The typical research methodology examining cervical muscle function in neck pain involves strength and endurance testing using various forms of dynamometry devices.  Deficits in isometric strength and endurance have been consistently documented for the cervical flexors, the cranio-cervical flexors and the cervical extensor muscles.  Importantly, neck pain sufferers exhibit a poorer steadiness of contraction at low load (20% of MVC) compared to controls, which may reflect other muscle fatigue manifestations such as muscle tremor.

In accordance with the general theories of muscle imbalance the theoretical model suggests an impairment of deep cervical muscle function produces a secondary overload in synergic muscles – which appears what we frequently observe clinically.  This would appear to correlate with patient subjective reports of difficulty in sustained postures, classically keyboards, reading and driving.

More subtle forms of investigation into muscle function attempt to explore the efficiency of motor control.  This relates more specifically to the timing and intensity of synergic muscle function and the appropriateness of activation for a given functional task.  One of the fundamental principles of an efficient motor control is the efficiency of motor recruitment whereby there is:

1)      minimal extraneous muscle recruitment for the task in hand.

2)      optimal force generation specific to the task at hand

3)      sequencing of motor unit activation in accordance with the level of demand and

4)      deactivation / switching off of the activated groups following execution of the task.

In clinical practice the analyses of these variables is not always possible to explore in depth so we are left extrapolating information from the results of more primitive strength/endurance/alignment/length-tension relationships.

One of the biggest challenges that we face clinically is evaluating the contribution of the axioscapular musculature as a contributory mechanism to cervical pain.  This is compounded by the fact that frequently patients report exacerbating activities that involve the simultaneous challenge of the neck and use of the arm i.e. reading, keyboards and driving and therefore the challenge clinically is to determine which mechanism is the dominant driver.  The conventional wisdom is to view the most superficial muscles of the posterior neck as prime axio-scapular muscles i.e. trapezius and levator scapula and to evaluate their function in the context of efficiency of scapular/arm control on the basis of a separate intrinsic muscular control system for the neck.  This of course is a hypothetical construct (originally discussed in Bergmarks paper postulating local and global muscle function) but one, which seems to have some relevance clinically, at least to provide a guiding framework for intervention.

Because the timescale to improve muscle function both around the neck and the scapular area is likely to extend over weeks rather than days it becomes a management priority to determine the most legitimate target to treat.  I find kinesio tape to be of great assistance in this regard because it is straightforward to apply a supportive taping technique to either the cervical spine or scapular and assess the response on the next patient review.  This is what the renowned Australian Physiotherapist Bill Vicenzino calls a “treatment direction” test and is very worthwhile applying in the clinical setting.

It is also much easier to achieve patient compliance with specific (often subtle) corrective therapeutic exercise if it can be demonstrated that their symptoms are eased by changing the pattern of muscle activation artificially and therefore provide an incentive to comply with the rehabilitation regime to reinforce this.

Enjoy the clinical challenge.

David

© David for PhysioDigest - an educational resource for the musculoskeletal rehabilitation community, 2010. | Permalink | 4 comments | Add to del.icio.us
Post tags: Kinesiotape, Muscle, muscle function, Musculoskeletal Disorders, Neck, neck exercises, neck muscle function, neck pain, neck pain causes, neck pain treatment, Scapula, Trapezius muscle

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