Core stability
core n central or essential part
stability n steadiness; ability to resist change of any kind
The term "core stability" has become a bit of a buzz word in athletic, training and rehabilitation circles. It has its basis in much of the work done by Gracovetsky and others in the 70's. It has also, in a way, been incorporated into Pilates exercises. But it was really the work of Richardson, Hides and Hodges in the 90's that the concept of core stability was realised and formalised.
Core stability refers to the central area of the trunk, around the lumbar spine. The core is seen as the area of transfer of force and energy from the lower half of the body to the top half of the body, and vice versa. If the core is not solid, the transfer of energy is inefficient. The core stabilising system also supports the lumbar spine to stiffen it, and it is proposed that the system can also take some of the load off the intervertebral discs.
So what comprises the core stabilising system (CSS)?? Here are the views of the front and the back, but remember that the system wraps right around the abdomen.
The most important muscle to note here is the transversus. It attaches to fascia at the front that wraps around the rectus abdominis, and to the fascia attached to the vertebra at the rear. It thus forms a sort of cylinder. The transversus does not attach to anything else and cannot cause any movement of the body. The muscle fibres run horizontally, which is something not found in any other abdominal muscle.
Contraction of the transversus causes 2 things to happen:
1. the abdominal wall is pulled inwards (like when you are vomiting)
2. the fascia is pulled tight
These two facts are important, as it gives a clue as to how the transversus contracts and how it helps to stabilise the abdomen. By pulling the fascia tight, it forms a rigid cylinder. The fascia in the lumbar area is also very interesting, as when it is pulled sideways by the transversus, it also contracts. This pulls on the rear part of the vertebra, causing an extension force, and opposing flexion forces. This action can help to absorb some of the compression forces on the intervertebral discs. It also prevents movement of the lumbar spine, making it less mobile throughout, and stiffer. This can be of great importance when forces are being applied through the lumbar spine. In conjunction with the transversus, the back extensors (erectores or sacrospinalis) have a role to play. Notice that the sacrospinalis muscles are wrapped in fascia. When they contract isometrically, they expand and tighten up the fascia. This also helps to tension up the whole CSS.
So, the CSS forms a natural "weight belt". It has the added advantages over a weight belt in that it supports and stiffens the whole lumbar spine, and not just part of it. Also, the CSS can sense the load being paced on the body and adjust its tension accordingly. By using a weight belt, the CSS is actually disabled.
The CSS is also important in activities such as running. The legs effectively push through the pelvis. If the lumbar area is not stable, then the pelvis is not a stable platform for the leg to push against, and it absorbs some of the energy from the leg, making the push against the ground less efficient. If the core is able to keep the lumbo-pelvic region solid, then the leg has a solid platform to push against, and is able to transmit the full force to pushing-off against the ground.
The CSS also operates to make the trunk rigid when you are moving the arms or carrying a load with the arms. In fact, the CSS contracts before you move or load your arms. Most other stabilising muscles come into play after the body part moves or is loaded.