You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
many smokers start smoking in their teens , and teenage smokers are 16 times more likely to 
 carry the smoking habit into adulthood than nonsmoking teenagers because the earlier people 
 begin smoking , the sooner they become habitual smokers1 . smoking increases the risk of lung cancer by causing dna damage in 
 lung cells2 , and it also decreases the 
 ability to exchange gases in the alveoli by irritating the airway mucosa , which raises 
 bronchial tube contraction and mucus secretion3 .
smoking particularly causes serious harm to the cells and tissues 
 of teenagers ' bodies , which are not yet fully developed , and it increases oxidative stress , 
 which promotes chronic diseases and aging , inhibits the growth of brain cells and bone 
 marrow , and leads to memory impairment and anxiety4 .
respiration performs the function of exchange between oxygen and blood via the lungs , vital 
 parts of the body 's ventilation system5 . 

the muscles involved in the stability of the trunk and respiration are divided into the 
 inspiratory muscles and the expiratory muscles .
the main inspiratory muscles include the 
 diaphragm and the external intercostals , which are recruited during normal respiration .
the 
 accessory muscles of inspiration include the sternocleidomastoid , the scalenes , the 
 trapezius , the pectoralis major , the pectoralis minor , and the serratus anterior , which are 
 recruited during deep , forced , or labored respiration . in comparison ,
the main muscles 
 involved in expiration do not act during normal respiration , while the accessory muscles , 
 including the rectus abdominis , the transverse abdominis , the internal / external oblique , and 
 the internal - intercostals , act during deep or strong respiration6 , 7 .
based on ultrasonic measurement of young men , kim and kim8 reported that the thickness of the io and tra muscles measured while 
 the subjects were at rest significantly increased when the thickness was measured while the 
 subjects were in a state of forceful expiration .
they also found significant differences in 
 the pcmt of the tra and in the rcr of both the io and the tra .
these results were obtained 
 from adults who had smoked for 56 months by only measuring the thickness of their 
 respiratory muscles , not by taking their vital capacity into account .
no research has 
 measured the vital capacity of teenagers whose duration of smoking is relatively short , 14 
 months on average .
thus , this study aims to determine the effects of smoking on teenagers ' io and tra 
 expiratory muscles by measuring the thickness of the muscles and by examining the teenagers ' 
 lung capacity .
a total of 30 subjects ( 15 smokers , 15 nonsmokers ) participated in the research .
their 
 average age , height , weight , and body mass index ( bmi ) were 13.03  years , 170.73  cm , 
 61.87  kg , and 18.07  kg / m , respectively .
prior to the experiment , a pulmonary function test using a spirometer ( sp-260 
 pneumotacho sensor , schiller , switzerland ) was performed on all prospective subjects to 
 examine their pulmonary functions . using a maximal - effort expiratory spirogram ,
the forced 
 vital capacity ( fvc ) , forced expiratory volume at one second ( fev1 ) , and fev1/fvc ratio were 
 measured in order to determine whether the subjects had obstructive or restrictive pulmonary 
 disease .
their airway resistance was then measured based on the peak expiratory flow 
 ( pef ) .
changes in the thickness of the io and tra were analyzed using ultrasonography ( esaote 
 europe b.v .
, netherlands ) while the subjects were resting and in a state of forceful 
 expiration .
ultrasonographic 
 imaging was obtained using a 7.5  mhz linear probe , with the midpoint of the transducer 
 placed along the midaxillary line in the transverse plane just above the right iliac crest . 

all subjects maintained an upright standing posture during both resting and forceful 
 expiration states , with their scapulars fixed on the wall during expiration to prevent 
 movement of the trunk during ultrasonographic imaging .
the changes in the thickness of the 
 io and tra of both the smokers and nonsmokers while resting and in a state of forceful 
 expiration were analyzed using a paired t - test .
the homogeneity of the subjects ' general 
 characteristics , the percentage of change in muscle thickness ( pcmt ) , and the relative 
 contribution ratio ( rcr ) while resting and in a state of forceful expiration were calculated 
 using the following formula and were compared using an independent t - test .
pcmt = [ ( muscle thickness during forceful 
 expiration  muscle thickness during resting)/ muscle thickness during resting ] 
  100 .
