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June 6, 2023

Kinesiology of the Trunk

An analysis of the functional roles of muscles for the joint actions of the trunk (lumbar spine).

Brent Brookbush

Brent Brookbush

DPT, PT, MS, CPT, HMS, IMT

Kinesiology of the joint actions of the trunk/spine: functional roles of muscles by joint action.

Kinesiology of the Trunk:

by Brent Brookbush DPT, PT, MS, CPT, HMS, IMT

From the Course:

Additional Courses

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

Trunk Extension

Trunk Lateral Flexion

Trunk Rotation

Trunk Flexion and Rotation

Trunk Extension w/ Rotation

© 2011 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged –

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