owing to the development of modern technology , the use of smartphones has been increasing 
 rapidly . according to the pew research center1 ,
smartphone users represent 56% of the entire us population , and the 
 average amount of time spent on a smartphone per day is 5.1 hours .
it was reported that the average time spent on a smartphone per 
 day has increased rapidly as the smartphone penetration rate has soared .
however , poor 
 posture while using a smartphone for continuous periods causes musculoskeletal problems2 .
forward neck posture ( forward head posture ) , a postural distortion , is regarded as a 
 typical musculoskeletal disorder , and it is commonly seen in patients with cervical 
 diseases3 .
if the horizontal distance 
 between the ear s tragus and the posterior angle of the acromion is more than 5  cm while a 
 person is standing , the occiput and upper cervical spine lean forward excessively and the 
 lower cervical spine and the upper vertebrae lean backward excessively .
all these symptoms 
 correspond to the features of forward head posture ( forward neck posture)4 .
when abnormal alignment of the vertebrae is 
 continuously maintained due to inappropriate posture , that is , forward head posture , the 
 vertebrae and surrounding soft tissues might be easily exposed to a sudden impact or chronic 
 stress , and this could lead to possible changes in the blood vessels , spinal disease , organ 
 dysfunction , degenerative diseases , and autonomic dysfunctions , such as headaches and 
 chronic fatigue5 .
the sling stabilization exercise can be used as a therapy for straight neck treatment and 
 kim and kim6 have noted that stretching 
 and sling exercises are effective at ameliorating cervical spine instability .
the curative 
 power of a sling stabilization exercise is found in its ability to enhance mobility , improve 
 sensorimotor function , and increase relaxation7 .
the sling stabilization exercise is a type of treatment in which 
 patients with neck pain can use their own body weight to resist gravity ; thus , this type of 
 exercise can be performed very safely . as the sling stabilization exercise enables patients 
 to perform unloading exercise in a gravity - reduced environment
, it has a similar effect to 
 what would be expected from an aquatic exercise .
a study was concluded to determine the 
 effect of the co - contraction of the masticatory muscles during neck stabilization exercises 
 on changes in the thickness of the neck flexors .
that study concluded that co - contraction of 
 the masticatory muscles during neck stabilization exercise is helpful , increasing the 
 thickness of the longus colli muscle8 .
a number of different types of stretching exercises can be used to treat patients with 
 chronic neck pain , including dynamic stretching , which a patient can practice alone for 
 prophylaxis9 , proprioceptive 
 neuromuscular facilitation , where the release and contraction of a muscle are repeatedly 
 practiced , and evjenth - hamberg stretching , where isometric contraction and static stretching 
 are applied to agonist and antagonist muscles using the hold - relax technique and the 
 contract - relax technique10 .
lee11 investigated the effects of stretching 
 exercises on forward head posture . in that study , the subjects were divided into three 
 groups , a balance exercise group , a stretching exercise group , and a control group , and the 
 respective groups performed the assigned exercises for four weeks .
that study found that 
 maximum muscle contraction was increased in the balance exercise group and the stretching 
 exercise group .
it also found that the forward head posture improved in those two groups . in 
 addition , park12 reported that the 
 symptoms of forward head posture improved after applying static stretching and 
 evjenth - hamberg stretching .
most of the existing studies have mainly focused on comparing stretching with other types 
 of exercises and they have concentrated only on demonstrating that stretching is effective 
 for the treatment of forward head posture . however , very few studies have investigated the 
 effect of training patients to use stretching and sling stabilization exercises in order to 
 treat straight neck symptoms . only a few studies have focused on how to treat straight neck 
 symptoms and correct spinal alignment . hence , this present study was conducted to compare 
 the pre- and post - test results of the craniovertebral angle ( cva ) , the cranial rotation 
 angle ( cra ) , and cervical range of motion ( rom ) , aiming to demonstrate whether or not 
 training by stretching and sling stabilization exercises has any remedial value .
from among people in their 20s who were suffering from straight neck syndrome , 20 patients , 
 diagnosed with straight neck , were recruited as the study s subjects .
the subjects were 
 divided into two groups : one sling stabilization exercise group , and one stretching exercise 
 group .
all the subjects voluntarily participated in the experiment and were thoroughly 
 briefed on the purpose of the study and the tasks to be performed .
the experiment began only 
 after the subjects fully understood the study s intention and had consented to 
 participation .
exclusion criteria included : heart disease , a mental health condition , 
 dementia , sensory disturbance , spinal tumor , spondylolisthesis , pelvic osteoporosis , spinal 
 osteoporosis , lumbar herniated intervertebral disc , or any other disease that might have 
 influenced the spine or musculoskeletal system during experiment . for rom ,
the angle of flexion , extension , rotation , and lateral bending were measured 
 within the active range of motion , using a standard goniometer ( table 2 ) .
