“The core can be described as a muscular box with the abdominals in the front, paraspinals and gluteals at the back, the diaphragm at the top and the pelvic floor at the bottom.” (1) In truth the core is a very complex system consisting of 29 pairs of muscles within this “box”. This can be further grouped into the following anatomical divisions:
- Transversospinalis group
- Erector spinae group
- Quadratus lumborum
- Latissimus dorsi
- Abdominal group
- Psoas group
- Gluteal group
- Hamstring group
A more simplified way to think about the core is to think about the body (trunk) without the arms and legs.
The main function of the core is simply to link the upper and lower body especially during movement. Ideally this link should be stable. This stable base should be seated in the lumbo-pelvic region of the body. Stability in this region is crucial to provide a foundation for movement of the upper and lower limbs, to support load and to protect the spine.
When this system works as it should there is proper force distribution and the ability to generate maximum force with minimal compressive, translational or shearing forces at the joints of the kinetic chain. Panjabi defined core stability as: “the capacity of the stabilizing system to maintain the intervertebral neutral zones within physiological limits.”
It is vital to understand that there is a difference between core strength and core stability. Core stability is a result of the 29 pairs of muscles working together in a very precise and timely manner whereas core strength is the strength or weakness of each individual muscle. According to Gray Cook of Functional Movement Screen people often confuse the issue. Someone may be doing a crunch and they’ll tell you that they are working on their core stability where they are in fact working on abdominal strength. Core stability at its essence requires great motor control.
This “system” of producing stability consists of the following parts:
- Neuromuscular control
- The passive subsystem (ligaments and bones)
- The active subsystem (muscles)
So it’s vital to note that spinal (core) stability is not only a function of muscular strength but that it also relies heavily on proper and timely sensory input which alerts the central nervous system, providing constant feedback and allowing refinement of movement. These tiny adjustments are what provide stability. Of course strength is an important factor in having good core stability but it is worth remembering that all strength is a gift from the neurological system. If the neurological system is impaired for one reason or another the strength of some or all of the core musculature will be reduced. An example of this will be back pain or pain after an operation.
This is a very complex system with the bones and ligaments acting as a constant and the neuromuscular system providing information causing the muscle system to change constantly from one millisecond to another.
There has been a lot of focus on what some consider the “deep core”. This is made up of the transversus abdominus and the multifidus muscle group. Another school of thought by biomechanists like Stuart McGill emphasize larger prime mover muscles such as the abdominal obliques and quadratus lumborum muscles in providing stability. My belief is that they are all important and even if some only work for a split second during certain movements they play an important role in that particular system. At the very least they act as a link and if you remove one link the chain is irreversibly compromised.
It is important to note that we have two types of muscle fibres making up the core system. Slow -twitch and fast- twitch fibres. The local muscle system (the deep layer) is made up primarily of slow-twitch fibres. These muscles are shorter in length and control inter-segmental movement and they respond well to changes in posture and extrinsic loads.
Fast twitch fibres on the other hand comprise the global subsystem (the superficial muscle layer). These muscles are long and possess large lever arms, allowing them to produce large forces and thus big movements. They are sometimes also known as prime movers. What makes these muscles unique is that they not only produce movement but also act as stabilizers in the core.
Why should I have a strong core?
- A strong core benefits everyday movements and protects you while carrying out these activities of daily living. Generally one would not even pay attention to these everyday acts of living until you have an injury or you pick up an injury performing one of these actions, something as simple as picking up a towel from the floor.
- Movement related to your job. When mentioning this one would immediately think of manual labour, lifting, carrying etc. What about sitting for 8 – 10 hours a day? A strong core will not only assist you in coping with this but also help and prevent you getting weaker and weaker which will eventually lead to an injury.
- A strong core will help combat back pain.
- A strong core will assist in sports and recreational activities. So apart from protecting your back during something like a golf swing it will also improve your performance by providing a stable base which allows for greater force production in the upper and lower extremities.
- A strong core will aid your balance and stability. Again this might be something one takes for granted until you lose your natural ability as a result of injury or old age.
