RESUMEN
BACKGROUND: As one of the most common work-related musculoskeletal disorders and postural deviations, forward head posture (FHP), is considered to lead to muscle imbalance. OBJECTIVES: The aim of this study is to investigate the bilateral cross-sectional area (CSA) of the deep neck flexor muscles at rest and during five stages of the craniocervical flexion (CCF) test in individuals with FHP and the controls with normal head posture. METHODS: Eighteen students with FHP and 18 controls with normal head posture, all females aged 18-35 years, participated in this study. Participants were categorized into two groups based on their craniovertebral angle. The CSA of the deep neck flexors was measured using ultrasonography while participants lay supine on the table with a pressure biofeedback unit placed under their necks in order to let the examiner measure the CSA of the muscles during rest and five stages of the CCF test including 22, 24, 26, 28, and 30 mmHg of the pressure biofeedback unit. RESULTS: A significant effect of contraction level was observed in both groups, indicating significant increases of the CSA of the deep neck flexors during contraction (F = 64.37, P < 0.001). No significant difference was evident for the CSA of the deep neck flexors between the groups, although the increase in the CSA of the deep neck flexors was up to 28 mmHg in the normal head posture group compared to 26 mmHg in the FHP group. CONCLUSIONS: The results of the present study showed no significant difference between the performance of the deep neck flexors during the CCF test in FHP and normal head posture individuals, which challenge the common belief of the deep neck flexors weakness in individuals sustaining FHP.