Intrinsic Stabilization Subsystem Integration (ISS)
By Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS
The Intrinsic Stabilization Subsystem (ISS) is comprised of:
- Transverse Abdominis (TVA)
- Pelvic Floor (Levator ani, coccygeus and associated fascia)
- Thoracolumbar Fascia
- Rotatores, Interspinales & Intertransversarii
- Note: The rotatores, interspinales and intertransversarii are not traditionally viewed as part of this muscular synergy; however, it is my assertion they should be added to this group. Based on my observations, research, and considerations of anatomy and function (especially their role in proprioception, joint position sense, and intersegmental stabilization), including these muscles to this subsystem adds congruence to our understanding of muscular synergies, motor behavior, and predictive models of movement impairment.
The intrinsic stabilization subsystem (ISS) increases intra-abdominal pressure, tension in the thoracolumbar fascia, segmental rigidity between vertebrae, sacroiliac joint stiffness, and improves segmental alignment (6). This results in optimal stabilization of the lumbo pelvic hip complex, enhancing the transfer of force between upper and lower extremities and the function of all other subsystems:
- Anterior Oblique Subsystem (AOS)
- Posterior Oblique Subsystem (POS)
- Lateral Subsystem (LS)
- Deep Longitudinal Subsystem (DLS)
The Intrinsic Stabilization Subsystem (ISS) by any other name:
- These muscles have been termed the "intrinsic stabilizers," "intrinsic core muscles," "local stabilizers," "deep stabilizers," "your internal weight belt", and my personal nickname for them "TVA and friends", but... the idea of adding this muscular synergy to the "core subsystems" is an original idea - in essence, I made it up. This was not my attempt to create a new language, but rather my attempt to integrate knowledge. In my "Search for Congruence" I realized that by viewing this synergy as a "Core Subsystem," I could integrate the ideas of Richardson et. al., McGill, Liebenson et. al, and Vleeming with a human movement impairment model based on the work of Janda, Sahrmann, Clark, and myself (1-9). With the additional muscles I suggest in these core subsystem articles, all core muscles are represented, and their integrated function considered. The intrinsic stabilization subsystem represents the intrinsics, while the global core muscles are represented by all other subsystems. Because the core subsystems divide the global musculature into functional groups their relative length and activity can be considered relative to postural dysfunction. This in-turn has a significant impact on exercise selection for rehab, fitness and performance enhancement.
Due to the lordotic curve and shape of the lumbar vertebrae in a normal healthy spine - compression and extension forces will include a vector that results in anterior translation (anterior shear force) of the lumbar vertebrae. The erector spinae, latissimus dorsi, quadratus lumborum, and iliopsoas are important movers and stabilizers of the core, but as extensors and compressors of the