when the rom was measured , the intraclass correlation 
 coefficient ( icc ) was used as an index of reliability .
as the icc ( 2 , k ) was 0.934 , the 
 reliability of the measurements was considered to be high .
the measurements were taken 
 twice , and the mean value of the two measurements was used for the analysis .
the 
 measurements were taken before the experiment began and then again after the 6-week 
 intervention had ended .
for the cva and cra measurements , the subjects were positioned so as to retain their 
 natural head posture while standing at ease with both of their arms relaxed and placed 
 alongside their torso . to measure the cervical angle ,
the 7th cervical ( c7 ) vertebra , ear 
 tragus , and the lateral canthus of each subject were linked by straight lines on the x - ray , 
 and then the cva and cra were measured .
if the x - ray showed a small cva and a large cra , the 
 subject was noted as having greater forward head posture . for the sling stabilization exercise ,
the cervical flexion - extension exercise and cervical 
 lateral bending exercise were performed with the aid of sling stabilization exercise 
 equipment . to perform the cervical flexion - extension exercise ,
the subjects were instructed 
 to maintain the head in a neutral position while in a supine position and to slowly extend 
 the neck , using the strap of the sling .
the cervical flexion exercise was performed with the 
 subjects in the prone position . in this position ,
the strap of sling was adjusted so that it 
 would be perpendicular to the surface of the ground in order to prevent the chin and 
 shoulders from being lifted during the exercise .
the subjects performed three sets of 
 exercise , and the exercise was repeated 15 times within each of the sets . between each set
, 
 the subjects rested for 30 seconds . to perform the cervical lateral bending exercise
, the 
 subjects slowly performed right and left lateral bending of the head while releasing their 
 neck .
the subjects performed three sets of 
 exercise , and the exercise was repeated 15 times within each of the sets . between each set
, 
 the subjects rested for 30 seconds . to perform the stretching exercise , this study adopted a 
 method in which active contractions and passive relaxations of the agonist muscles were 
 repeated , and active contraction of antagonist muscles was added , finally . modifying the 
 stretching exercise used by park12 ,
this 
 stretching exercise was performed for six weeks , and it was practiced three times each week . 
 to stretch the sternocleidomastoid muscle ,
the subjects were instructed to lie in the supine 
 position , to let their head and neck hang over the end of a hospital bed , and to place their 
 shoulders at the edge of a bed .
the therapist was told to stand at the head of the hospital 
 bed after fixing the subject s shoulder and chest to the table using a belt .
the head and 
 neck posture were arranged so that the subjects would easily feel the tension created by the 
 muscle contraction .
when the therapist held the subject s head , both of the subject s ears 
 were covered by both of the therapist s palms , and the subject s sternocleidomastoid muscles 
 were held by the therapist s fingers . while holding this posture , the therapist fully 
 rotated the subject s head to the right and pulled the head , making it perform left lateral 
 bending .
the subject pressed the therapist s right hand in order 
 to signal that the therapist should apply a similar amount of force in the opposite 
 direction .
using these balanced forces , the therapist guided the subject in performing 
 isometric contractions .
the subject performed the isometric contraction for six seconds , 
 counting from one to six , and gradually increased the intensity of the contraction , in order 
 to prevent the valsalva maneuver from occurring . while the subject relaxed for two to three 
 seconds after the contraction , the therapist moved the subject s head in the direction in 
 which greater stretching was possible .
the therapist had to move the subject s head beyond 
 the point which the muscle did not allow further movement , and held the stretch for 1516 
 seconds .
finally , the therapist asked the subject to look to the right side and to move the 
 head in the direction where the subject could extend the head further . by resisting this 
 type of movement ,
this movement 
 was continued for six seconds and the subject was allowed to rest for 10 seconds .
these 
 movements were repeated four times , and a total of 160 seconds were assigned to the 
 stretching exercises . for the upper trapezius ,
the subject was instructed to hang his head 
 and neck over the end of a hospital bed in the supine position and the therapist used a belt 
 to fix the subject s shoulder and chest to the bed .
the therapist was required to stand at 
 the head of the bed , to hold the back of subject s head in his right hand , and to hold up 
 the subject s head using his wrist and arm .
the subject s jaw was held by the therapist s 
 left hand and the therapist pulled up the subject s head . in this condition ,
the therapist 
 arranged the subject s cervical vertebrae to first slowly rotate fully to the right and then 
 to engage in left lateral bending .
this time , the therapist s body moved along with the 
 subject s head . afterwards , isometric contraction was implemented and maintained for six 
 seconds . in order to strengthen the antagonist muscle ,
the therapist kept his hands in the 
 same place and pulled the subject s jaw to the right .
the therapist then asked the subject 
 to look towards the direction in which the head was to be extended to and move the head 
 further in that direction . by resisting these movements , the therapist strengthened the 
 subject s antagonist muscles .
the time assigned for the isometric contraction , the method 
 used to relax the muscle , and the entire time assigned for the stretching exercise were 
 identical to the conditions used for the sternocleidomastoid stretches .
the 
 kolmogorov - smirnov ( k - s ) test was used to verify the normality of the data . in order to 
 analyze the way in which the straight neck symptoms varied depending on the type of 
 treatment , the independent t - test
the paired t - test was used to investigate 
 variations in the pre- and post - test measusres of straight neck and spinal posture , 
 depending on the type of treatment . a statistical significance level of  = 0.05 was used . 

