Kinesiology of the Trunk:

by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS

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

Questions, comments, and criticisms are welcomed and encouraged –

Kinesiology of the Trunk