Intrinsic Stabilization Subsystem (ISS) Integration:
By Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, H/FS
The Intrinsic Stabilization Subsystem (ISS) is comprised of:
- Transverse Abdominis (TVA)
- Internal Obliques
- Pelvic Floor (Levator ani, coccygeus and associated fascia)
- Rotatores, Interspinales & Intertransversarii
- Abdominal Fascia (posterior layer)
- Continuous with investing fascia of Diaphragm and Pelvic Floor
- Thoracolumbar Fascia (TLF) (anterior and middle layer)
The ISS is comprised of muscles of the lumbar spine and pelvis that do not contribute, or contribute very little to motion. The function of this subsystem is to increase intra-abdominal pressure, tension in the thoracolumbar fascia (TLF), increase sacroiliac joint (SIJ) stiffness, and enhance segmental rigidity and alignment of the lumbar vertebrae. Although the ISS does not actively contribute to motion, the increased intra-abdominal pressure may decompress/traction the spine during motion. Further, an increase in intra-abdominal pressure, segmental rigidity and TLF stiffness may aid in eccentrically decelerating spinal flexion and lateral flexion. The ISS is "the stabilization subsystem". Analogous to the rotator cuff of the shoulder, its optimal function may be essential for optimal performance of the other subsystems (muscles of the trunk). Inhibition of the ISS most often results in synergistic dominance of the Anterior Oblique Subsystem (AOS).
- Concentric Function: None (potentially traction/decompression)
- Isometric Function: Stabilization of the lumbar spine, SIJ and pelvis
- Eccentric Function: Contributes to eccentric deceleration of lumbar flexion and lateral flexion.
Common Maladaptive Behavior