this study was approved by the institutional review board of namseoul university ( cheonan , 
 korea , nsu-140609 - 2 ) .
this study investigated whether sling stabilization and stretching exercises could cause 
 structural changes in the cervical spine of straight neck patients . in terms of the change 
 in the cervical angle
, there was no significant difference between the sling stabilization 
 exercise group and the stretching exercise group .
when a comparison of the pre- and 
 post - test results was conducted , focusing on changes in cra and cva , the stretching exercise 
 group was found to show a statistically significant changes while the sling stabilization 
 exercise group did not ( table 1table 1.changes in cva and cra of the two groups ( degrees)variablegrouppre - testpost - testcvasling73.16.969.15.4stretching71.36.265.35.2crasling153.011.2148.715.9stretching150.611.2142.710.5values are expressed as mean  standard deviation ; cva : craniovertebral angle ; cra : 
 craniovertebral angle ; * < 0 .05 ;  p < 0.05 : significance difference between pre- 
 and post- exercise ) . in terms of rom
when the pre- and post - test results of the sling stabilization exercise group were compared , 
 a significant difference was found in flexion , right rotation , left lateral bending , and 
 right lateral bending .
a significant difference was found in left rotation , left lateral 
 bending , and right lateral bending , when the pre- and post - test results of the stretching 
 exercise group were compared ( table 2table 2.changes in rom of the two groups ( degrees)variablegrouppre - testpost - testflexionsling46.59.849.68.4stretching 50.24.852.46.0extensionsling37.011.741.78.0stretching 38.46.541.05.7left rotationsling49.16.954.48.4stretching 48.46.254.54.9right rotationsling48.58.456.39.2stretching 51.53.554.56.5left lateral bendingsling34.27.242.05.4stretching 34.34.438.34.5right lateral bendingsling ex30.13.336.64.7stretching 33.84.837.35.1values are expressed as mean  standard deviation ; *
< 0.05 ;   p < 
 0.05 : significance difference between pre- and post - exercise ) .
values are expressed as mean  standard deviation ; cva : craniovertebral angle ; cra : 
 craniovertebral angle ; * < 0 .05 ; 
p < 0.05 : significance difference between pre- 
 and post- exercise values are expressed as mean  standard deviation ; *
< 0.05 ;   p < 
 0.05 : significance difference between pre- and post - exercise
people today commonly experience neck diseases because of repetitious jobs and 
 inappropriate posture resulting from industrialization13 .
sling exercise has the major therapeutic advantage of underwater 
 exercise , a reduction of the influence of gravity , on hard ground .
the 
 present study found that only the stretching exercise group displayed a significant 
 difference in terms of cva and cra changes when the pre- and post - test results were 
 compared . in the stretching exercise group , cva decreased from 71.336.28 to 65.335.22 
 degrees and cra decreased from 150.6611.21 to 142.7010.53 degrees .
yang et al.15 conducted a study of 
 subjects with forward head posture , who performed neck flexion and extension exercises , 
 stretching exercises , and neck stabilization exercises using sling exercise equipment . that 
 study compared the pre- and post - test results of threshold measuring pressure pain , cva , and 
 cra .
no significant difference was found in threshold pressure pain , while significant 
 differences were found in the cva and cra values of the rapid upper limb assessment ( rula ) . 
 in another study ,
25 subjects were divided into two groups , a sling stabilization exercise 
 group and a control group , and they were instructed to conduct the assigned exercise for 
 four weeks .
cva , cra , muscle activity , and cervical alignments were measured after the 
 completion of the exercise .
when the pre- and post - test results of cva and cra were 
 compared , the sling stabilization exercise group displayed significant differences were both 
 cva and cra , while a significant difference was found in the cva value of the control group , 
 which only performed the stretching exercise16 .
as shown in this study , the stretching exercise returned the shortened muscle to normality , 
 and the abnormal cervical range of motion caused by the shortened muscle also returned to 
 normality .
thus , the stretching exercise was found to be effective at normalizing abnormal 
 forward head posture . the sling stabilization exercise was also found to have exerted a 
 positive influence . in the sling stabilization exercise group ,
the subjects were able to 
 exercise with no influence of gravity , within their own cervical rom , under the therapist s 
 control , using the sling equipment .
