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Related Experiment Videos

Was Sherrington right about co-contractions?

A E Tyler, R S Hutton

    Brain Research
    |April 2, 1986
    PubMed
    Summary

    Investigating muscle activation during co-contractions revealed that agonist-antagonist muscle pairs show reduced electromyographic (EMG) activity. This neural circuitry may protect joints from excessive forces during movements.

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    Area of Science:

    • Neuroscience
    • Biomechanics
    • Human Physiology

    Background:

    • Understanding muscle activation patterns is crucial for biomechanics and neuroscience.
    • Agonist-antagonist muscle co-contractions are fundamental for joint stability and controlled movement.
    • Sherrington's 'double reciprocal innervation' theory provides a framework for understanding neural control of opposing muscles.

    Purpose of the Study:

    • To quantify and compare electromyographic (EMG) activity during maximal voluntary contractions of elbow flexors and extensors.
    • To investigate the influence of agonist-antagonist co-contraction on the EMG activity of individual muscles.
    • To examine how joint position affects EMG activity during co-contraction.

    Main Methods:

    • Electromyographic (EMG) activity was recorded from elbow flexors (biceps brachii) and extensors (triceps, long head).
    • Participants performed brief isometric maximum voluntary contractions under two conditions: agonist contraction only and agonist-antagonist co-contraction.
    • Maximum EMG activity during co-contraction was expressed as a ratio relative to maximum EMG activity during isolated agonist contraction.

    Main Results:

    • EMG ratios of co-contraction to agonist activity were consistently below 1.0 for both flexors (mean = 0.48) and extensors (mean = 0.76).
    • Elbow flexor EMG ratios were independent of elbow joint position.
    • Elbow extensor EMG ratios increased towards 1.0 or higher at shorter muscle lengths (elbow extension).

    Conclusions:

    • Neural mechanisms limit full muscle activation during co-contractions, supporting Sherrington's 'double reciprocal innervation' principle.
    • These neural circuits likely play a protective role, preventing excessive joint forces (tangential or compressive) during co-contraction.
    • Muscle length influences the degree of reciprocal inhibition in extensor muscles during co-contraction.

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