The theory of core stability
Core stability training specifically targets the smaller and deeper lumbar spine and trunk muscles – the ‘core muscles’ of your body. Core stability training aims to 'engage' the trunk musculature and helps learn to control the position of the lumbar spine during dynamic movement in order to keep you strong, to keep you in a neutral, correct posture, and to prevent injury.
The lumbar spine
Theracolumbar Fascia (TLF)
These deep trunk muscles provide flexible support to the lumbar spine. The Transversus Abdominus (TA) and Internal Oblique (IO) muscles attach to the TLF, and the fascia (layers of tissue) wrap around and connect the deep trunk muscles to the spine. Contractions in the TA increase tension in the TLF and this compresses and stabilises the lumbar spine. When the TLF is under tension, the Erector Spinae (ES) and Multifidus (MF) muscle groups compress and are encouraged to contract and resist spinal flexion.
Intra-abdominal Pressure Mechanism (IAP)
Contraction of the TA, IO, MF and ES muscles exerts forces on the rectus muscle sheath – this is the sheath that encloses the Rectus Abdominus (RA) muscles. The RA muscle group attaches to the IO and TA, surrounding the abdomen, and when all of these muscles are contracted together, the exertion of these muscles creates intra-abdominal pressure within the abdomen (similar to a bag of air), that reduces compression and limits the shear forces on the lumbar spine. IAP has been shown to increase before weightlifting, or running, and therefore has a crucial role in lumbar stability.
These muscles, such as the Interspinalas and Intertransversarii, exert an individual stabilizing effect on adjacent vertebrae, and act in a similar fashion to ligaments in the knee or elbow.
Deep lumbar muscles
Deep lumbar extensors, such as the MF, are active through a full range of movement of the lumbar spine and during upper and lower limb movement. They can be trained to control the lumbar spine under motion at low forces and long timescales. These muscles are continually active.
Deep, trunk muscles, act as stabilisers, and they do not induce movement. They are static and work through isometric contraction – the muscles stay the same length, but undergo tension upon activation. These core muscles work throughout the day, continuously, and need stamina, but at low forces (due to the isometric contraction). Core stability training therefore need not make these muscles very strong, but to recruit them and help them coordinate correctly and continuously, and to act neutrally – to keep the natural ‘S’ curve of the spine.
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