Dynamic Stabilizer Articles
I can read scientific articles regarding the concept 'dynamic
I coined the term 'Dynamic
Stabilizer' many years ago to describe a biarticulate muscle
that since it simultaneously moves through both joints with no
appreciable difference in length, virtually shortening at one
joint and lengthening at the adjacent joint. At the time, I could
not find a term for a muscle with this characteristic even after
consulting with professors of biomechanics.
The most cited example of this concept is the hamstring's stabilizing
effects on the knee, counteracting the powerful anterior dislocating
effects of the quadriceps during closed
chained pushing movements, such as with the squat and leg
weakness is of particular concern when there has been a compromise
to the anterior cruciate ligament of the knee.
To fully understand this concept, it helps to study how the force
vectors act within the structures of the body. I remember seeing
a vector diagram of these counteracting forces in a biomechanics
text book (Kreighbaum & Barthels 1996), but to my understanding,
it incorrectly illustrated the true location of the fulcrum and
angle of pull of the quadriceps. I now exhibit a corrected
diagram on the Angle of Pull page.
Actually, on that diagram, I have used the corrected force vectors
and added muscle's force vectors to understand a nearly opposite
movement, open chain knee flexion, as in a lying leg curl. See
how the tibialis anterior has the ability to activate the gastrocnemius
as a synergist in knee flexion? And the Rectus Femoris has the
potential to position the hip in a more favorable position for
knee flexion, by decreasing active insufficiency of the hamstring.
I call these sort of muscle 'antagonistic
stabilizer', another term I have created because I found
no better way to describe their actions.
But if you only look at the force vectors within the purple rectangles
only, how they were originally 'intended to be viewed in that
textbook with its errors, you can use that part of the diagram
to better understand how the hamstrings can counteract the dislocation
forces of the quadriceps in a close chained leg press or squat
As you have seen on ExRx.net, you can find other examples how
other biarticulate muscles
can be involved as dynamic stabilizers.
Kreighbaum, E., Barthels, K.M., (1996). Biomechanics; A
Qualitative Approach for Studying Human Movement, Allyn &
Questioning Dynamic Stabilizer
definition of a dynamic stabilizer is not correct. Its not even
in the ballpark. Who should I contact about correcting this?
Thanks for your message. You can direct your correspondence
to me. I have an idea why there might be some confusion. Please
cite your accepted definition with its earliest know reference/usage.
Thank you for your prompt response and thoughtfulness in
this matter. Can I presume that we agree the four muscles of
the rotator cuff act as dynamic stabilizers? If so, then the
portion of the definition re. dynamic stabilizers being biarticulate
is out. Strictly speaking, sliding filament theory does not allow
for a muscle to simultaneously lengthen and shorten. So there's
that part. Kisner & Colby, Therapeutic Exercise: Foundations
and Techniques, 6th Ed. FA Davis Co. defines dynamic stabilizers
as "muscles whose isometric or stabilizing contraction maintains
control of the functional position in response to imposed fluctuating
forces through the moving extremities."
My concern here is two-fold. First, as a reputable website,
numerous other internet resources are parroting your definition,
which confuses readers. Second, at least one very well known
Internet fitness guru cited your website re. the hamstrings as
dynamic stabilizers in the deadlift, then based on your definition
proceeded to inform people that the hamstrings are simultaneously
in eccentric AND concentric contracting throughout the movement,
which is the only way to explain how the hip and knee can both
extend. Of course, this isn't the case, as the reason the knee
extends is the greater force exhibited by the quads and the fact
that the hamstrings can not lengthen enough to extend the hip
and flex the knee simultaneously.
Am I rambling or is this a clear perspective? Thanks again
for your time and correspondence.
Thank you for expressing your concerns. I understand you have
issue with my use of the term, Dynamic
Stabilizer, in contrast to how a few academicians have
recently used the same term. Before I published what was to become
the start of ExRx,net in 1999, I introduced the term Dynamic
Stabilizer to describe a biarticulate muscle that simultaneously
moves through both joints with no appreciable difference in length,
in effect being shortening through the target joint while being
lengthening at the adjacent joint (eg: hamstrings during bodybuilding
Before deciding on the term Dynamic Stabilizer
I referred to various textbooks and consulted with a Kinesiology
Professor at University of Kansas about the appropriateness the
term I had intended to use. This term was chosen to distinguish
it from the established Isometric Stabilizer, or
(eg: Erector Spinae during squats), since a Dynamic Stabilizer
was essentially transferred through both joints yet the muscle
itself essentially contracted isometrically. This description
was not to suggest that half the muscles itself contracts while
the other half lengthens as you suggested.
It appears you may be confusing the term Dynamic Stabilization
you had cited in Kisner and Colbys textbook with my usage
of the term Dynamic Stabilizer. Please see Prof Colbys
reply below, the co-author of the text you had cited. As far
as I can see from a few PubMed searches, a few academic authors
have only recently begun using the term Dynamic Stabilizer
in describing muscles that engage in Dynamic Stabilization. Although
they describe somewhat related, yet distinct phenomenon, my definition
of Dynamic Stabilizer appears to predate the relatively more
recent usage of that specific term pertaining to Dynamic Stabilization.
