A bit of background
‘The core’ has become popular in both the medical and fitness industries, with both at one point, assuming that the core is only your abdominals and by strengthening them you will reduce back pain. However, there is no science behind this. This article is a great way of helping you to understand exactly what the core is, why it is not just the abdominals, how it functions normally and how it is commonly changed in people with spine or pelvic pain.
A lot of clinicians find that people who have spinal or pelvic pain, or a combination of both, cannot organise the basic elements of ‘core control’. As a result, a patient will often try to strengthen their abdominals. However, this could be further imprinting poor movement patterns and strategies. The debate around what the ‘core’ is and how it could help began around 2008. Despite this, it is difficult for people to give an exact definition of what ‘the core’ is.
From 1999, an Australian group looked at postural control in healthy people compared with chronic lower back pain. They particularly looked at the role of the motor system and analysed how the nervous system organises to give appropriate responses to a task. This supports the spine, gives postural control and balance and at the same time allows for important actions like breathing and continence. They showed that when back pain was present, the strategies used by the brain and spinal cord changed. Also, they looked at how the diaphragm, pelvic floor, deep fibres of multifidus (a muscle deep in the spine), and transversus abdominis (the deepest abdominal muscles), work together to spontaneously co-activate before you move your limbs.
They also found that in patients with pain around their spine or pelvis, the pre-activation of these muscles was delayed and/or reduced during movement, therefore reducing intrinsic stability. However, since this research was published, their results have been mis-interpreted and we have singled out transversus abdominis as ‘the core’.
In 2004, Ida Rolf, a biochemist who also studied homeopathy, osteopathy and yoga, defined an expanded view of the ‘inner being’ muscles as the core, and the extrinsic as the sleeve or ‘doing’ muscles.
Pilates has also become strongly linked with the ‘core’, although Joseph Pilates never used the term. He focused on whole body health and complete co-ordination of body, mind and spirit. After his move to America, his work was mainly with elite dancers and athletes and looked at high load exercises. In 2002, Unagaro described the Pilates method as ‘the powerhouse’ which gives you the image of large powerful muscles rather than internal structures. Again, you can see how ‘the core’ has changed.
What is the ‘core’?
The core is often referred to as the muscles that wrap around and pull in your stomach. However, it is a lot more complex than that.
The pelvis is the centre when looking at transferring load and weight around the body. In standing, your centre of gravity sits naturally just in front of the sacrum (see the spine anatomy handout).
When looking at ‘the core’, the diaphragm and trunk are essential in movement control and support. It has been well documented that if your head, rib cage, and pelvis are lined up around your centre of gravity then you will use the least energy during movement. This is often known as a ‘neutral spine’. This area surrounds a space which can change the volume within it by expanding and contracting. The diaphragm divides this space into the thoracic and thoraco-abdominal-pelvic cavity. The latter is our ‘core’.
Functional mechanics of the core
There are three important things to think about with a healthy ‘core’.
This generates intra-abdominal pressure and natural stability around the spine.
- Postural control
Balanced activation between the muscles on the front (flexor) and the back (extensor).
- Control of the pelvis
Pelvic control directly links to how you control the flexor and extensor muscles.
Having good co-ordination of these three systems gives you complex patterns of control and includes many deep muscles and structures including:
- Pelvic floor
- Transversus abdominis
- Interspinales and intertransversarii (small muscles between your vertebrae)
- Psoas and iliacus
- Quadratus lumborum (particularly the medial fibres)
- Internal oblique
- Deep hip rotators
These muscles create a sleeve around you which adapt to provide ‘core control’.
Your core does lots of important things including:
Regulating internal pressure changes
This means that when you sneeze, laugh, blow your nose, or are sick, it adapts to the load automatically. When you run or jump it also helps with continence.
Breathing and postural control
Breathing is described as the most fundamental motor pattern and linked inextricably with postural control. For us to stand against gravity, we need to develop postural control. In our developmental sequence, breathing becomes integrated into our evolving patterns of movement control. As a result, breathing and postural control support each other.
A healthy breathing pattern is said to be one of lateral expansion of the lower rib cage. To get the ribs to ‘push out’, you need to be able to generate enough intra-abdominal pressure. When you have pain or poor posture your breathing changes. However, if posture is good then breathing is facilitated and vice versa.
