetitions to failure for Normoxic and Hypoxic conditions. CONCLUSION: The EMG and oxygenation measurements non-invasively suggest a sympathoexcitatory response (indicated by EMG frequency) and provided complimentary information regarding the process of fatigue in normoxic and hypoxic states.