respiration is the exchange of blood and oxygen via the lungs , which are the essential part 
 of the ventilation system1 .
the major 
 inspiratory muscles that engage during inspiration are the diaphragm and external 
 intercostal muscles .
meanwhile , the accessory inspiratory muscles that engage spine movement 
 are the sternocleidomastoid , scalene , trapezius , and serratus anterior muscles2 . among the methods for improving respiratory 
 function
, inspiratory muscle training improves the strength and endurance of the diaphragm 
 and accessory inspiratory muscles3 . 

moreover , it improves ventilation function even when the inspiratory muscles are damaged by 
 neurological or non - neurological lesions4 .
self - stretching of the inspiratory muscles not only improves pulmonary function , but can 
 also increase joint mobility in the thoracic cage , further improving respiratory 
 function5 .
although the self - stretching 
 of accessory inspiratory muscles improves respiratory function , most previous studies 
 involve interventions targeting respiratory muscles or exercises for thoracic cage 
 mobility6 .
furthermore , few studies have 
 investigated the effects of cervical muscle ( i.e. , accessory inspiratory muscle ) stretching 
 on the respiratory function .
therefore , this study examined the effects of cervical muscle 
 self - stretching on pulmonary function , especially slow vital capacity .
the study sample consisted of 30 subjects ( 10 males and 20 females ) who were studying at a 
 university in busan , korea .
all subjects were informed of the purpose and methods of the 
 study beforehand and voluntarily agreed to participate .
this study complied with the ethical 
 standards of the declaration of helsinki , and written informed consent was obtained from all 
 subjects .
the inclusion criteria were as follows : no lung disease , history of respiratory 
 dysfunction , or cervical injury ; ability to perform cervical stretching without difficulty ; 
 no experience with any exercise program aiming to promote pulmonary function ; and agreement 
 to not take any drugs or perform other exercise during the study period .
the subjects were randomly divided into 2 groups of 15 each : the experimental group 
 performed stretching , while the control group received no treatment . for the stretching 
 program ,
the muscle was stretched slowly and gently without pain , and each posture was held 
 for 30 seconds .
the stretching was performed twice per day , 4 times per week for 4 weeks . 

the main self - stretching exercise 
 consisted of 4 types of muscle exercises targeting the sternocleidomastoid , upper trapezius , 
 scalene , and levator scapulae muscles were performed 3 times for 30 seconds each .
cervical 
 flexion and rotation were performed again as a cool - down exercise . meanwhile
, the control 
 group did not perform the stretching program and was merely revaluated after 4 weeks .
before 
 measuring slow vital capacity , the subject breathed normally 4 times ; the machine 
 subsequently beeped , and the subject inhaled slowly as much as possible .
the items of 
 slow vital capacity include expiratory vital capacity ( evc ) , expiratory reserve volume 
 ( erv ) , inspiratory reserve volume ( irv ) , expiratory minute ventilation ( ve ) , and inspiratory 
 capacity ( ic ) . the wilcoxon signed - rank test was used to examine the effects of cervical muscle 
 self - stretching on pulmonary function .
the changes of pulmonary function were determined by 
 subtracting the data after self - stretching from those before self - stretching .
furthermore , 
 the mann - whitney u - test was used to analyze differences between groups . 

in the experimental group , evc increased significantly from 2.71 to 3.18 after 
 self - stretching ( p < 0.05 ) .
ve decreased from 8.25 to 8.08 
 after self - stretching , but the difference was not significant ( p > 0.05 ) .
although ic 
 increased from 1.74 to 1.85 , the difference was not significant ( p > 0.05 ) ( table 1table 1.pulmonary function changes in the experimental grouppre - exercisepost - exercisemean rankrank sumslow vital capacityevc ( l)*2.71  0.683.18  0.5510.0010.007.86110.00erv ( l)*0.98  0.421.41  0.461.001.008.50119.00irv ( l)*1.31  0.341.64  0.672.678.009.33112.00ve ( l / min)8.25  4.118.08 3.887.8863.008.1457.00ic ( l)1.74 
data are mean  sd , * p < 0.05 meanwhile , in the control group vc decreased significantly from 3.15 to 2.99 ( p < 0.05 ) . 

erv decreased from 1.15 to 1.05 , although the difference was not significant ( p > 0.05 ) . 

