The purpose of this article is to provide insight into what core stability actually is and how it can impact your training. If you ask twenty different clinicians/coaches to define stability you will probably get twenty different answers. A lot of progress has been made in recent years on the concepts of stability in musculoskeletal linkages and joints.
In the late 1980s Anders Bergmark, a professor of solid mechanics at the University of Lund in Sweden, formalized stability in a muscular system using a very simplistic model of the spine. He was able to formalize mathematically the concepts of "energy wells," stiffness, stability, and instability. His work did not seem to go far at the time because the engineers who understood the mechanics did not have the clinical perspective, while the clinicians were unable to interpret the engineering-mechanics. This pioneering work has been embellished by the work of many especially Dr. Stewart McGill.
Stability is defined as remaining unchanged even in the presence of forces that would normally change the state or condition. So when the star tailback is clobbered by the star linebacker what prevents the joints subjected to the hit/force from buckling and consequently in injury? The easiest way I have found to explain the concept of spinal stability with my patients is to use the analogy of the rigging on a ship's mast. This will be real easy for all you sailors out there!
The muscle activity around the spine (or any joint for that matter) acts like the rigging on a ship's mast. The rigging basically supports the mast. Without the rigging a gust of wind would knock it over. Think of the muscles as the rigging and the spine as the ship's mast. Co-contraction of the muscles around a joint is what provides stabilization and prevention of buckling.
Back To The Spine
The lumbar spine is a complex system comprised of 6 dimensions or degrees of freedom of movement per joint (3 rotational and 3 translational). Stability is achieved by symmetric "balanced" stiffness in 3 rotations and 3 translations. Therefore regardless of joint position this is what must be attained for the joint to be considered stable.
How can all of this affect your spine during training? Without proper stability the joints will be penalized by very high loads. The effects may manifest themselves immediately, the next day, or possibly following a number of workouts. What are the effects you ask? Dysfunction and pain!
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Neither one is compatible with proper training. Think of someone performing a back squat without proper hip flexibility. The likely result is too much spinal flexion (forward bend) to reach adequate squatting depth. The joint(s) may be able to withstand the abnormal loads for a while. Maybe even years if the amount of flexion is not severe enough, but eventually the spine will reach a tolerance threshold. You can bend a paper clip and break it immediately, or you can bend it a little each day and still break it!
lower back pain at some point.
The likelihood of suffering a recurrence is also very high. So obviously anything you can do to avoid low back injury is an important key to a successful long-term training program.
I have begun to lay down the foundation of what core stability is all about. I will now go into greater depth. I recommend reading this article and the article's to follow to gain a general understanding of core stability.
To achieve stability in the lumbar spine there must be symmetric "balanced" stiffness in 3 rotations and 3 translations. You must understand is the connection between stiffness and muscle activation. When a muscle contracts it increases stiffness not only in the muscle but also in the joint. So when a group of muscles is activated it now becomes critical when and to what degree those muscles are activated. There must be a synergism to the process.
Think of how a great band sounds. Now imagine if one instrument is missing or playing the wrong song. This does not sound too good! Just like the band must be in sync, the neuromuscular system must be in sync to create stability and coordinated movement. So you need not only a coordinated neuromuscular system but appropriate muscle balance as well.
Are you beginning to wonder how much stiffness is necessary to stabilize the spine? When there is too little stiffness, the joint will buckle under load. Too much stiffness will cause massive loads and limit joint motion. Interestingly the literature shows that in most situations only a modest amount of stability is required to stabilize a joint. Cholewicki and McGill, and Cholewicki et al. have demonstrated that sufficient stability of the lumbar spine (neutral spine) is achieved with modest levels of co-activation.
It appears that for most tasks rather low levels of activation are necessary for long periods of time. This suggests that endurance and not necessarily strength is most important for the muscles that are involved in stabilizing the spine. Dr. McGill has evaluated a variety of stabilization exercises and quantified and ranked them for muscle activation magnitudes together with the resultant spine load.
Now I want to expand a little further on the muscle balance issue and how it impacts core/spine stability. It amazes me how many articles are written on the topic of abdominals or core stability and most if not all of the exercises are for the abdominal muscles.
In addition, most will have you believe that abdominal training is the key to prevention of low back pain as well. Unfortunately the literature does not support this. Having strong abdominal muscles did not provide the preventative effect that was hoped for------but the evidence seems to suggest that endurable muscles of the low back play a greater role.
Remember, you must have symmetric balanced stiffness in 3 rotations and 3 translations. So this is where muscle balance comes into play. The muscles of the lower back need to be targeted in training just as much as the abdominal muscles. This is even more important for those with existing low back problems.
Finally there is the factor of the neuromuscular system. Remember, not only do we need balanced symmetric stiffness, but it needs to be coordinated as well. If certain muscles are slow in responding or are of the wrong sequence, it does not matter if the amount of tension is appropriate.
Buckle Up For Balance
It has been well documented following injury that the motor system loses its ability to optimally sequence motor patterns to muscles. These motor control "errors" appear to lead to brief spine buckling situations and a high risk of injury. Therefore, we need to select the correct muscles to train to attain balance, but we also must select the correct exercises for each individual to target the control system as well.
I hope you are beginning to have a greater understanding of what core stability is all about. Once you begin to understand the concepts of what core stability really is the selection of exercises and program design will make more sense. In upcoming articles I will start to look at a variety of exercises and how to implement them.
1. Bergmark A. Stability of the lumbar spine: A study in mechanical engineering. Acta Orthop Scand 1989; 60:3-53.
2. McGill SM. Stability: from biomechanical concept to chiropractic practice. J Can Chiropr Assoc 1999; 43(2):77.
3. Cholewicki J, McGill SM. Mechanical stability of the in vivo lumbar spine: Implications for injury and chronic low back pain. Clin Biomech 1996; 11(1):1-15.
4. Cholewicki J, Panjabi MM, Khachatryan A. Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture. Spine 1997; 22(19):2207-2212.
5. Luoto S, Heliovaara M, Hurri H, Alaranta M. Static back endurance and the risk of low back pain. Clin Biomech 1995; 10(6):323-324