in recent times in some occupations work in static sedentary postures for long hours in 
 order to perform the tasks required of them .
this can cause continuous muscle contraction in 
 the neck and shoulders , which subsequently leads most people to adopt a forward head posture 
 ( fhp ) in which their chins stick out1 . when fhp is maintained for prolonged periods the neck flexors and the erector spinae ( es ) 
 muscles in the upper thoracic region
are weakened due to their lengthening , and the scapula 
 is elevated due to tension in the levator scapula , sternocleidomastoid ( scm ) , splenius 
 muscles , and the suboccipitalis , which also causes tension in the upper trapezius ( ut)2 .
therefore , because of an imbalance in the 
 muscles , such as the shortening or lengthening , or straining or loosening of the muscles 
 around the neck , a rounded shoulder posture is exhibited , in which the upper thoracic region 
 is slightly bent while in a sitting posture3 , and chronic neck pain results due to mechanical stress1 .
these changes in muscle activity result 
 from changes in motor strategies to minimize the activities of muscles that are sensing pain 
 and to compensate for these suppressed muscles4 .
in addition , fhp is known to have a large influence on respiratory function by weakening 
 the respiratory muscles5 , 6 .
the scm , scalene muscles , ut , pectoralis major ( pm ) , and 
 thoracolumbar es muscles are important accessory respiratory muscles involved in 
 inspiration7 , 8 and prolonged fhp weakens these muscles , thereby decreasing their 
 respiratory function7 .
because of this , patients with fhp accompanied by chronic neck pain have been shown to have 
 less respiratory muscle strength than normal individuals9 and their accessory respiratory muscles are shortened , which largely 
 affects their respiratory function10 . in 
 addition , a study reported that fhp changes the alignment of the thoracic spine and rib cage 
 due to a slightly bent posture , thereby causing respiratory dysfunction5 .
however , most previous studies on this topic were conducted on patients with neck pain or 
 on patients with neck pain accompanied by fhp , whereas the number of studies that have 
 identified the specific effects of just fhp on respiration is limited .
therefore , this study 
 measured the forced vital capacity ( fvc ) and the forced expiratory volume in 1 second ( fev1 ) 
 in healthy normal adults and healthy adults with fhp to determine the effects of fhp on 
 respiratory dysfunction .
in addition , the present study attempted to determine the 
 relationship between fhp and accessory respiratory muscle activity by measuring the activity 
 of the scm , ut , pm , and thoracolumbar es muscles during deep breathing .
twenty - six subjects ( 14 males , 12 females ) participated in this study .
because lung capacity and muscle activity 
 differ between the genders11 , results 
 between the normal and fhp groups were compared separately for males and females .
before 
 participation in this study , all subjects signed an informed consent document that was 
 approved by the institute research board of kyungsung university .
fvc , fev1 , and accessory 
 respiratory muscle activity during deep breathing were measured for each group . to measure 
 fvc and fev1 ,
the subjects are asked to perform a rapid full inspiration through the 
 mouthpiece and then , without hesitation , perform a full expiration with maximum force , 
 followed by another rapid maximum inspiration .
fvc and fev1 were measured using pulmonary 
 function equipment ( spiropalm , cosmed , italy ) that met the american thoracic society s 
 recommendation for diagnostic spirometry .
an electromyography unit ( telemyo direct transmission system , noraxon , usa ) was used to 
 measure the activity of the following accessory respiratory muscles during deep breathing : 
 scm , ut , pm , and es muscles .
data are expressed as percentages of the reference voluntary 
 contraction ( % rvc ) .
a mann - whitney test was used to compare the fvc , fev1 , and breathing muscle activity 
 between the normal and fhp group .
spss software ( version 21.0 ; spss , chicago , il , usa ) was 
 used to generate the statistics , and p - values less than 0.05 were considered statistically 
 significant .
the characteristics of the subjects are shown in table 
 1table 1.subject characteristics ( meansd)variablegroupmale ( n=14)female ( n=12)normal ( n=7)fhp ( n=7)normal ( n=5)fhp ( n=7)age ( years)23.32.224.23.622.80.323.22.8height ( cm)174.68.5176.78.9161.44.2162.95.4weight ( kg)70.18.272.65.554.35.653.94.6cva ( )53.12.340.94.055.42.143.12.5sd : standard deviation , fhp : forward head posture , cva : craniovertebral angle .
the craniovertebral angle was significantly different between normal and fhp 
 subjects in both males and females ( p < 0.05 for both genders ) .
fvc and fev1 of the fhp 
 group were both significantly lower than they were in the normal group , in both males and 
 females ( p < 0.05 for both genders ) ( table 
 2table 2.comparisons of fvc and fev1 between normal and fhp subjects ( mean  sd)variablegroupmale ( n=14)female ( n=12)normal ( n=7)fhp ( n=7)normal ( n=5)fhp ( n=7)fvc4.60.43.90.3 * 3.20.22.70.4*fev14.50.43.60.4 * 3.20.42.50.4**p < 0.05 .
sd : standard deviation , fhp : forward head posture , fvc : forced vital 
 capacity , fev1 : forced expiratory volume at 1 second ) .
activity of the scm and pm in the fhp group was significantly 
 lower than that of the normal group in males ( p < 0.05 ) .
activity of the ut and es in the 
 fhp group was generally lower than that of the normal group in men but the difference was 
 not significant ( p > 0.05 ) ( table 
 3table 3.comparisons of respiratory muscle activity between normal and fhp subjects ( mean 
  sd)variablegroupmale ( n=14)female ( n=12)normal ( n=7)fhp ( n=7)normal ( n=5)fhp ( n=7)scm816.6350.0353.3192.0 * 1,243.6762.2514.2123.0*ut273.2114.3177.539.7596.6350.6244.8103.0*pm274.895.7183.639.4 * 290.868.2200.367.9*es197.171.3184.237.4229.082.5171.153.9*p < 0.05 .
