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Knee extensor torque, work, and EMG during subjectively graded dynamic contractions.

Danny M Pincivero1, Paul T Dixon, Alan J Coelho

  • 1Department of Kinesiology, University of Toledo, 2801 Bancroft Street, Toledo, Ohio 43606, USA. danny.pincivero@utoledo.edu

Muscle & Nerve
|June 18, 2003
PubMed
Summary

This study found that perceived exertion levels do not accurately reflect actual knee extensor force during dynamic contractions. Muscle activation increases with perceived exertion, but torque production plateaus, suggesting a protective mechanism.

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Area of Science:

  • Exercise Physiology
  • Biomechanics
  • Neuromuscular Control

Background:

  • Perceived exertion is a subjective measure of exercise intensity.
  • Understanding the relationship between perceived exertion and objective measures like torque and muscle activation is crucial for exercise prescription and rehabilitation.

Purpose of the Study:

  • To investigate the relationship between perceived exertion levels and objective measures of knee extensor performance (peak torque, work, and electromyogram - EMG).
  • To determine if men and women differ in their perception of exertion relative to knee extensor output.

Main Methods:

  • Thirty participants performed maximal voluntary knee extensions and submaximal contractions at nine perceived exertion levels.
  • Knee extensor peak torque and work were measured isokinetically.

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  • Surface electromyogram (EMG) of vastus medialis, vastus lateralis, and rectus femoris muscles was recorded.
  • All measures were normalized to maximal voluntary contraction (MVC) values.

    • Main Results:

    • A significant linear increase in knee extensor peak torque and work was observed across perceived exertion levels.
    • However, peak torque and work were consistently lower than predicted at higher perceived exertion levels (e.g., <70% MVC at level 7).
    • EMG activity of vastus medialis, vastus lateralis, and rectus femoris increased significantly with perceived exertion, with the vastus lateralis showing the greatest increase.

    Conclusions:

    • Dynamic contractions guided by perceived exertion result in underproduction of torque at high perceptual intensities.
    • Increased reliance on vastus lateralis activation occurs across submaximal torque levels.
    • The overestimation of force at high perceived exertion may indicate a subconscious protective mechanism against excessive muscle and joint forces.