Lateral Subsystem Integration:

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

The Lateral Subsystem (LS) is comprised:

  • Gluteus Medius
  • Adductors
  • Contralateral Quadratus Lumborum (QL)
  • Tensor Fasciae Latae (TFL)
    • Note: The TFL is not traditionally viewed as muscles of the LS.  However, based on my considerations of anatomy, function, and available research, and observations in practice, adding this muscle to this subsystem adds congruence to our understanding of muscular synergies, motor behavior, and predictive models of movement impairment.
Function (Brief): Frontal plane stabilization of the lumbo-pelvc hip complex (LPHC), transfer of force between lower and upper extremities, active role in all integrated (whole body) frontal plane and single-leg movement patterns. Functional Arthrokinematics: This subsystem plays a key role in the optimal alignment of the hip joint, pelvis, sacroiliac joint and lumbar spine. Most notably the maintenance of pelvic neutral in the frontal plane with the spine perpendicular to it.  This subsystem is likely most active during single-leg stance and frontal plane movement patterns.  The inability of the lateral subsystem (LS) to maintain this position results in ipsilateral flexion of the spine, depression of the contralateral innominate (point of reference - iliac crest), and relative adduction of the ipsilateral femur; resulting in arthrokinematic dysfunction including ipsilateral facet joint and disk compression, sacroiliac joint rotation and inferior glide, and a superior glide of the femoral head in the acetabulum.  Dysfunction of the LS may also result in "knees bow in" (gluteus medius inhibition and anterior adductor synergistic dominance), or "knees bow out" (posterior adductor magnus dominance) during movement (including the overhead squat assessment) - in time this leads to adaptive shortening of the posterior and inferior capsule and may further contribute to a superior glide of the femoral head in the acetabulum in conjunction with an anterior glide of the femoral head.  Common pathologies that may result from this dysfunction include hip-impingement syndrome, groin strains, and over a lifetime - osteoarthritis of the superior/anterior surface of the acetabulum and degenerative changes to the labrum. Positive Trendelenburg Sign - Note the right hip drop resulting in relative adduction of the left femur, and lateral flexion of the spine to the left - http://eso-cdn.bestpractice.bmj.com/online-courses/online-courses/best-pr

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