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Related Experiment Videos

Repeated spinal flexion modulates the flexion-relaxation phenomenon.

James P Dickey1, Sara McNorton, James R Potvin

  • 1Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ont., Canada N1G 2W1. jdickey@uoguelph.ca

Clinical Biomechanics (Bristol, Avon)
|October 7, 2003
PubMed
Summary

Repeated trunk flexion alters the lumbar muscles' ability to deactivate near full spinal flexion. This change, observed at a greater angle and proportion of maximum flexion, may increase injury risk.

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Area of Science:

  • Biomechanics
  • Neuromuscular physiology
  • Spinal health

Background:

  • Repeated trunk flexion can lead to muscle fatigue, passive tissue creep, and reduced protective reflexes.
  • The effect of repeated trunk flexion on the flexion-relaxation phenomenon is not well understood.
  • Understanding flexion-relaxation is crucial as it may be linked to an increased risk of low-back disorders.

Purpose of the Study:

  • To investigate how repeated spinal flexion and loading influence the deactivation of lumbar muscles during full flexion (flexion-relaxation phenomenon).

Main Methods:

  • A repeated measures experimental design was employed.
  • Thirty healthy young adults performed 100 trunk flexion movements with and without added mass.
  • Erector spinae electromyography and lumbar spine flexion were measured to determine the spinal flexion angle at myoelectric silence.

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Main Results:

  • The flexion-relaxation phenomenon was observed in most subjects throughout the repeated trunk flexion.
  • Both the flexion-relaxation angle and maximum flexion angle increased by the end of the experiment.
  • This increase was more pronounced under unloaded conditions compared to loaded conditions.

Conclusions:

  • Repeated trunk flexion significantly alters the flexion-relaxation phenomenon.
  • The observed changes suggest modifications in the neuromuscular control system.
  • Deactivation of erector muscles occurs at a greater spinal flexion angle and proportion of maximum flexion, potentially increasing injury risk.