As you had alluded, Dynamic Stabilization is the phenomenon of
stabilizing a moving joint, where as, the Dynamic Stabilizer
(using my intended definition) could be a muscle responsible
for Dynamic Stabilization. However my definition of Dynamic stabilizer
would not necessarily be descriptive of a Target
or Synergist muscles
involvement in Dynamic Stabilization, as in your example of the
rotator cuff muscles involvement in in stabilizing the moving
shoulder. This is because my definition of a dynamic stabilizer
only applies to a biarticulate muscle inversely moving
through two articulating joints.
Im am not suggesting that the authors of these more recent
papers are incorrect in the way they have recently begun to use
the term Dynamic Stabilizers to describe muscles
involved in Dynamic Stabilization. They simply have a definition
of this term which presumably fits the phenomenon in which they
are describing, as with my definition and the coincidentally
usages of this same term. Although it can me a bit confusing,
there are countless of other examples of words or terms that
have different meanings in different contexts (AKA: Polysemy
I agree I need to make a slight adjust to my definition of Dynamic
Stabilizer by adding 'in effect' so visitors do not get the idea
that the muscle itself is simultaneously contracts and lengthens.
Thank you for pointing that out. I never imagined it could be
interpreted that way being that a muscle contracts uniformly
from its origin to insertion.
It is obvious that the knee extends at a greater force, but
I'm afraid might be missing your point about how the hamstrings
cannot lengthen enough to extend the hip and flex the knee simultaneously.
Perhaps your referring to the how Passive
Insufficiency explains why the hamstring cannot lengthen
enough to extend simultaneously through both a fully flexed hip
and a fully EXTENDED knee, as you would observe in the lowest
portion of a Straight-leg
Deadlift? So I'm guessing your referring to the need/tendency
to flex the knee in order to gain fuller range of motion through
the hip? In any event, I've clarified the role of the Hamstrings
in the Deadlift in more detail. I hope this clears things
up for you and everyone else.
Heres a strange question, perhaps seemly out of the
blue. :-) Can you tell me where the definition of Dynamic
Stabilizer originated and possibly when it was first used
in the context of the definition in your text, Therapeutic
Exercise: Foundations and Techniques. Ive been using
a different meaning of Dynamic Stabilizer before 1999 and apparently
this discrepancy has seemed to confuse a few people. The only
thing I can find close this term which pre-dates this is 'Dynamic
Stabilization' as pertains to spinal surgery and orthopedic braces.
Thank you for your inquiry regarding terminology from Therapeutic
Exercise: Foundations and Techniques. I've forwarded your inquiry
to my co-author, Carolyn Kisner.
I see in the glossary of the 6th edition that "dynamic joint
stability" is defined on page 988. I also see in the index
that on page 508 of Chapter 16 that the term, "dynamic stabilization"
is used. However, when I superficially scanned Chapter 16, I
was not able to find the term, "dynamic stabilizers"
In another textbook, "Joint Structure and Function, ed 5"
beginning on page 253 the authors of the chapter on the shoulder
complex discuss the concept of dynamic stabilization related
to the gloenhumeral joint. The authors cite 2 journal article
(reference # 78 and 79) dating
back to 1973 and 1975 that address the musculature involved in
dynamic stabilization. Perhaps one of those articles might be
considered an original source of the concept.
From my experience and reading, I can't specifically tell you
the origin of the terms, "dynamic stabilization and dynamic
stability." However, I can tell you that I first heard the
term, "dynamic stability" in the early to mid-1970s
at neurorehabilitation courses. The concept was described as
the ability to maintain a stable posture combined with superimposed
movement on the body.
I'm hoping Professor Kisner can add her perspective regarding
the term "dynamic stabilizers.".
Lynn A. Colby, MS, PT
Asst Prof Emeritus
Pectoralis Major Adducts and Abducts
articulations, pectoralis major (clavicular part) appears as
a weak adductor as well as a weak abductor. How is this possible
- that a muscle behaves in the same way in contrasting activities?
When the shoulder is externally rotated, the clavicular
pectoralis assists in abduction; particularly beyond where
the arm is already abducted 90º. (Thompson & Floyd 1994)
This muscle is even more involved in abduction, or pushing an
object overhead in an individual with a deep rib cage (barrel
chest) and/or with their chest held high, as in the military
The clavicular pectoralis assist the sternal
pectoralis in adduction, particularly when the shoulder is
internally rotated (Moore 1985; Thompson & Floyd 1994) where
the arm is already adducted 90º. It is even more involved
when the adduction is accompanied by slight horizontal flexion
as with bending over slightly when performing the chest dip or
standing cable fly.
Moore KL (1985). Clinically Oriented Anatomy, Williams
& Wilkins, 2.
Thompson CW, Floyd RT, (1994). Manual of Structural Kinesiology,
Mosby-Year Book, Inc., 12.