Changes in the thickness of the cervical flexor depending on the contraction level of the masticatory muscle during deep cervical flexor training.

[Purpose] This study examined the changes in the thickness of the deep cervical flexor according to the contraction intensity of the masticatory muscle during deep cervical flexor training. [Subjects and Methods] Twenty healthy adults were randomly selected and the thicknesses of their longus colli and sternocleidomastoid were measured with ultrasound when the masticatory muscle contracted during deep cervical flexor training. [Results] The thickness of the longus colli tended to increase in proportion to the contraction intensity of the masticatory muscle, with a significant difference. However, the thickness of the sternocleidomastoid did not significantly differ with the contraction intensity of the masticatory muscle. [Conclusion] During deep cervical flexor training, when co-contraction of the masticatory muscle occures, changes in the thickness of the longus colli may be selectively increased. Deep cervical flexor training was most effective during contractions of a submaximal intensity.