Original ArticleThe effect of therapeutic exercise on activation of the deep cervical flexor muscles in people with chronic neck pain
Introduction
There is increasing evidence of impaired cervical flexor muscle function in neck pain disorders. Although earlier studies focused on, and demonstrated, a reduction in flexor strength and endurance (Watson and Trott, 1993, Barton and Hayes, 1996), recent research has provided evidence of more specific deficits. Studies of the coordination of the deep and superficial cervical flexor muscles in a low load cranio-cervical flexion (C-CF) task have revealed increased electromyographic (EMG) amplitude of the large superficial sternocleidomastoid (SCM) (Jull et al., 2004) and anterior scalene (AS) muscles in patients with neck pain (Falla et al., 2004b). This was associated with reduced activation of the deep cervical flexors (DCFs), longus capitis and longus colli, and reduced range of C-CF motion to perform the task (Falla et al., 2004b). Furthermore a delay in activation of both the deep and superficial cervical flexor muscles has been demonstrated during rapid arm movements, indicating a change in the automatic feedforward control of the cervical spine (Falla et al., 2004a).
Two contrasting exercise programs have been used to address impaired cervical flexor muscle function: general strengthening exercises (e.g. head lift exercise) (Berg et al., 1994, Bronfort et al., 2001); and a low load program designed to focus more specifically on motor control aspects to train the coordination between the layers of neck flexor muscles and the quality of C-CF movement (Jull et al., 2008). Clinical trials of both exercise regimes have demonstrated outcomes of reduced neck pain and headache (Bronfort et al., 2001, Jull et al., 2002). Although the low load exercise regime improved performance in the cranio-cervical flexion test (CCFT), this was judged clinically by the subject's ability to successfully complete higher stages of the test (Jull et al., 2002). It is unknown whether the coordination of the deep and superficial cervical flexor muscles was modified or restored by the exercise. Nor is it known if such specific task retraining is necessary or whether a general exercise, such as conventional strengthening exercises, would achieve the same effect. Finally, it is unknown if improvements following exercise with either regime translate to improvements in automatic function of the cervical muscles. Changes in activation of deep trunk muscles in an untrained task, following motor training in patients with low back pain, suggest that such transfer could be expected (Tsao and Hodges, 2007, Tsao and Hodges, 2008).
This study compared the physiological effects of low load C-CF exercise and neck flexor strengthening to evaluate effects on deep and superficial cervical muscle activity during the CCFT and on their automatic activation during rapid, unilateral arm movements in patients with non-severe chronic neck pain. We hypothesised that specific training would be more efficient than general strengthening in addressing deep and superficial muscle control in the CCFT and in automatic function when the neck is perturbed during rapid arm movements.
Section snippets
Subjects
Participants were 46 female subjects with chronic neck pain greater than 3 months duration. Sample size was based on the difference in EMG amplitude of the SCM between patients with neck pain and controls in the CCFT (Sterling et al., 2003). Forty-two patients (21 per group) were required to detect a 70% (0.195) difference in EMG amplitude between patients with neck pain and controls with a SD of 0.223 at 80% power, and 95% confidence. The sample was increased to 46 to allow for a 10% dropout
Results
No subjects were lost to follow up assessment. Table 1 presents subject descriptive data. Baseline characteristics, pain and disability levels, EMG amplitude, ROM for the CCFT and relative latencies during the arm movement task were not different between groups (all: P > 0.05). All participants in the strength group and all but three in the C-CF group received all treatments. Procedural difficulties with insertion of the nasopharyngeal electrode resulted in a reduced number of subjects for the
Discussion
Specific deficits in DCF muscle activation have been identified in patients with neck pain compared to asymptomatic individuals (Jull et al., 2004, Falla et al., 2004b). This study showed that activation of the DCF was increased at each of the five levels of the CCFT and activity of the SCM and AS muscles reduced following C-CF training. The interaction between the deep and superficial flexors during the test changed so that it closely mirrored that measured previously in asymptomatic subjects (
Conclusion
As hypothesised, specific low load C-CF training but not strength training enhanced the pattern of deep and superficial muscle activity in the CCFT. In addition, a greater proportion of patients showed improved temporal characteristics of DCF muscle activation following cranio-C-CF training compared to strength training. These observations may partially explain the efficacy of this exercise in rehabilitation of individuals with chronic neck pain.
Acknowledgement
Financial support was provided by a grant from the National Health and Medical Research Council of Australia.
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