Thanks to Francesca Testa, medical student at Kings College London, for writing this piece and for Bradley Scanes, specialist physiotherapist for editing. You can read Francesca’s other pieces for The Food Medic here and take a look at Bradley’s other pieces here.
The terms “core stability” (CS) keep buzzing around the fitness world. You might have heard of it from fitness blogs, magazine articles, PTs (personal trainers) or gym instructors.
What does it exactly mean? And why is there such a huge fuss about it?
If you are thinking of the word “core” being somehow related to your “abs” (or abdominal muscles), then, yes, you are on the right track. Nevertheless, most people misinterpret having a stable and strong core with having a six-pack. Although effective training of your abdominal muscles might result in visible abs, core stability actually describes a function of the core.
Borrowing the formal definition from the Dictionary of Sport and Exercise Science and Medicine, core stability is “the ability to control the movement and position of the muscles of the central ‘core’ of the body which are responsible for posture and limb movement”. 
In simple terms, a stable core is what assists us in the maintenance of good posture and balance, and what helps us achieve better control of our body during movement. Think of the core as the “centre” of our body, and as what links the trunk with the arms and legs (what in anatomy is called the axial and the appendicular skeleton, respectively). Basically, the greater the core stability, the greater the control provided for limb movements.
Now, the term “stability” inevitably leads to consider the idea of “instability” which has been associated with some misconception regarding the range of movements that can be achieved and fear towards them . In order to avoid any misinterpretation, we are going to use the terminology “core strength” throughout this article.
How is the body controlled during movement achieved?
Imagine your core as a box, with each side being a muscle or set of muscles of the trunk. At the front of this “box”, you have your abdominal muscles, at the back the muscles of your spine (such as multifidus) and your gluteals. The roof of this muscular box is your diaphragm (the muscle that helps with breathing), and the bottom is made of the muscles of your pelvis (also known as pelvic floor) and hips.
Fig. 1: the core stability “box”
Most of these muscles are “active” at all time to keep the spine in a neutral position. They provide support from the front, back, top or bottom according to their anatomical position. The function of these muscles related to core strength is also known as the active subsystem. [2-3, 5-6]
In addition to muscles, there are other elements that play a role in the strength of the core and spine. Some ligaments, such the anterior and posterior longitudinal ligaments, run across the entire spine, connecting one vertebra to another. These prevent excessive movement of the trunk when bending down (also known as flexion) and stretching out (also known as extension).
Fig. 2: Ligaments of the spine: Posterior and Anterior Longitudinal Ligaments
Another key component is the “thoracolumbar fascia” (TLF), that is basically a “belt” around our lower back where all the main muscles join. Keeping those muscles tight, the TLF helps maintain a neutral spine.
The ligaments and the TLF are part of the so-called “passive sub-system”.[2-6]
The final component of the core strength are receptors in the muscles and all over the trunk that feedback the brain about the body position, so that it can be adjusted if necessary. 
In a nutshell, core strength is a very complex function of the trunk and essential to keep us balanced on two limbs.
What can we do to strengthen the core?
We saw how the active subsystem is mainly composed of all those muscles that surround the core. We actually exercise most of those in our everyday life.
When walking or climbing the stairs, we use our hip flexors and gluteals. The pelvic floor is constantly active, as it is made of a set of very deep and strong muscles that controls urinary and faecal continence (although the strength of these muscles and the degree of activation decreases with age). When we breath, we engage the diaphragm; and just by standing or sitting straight, we use our muscles of the spine. It might come as a surprise, but we actually engage our abdominal muscles in every single activity we do, from sitting down to bending – as much as we use all the other muscles of the “core box”.
So let’s take a closer look at the muscles of the abdomen– there are four main muscle groups:
- The rectus abdominis – the “six-pack” muscle, which runs superficially in the front part of the abdomen
- The external obliques – running superficially along each side of the trunk
- The internal obliques – running deeply along each side of the trunk
- The transverse abdominis – another deep muscles located at each side, just below the ribs
Fig. 3: Abdominal muscles
For optimal core strength, we should train each muscle involved in this active subsystem (and not just the abs!). As muscular imbalances might result in changes to the way we move, this can increase stresses on certain areas of the body, in particular the back and neck. [3-6]
Why do we need to strengthen our core?