‘Core control’ and intra-abdominal pressure
The spine is the backbone of the body and helps us to move and bend freely. However, there are a lot of things which need to happen for it to be supported.
Intra-abdominal pressure has been looked at for many years when analysing adding weight to your body. These studies focus on trunk strength rather than control. However, later studies show this pressure is important in the posture and support required in normal activities of life.
Intra-abdominal pressure is generated when the diaphragm descends. A co-contraction of the known transversus abdominis and pelvic floor is created. This is an automatic response which acts like a ‘pre movement’ stabiliser. It is important that the activity level and timing between these are well balanced. Problems occur when there is not only underactivity, but also overactivity, for example gripping or bracing.
For healthy people the amount of intra-abdominal pressure that you generate should be appropriate for the task. This means that the pressure should increase in proportion to the forces that your limbs are generating. For example, if you are lifting an extremely heavy weight, you need to splint the abdominal wall and sacrifice good breathing patterns to generate enough intra-abdominal pressure for appropriate support.
Your spine stiffness will also change through your breathing cycle. Holding your breath at the end of inspiration increases your intra-abdominal pressure and creates spine stiffness. However, breathing throughout movement creates optimal pressure which reduces the risk of unwanted spinal compression.
Importantly, intra-abdominal pressure is constantly variable. This means that it is buoyant and gives you the natural internal stability to help you maintain an upright posture against gravity. Because of this constant change in pressure, the deeper muscles work constantly but at a low level to achieve this postural uprightness and at the same time generate the support required for activity.
In movement, you can see if you have underactive or overactive abdominals. In underactive, the abdomen will protrude or dome and the ‘neutral’ spino-pelvic posture is lost as well as the relationship between the thorax and the pelvis changes.
When the superficial abdominals are too strong, the neutral spino-pelvic posture is also lost, the thoracic opening is constricted and intrabdominal pressure is constricted, also loosing stability. This is why the balance between the systems is so important.
Is the pelvic floor part of ‘the core’?
In short, yes. The pelvic floor must contract during tasks which require higher intra-abdominal pressure to both help contribute to this pressure but also to maintain continence. More and more research is showing a link between continence and poor breathing patterns.
It is about co-ordination rather than strength
As plenty of research has shown, the ‘core response’ is about muscle activation and co-ordination rather than strength. It is reliant on sensory input and is the activation of many muscles which produce complex patterns of control and movement, not the strength of an individual muscle. No muscle can work alone and trying to do this creates dysfunctional spines and poor movement. To re-train ‘core control’, you must train basic muscular patterns.
What can go wrong with your core?
All it takes is subtle changes to this fine balance to create problems. In people with chronic lower back pain it is heavily documented that their spines move less and with excess superficial muscle tension and effort. The deep system is also uncoordinated, and people hold their breath.
You can often see when there is something wrong by looking at posture from the side. A larger curve in the lumbar spine generally facilitates breathing from the upper chest and expiration is shorter. The muscles in the extensor system over-recruit, and those in the anterior under-recruit.
In rehab these people need to have more activity in their abdomen. However, not through multiple sit-ups or crunches. The best way to do this is in training the exhalation and trying to lengthen it. This must then be maintained whilst performing a task. The easiest place to start this is on your back with the hips flexed.
In people with a flat lower back, in general they are more anteriorly dominant with overactivity in the upper abdomen. This is generally a bracing response. Normally people here rely on slumping to generate stability. Again, there is an upper chest breathing pattern. In rehabilitation this group needs to down train their pelvic floor and upper abdomen to encourage better diaphragm activity.
What all this means
‘Core’ problems are common in patients who have difficulty sitting up and breathing properly. Correcting breathing patterns can help to improve ‘core control’ as it is a fundamental part of the intrinsic stability mechanism. Once breathing has been re-trained, it is important to then load the limbs in order to challenge this patterning.
Overly focusing on the abdominals alone without looking at the timing and mechanics of the trunk and pelvis, can further increase this dysfunction creating more instability and pain.
In order to have a well-functioning ‘core’ you must expand your knowledge and thoughts of what the area is and understand the timing. Most importantly, you must remember that like Goldilocks and the three bears, the activity should be neither too high, or too low, but just right.