“The deep neck flexor muscles sit deep in the front of the neck, behind the trachea (windpipe).” “... they have an important role in providing stability to the neck.” “People with a history of neck or upper back injury, such as whiplash, can show great improvement in pain and function if they strengthen these muscles. Those with postural neck pain often have weakness in these muscles and overuse in the muscles on the top of the shoulders.”

http://sprintphysio.co.uk/patient-exercises/back-and-neck/deep-neck-flexor-exercises.html 

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