Local versus global muscles

 

In our previous post, "Core strengthening versus stabilization" we discussed how the muscles of the spine affect the stability/rigidity of the spine. Today, I would like to look deeper at each muscle group and their role within our movement patterns. 
Muscle classification has been performed as early as Leonardo de Vinci.  Bergmark was the first to define the muscles of the spine as local muscles or global muscles. 
The local musculature consists of:
• Multifidi
• Transverse abdominals
• Internal Oblique
• Medial fibers of external oblique
• Quadratus lumborum
• Pelvic floor musculature
• Iliocostalis
• Longissimus
In general, the primary muscle's job is to generate sufficient force for segmental stability of the spine during normal activity.  Did you know research indicates that the spine is inherently unstable?  Without musculature support the spine will collapse with only 4.4 lbs applied to it.   Walking alone creates 308 lbs of force.  In fact, the transverse abdominals and multifidi have been shown to react 100 milliseconds prior to movement, promoting spinal stability before movement in the body occurs.  
The local muscle group can actually be  divded in to two subcategories; the primary and secondary local muscles.  I have highlight in red the multifidi and transverse abdominals as they are defined as primary local muscle group secondary to the anticipatory muscle firing mechanism discussed above.  More importantly, their primary function is stability of the spine NOT movement of the spine.
Secondary local muscles have the same characteristic of the local muscle groups (stabilize spine, short muscle groups, attach directly to the spine, endurance based and require 30-40% maximum contraction etc.) , but also provide significant movement of the spine.   The secondary muscle group provide BOTH movement AND stability of the spine.
Global muscles responsibility is to produce torque and movement of the spine.  The include:
• Rectus abdominis
• Lateral fibers of the external oblique
• Psoas major
• Erector spinae
• Illiocostalis
Global muscles have long muscle bellies, with large levers and moment arms, capable of producing large forces.  The forces created are large enough for function movements and provide speed, power (involve over 40% of maximal voluntary contraction) and have the ability to absorb large multidirectional forces. 
It can be clear now that when implementing a strengthening program, one should focus first on local musculature to provide stability and rigidity progressing to global muscles to promote functionality.  

 

 

Source:
Core Strength: Stabilization the Confusion
Strength and conditioning journal April 2007
Mark D. Faries and Mike greenwood

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