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Differences in activation patterns between eccentric and concentric quadriceps contractions.

Malachy P McHugh1, Timothy F Tyler, Scott C Greenberg

  • 1Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY 10021, USA. mchugh@nismat.org

Journal of Sports Sciences
|January 29, 2002
PubMed
Summary
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Fast-twitch motor units are more active during low-intensity eccentric contractions than concentric ones. Surface EMG analysis reveals higher mean frequencies in eccentric contractions, supporting selective motor unit recruitment.

Area of Science:

  • Exercise Physiology
  • Biomechanics
  • Motor Control

Background:

  • Previous research using indwelling electrodes suggests selective recruitment of fast-twitch motor units during low-intensity eccentric contractions.
  • Understanding motor unit recruitment patterns during different contraction types is crucial for optimizing training and rehabilitation.

Purpose of the Study:

  • To compare the frequency content of surface electromyograms (EMGs) from quadriceps muscles during eccentric and concentric contractions across varying intensities.
  • To investigate the influence of contraction intensity on motor unit activation patterns during different contraction modes.

Main Methods:

  • Surface EMGs were recorded from the rectus femoris, vastus lateralis, and vastus medialis muscles of 10 men.
  • Isokinetic knee extension (eccentric and concentric) and isometric contractions were performed at 25%, 50%, 75%, and 100% of maximal voluntary contraction (MVC).

Related Experiment Videos

  • Mean frequency and root mean square (RMS) of the surface EMG signals were calculated.

    • Main Results:

    • Mean EMG frequency was significantly higher during eccentric compared to concentric contractions at 25%, 50%, and 75% MVC (P < 0.05).
    • Mean frequency increased with intensity for isometric and concentric contractions but not for eccentric contractions.
    • EMG amplitude (RMS) increased with intensity similarly across all contraction modes (P < 0.0001).

    Conclusions:

    • The findings support the hypothesis that fast-twitch motor units are more active during submaximal eccentric contractions compared to concentric contractions.
    • Surface EMG frequency analysis can provide insights into motor unit recruitment strategies during different types of muscle contractions.
    • These results have implications for understanding muscle fatigue, performance, and injury mechanisms.