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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. Core stability training
has become popular among military service members, specifically
Special Operations Forces (SOF). The high
level of physical fitness required of these elite solders requires a strong
core.
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.[1] 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.
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 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!
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!
Somewhere between 80 and 90% of people in this country experience 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.
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Lumbar Balance
 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.[3] Cholewicki and McGill,[2] and Cholewicki et
al.[4] have demonstrated that sufficient stability of the lumbar spine (neutral
spine) is achieved with modest levels of co-activation.
Spinal Load
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.[2]
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.
If one did not know any better you would begin to believe that strong abdominal
muscles equals strong/stable core!
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.[5]
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.[3] 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.
Check out our Military Core Training
Workouts for descriptions and pictures of Core Training exercises with the
Fitball. Do you experience lower back pain? Most people will
experience at least one episode of severe, debilitating back pain in their
lives. Active people such as athletes and military service members will
experience back pain more frequently. Check out our section on
exercises to strengthen your lower back.
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