ve increased from 9.12 to 9.38 , 
 but the difference was not significant ( p > 0.05 ) .
ic decreased significantly from 2.03 
 to 1.88 ( p < 0.05 ) ( table 2table 2.pulmonary function changes in the control grouppre - exercisepost - exercisemean rankrank sumslow vital capacityevc ( l)*3.15  0.812.99  0.828.58103.005.6717.00erv ( l)1.15  0.341.05  0.288.8088.006.4032.00irv ( l)*1.50  0.511.29  0.488.69113.003.507.00ve ( l / min)9.12  3.129.38  2.568.0056.008.0064.00ic ( l)*2.03  0.601.88
data are mean  sd , * p < 0.05 comparison of the changes in pulmonary function between groups showed evc , erv , irv , and ic 
 were significantly higher in the experimental group ( p < 0.05 ) .
ve was lower in the 
 experimental group than the control group , although the difference was not significant ( p 
 > 0.05 ) ( table 
 3table 3.comparison of pulmonary function between groupsgroupvaluesmean rankrank sumslow vital capacityevc ( l)*experimental0.47  0.4821.67325.00control0.16  0.219.33140.00erv ( l)*experimental0.43  0.3721.80327.00control0.10  0.189.20138.00irv ( l)*experimental0.33  0.6522.20333.00control0.21  0.188.80132.00ve ( l / min)experimental0.18  1.9614.97224.50control0.26  2.3316.03240.50ic ( l)*experimental0.12
thus , improving thoracic cage movement and respiratory muscle strengthening can 
 improve pulmonary function .
kim7 found 
 that lumbar stabilization movement and trunk muscle stretching significantly increase vc , 
 fvc , and mvv .
meanwhile , choi and oh8 
 report that chest mobilization exercise improves the pulmonary functions of stroke patients . 

these studies demonstrate that it is vital to promote thoracic cage mobility in order to 
 improve pulmonary function .
joint mobilization and stretching are effective interventions 
 for this purpose . however , previous studies only investigated the effects of interventions 
 targeting the respiratory muscles ( e.g. , intercostal muscles and diaphragm ) on pulmonary 
 function . on the other hand , although thoracic cage movement is known to be affected by cervical 
 muscles , studies about the effects of interventions targeting the cervical muscles on 
 pulmonary function are insufficient .
hence , the present study determined if self - stretching 
 of the accessory inspiratory muscles can improve pulmonary function .
the self - stretching 
 program targeted the sternocleidomastoid , upper trapezius , scalene , and levator scapulae 
 muscles .
the origins of the sternocleidomastoid are the clavicle and sternum , and its 
 insertion is the mastoid process of the temporal bone and superior nuchal line9 .
the upper trapezius originates from the 
 occipital bone and inserts at the clavicle , acromion , and scapular spine10 .
the scalenes originate from the second to 
 seventh transverse process and the costal process of the cervical vertebra and insert at the 
 first and second ribs11 .
the levator 
 scapulae originate from the first to fourth transverse process of the cervical vertebra and 
 insert at the scapular superior angle12 . as these 4 muscles are not only involved in cervical movements , but also thoracic cage 
 movement , we hypothesized thoracic cage movement would increase after self - stretching , thus 
 improving pulmonary function . indeed , self - stretching improved evc , erv , and irv .
these 
 findings are very similar to those of han et al.13 , who found that stretching and strengthening exercises targeting 
 the cervical muscles improved pulmonary function in 18 patients with allergic rhinitis 
 patients .
han et al.13 also report that 
 the cervical muscle intervention improved thoracic cage movement , which consequently 
 improved pulmonary function .
this phenomenon also explains the results of the present study . 
 in other words ,
self - stretching of the accessory inspiratory muscles improved chest muscle 
 length and thus improved pulmonary function . in conclusion ,
self - stretching of the accessory 
 inspiratory muscles should be included in intervention programs aiming to strengthen 
 pulmonary function .
 [ purpose ] this study investigated the effects of self - stretching of cervical muscles , 
 because the accessory inspiratory muscle is considered to improve pulmonary function . 
 [ subjects ] the subjects were 30 healthy university students 1921  years old who did not 
 have any lung disease , respiratory dysfunction , cervical injury , or any problems upon 
 cervical stretching . 
 [ methods ] spirometry was used as a pulmonary function test to measure 
 the slow vital capacity before and after stretching . 
 the slow vital capacity of the 
 experimental group was measured before and after cervical self - stretching . meanwhile , 
 the 
 slow vital capacity of the control group , which did not perform stretching , was also 
 measured before and after the intervention . 
 [ results ] the expiratory vital capacity , 
 inspiratory reserve volume , and expiratory reserve volume of the experimental group 
 increased significantly after the cervical self - stretching . 
 [ conclusion ] self - stretching 
 of the cervical muscle ( i.e. , the inspiratory accessory muscle ) improves slow vital 
 capacity . 