- Good posture. As a result of the western way of living, sitting for hours on end looking down at cellular phones etc., people are developing poor posture. More often than not the initial changes take place in the lumbo-pelvic region which can then move up the spinel eading to changes to the natural curves of the spine and causing strain on the soft tissue structures surrounding the bones and eventually even degeneration and bony changes. A strong core helps combat poor posture.
How do I train my core?
It is important to remember that exercise for core stability is more than strengthening the muscles of the trunk. If you are recovering from an injury there will most probably be insufficient coordination in the core musculature. This can lead to decreased function and compensatory movement patterns. This will again predispose you to a recurring injury. As such the motor relearning of the inhibited muscles my end up as being more important than pure strength training. It is probably best to get professional help in situations like these.
Even if you aren’t recovering from an injury your core exercise program should be done in stages with gradual progression. This is especially true for people who are returning to physical activity after a long sedentary period.
The first stage should focus on correcting mobility issues. Any muscle imbalances or restrictions in mobility should be corrected by restoring normal muscle length. If you sit for many hours daily chances are that your hip flexors have shortened. When this happens it generally causes an inhibition in the opposing muscle (antagonist) in this case it is the gluteus maximus muscles which will become inhibited. This is just one example of changes which needs to be addressed. Postural muscles also have a tendency to become tight as a result of constant activation against the forces of gravity.
During the second stage activation of the deep core musculature should be taught through lumbo-pelvic stability exercises.
Once these exercises have been mastered one can progress by adding a stability ball in sitting and lying.
Finally there should be transitioning to standing with functional movement exercises that promote balance and precise movement. The role of advanced core stabilization is to train functional movements rather than individual muscles. There are those who preach that functional training can only take place in the transverse plane (rotation). I believe that is a bit one dimensional.
Food for thought
- To me it seems that there are two schools of thought at the moment in using instability to train core stability. There have been a good number of studies which suggest that unstable modalities like the use of a stability ball lead to greater muscle activation. On the other hand there is a school of thought which suggests that training on unstable surfaces aren’t functional and does not relate to what we do in real life. They even suggest that by taking the body that far out of its comfort zone you may even cause “shock” which can lead to inhibition. According to Behm (3) training programs which must prepare athletes for a wide variety of postures and external forces should include exercises with a destabilizing component. However, he also states that these kinds of exercises are not recommended as the primary exercises for hypertrophy, absolute strength or power, especially in trained athletes. For athletes, ground based free-weight exercises with moderate levels of instability should form the foundation of exercises to train the core musculature. It should be noted though that instability resistance exercises can play an important role in rehabilitation and periodization.
- In his paper “The myth of core stability” Lederman states the following: “Core stability exercises are no more effective than, and will not prevent injury more than, any other forms of exercise.” He goes as far as to suggest that there may even be a potential danger of damaging your spine with continuous tensing of the trunk muscles …… you decide.
- Is what you are doing promoting core stability through training this complex system as a whole or are you trying to isolate specific muscles and strengthen them? Is it possible to have strong core muscles and yet little or no core stability?
Core stability is a product of three systems integrating to produce a complex mechanism which changes with the smallest variations in movement. There are many factors which may cause dysfunction from tightness, pain, muscle weakness poor motor control, structural changes and even poor posture. If you aren’t sure if your core is compromised or don’t know where to start see your health care practitioner.
- Akuthota V. et al. Core stability exercise principles. Curr. Sports Med. Rep. Vol. 7, No. 1, pp. 39-44, 2008.
- Willardson J.M. Core stability training: Applications to sports conditioning programs.J of Strength & Conditioning research, 21 (3), 979-985, 2007.
- Crisco J.J. et al. Stability of the human ligamentous lumbar spine. Part 2: experiment. Clin Biomech, 7:27-32, 1992.
- Behm D.G. et al. Muscle force and activation under stable and unstable conditions. J. Strength Con. Res. 16:416-422. 2002.
- Behm D.G. et al. The use of instability to train core musculature. Appl. Physiol. Nutr. Metab. 31(1):91-108. Feb. 2010.
- Hibbs A.E. et al. Optimizing performance by improving core stability and core strength. Sports Med 38(12): 995-1008. 2008.
- E. Lederman. The myth of core stability. CPDO online journal. June 2007:1-17