Kinesiology

Question & Answer

ExRx.net > Questions > Q&A

Dynamic Stabilizer Articles

Where I can read scientific articles regarding the concept 'dynamic stabilizer'?

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 press. Hamstring 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 movement.

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 & Bacon, 4.


Questioning Dynamic Stabilizer Definition

Your 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 style squat).

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 simply ‘Stabilizer’ (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 Colby’s textbook with my usage of the term ‘Dynamic Stabilizer’. Please see Prof Colby’s 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 muscle’s 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.

I’m 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 Homonyms).

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.


Professor Colby,

Here’s 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’. I’ve 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,
James Griffing
ExRx.net

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.".

Sincerely,
Lynn A. Colby, MS, PT
Asst Prof Emeritus


Pectoralis Major Adducts and Abducts

In shoulder 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 press.

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.


Main Menu | Kinesiology Menu | Muscular Analyses | Mechanical Analysis | Muscle Groupings | Speak to an Expert