differences in cervical extensor muscles thickness on subjects with normal head posture and forward head posture: an ultrasonography study

background: forward head posture (fhp) is recognized as a common postural disorder of modern societies. increase in anterior cervical convexity and anterior displacement of the line of gravity of head in individuals with fhp is assumed to result in altered moment arms and muscle activity on cervical spine. measurement of muscle thickness seems to be an appropriate index for muscle activity. this study was aimed to compare cervical extensor muscle thickness in individuals with normal head posture with those suffering from fhp. methods : twenty volunteers with fhp and 20 matched controls (11 females and 9 males in each group) participated in this cross-sectional study. the thickness of cervical extensor muscles including multifidus, semispinalis cervicis, semispinalis capitis, splenius capitis and upper trapezius were measured using ultrasonography at the level of forth cervical vertebrae at rest. results: no significant differences of thickness of cervical extensor muscles were observed between the two groups (p<0.05) at of rest. conclusion: the results of this study showed that the thickness of cervical extensor muscles at the level of forth cervical vertebrae in individuals with fhp did not change in comparison with normal head posture at rest. further studies are recommended to evaluate extensor muscles at other levels of cervical spine.