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Related Experiment Videos

Active trunk stiffness increases with co-contraction.

Patrick J Lee1, Ellen L Rogers, Kevin P Granata

  • 1Musculoskeletal Biomechanics Laboratories, Department of Engineering Science and Mechanics, School of Biomedical Engineering and Science, Virginia Polytechnic Institute and State University, 219 Norris Hall, 0219, Blacksburg, VA 24061, USA.

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology
|August 16, 2005
PubMed
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Voluntary co-contraction significantly increases trunk stiffness by 37.8%. This finding empirically supports biomechanical models suggesting co-contraction enhances spinal stability during trunk extension exertions.

Area of Science:

  • Biomechanics
  • Human Movement Science
  • Spinal Physiology

Background:

  • Voluntary co-contraction increases joint stiffness in extremities.
  • Biomechanical models hypothesize co-contraction enhances trunk stiffness.
  • Empirical evidence for co-contraction's effect on trunk stiffness is lacking.

Purpose of the Study:

  • To empirically evaluate the influence of voluntary co-contraction on trunk stiffness.
  • To investigate changes in trunk dynamics with varying co-contraction levels.

Main Methods:

  • Quantified trunk dynamics (stiffness, mass, damping) during trunk extension.
  • Used pseudorandom force disturbances to elicit small trunk displacements.
  • Recorded electromyography (EMG) from eight trunk muscles across minimal and maximal co-contraction conditions.

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Main Results:

  • Trunk stiffness increased by 37.8% (p < 0.004) from minimal to maximal voluntary co-contraction.
  • Increased EMG activity confirmed distinct muscle recruitment patterns between conditions.
  • Impulse response functions (IRFs) analyzed trunk dynamics.

Conclusions:

  • Empirically demonstrate that voluntary co-contraction significantly increases trunk stiffness.
  • Results support existing biomechanical models of spine function.
  • Co-contraction likely contributes to spinal stability during dynamic exertions.