rcr = [ pcmt of io ( or tra)/(pcmt of io + pcmt of tra ) ] 
  1008 .
pf : pulmonary function , fvc : forced expiratory vital capacity , fvc1 : forced expiratory 
 volume in 1 sec , fvc1/fvc : forced expiratory vital capacity in 1 sec as a percentage of 
 fvc , pef : peck expiratory flow the thicknesses of the subjects ' io and tra muscles were measured while they were at rest 
 and while they were in a state of forceful expiration , and then the results were compared . 
 according to the results ,
both smokers and nonsmokers did not showed no significant 
 differences in the thickness of the muscles during forceful expiration .
no significant 
 differences were found between smokers and nonsmokers in the pcmt and rcr of both the io and 
 tra . in terms of vital capacity
, the subjects did not show differences in the fvc1 and 
 fev1/fvc , while they revealed significant differences in the fvc ( for both groups , p=0.03 ) 
 and pef ( for both groups , p=0.00 ) ( table 1 ) .
smoking decreases fev1 and lung diffusing capacity and causes lung growth disorders in 
 children or teenagers9 , and it has been 
 reported that smoking increases the risk of bronchial infection to the level of the risk 
 experienced by chronic lung disease patients10 .
it also increases airway resistance and causes ventilation 
 impairments , which decreases fvc and pef to between 25% and 75%11 .
this study also found that teenage smokers showed 
 decreased vital capacity in terms of fev1 and ref compared with nonsmokers . regarding the thickness of the respiratory muscles ,
not many studies have reported cases of 
 musculoskeletal dysfunction resulting from smoking8 , but such cases did show decreased oxidative enzymes , slow recovery 
 of phosphocreatine after exercise , early appearance of lactate , a high level of oxidative 
 stress , and fiber - type redistribution in copd patients resulting from long - term 
 inactivity12,13,14,15,16 .
moreover , it has been 
 reported that smoking decreases the cross - sectional area of type i and type ii muscle fibers 
 of the vastus lateralis of non - copd smokers , warning against skeletal muscle damage caused 
 by smoking17 .
teenage smokers , whose average duration of smoking was relatively short , did not show 
 significant differences in respiratory muscle imbalance in comparison with teenage 
 nonsmokers , but the teenage smokers revealed clear differences in terms of decreased 
 pulmonary function . considering that smoking causes lung growth disorders and decreased 
 respiratory function in teenagers , antismoking campaigns are extremely necessary at this 
 point .
in addition , research showed that a significant increase in the io 's contribution 
 during forceful expiration in healthy subjects in their twenties without musculoskeletal 
 disorders , such as lbp , indicates that smoking affects the lumbar stabilizers ' recruitment 
 patterns8 .
this finding emphasizes the 
 necessity of calling teenage smokers ' attention to the fact that continuation of smoking 
 habits from adolescence to adulthood may cause an imbalance in their respiratory 
 muscles .
[ purpose ] the purpose of this study was to examine the effects of smoking on teenagers ' 
 internal oblique ( io ) and transverses abdominis ( tra ) expiratory muscles and their 
 pulmonary function . 
 [ subjects ] a total of 30 healthy teenagers ( 15 smokers ; 15 nonsmokers ) 
 voluntarily participated in the study . 
 [ methods ] the subjects were instructed to maintain 
 an upright standing posture with their scapulars against the wall . 
 measurements were then 
 taken to determine the thickness of their right io and their right tra while they were at 
 rest and in a state of forced expiration using a 7.5  mhz linear probe of an ultrasonic 
 imaging system . 
 the measured thickness was converted into the percentage of change in 
 muscle thickness ( pcmt ) and the relative contribution ratio ( rcr ) using a calculation 
 formula , and then the data were analyzed . 
 [ results ] no significant differences were found 
 between the two groups in the thickness , pcmt , and rcr of both the io and tra muscles , 
 while there were significant differences in the forced expiratory volume at one second 
 ( fev1 ) and the peak expiratory flow ( pef ) . 
 [ conclusion ] this study examined teenage 
 smokers whose duration of smoking was relatively short . 
 the two groups did not show 
 significant differences in the thickness of both the io and tra muscles . 
 however , based on 
 the forced expiratory volume at one second ( fev1 ) and pef measurements , the smokers showed 
 greater decreases in pulmonary function than the nonsmokers .