Research defined two main stabilization systems of the body, the interior unit, an outer unit. The interior unit pertains to the functional synergy between the deep muscles of the core. The interior unit is made up of the abdominal transverse, the posterior fibers of the Obliquus internus abdomen, the diaphragm, the pelvic floor muscles, the Multifidus and lumbar parts of the Longissimus and Iliocostalis. These muscles have their origin or insertion at the vertebrae and generate little or no movement during activation. Contraction of those deep core muscles provides segmental stabilization of the backbone. The outer unit consists of many muscles like the Obliquus externus, Obliquus internus, Erector spinae, Latissimus dorsi, Gluteus muscles, the Quadratus lumborum, adductors, and hamstrings.
The interior unit and an outer unit.
The outer unit muscles have an essential stability function when the body is under load or during high-speed movements. The outer unit controls the motion range, generates movement and provides gross stability. The interior unit – The interior unit muscles are tonic muscles that function as stabilizers. They efficiently stabilize the backbone and sacroiliac joint at low levels of contraction with low susceptibility to fatigue. Coordination is crucial for proper stabilization. The capability of the interior unit muscles to contract prior to force production of phasic muscles is more essential than their strength. Research demonstrates that in people with no history of low back pain, the Transversus abdominis fires 30 milliseconds before arm movements and 110 milliseconds before leg movements.
Important role of the transverse abdominis
Prior to movement of the body, the interior unit is activated, contracting the Transversus abdominis and the multifidi. Since the fibers of the abdominal transverse are oriented horizontally, the navel is drawn in toward the backbone on contraction. This drawing in of the abdomen wall compresses the internal organs. The up- and downwards pressure generated by the compressed internal organs activates the diaphragm and the pelvic floor muscles. This simultaneous activation of the interior unit muscles stiffens the backbone and provides segmental stabilization. Contraction of the abdominal transverse plays a very important role in inner unit stabilization for numerous reasons! The drawing in of the abdomen wall on Transversus abdominis contraction increases the intra abdomen pressure.
The Transversus abdominis and Obliquus internus abdominis are connected with the thoracolumbar fascia. The contraction of those muscles tightens the thoracolumbar fascia in a weight belt-like fashion. The thoracolumbar fascia attaches to the thorny and transverse processes of every lumbar vertebra. The generated lateral tension on the thoracolumbar fascia by the contraction of the abdominal transverse and Obliquus internus abdominis stabilizes each vertebra. The Multifidus and extensors of the back are wrapped in the thoracolumbar fascia. When these muscles contract, they’ll expand inside the confined area of the thoracolumbar fascia. The increased intra compartmental pressure produces an extension force. This is referred to as the hydraulic amplifier mechanism.