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Exploring the Acute Muscle Fatigue Response in Resistance Trained Individuals During Eccentric Quasi-Isometric Elbow Extensions

A Cross-Sectional Comparison of Angular Kinetics, Kinematics, Surface Electromyography, and Sex


  • Zachariah Henderson University of Manitoba
  • Shizhen Wang
  • Stephen Cornish
  • Trisha Scribbans



Resistance Exercise, statistical parametric mapping, SPM, time under tension


Eccentric quasi-isometrics (EQIs) are a novel, low-velocity resistance exercise technique with increasing notoriety, yet limited research. As females are typically more fatigue resistant than males during isometric and low-velocity dynamic muscle actions, this study explored sex-differences in the muscle fatigue response to an EQI protocol. Twenty-five (n = 12 female) participants completed 4 unilateral EQI elbow extensions. Absolute and relative surface electromyography (sEMG) amplitude (iEMG, LE Peak), mean power frequency (MPF), angular impulse (aIMP), and elbow kinematics were compared across repetitions and between sexes using discrete values and statistical parametric/non-parametric mapping. There were significant (p < .001 to .032) and substantial (ηp2 = .15 to .55) sex and repetition differences in absolute iEMG, MPF, and aIMP, with males and earlier repetitions generally having larger values than females and later repetitions. When expressed relatively, there were no significant sex-differences, but significant decreases in iEMG, aIMP, and elbow angle (p < .001 to .007) with an increasing number of repetitions. The current study suggests that sex-differences in EQI induced muscle fatigue are diminished when expressed relatively, and consecutive repetitions leads to significant decreases in sEMG, kinematic, and kinetic characteristics, with the largest differences between repetition 1 and 2.


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