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Electromyography and fatigue during prolonged, low-level static contractions.

K Jørgensen1, N Fallentin, C Krogh-Lund

  • 1August Krogh Institute, University of Copenhagen, Denmark.

European Journal of Applied Physiology and Occupational Physiology
|January 1, 1988
PubMed
Summary
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Muscle fatigue occurs even at low contraction intensities, challenging the idea of indefinite endurance. Prolonged static contractions below 15-20% MVC lead to reduced maximal voluntary contraction (MVC) and significant EMG changes.

Area of Science:

  • Exercise Physiology
  • Muscle Physiology
  • Biomedical Engineering

Background:

  • Muscle fatigue is a complex phenomenon affecting performance.
  • Understanding fatigue mechanisms during low-level static contractions is crucial for occupational health and sports science.
  • Previous research suggested indefinite endurance times at low contraction intensities.

Purpose of the Study:

  • To summarize findings on electromyography (EMG) changes during prolonged low-level static muscle contractions.
  • To investigate the endurance time and physiological mechanisms of muscle fatigue.
  • To challenge the concept of indefinite endurance at submaximal contraction levels.

Main Methods:

  • Analysis of data from five studies involving sustained static contractions (5-10% MVC) and intermittent contractions (10-14% MVC).

Related Experiment Videos

  • Measurements included maximal voluntary contraction (MVC), EMG amplitude, and mean spectral frequency.
  • Electrophysiological assessments, including transcutaneous electrical stimulation, were employed.

    • Main Results:

    • Endurance time for sustained contractions was approximately one hour at 10% MVC.
    • Sustained 5% MVC contractions for one hour resulted in a 12% MVC reduction and significant EMG alterations.
    • Low-frequency fatigue was observed in knee extensors after contraction; intermittent contractions showed similar EMG changes after 2-3 hours.

    Conclusions:

    • The concept of indefinite endurance times below 15-20% MVC is not supported by findings.
    • Prolonged low-level static contractions induce muscle fatigue and detectable EMG changes.
    • Increased extracellular potassium concentration is a potential mechanism contributing to observed muscle fatigue.