thus , the normalization of abnormal forward head posture is 
 possible using the sling stabilization exercise .
this can be attributed to the fact that the subjects living 
 habits could not be thoroughly controlled and the therapist s contribution to the sling 
 stabilization exercise group was less than the interference in the stretching exercise 
 group .
therefore , the patient s weakened muscle could not be fully used , which could 
 resulted in the lack of a significant difference in the findings . in terms of rom changes , the measurement of cervical rom , is regarded as the standard test 
 by which a patient with a disorder such as straight neck syndrome is assessed , because it 
 enables investigators to focus on the factors of pain and functional movement .
rom is also 
 frequently used as a yardstick to judge whether actual remedial value has occurred . in many 
 studies
chun et al.18 reported that the older patients who had performed 
 stretching exercises were found to have increased their cervical range of motion .
the neck 
 pain group that had been treated by both the rom technique ( joint mobilization ) and the 
 physical therapy technique , displayed better results , thereby demonstrating that flexion , 
 extension , left lateral bending , right lateral bending , left rotation , and right rotation 
 were all improved in comparison to the other neck pain group , which had only been treated 
 using the physical therapy technique19 .
a 
 study , in which the head - neck flexion exercise was performed using sling equipment , reported 
 that the rom for flexion and extension was significantly improved20 . in the present study the sling stabilization exercise group showed a significant difference 
 in the flexion , right rotation , left lateral bending , and right lateral bending results , and 
 the stretching exercise group showed a significant difference in the left rotation , left 
 lateral bending , and right lateral bending results .
it seems that the muscular asymmetry , 
 caused by the straight neck symptom , was returned to the symmetric state by the sling 
 stabilization exercise .
hence , the normal alignment of the cervical spine was realized by 
 the exercise conducted by the sling stabilization exercise group and this led to the 
 improvement in rom .
moreover , the stretching exercise used in the stretching exercise group 
 contributed to the normalization of muscle length by extending the shortened muscle , and 
 this normalization of muscle length led to the improvement in rom .
the results of this study coincide with the findings presented in many previous studies ; 
 thus , it is possible to infer that the stretching exercise and the sling stabilization 
 exercise exert a positive influence on rom .
the reason why not all of the rom variables in 
 this present study showed improvements that were as significant as the improvements found in 
 other studies , is attributed to the fact that the exercise methods used in this present 
 study were different from those used in other studies ; moreover , in this present study , the 
 individual subjects daily living habits could not be thoroughly controlled .
this study found that the sling stabilization exercise group showed significant improvement 
 in the rom , while the stretching exercise group showed a significant improvement in cervical 
 alignment and rom .
all parts of the human body are intimately connected to one another , and 
 imbalance causes abnormal body phenomena to appear when a problem breaks out even in a 
 single part of human body . because muscles in the human body control musculoskeletal 
 posture , they play a fundamental role in movement .
thus , the work load on human muscles is 
 always heavy . due to this peculiar nature of muscles
, they are vulnerable to irregular 
 posture , unsafe movements , over - use , and unusual usage . therefore , structural damage and 
 functional disorders are apt to occur frequently in the muscles of the human body21 .
one study revealed that pains around the 
 neck might develop into a more serious disease because of the psychological stress they 
 cause22 . in relation to cervical spine alignment and rom
, this study s findings suggest that future 
 studies should try to identify the way in which different types of therapies could be used 
 to treat straight neck patients , in addition to current treatment approaches .
future studies 
 should also examine how psychological treatment could be given along with various types of 
 existing treatment , to help ensure better patient outcomes .
 [ purpose ] the purpose of this study was to assess how stretching exercise training and 
 sling exercise training for stabilization influences the cervical spine angles and 
 cervical range of motion of straight neck patients . 
 [ subjects and methods ] twenty straight 
 neck patients were selected as subjects and they were randomly divided into two groups , 
 the stretching and sling stabilization exercise groups which 60 minutes of exercise three 
 times a week for 6weeks . all the subjects in each of the two respective study groups 
 received an x - ray and had their cervical range of motion measured , both before and after 
 the exercise . 
 [ results ] when differences in the cervical spine angle between the pre- and 
 the post - test were checked , it was found that only the stretching exercise group showed 
 statistically significant decreases in the craniovertebral angle and the cranial rotation 
 angle . 
 when differences in the range of motion between pre- and post - test were checked , 
 the sling stabilization exercise group showed a significant change in flexion , right 
 rotation , left lateral bending , right lateral bending , and the stretching exercise group 
 showed a significant change in left rotation , left lateral bending , and right lateral 
 bending . [ conclusion ] 
 these results indicate that both types of exercises are effective at 
 improving the cervical range of motion of straight neck patients , and that the stretching 
 exercise was more effective than the sling stabilization exercise at improving cervical 
 spine angles . 