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.
Competing Interests: The authors have no conflict of interest.