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      Have you ever had a stiff joint?  A stiff knee, perhaps a stiff or painful shoulder!?  If you've ever played rugby, thats a strong YES!  For most everyone else I'm sure it may not be so exact but most of you have experienced joint pain, not directly caused by injury.  By that I mean something like back pain, most everyone knows about back pain.  As the 2nd most common cause of disability in America, either you or someone you know knows about back pain!  So you might be thinking "how does back pain have anything to do with Dynamic stabilizers"?  Well thats the easy part, but first we need to establish a little foundation .

The anterior view of the shoulder, the pectoralis muscles are a big source of forward shoulder carriage, usually associated with spending extended time at a computer or any occupation involving sitting.

The anterior view of the shoulder, the pectoralis muscles are a big source of forward shoulder carriage, usually associated with spending extended time at a computer or any occupation involving sitting.

     Dynamic stabilizers:  What are dynamic stabilizers (DS)?  DS are muscle crossing the joint responsible for keeping the opposing surfaces of the joint in alignment for proper joint mechanics.  These muscles provide guidance through ranges of motion so that the joint can move with stability.  A good example is in the shoulder with the rotator cuff.  The rotator cuff consists of The following muscles: Supraspinatus, Infraspinatus, Teres Minor and Subscapularis.  Together these muscles work together with coordinated and graded contractions in an effort to ensure the head of the humerous, moves as designed, with in the Glenoid fossa of the scapula.  In the event any of these muscles are injured the dynamic stability of the shoulder is compromised and the subsequent motion is altered which invariably results in pain in the joint or, as the doctors like to say, arthritis ("arthro"- joint + "itis"-pain = joint pain).  This relates to the low back on a more complex level in that rather than 4 muscles responsible for stability the low back relies on 28-30 to work together.  not only that but the low back isn't just one joint, it's a series of vertebra stacked on the pelvis which can be very complicated.  

This is the posterior view of the shoulder showing the retractors, elevators and depressors.  The Rhomboids are of particular interest in that they are usually problematic when one experiences bad posture.

This is the posterior view of the shoulder showing the retractors, elevators and depressors.  The Rhomboids are of particular interest in that they are usually problematic when one experiences bad posture.

    Its important to understand that not all muscles that cross a joint are responsible for joint stability.  In the case of the shoulder we have numerous muscles that move the joint that aren't designed to stabilize the joint itself.  To expound on that thought, you have the 4 muscles of the rotator cuff that are the dynamic stabilizers then you have Pec major/minor that are the projectors (forward movement), Rhomboids are the retractors (think about pinching your shoulder together), Upper Trapezius are the elevators and Latissimus dorsi are the depressors of the shoulder.  None of these muscles are responsible for stabilizing the Glenohumoral joint, better known as the shoulder.

As you can see the knee is a much simpler joint with only a few muscles.  The quadriceps and hamstrings do the majority of the dynamic stability in the knee. 

As you can see the knee is a much simpler joint with only a few muscles.  The quadriceps and hamstrings do the majority of the dynamic stability in the knee. 

   So to help you understand your shoulder pain, as well as other joint pain, here's a general explanation of what happens to cause joint pain.  One of the most common situations is where an injury occurs to the joint involving the dynamic stabilizers.  From there the joint becomes unstable, the brain recognizes this instability and attempts to stabilize motion by recruiting one or more other muscles to do so.  The problem, joint pain, comes in at some point after when this compensatory mechanism fails and the joint is longer functional due to the overall instability.  You see, not every muscles is created equally, therefore its not a simple matter of "next man up" when injury occurs.  Every muscles has a specific job or function to perform and when its recruited to do another's job it does it poorly.  It'd be like having your starting QB getting injured during a game and having the punter take his place, yeah he can throw the ball around but does he know the plays or even where to go..... No, He doesn't have a clue!  

    This information is important after an injury, when a joint hurts and/or when rehabbing after surgery.  If you don't get the right muscles stabilizing the joint prior/during movement it will be painful and eventually fail again later on down the line.