The longus colli is a thin muscle and tendon structure.  It is attached to either side of the cervical spine and the upper three thoracic vertebrae.  The longus colli muscle is an active flexor and acts as a stabilizer of the cervical spine during swallowing and coughing. 

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When injured in sport through direct contact or in a whiplash type incident the spasm post injury effect may contribute to postural issues.  These issues affect the strength of other muscular groups or lead to neck related lingering problems.  The important point is once injured neck muscles must be rehabilitated.

 What is most interesting about the longus colli muscle is that it doesn't have a true antagonist.  Muscles in general work in pairs.  The 'antagonist' classification is used to describe a muscle that acts in opposition to the specific movement generated by the agonist.  Thus the longus colli in a relaxed position is almost completely inactive.  This muscle when damaged has a tendency to atrophy severly. 

When injured relaxation is a normal part of the recuperative process. Upon returning to activity movement helps in healing and strengthening. Yet the longus colli in many positions still remains almost totally inactive. It is imperative once any head or whiplash type injury occurs muscles must be restored to their normal known measured strength.

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Get your neck as Strong as possible. Measure it's strength and always return it to normal pre-injury levels. This is what 'preventative sports medicine' is about.