Kinesiology of the Trunk:
by Brent Brookbush DPT, PT, MS, CPT, HMS, IMT
From the Course:
Additional Courses
- Lesson 18: The Spine and Trunk Muscles (Introductory Course)
- Lesson 19: Trunk Muscles Graph, Additional Core Muscles, and Core Exercise Challenge (Introductory Course)
Definitions:
- Prime Mover : The muscle that can produce the most force for a joint action. Generally, this is the muscle that will generate the most force during a joint action when exerting force against an external load.
- Agonist : Muscles that perform a joint action, including the prime mover and synergists. That is, unlike the terms prime mover and synergist, agonist refers to all of the muscles that can perform a joint action.
- Synergist : Synergists are muscles that assist the prime mover in performing a joint action. By definition, all agonists that are not the prime mover are synergists.
- Antagonist : Muscles that oppose the agonists (including the prime mover and synergists) for a given joint action. That is, all of the muscles that can perform the opposing joint action.
- Neutralizer : During a joint action, neutralizers are muscles that oppose the unwanted or ancillary joint motions that result from the force generated by the prime mover and/or synergists.
- Fixator : Fixators are muscles that act to reduce or prevent movement of joints proximal to the joint in motion.
- Stabilizer : The role of a stabilizer is to improve arthrokinematics by maintaining optimal alignment of joint surfaces during joint actions. Most often, these muscles are the most intrinsic muscles of a joint. For example, the muscles of the rotator cuff of the shoulder.
Kinesiology of the Trunk
Trunk Flexion
- Prime Mover: Rectus Abdominis
- Synergists: External Obliques , Internal Obliques , Psoas
- Antagonists: Erector Spinae (Iliocostalis, Longissimus, Spinalis) , Latissimus Dorsi
- Neutralizers: External obliques and internal obliques when bilaterally contracted neutralize rotation.
- Stabilizers: Intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex.
Trunk Extension
- Prime Movers: Erector spinae (Iliocostalis, longissimus, spinalis) , latissimus dorsi , Intrinsic musculature of the spine
- Synergists: Intrinsic musculature of the spine
- Antagonists: Rectus abdominis , external obliques , internal obliques , psoas
- Neutralizers: Bilateral contraction of erector spinae and quadratus lumborum
- Stabilizers: Intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex.
Trunk Lateral Flexion
- Agonists: Quadratus Lumborum
- Synergists: Ipsilateral external oblique and internal oblique , ipsilateral erector spinae , ipsilateral latissimus dorsi
- Antagonists: Contralateral quadratus lumborum , contralateral external and internal obliques , contralateral erector spinae , contralateral latissimus dorsi
- Neutralizers: Erector spinae neutralizes flexion force created by internal and external obliques , intrinsic stabilization system creates posterior shear force on lumbar spine to neutralize lumbar extension, rectus abdominis and psoas prevent ancillary extension.
- Stabilizers: Rectus abdominis , psoas , intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex.
Trunk Rotation
- Prime Movers: Contralateral external oblique and ipsilateral internal oblique
- Synergists: Ipsilateral latissimus dorsi , contralateral psoas
- Antagonists: Opposing external and internal oblique
- Neutralizers: Erector spinae neutralize the flexion force created by the internal and external obliques , quadratus lumborum neutralizes lateral flexion force created by the internal and external obliques , and rectus abdominis prevent ancillary lumbar extension (anterior pelvic tilt) created by the latissimus dorsi
- Stabilizers: Intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex
Trunk Flexion and Rotation
- Prime Movers: Rectus abdominis , contralateral external oblique , ipsilateral internal oblique
- Synergists: Ipsilateral latissimus dorsi , contralateral psoas
- Antagonists: Opposing external and internal oblique , erector spinae
- Neutralizers: Quadratus lumborum neutralizes lateral flexion force created by the internal and external obliques
- Stabilizers: Intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex
Trunk Extension w/ Rotation
- Prime Movers: Erector spinae (iliocostalis, longissimus, spinalis) , contralateral external oblique , ipsilateral internal oblique , latissimus dorsi
- Synergists – Latissimus dorsi , contralateral psoas
- Antagonists – Rectus abdominis , ipsilateral external obliques , contralateral internal obliques , ipsilateral psoas
- Neutralizers: Quadratus lumborum neutralizes lateral flexion force created by the internal and external obliques
- Stabilizers: Intrinsic stabilization subsystem (Transverse abdominis , intrinsic muscles of spine, diaphragm, pelvic floor)
- Fixators: All musculature of the hip, especially the glute complex
© 2011 Brent Brookbush
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