an ideally aligned posture is regarded as 
 one in which there is perfect alignment of the weight - bearing segment , and it is commonly 
 described by the vertical line of gravity passing anterior to the knee , posterior to the 
 hip , through the bodies of vertebrae in both the cervical and lumbar spine , through the 
 shoulder joint , and through the external auditory meatus2,3,4 . proper posture is achieved by maintaining the musculoskeletal 
 balance associated with minimal stress on the body and is considered an important factor in 
 assessment of health condition . among many factors , including vision , vestibular function , 
 the somatosensory system , and the musculoskeletal system , proprioception is considered an 
 essential factor for the maintenance of balance1 , 
 5 , 6 . however , several factors , including neck pain and/or shoulder pain , 
 can disrupt this balance , leading to development of a postural problem5 , 7 , 8 . forward head posture ( fhp ) , one of the most common abnormal head postures , is a postural 
 head - on - trunk misalignment , which is defined as a head that is positioned anterior to a 
 vertical line of gravity7,8,9,10 . it is commonly quantified by measurement of craniovertebral ( cv ) 
 angle , which assesses the head posture2 , 11 , 12 . fhp can lead to development of several musculoskeletal problems , 
 including neck pain , cervicogenic headache , temporomandibular disorder , and muscular 
 dysfunction7 , 13 . the close relation of fhp to chronic neck and shoulder pain has 
 been well documented12 . however , only a few studies investigating the correlation between fhp and proprioceptive 
 function have been reported . therefore , the question of whether there is a correlation 
 between head posture and proprioceptive function in the cervical region was investigated in 
 the current study . seventy - two subjects ( 35 males and 37 females ) with no history of fracture , neuromuscular 
 disorder , or pain in the cervical region , participated in this study . their mean age , 
 height , and weight were 22.26 ( 2.10 ) years , 167.98 ( 11.89 ) cm , and 62.56 ( 11.89 )  kg , 
 respectively . the purpose and procedures of this study were explained to all subjects , and 
 they provided written informed consent prior to participation . all subjects were instructed to 
 stand in a self - selected comfortable upright posture . then , the skin overlying the spinous 
 process of the seventh cervical vertebra ( c7 ) and tragus of the ear was marked . the cv angle was calculated based on the 
 angle between a horizontal line passing through c7 and a line extending from the tragus of 
 the ear to c7 . the x - axis values for the craniovertebral angle were measured prior to 
 movement . regarding measurement of fhp , a previous assessment of the test - retest reliability 
 of the cv angle measurement revealed an icc of 0.880.9815 . for assessment of proprioceptive function , joint position sense was evaluated using a dual 
 digital inclinometer ( acumar , lafayette instrument , lagatette , in , usa ) , which used to 
 measure the joint position error between the starting standard position and the returned 
 standard position . notably , joint position sense becomes 
 more inaccurate as the degree of position sense error increases . subjects were instructed to 
 stand upright and to memorize their head position as a neutral start position . while keeping 
 their eyes closed , the main unit of the dual digital inclinometer was placed on the top of 
 their head in the sagittal plane , and the companion unit of the inclinometer was placed on 
 the c7 spinous process . then , subjects performed a maximal cervical range of the movement ( flexion / extension ) for 
 approximately 2 seconds and returned to their memorized neutral position . to measure the 
 reposition error value , this 
 was repeated three times , and the sequence of movement ( flexion / extension ) was assigned 
 randomly . demographic data ( age , weight , and height ) spearman s correlation coefficient was used to examine the correlation between the joint 
 position sense and cv angle . subjects had an average cv angle of 53.70 ( 5.05 ) degrees , an average position sense error 
 for flexion of 2.86 ( 1.74 ) degrees , and an average position sense error for extension of 
 2.65 ( 1.58 ) degrees . in addition , there was no significant difference between genders and 
 head posture ( p=0.734 ) . significant negative correlation was observed between the cv angle 
 and position sense error for flexion ( r=0.655 , p=0.000 ) and extension ( r=0.557 , p=0.000 ) . a summary of the statistical values is shown in table 
 1table 1.correlation between craniovertebral angle and cervical joint position 
 errorcraniovertebral angle ( degree)correlation coefficient ( r)cervical joint position error ( degree)flexion0.665*extension0.557**p<0.05 . the present study investigated the cv angle and joint position error in the cervical region 
 to elucidate the correlation between head posture and proprioceptive function . in this 
 study , the position - reposition error in the cervical region after cervical flexion and 
 extension was measured . as a result since fhp can be quantified by the cv angle2 , 11 , 12 , this result implies that severe fhp might be relevant to 
 poor proprioceptive function . use of visual display terminals is associated with an increase of musculoskeletal disorders 
 accompanying posture problems . in particular , the combination of extension in the upper cervical region and 
 flexion in the lower cervical region appears in patients with fhp because of a misalignment 
 in head posture . changes in the cervical region , induced by sustained poor head posture , 
 cause excessive joint and muscle loading , and subsequently influencing weakness of the deep 
 cervical muscles8 , 20 , 21 . among many body 
 structures located in the cervical region , the muscle is regarded as a main element for 
 position sense through its receptors , such as muscle spindles22 . mechanoreceptors , including muscle spindles , are densely concentrated in the cervical 
 region , and therefore play a key role in providing proprioceptive information23 . furthermore , several studies have 
 reported that precise movement requires proper input from the muscle spindle24 , 25 . muscle imbalance , including weakness of cervical flexors and 
 shortening of cervical extensors , has been reported in patients with fhp8 , 26 . these abnormal changes in the muscles can lead to disruption of afferent input from the 
 muscle spindles , which may have an adverse effect on joint position sense27 . thus , it is suggested that fhp may 
 influence joint position sense via muscle spindles influenced by muscle conditions . consequently , the current study concluded that fhp is correlated with greater repositioning 
 error than a more upright posture . our results imply that changes of muscle condition 
 following fhp can lead to disruption of afferent input from the muscle spindles . thus , it is 
 suggested that this alteration in the muscle spindle plays a major role in the poor 
 proprioceptive function shown in fhp . firstly , as it did not report any 
 measured values of muscle conditions such as muscle length and activity , the results of the 
 current study might not be sufficient to demonstrate the effect of muscle spindles on 
 position - reposition error . secondly , there are various types of receptors that receive 
 sensory information in the human body . since the muscle spindle is just one of the sensory 
 receptors , it is necessary to investigate whether there are other receptors that influence 
 repositioning error . thus , it is thought that further study is needed to elucidate the effects of the other 
 sensory receptors . also , further research is needed to determine whether correction of 
 forward head posture has any impact on repositioning error .