Core stability relates to the bodily region bounded by the abdominal wall, the pelvis, the lower back and the diaphragm and its ability to stabilise the body during movement. The main muscles involved include the transversus abdominis, the internal and external obliques, the quadratus lumborum and the diaphragm. The diaphragm is the main muscle of breathing in the human and so breathing is important in providing the necessary core stability for moving and lifting. It is the action of these muscles contracting together upon the incompressible contents of the abdominal cavity (i.e. the internal organs or viscera) that provides support to the spine and pelvis during movement.
Core stability is a misunderstood term. Typically, the core is associated with the abdominal muscles groups and stability is associated with isometric or static strength. However in actuality, the core consists of the abdominal muscles groups (transverse abdomens, internal obliques, external obliques, rectus abdomens), hip abductors/ adductors, hip flexors, the pelvic floor, and lumbar spine. In addition, it is lumbar spine that is primarily responsible for posture and stability providing the strength needed for stability especially utilized in dynamic sports.
Whenever a person moves, to lift something or simply to move from one position to another, the core region is tensed first. This tension is usually made unconsciously and in conjunction with a change in breathing pattern. An example to try is to sit in a chair and to reach forward over a table to pick up a cup. This movement is first accompanied by a tension in the core region of the abdomen and can be felt by placing one hand on the abdomen as the movement is made.
As the load increases the key muscles contract around the viscera, which are incompressible, to form a stable ball-like core region against which the forces are balanced in coordination with posture. In martial arts there is a saying that 'power is generated from the ground up' and core stability is necessary for the transfer of force and power from the ground across the body into any movement.
It is commonly believed that core stability is essential for the maintenance of an upright posture and especially for movements and lifts that require extra effort such as lifting a heavy weight from the ground to a table. Without core stability the lower back is not supported from inside and can be injured by strain caused by the exercise. It is also believed that insufficient core stability can result in lower back pain, poor posture and lethargy.
There is little support in research for the core stability model and many of the benefits attributed to this method of exercise have not been demonstrated. At best core stability training has the same benefits as general, non-specific exercise  (see review by Lederman 09) and walking.  Trunk or core specific exercise have failed to demonstrate preventative benefits against injuries in sports  or to improve sports performance.
Although Lederman remains a figurehead skeptic against core stabilization, there are several favorable studies that exist to support the role of core stabilization in protecting the spine from unnecessary shifting and shearing of vertebral structures. The core stability model consists of passive and active stabilization structures as well as a third, often disregarded subsystem, called the neuromotor system. This vital system is required for the active structures such as muscles to provide preemptive or rather quick responses to the body's demands.
Training methods for developing and maintaining core stability include:
- Exercise ball, also known as a Swiss ball, stability ball, yoga ball, Pilates ball or fitness ball
- Halo exercises
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