The muscle activity of the deep cervical flexors is emphasized more than that of the superficial cervical flexors, and it has been reported that functional disorders of the longuscolli are seen in patients who experience neck pain. The goal of this study was to analyze the recruitment patterns and muscle activities of the cervical flexors during Cranio-Cervical Flexion Tests (CCFTs) through real-time ultrasonography and surface electromyography with a view to presenting appropriate pressure levels for deep cervical flexor exercise protocols based on the results of the analysis. The twenty subjects without neck pain were trained until they had gotten used to CCFTs, and the pressure level was increased gradually from 20 mmHg to 40 mmHg by increasing the pressure level 5 mmHg at a time. Real-time ultrasonography images of the longuscolli and the sternocleidomastoid were taken to measure the amounts of changes in the thicknesses of these muscles, and surface electromyography was implemented to observe the muscle activity of the sternocleidomastoid. The measured value is RMS. Based on the results of the ultrasonography, the muscle thicknesses of both the longuscolli and the sternocleidomastoid exhibited significant increases, as the pressure increased up to 40 mmHg (p< 0.05). The differences in the muscle thicknesses at all individual pressure levels showed significant increases (p< 0.05). According to the results of the electromyography, the muscle activity of the sternocleidomastoid gradually increased as the pressure increased up to 40 mmHg, the increases were significant between 20 mmHg and 25 mmHg, between 30 mmHg and 35 mmHg (p< 0.05).
The study found the pressure levels of exercise methods at which the muscle activity of the deep cervical flexors is maximally increased and the muscle activity of the superficial cervical flexors is minimally increased to be 25 mmHg-30 mmHg.