Similar performance fatigability and neuromuscular responses following sustained bilateral tasks above and below critical force



The present study examined the magnitude of performance fatigability as well as the associated limb- and intensity-specific neuromuscular patterns of responses during sustained, bilateral, isometric, leg extensions above and below critical force (CF).


Twelve women completed three sustained leg extensions (1 below and 2 above CF) anchored to forces corresponding to RPE = 1, 5, and 8 (10-point scale). During each sustained leg extension, electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) were assessed from each vastus lateralis in 5% of time-to-exhaustion (TTE) segments. Before and after each sustained leg extension, the subjects completed maximal voluntary isometric contractions (MVIC), and the percent decline was defined as performance fatigability. Polynomial regression was used to define the individual and composite neuromuscular and force values versus time relationships. Repeated-measures ANOVAs assessed differences in performance fatigability and TTE.


The grand mean for performance fatigability was 10.1 ± 7.6%. For TTE, the repeated-measures ANOVA indicated that there was a significant (p < 0.05) effect for Intensity, such that RPE = 1 > 5 > 8. There were similar neuromuscular patterns of response between limbs as well as above and below CF. EMG MPF, however, exhibited decreases only above CF.


Performance fatigability was unvarying above and below CF as well as between limbs. In addition, there were similar fatigue-induced motor unit activation strategies above and below CF, but peripheral fatigue likely contributed to a greater extent above CF.

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Fig. 1
Fig. 2





Conduction velocity


Critical force




Ratings of perceived exertion


Time to exhaustion


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We would like to thank all the participants for their time and for volunteering to comply with the protocol of the study. Also, we would like to thank the National Strength and Conditioning Association as well as the Northlands American College of Sports Medicine Chapter for funding this study.


This study was at least in part funded by the National Strength and Conditioning Association as well as the Northlands American College of Sports Medicine Chapter.

Author information




All authors conceived and planned the experiment. JLK, JPVA, and TJN carried out the data collection. JLK with support from TJH wrote the manuscript. JLK, JPVA and TJN performed the data analysis support. RJS and GOJ helped supervise the project. All authors provided critical feedback and contributed to the final version of the manuscript.

Corresponding author

Correspondence to Joshua L. Keller.

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The authors have no conflicts of interest to report.

Ethical approval

The University Institutional Review Board for Human Subjects approved the study (IRB#: 20190619436EP).

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During the familiarization visit, the subjects completed a health history questionnaire and gave written informed consent.

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Communicated by William J. Kraemer.

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Keller, J.L., Housh, T.J., Anders, J.P.V. et al. Similar performance fatigability and neuromuscular responses following sustained bilateral tasks above and below critical force. Eur J Appl Physiol (2021).

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  • Fatigability
  • Ratings of perceived exertion
  • Critical force
  • Neuromuscular