Smith CM, Salmon OF, Jenkins JR. Neuromuscular and Muscle Tissue Hemodynamic Responses When Exposed to Normobaric Hypoxia during Lower-Body Fatiguing Muscle Actions.
JOURNAL OF MUSCULOSKELETAL & NEURONAL INTERACTIONS 2023;
23:26-35. [PMID:
36856097 PMCID:
PMC9976181]
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Abstract
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 (OxyHb), deoxygenated hemoglobin (DeoxyHb), total hemoglobin (TotalHb), and muscle tissue oxygenation saturation (StO2) 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 (FiO2:21%) and Hypoxic (FiO2:12.9%) conditions. Electromyographic amplitude, EMG frequency, OxyHb, DeoxyHb, TotalHb, and StO2 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, OxyHb, or DeoxyHb between Normoxia and Hypoxia. For EMG frequency, Hypoxia was greater than Normoxia and decreased with fatigue. TotalHb and StO2 were greater under Normoxia compared to Hypoxia. The patterns of responses for EMG amplitude, DeoxyHb, and TotalHb increased throughout the repetitions to failure. OxyHb and StO2 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.
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