So core stability is important for our health and fitness, but what is it? Core stability put simply means keeping our core stable. But what is the core, why do we want to keep it stable and how do we do it?

The word core generally refers to something that is in the middle of and inside of something, the inner sanctum, the central part of something, that is centrally important to the existence of the whole, and to the end result of a process. That is pretty much what our core is to the muscular-sceletal part of us, i.e. the bones and the muscles, the part of us that enables us to stand up and move around, and perform our daily tasks. Well, we need all the other body systems for the muscular-sceletal us to stay alive and well and be told what to do, but that’s another story.

What is the core?

Basically if we ripped our arms, legs and the head off, what remains is the core (ignoring all internal organs for the sake of this argument). Often the word core is used to refer to only the abdominal and the lower back muscles, but that is a much too simplified way of looking at the core, because of all the interaction between those and the hip, glute, pelvic floor, diaphragm, and upper back muscles. The vertebral column, i.e. the spine, holds us upright and enables us to move around. It can also bend forward, to the sides and backwards to differing extents, and twist. It holds the head at the top and limbs are connected to it via muscles and connective tissue. The muscles attached to it make it bend and twist, hold it upright and in correct alignment, and pull on it as we move. It is made up of 33 individual vertebrae connected together with facet joints and discs, and some of them are fused together. The joints give us the movement but we all know sometimes they don’t play nicely. And when there is a problem with the spine it can be extremely painfull, debilitating and at times persistent. Often it is difficult to diagnose the exact root of the problem. But the spinal column has an extremely tough job to do and needs a lot of support and protection. This is the job for the core. In fact they are best mates and without the core the spinal column would be nothing. The core is the strong one in the relationship, and when the core looses it’s strength, i.e. it’s stability, the spinal column has no support and starts to fall out of correct alignment. This is why we want the core to remain strong and stable and should help it to stay so however we can.

What is the core made of?

The core has 3 layers of muscles. There is a deep muscle layer, also called position sense muscles, which are accessory muscles. This means they control small movements within a joint, in this case between each individual vertebra. They control, support and allow movement between each vertebra while a larger movement is performed over the whole of the spine, and are very important for the protection of the spine. These are called the rotatores, the intertransversarii, and the interspinalis.

The middle muscle layer, also called the inner unit, is arguably the most important, as if it can’t do it’s job of supporting the spine, the position sense muscles are put under too much stress. The inner unit muscles work as a unit, making up a cylinder together, sometimes referred to as the barrel. The barrel lid is made up of the diapragm underneath the lungs at the bottom of the ribcage. The circular part is made up of the Transversus abdiminis (TVA) at the front, internal obliques at the sides, and lumbar multifidus at the back. The bottom of the barrel is the pelvic floor.

The outer layer of muscles, also called the outer unit, is made up of the rectus abdominis at the front, external obliques at the sides, erector spinae and latissimus dorsi at the back, the gluteals (buttocks) and adductors (inner thigh).

What does the core do?

When the inner unit is working correctly , the muscles work together to form a strong stable cylinder which supports the spine, holds the insides in, holds us upright with a correct posture, and allows us to balance. When we prepare to move we contract the inner unit to support the core in preparation for the movement. The diaphragm pulls down, the walls of the core pull in and up, the the thoracolumbar fascia at the back pulls tight, and the pelvic floor resists the downward pressure. This is called intra-abdominal pressure (IAP). Not only does this support the spine and the core itself, it supports the movement of all the limbs. The function of the inner unit is to purely stabilize and not to create movement, therefore it’s muscles contract statically i.e. isometrically, meaning they don’t shorten.

The outer unit muscles contract in an isotonic way as they need to shorten and lengthen in order to create movement. They are responsible for moving the trunk as we bend or twist.

What if the core isn’t stable?

Faulty inner unit increases the chance of back problems. The inner unit not working properly may be because all of it is weak, or because some parts of it are weak. The core muscles can only stay strong if they are used, same as any muscle. Therefore sedentary lifestyle where the core muscles don’t get use is probably the biggest cause of back problems. Many studies have found a link between ineffective trunk muscle recruitment and acute (short term) and chronic (long term) back pain (Richardson et al 1999; Hodges 2001; Hodges et al 2003). Seated slouched positions do not encourage a neutral spine position which is important for core stability. Our exercise choices can also put our core stability at risk by creating unequal strength within the core muscles, or by not training the muscles to work in an integrated way. This can happen for example when we only ever train the abdominal muscles but not the back, or we train muscles in isolation such as when using fixed movement machines in the gym.

How do we keep our core strong?

Core exercise includes any activity where the core muscles are used. This can be any activity where the core needs to be activated to support movement. Merely by standing up and moving around you are using the core more than sitting down. As the inner unit functions by static contraction, the exercises to strengthen it do not need to involve movement in the trunk. This is the idea behind exercises such as planks, straight legs bridges and leanbacks. Adding movement of the limbs at the same time ads to the challenge of supporting the core. Also any movement where the balance is challenged necessitates the bracing of the core, such as standing on one leg, balancing on a stability ball. Adding movement of limbs with extra weight can add to challenge. However before attempting these exercises we need to understand how to deliberately brace our core in order to minimize risk of injury. We can practise to engage the core muscles by “squeezing in” lower abdominal muscles in a “tightening a belt” or “zipping up” type of motion. To exercise the outer unit we use exercises involving movement at the trunk i.e. involving lifting/lowering, bending or twisting at the trunk. The inner unit is also working during these exercises in a stabilising capacity. These may include ab curls, leg lifts (on front and on back), russian twist, “swimming” etc. Doing core exercises using a stability ball or another device to add extra balance challenge is good for the core. Also doing functional exercise where we are using the whole of the body in an integrated way means we are always needing to involve the core. Exercising with free weights, kettlebells, ropes or just with bodyweight can achieve this.

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