It is now well known that core stabilisation improves athletes’ performance, as they achieve a better control of their body during movement. [3,7-8]
Nonetheless, core strengthening should not concern only professional sports-men and women, but all of us. Indeed, a strong core may assist us in numerous everyday life activities, minimising the risk of injuries as well as preventing the onset of lower back pain: [4,7]
- Daily acts: simple movements like bending to put a shoe on, lifting a heavy package, or any housework and gardening activities have the potential to cause injuries. When we flex our spine (e.g. bending down), we are strongly engaging our abs – yet if our back muscles or gluteals are not as strong, we might perform the action with a poor posture, putting us at risk of injuries, and muscle strains. In order to achieve better control of the action and minimise abrupt movements of the trunk, we may strengthen up the muscles at the back.
- ‘Office jobs / studying: spending most day at your desk working on a laptop, or answering the phone forces the vertebral column to temporarily deviate from its neutral position. This isn’t necessarily a bad thing as varying movement is good for the body. Nonetheless, being in one position for too long can cause ourselves some pain. The most common position we tend to adopt when sitting at the desk is a slumped, rounded posture, which in the long runway may potentially cause back pain if done too often. This can be offset by moving regularly through the day and ensuring we carry out regular exercise.
In summary, to move well and support and shock absorb for our back, it is essential to have strong back muscles and gluteals – not just strong abs.
Is it always safe to train the core?
Targeted abdominal training is no-impact, thus suitable for the majority of the individuals. Of course, the effectiveness of the training depends on the quality of the technique. If you are new to core training, it might be useful to have someone spotting your technique, or to exercise in front of a mirror, so that any poor technique or wrong posture can be promptly recognised and corrected.
It is extremely important to perform the exercises with good technique, not only for effectiveness, but, most importantly, for safety. On some occasions, we might advise to temporarily avoid some core exercise for health reasons. A good example is planks. This exercise is great for core training, yet it might not be suitable if you have a painful back – indeed, in those instances, we might actually want to relax the abdominal muscles to provide some relief. It is always advisable to consult a health care professional for more tailored indications regarding exercise and pain.
In some special circumstances certain exercises for the abdominals are an absolute contradiction, as they might endanger the integrity of the pelvic floor muscles, such as recent surgery of the abdomen or the pelvis. It’s important to speak to your GP or health care provider if you have any health concerns with regards to performing any type of physical activity.
Putting it into practice
Here’s some inspiration for a short and effective workout that requires no equipment. Even though there is a focus on the abs, the following are complex exercises – that means they work several muscles at the same time, which, as we saw, is ideal to enhance core strength.
- Dead bug: lie flat on your back with your arms pointing to the ceiling. Bring your legs up, and bend your knees at a 90 degree-angle. This is your starting position. Slowly, extend your right arm and, at the same, straighten and lower your left leg, while exhaling. Repeat the same movement with the opposite arm and leg. Your back must remain flat and in contact with the ground throughout.
- Plank: place your forearms (or wrists, for a more advanced version) onto the ground, in line with your shoulders. Squeezing your gluteals and engaging your abs, push your trunk off the ground. Neutralise your back, and hold the position.
To progress your plank, make your “base of support” less stable, for example raising one leg or arm at a time, or using a bosu or a Swiss ball.
- Side plank: lie on your side with your legs fully extended and feet together, keeping the forearm (or wrist, for a more advanced version) you are resting on in line with your shoulder. Engaging your abs and squeezing your gluteals, push your trunk off the ground. Neutralise your back and hold the position.
Again, to progress this exercise, opt for a less stable base of support (e.g. raising your leg)
- Bird dog: kneel onto the ground with your knees and feet in line with your hips. Make sure that your wrists are in line with your shoulders and that your back is neutral. This is your starting position. Engaging your core, simultaneously raise your right arm and left leg in a slow and controlled movement. Hold for a few seconds, then return to your starting position. Repeat the same with the opposite arm and leg.
Try 30 seconds of each exercise for 3 rounds in total, rest for 10-20 seconds in between.
(1) Dictionary of Sport and Exercise Science and Medicine by Churchill Livingstone. S.v. “core stability.” Retrieved September 21 2018 from https://medical-dictionary.thefreedictionary.com/core+stability