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Flexion-relaxation response to gravity.

Michael Olson1, Moshe Solomonow, Li Li

  • 1Department of Kinesiology, Louisiana State University, Baton Rouge, LA, USA.

Journal of Biomechanics
|November 1, 2005
PubMed
Summary
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The orientation of gravitational loading significantly impacts trunk muscle activity and the flexion-relaxation phenomenon (FRP). Gravity

Area of Science:

  • Biomechanics
  • Human Physiology
  • Neuromuscular Control

Background:

  • The flexion-relaxation phenomenon (FRP) is a key aspect of spinal biomechanics.
  • Understanding trunk muscle activation patterns under different gravitational loads is crucial for injury prevention and rehabilitation.

Purpose of the Study:

  • To investigate how gravitational loading orientation affects anterior and posterior trunk muscle behavior during flexion-extension movements.
  • To analyze the influence of gravity on the flexion-relaxation phenomenon (FRP) in various trunk muscles.

Main Methods:

  • Surface electromyography (EMG) was used to record muscle activity from lumbar paraspinal, abdominal, and thigh muscles in 13 participants.
  • Trunk flexion-extension movements were performed in two conditions: standing (gravity parallel to the body axis) and supine (gravity perpendicular to the body axis).

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  • EMG signals were synchronized with lumbar flexion and trunk inclination angles.

    • Main Results:

    • Standing flexion-extension demonstrated the FRP in lumbar posterior and hamstring muscles, with abdominal muscles active at deep angles.
    • Sit-up movements (supine) showed a silent period in abdominal and quadriceps muscles, with posterior lumbar muscles active, and the FRP was absent in posterior muscles.
    • The orientation of gravity profoundly influenced the FRP and muscle activation patterns.

    Conclusions:

    • Gravitational moments, rather than just kinematics or motor programs, are dominant factors in the FRP.
    • Muscle activation and inhibition patterns are significantly altered by gravitational load orientation.
    • Findings enhance understanding of spinal biomechanics and low back disorders.