Stabilizing Function

Posted by Hans Lindgren DC on 12 July 2013 | 0 Comments

Tags: DNS, Functional

It was not that long ago that muscles were simply classified into postural or phasic muscles depending upon their main function. The more we learn about muscles and their function the clearer it becomes that most muscles have both stabilizing and phasic functions depending upon the demand at that time. Our movements are controlled by stabilizing muscles as well as antagonistic muscles performing eccentric contractions. Sometimes will a section of a muscle perform a concentric contraction to produce a specific movement, and another part of the same muscle is performing an eccentric contraction to control the movement, while they both simultaneously stabilize the joint in a centrated position throughout the range of the movement.   

One of the most commonly made mistakes in rehabilitation programs is that muscles which are not performing their stabilizing function properly get classified as weak and a strengthening program is designed to bring the muscle up to required strength – unfortunately however, most of the strengthening exercises are performed in a phasic function.

A muscle’s stabilizing function cannot be trained using only phasic movements. 

Insufficient stabilization is usually not a straight strength issue, but an activation problem. The brain is for some reason choosing the wrong stereotype of stabilization. Strengthening a muscle phasically is certainly beneficial, but it will not guarantee that the brain would use the muscle better for stabilizing purposes.

The stabilizing function of muscles are most evident in the girdle muscles (hip and shoulders), where faulty stereotypes of stabilization often recruit the big multi joint muscles to perform the work of the single joint muscles designed for the task. Examples are Pectoralis and Latissimus being recruited for shoulder stabilization and hamstrings, quads and adductors being involved in hip stabilization. The big multi joint muscles are mainly designed for generating movement while smaller muscles like the Glutei muscles and Serratus anterior are better suited for stabilization.

To improve a muscle’s stabilizing ability the muscle has to be trained in its stabilizing function, and this is where the choice of exercises is important. Open chain exercises where the limbs moves in the hip and shoulder joint are not as effective as closed chain exercises where the joint cavities (trunk) move over the extremities.

To improve a muscle’s stabilizing function the joint it stabilizes has to be placed in a centrated position and the resistance cannot exceed the muscle’s ability to maintain that ideal position throughout the entire movement. Once joint centration is lost the muscle’s stabilizing function is not challenged and will not be improved.

A very effective method to improve the stabilizing function of the shorter single joint girdle muscles is to place the joint in an ideal centrated position and then slowly and in a controlled manner, move the joint cavity (trunk) back and forth over the supporting limb. To create the maximal stimulation for the muscle’s stabilizing function the supporting limb must be kept in a centrated position. The more joints that are in centration the stronger will the facilitation of the stabilization be.  Another very useful method to facilitate ideal stabilization is to apply a very gentle pressure along the limb to approximate the head of the bone into the joint cavity.

Taking the above into consideration, programmes  to activate (for example) ideal hip stabilization would involve movements whereby the trunk and pelvis move over the Femur of the stabilizing leg. The positioning of the ankles, knees and hips will affect the quality of the stabilizing function of involved muscles. Single leg exercises are a very effective way of facilitating the stabilization, but attention to form is crucial.  Another example would be shoulder stabilization which can be effectively trained with support on the elbows or hands with the scapula moving over the Humerus. Good general exercises are planks and side-planks where movement is induced into the Gleno-humeral joint by the big multi joint muscles (lats and pecs) while the shorter single joint muscles maintain ideal alignment of the joint.

Summary:

• Insufficient stabilization is usually an activation issue and not a lack of strength.
• To facilitate a muscle’s stabilizing ability it has to be trained in its stabilizing function.
• A muscle should always be activated and trained in both its functions. Either the distal part moves over the proximal part or the proximal moves over the distal (open or closed chain).
• A muscle’s stabilizing function is often performed as an eccentric contraction and should therefore be trained in the same way, moving the joint back and forth in a controlled manner.