The relationship between superficial muscle activity during the cranio-cervical flexion test and clinical features in patients with chronic neck pain

Changes in motor behavior are a known feature of chronic mechanical neck pain disorders. This study examined the strength of the association between reported levels of pain and disability from 84 individuals (63 women, 21 men) with chronic mechanical neck pain and levels of electromyographic activity recorded from superficial cervical flexor (sternocleidomastoid; SCM and anterior scalene; AS) muscles during progressive stages of the cranio-cervical flexion muscle test. A significant positive association was observed between superficial muscle activity and pain intensity (P < 0.003), but not pain duration (P > 0.5) or perceived disability (P > 0.21). The strongest relationship between pain intensity and superficial muscle activity occurred at the final increment of the cranio-cervical flexion test (inner-range test position) for both the SCM and AS muscles (R(2) = 0.16). Although a positive and significant relationship between pain intensity and superficial muscle activity was shown, the relationship was only modest (16% explained variance), indicating that multiple factors contribute to the altered motor function observed in individuals with chronic mechanical neck pain.