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 .
 [ purpose ] the aim of the present study was to investigate correlation between head 
 posture and proprioceptive function in the cervical region . [ subjects and methods ] 
 seventy - two subjects ( 35 males and 37 females ) participated in this study . for measurement 
 of head posture , 
 the craniovertebral 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 joint position sense was evaluated using a dual digital inclinometer ( acumar , 
 lafayette instrument , lafayette , in , usa ) , which was used to measure the joint position 
 error for cervical flexion and extension . 
 [ results ] a significant negative correlation was 
 observed between the craniovertebral angle and position sense error for flexion and 
 extension . 
 [ conclusion ] forward head posture is correlated with greater repositioning 
 error than a more upright posture , and further research is needed to determine whether 
 correction of forward head posture has any impact on repositioning error . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION