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The Sex-Specific Contributions of Neuromuscular and Muscle Blood Flow Responses to Performance Fatigability following Fatiguing Bilateral Muscle Actions above and below Critical Force
The purpose was to examine the sex differences in performance fatigability, neuromuscular responses, and blood flow during sustained, bilateral, isometric leg extensions anchored to ratings of perceived exertion (RPE) and forces above and below critical force (CF). Thirty adults (mean±SD; men: 20.9±1.7 yr, women: 19.5±0.8 yr) completed four sustained leg extensions anchored to percentages of maximal voluntary isometric contraction (MVIC) to determine CF. Six sustained leg extensions were used to assess neuromuscular, force, and blood flow responses: 3 anchored to RPEs (1, 5, and 8) and 3 anchored to forces corresponding to RPEs (defined as FRPE trials). Before and after the sustained leg extensions, the subjects performed MVICs. The percent decline in MVIC was defined as performance fatigability. During the sustained leg extensions, amplitude (AMP) and mean power frequency (MPF) of the electromyography (EMG) and mechanomyography (MMG) signals were calculated. Normalized force, EMG AMP, EMG MPF, MMG AMP, and MMG MPF were calculated every 5% of time-to-exhaustion. Blood flow was determined before, immediately after, and 5-min after each sustained leg extension. Regression was used to define the individual and composite neuromuscular and force values vs. time relationships. Mixed-factorial ANOVAs were used to examine difference in performance fatigability and blood flow. The relative CF (collapsed across sex) was 14.6%. For performance fatigability, there was no significant (p>0.05) interactions or main effects and resulted in a mean value (collapsed across sex, anchor, and force) of 10.97±10.8%. For the neuromuscular responses, there was more interindividual variability during the RPE trials compared to the FRPE trials. For the FRPE trials, there were similar patterns of responses above and below CF, whereas there were no consistent responses among the RPE trials. The blood flow responses indicated that the men and FRPE trials demonstrated the greatest increases from rest. In conclusion, the unvarying performance fatigability was not explained by sex, anchor, or intensity differences in neuromuscular or blood flow responses. Therefore, it was hypothesized that the sum of feedforward and feedback signals reached a sensory tolerance limit resulting in consistent performance fatigability among the trials, except for RPE=1, which was likely predominantly influenced by feedforward mechanisms.
Keller, Joshua Lee, "The Sex-Specific Contributions of Neuromuscular and Muscle Blood Flow Responses to Performance Fatigability following Fatiguing Bilateral Muscle Actions above and below Critical Force" (2020). ETD collection for University of Nebraska - Lincoln. AAI27955335.