sd : standard deviation , fhp : forward head posture , scm : 
 sternocleidomastoid , ut : upper trapezius , pm : pectoralis major , es : erector spinae ) .
activity of the scm , pm , and ut in the fhp group was significantly lower 
 than that of the normal group in women ( p < 0.05 ) .
the activity of the es in fhp group 
 was generally lower than that of the normal group in women but the difference was not 
 significant ( p > 0.05 ) ( table 3 ) .
sd : standard deviation , fhp : forward head posture , cva : craniovertebral angle * p < 0.05 .
sd : standard deviation , fhp : forward head posture , fvc : forced vital 
 capacity , fev1 : forced expiratory volume at 1 second * p < 0.05 .
sd : standard deviation , fhp : forward head posture , scm : 
 sternocleidomastoid , ut : upper trapezius , pm : pectoralis major , es : erector spinae
the present study measured fvc and fev1 , as well as the muscular activity in the scm , ut , 
 pm , and es muscles during inspiration to identify the effects of fhp on vital capacity and 
 the activity of the accessory respiratory muscles .
the fhp group showed statistically 
 significantly lower fvc and fev1 levels than the normal group . in terms of the activity of 
 the accessory respiratory muscles ,
the fhp group also exhibited statistically significant 
 decreases in the activation of the scm , ut , and pm relative to muscle activation in the 
 normal group .
while the fhp group did not show a significant decrease in the es muscle s 
 activity , its activity in this group was generally lower than in the normal group .
fhp causes shortening and weakening of the accessory respiratory muscles , thereby 
 decreasing the ratio of fev1 to fvc10 . 

kapreli et al . reported that an increase in fhp resulted in a corresponding increase in 
 respiratory dysfunction6 .
in addition , 
 even among the subjects without neck pain , an increase in fhp led to a corresponding 
 statistically significant decrease in vital capacity3 .
dimitriadis et al . reported that maximal inspiratory and expiratory pressure showed 
 statistically significant decreases for complex reasons , such as weaknesses of the scm , 
 scalene muscles , and the trapezius , which are accessory respiratory muscles , and a reduction 
 in kinetic control of the cervical area9 . 

in addition , wirth et al . reported that weaknesses of the neck muscles and accessory 
 respiratory muscles in patients with neck pain resulted in a decline in thoracic mobility , 
 thereby decreasing maximal voluntary ventilation , maximal inspiratory pressure , and maximal 
 expiratory pressure , and that these effects were closely related to fhp12 .
however , some studies reported that an increase in fhp 
 resulted in a corresponding increase in maximal expiratory pressure6 , 9
. this result may be 
 explained as follows : while fhp represents an abnormal posture , this posture can increase 
 the trunk s internal pressure during expiration and therefore may increase dynamic 
 mechanisms . in the present study ,
the observed decrease in fev1 may have been due to 
 increased kyphosis in the upper thoracic region , which is characterized by fhp , causing a 
 reduction in the volume of the thoracic cage .
this would not only reduce the expiratory 
 reserve volume , but also create resistance to the exhalation . in general , respiration is an activity influenced by complex biomechanical factors and the 
 stability of the cervical and thoracic regions of the spine is of great importance to smooth 
 respiratory function5 .
however , fhp causes 
 the shortening and weakening of the scm , scalene muscles , trapezius , and es muscles7 , and therefore , reduces the endurance and 
 proprioception of these muscles5 . in 
 addition ,
fhp increases muscle tension around the thoracic spine , thereby restricting the 
 range of motion in the upper thoracic spine3 .
the present study compared normal adults without neck pain based on the presence or absence 
 of fhp .
the results were similar to those of a number of previous studies on patients with 
 fhp and neck pain , as well as those of the previous studies on normal adults with fhp but 
 without neck pain3 .
the results presented 
 here may be important in confirming that fhp without neck pain can still influence 
 respiration . therefore , when treating patients with fhp or lung dysfunction , improvements in 
 respiratory function through the correction of posture and the strengthening of weakened 
 accessory respiratory muscles may be clinically important .
 [ purpose ] this study investigated the effects of forward head posture on forced vital 
 capacity and deep breathing . [ subjects ] twenty - six subjects , divided into the two groups 
 ( normal and forward head posture groups ) , participated in this study . 
 [ methods ] forced 
 vital capacity and forced expiratory volume in 1 second were measured using respiratory 
 function instrumentation that met the american thoracic society s recommendation for 
 diagnostic spirometry . 
 accessory respiratory muscle activity during deep breathing was 
 measured by electromyography . 
 a mann - whitney test was used to compare the measure 
 variables between the normal and forward head posture group . 
 [ results ] forced vital 
 capacity and forced expiratory volume in 1 second were significantly lower in the forward 
 head posture group than in the normal group . 
 accessory respiratory muscle activity was 
 also lower in the forward head posture group than in the normal group . 
 in particular , the 
 sternocleidomastoid and pectoralis major activity of the forward head posture group was 
 significantly lower than that of normal group . 
 activities of the other muscles were 
 generally decreased with forward head posture , but were not significantly different 
 between the two groups . 
 [ conclusion ] these results indicate that forward head posture 
 could reduce vital capacity , possibly because of weakness or disharmony of the accessory 
 respiratory muscles . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION