For explanation purposes, the core can be broken down into three systems (local stabilisation, global stabilisation, and movement), but, it is important to remember that these systems are constantly working together to bring about stability, as well as movement. In laymen’s terms, it has been said that movement systems work from the inside out i.e. to produce the most effective movement possible, the body needs to stabilize at a deep level before producing gross motor movement.
Local Stabilisation System
The local core stabilisers are the muscles which attach directly to the vertebrae. They consist of primarily type 1 fibres, and have a high density of muscle spindles. Their main function is intervertebral, and intersegmental, stabilisation, and they work to limit sheering, rotation and compression, between segments of the spinal column. In other words, they stabilise each vertebra, relative to the adjacent vertebrae, and have primarily a strength endurance role (hence the high percentage of slow twitch fibers). Also, due to the high density of muscle spindles, they add to the proprioceptive function, and increase balance and stability. The primary muscles making up this system are: the transverse abdominus, multifidus, internal obliques, pelvic floor and diaphragm, and they increase stability through increasing intra-abdominal pressure when they contract as a unit. This increases spinal stiffness, as well as improving intersegmental neuromuscular control.
The Global Stabilisation System
The muscles of the global stabilisation system are those which connect the pelvis and the spine. They act to stabilise the spine on the pelvis, while also transferring forces between upper and lower body through eccentric control during functional movements. These muscles lie more superficial to the ones of the local stabilisation system, and include: quadratus lumborum, psoas major, external obliques, rectus abdominus, gluteus medius and the adductor complex.
The Movement System
This system includes muscles which attach the spine, or pelvis, to the extremities. They are primarily responsible for concentric force production and eccentric deceleration of forces during dynamic and functional activity. The primary muscles of this complex include: latissimus dorsi, hip flexors, hamstring complex and the quadriceps.
Collectively, the muscles of all three systems work to bring about dynamic and static stability, and neuromuscular control of all movements. The best way to think about their functions (and therefore how to go about training them) is from an inside-out perspective. In other words, the deeper, more central muscles need to perform their job effectively, in order for the next layer to follow suit. The foundation must be strong and secure enough to be the base for the next layer. Failure to follow this concept will result in predictable patterns of injury, as excessive strain is seen in movements which are not adequately stabilised.