The Mode of Activity of Cervical Extensors and Flexors in Healthy Adults: A Cross-Sectional Study

Background and Objectives: The purpose of this study was to investigate the activity of bilateral cervical extensors and flexors on the sagittal, frontal, and horizontal planes of healthy adults during motions of the neck in a sitting position, which has not been satisfactorily investigated by surface electromyogram (sEMG). Material and Methods: We recruited 35 healthy participants (mean ± standard deviation of age, 20.3 ± 2.4). sEMG recordings of the cervical extensors and flexors were performed for a total of nine seconds in three phases: Phase I involved the motion of the neck from the neutral position to the maximum range of motion; Phase II involved maintaining the neck at the maximum range of motion; and Phase III involved the motion of the neck from the maximum range of motion to the neutral position during neck flexion, extension, right and left lateral flexion, right and left rotation, and maintaining the neck in the neutral position. Muscle activities in each motion were normalized as a percentage of maximal voluntary contraction (%MVC) so that the muscles could be compared. Results: The %MVC of the extensors was significantly larger than that of the flexors in the neutral position (p < 0.001). In addition, the %MVCs of the following were significantly larger than the %MVC in the neutral position: the extensors in flexion (p = 0.014) and extension (p = 0.020), the ipsilateral extensors (p = 0.006) and flexors (p < 0.001) in lateral flexion in Phase I; the flexors in flexion (p < 0.001), the extensors in extension (p = 0.010), and the ipsilateral extensors and flexors in lateral flexion (p < 0.001) in Phase II; the extensors and flexors in flexion (p < 0.001), the flexors in extension (p < 0.001), the ipsilateral flexors (p < 0.001), the contralateral flexors (p = 0.004) and the contralateral extensors (p = 0.018) in lateral flexion in Phase III; and the bilateral extensors and contralateral flexors during rotation in all three phases (p < 0.001). Conclusion: The typical sEMG activities of the extensors and flexors during motion of the neck in healthy adults were identified in this study; this information can be used to understand the pathophysiology of non-specific neck pain and to provide an index for evaluating the effect of treatment.