patients with lumbar pain have greater atrophy of the deep trunk muscles than healthy 
 subjects and they also have weakened proprioceptive senses , which trigger spinal 
 instability , which in turn becomes the cause of recurrent lumbar pain1 . lumbar stability is a prerequisite element that enables 
 movement of the limbs by maintaining the spine upright in postural changes and under 
 loading2 .
muscles that contribute to 
 lumbar stability include the transversus abdominis , and the internal , and external obliques 
 of the abdomen , quadratus lumbrum and multifidus of the trunk posterior region , and the 
 pelvic floor muscle3 , 4 .
in particular , the multifidus and the transversus abdominis are 
 activated faster than the other muscles when the human body moves , adjusting trunk balance , 
 and the bilateral internal obliques are important for maintaining the lateral stability of 
 the spine and spinal bending ability .
various lumbar stability exercises have been used to maintain and improve lumbar stability 
 through isometric contraction of the abdomen and the lumbar region .
bridge exercise , one of 
 lumbar spine exercises , is a closed kinetic chain , weight bearing exercise , which induces 
 contraction of the multifidus and transversus abdominis .
it also improves the coordination 
 of the large muscles of the body surface surrounding the trunk , and is effective at 
 recovering adjustment capabilities of the trunk3 , 
 5 .
abdominal drawing - in contracts the transversus abdominis and the 
 internal obliques and induces concurrent contraction of the muscles during lumbar stability 
 exercise , reducing excessive lumbar lordosis or pelvic anterior tilt that may occur during 
 bridge exercise2 .
recent research concerning lumbar stability exercise has used equipment such as an unstable 
 base , a balance plate , a ball for treatment , and a sponge pad . osullivan et al.7 noted that performing stabilization 
 exercises in a dynamic environment , for example , using a ball for treatment rather than a 
 static environment , maximized balance ability .
page8 also observed that exercise using an unstable device was effective 
 for postural control and recovery of the somatic senses .
previous studies compared trunk stability using an abdominal drawing - in method during 
 bridge exercise or compared trunk stability and muscle activity using bridge exercise on an 
 unstable base of support .
however , research that compares lumbar stability and the thickness 
 of abdominal muscles by conducting bridging exercise with an abdominal drawing - in method on 
 stable and unstable bases of support has been lacking .
accordingly , this study of support 
 examined the effects of the abdominal drawing - in bridge exercise using a pressure 
 biofeedback device on different bases on the thickness of trunk and abdominal muscles and 
 lumbar stability .
thirty young adults ( 2 males , 28 females ) were recruited for this study .
subjects were 
 randomly and equally assigned to a stable bridge exercise group ( sbeg ) ( 1 male , 14 female ) 
 and an unstable bridge exercise group ( ubeg ) ( 1 male , 14 females ) . those who had problems 
 with muscles , the skeletal system , or the nervous system or had pain in the lumbus or the 
 pelvis during ordinary activities , or could not performt bridge exercise because they had 
 pain in the knees or ankles were excluded .
the intent of this study and the content of the 
 entire experiment were sufficiently explained to the subjects and voluntary consent was to 
 participation was received from them .
the meansd age , height , and weight of the sbeg were 
 respectively 19.870.35  years , 162.846.62  cm , and 58.349.36  kg , and the meansd age , 
 height , and weight of the ubeg were respectively 20.620.42  years , 162.744.85  cm , and 
 57.379.73  kg .
analysis of gender was made with the  test , and that of age , 
 height , and weight was conducted with the independent t - test .
the subjects performed a bridge exercise using an abdominal drawing - in method on a stable 
 base and an unstable base . in order to provide an unstable base for the bridge exercise 
 using an abdominal drawing - in method of an airex balance pad ( alcan - airex ag , sins , 
 switzerland ) with a width of 50  cm , length of 41  cm , and height 6 
, the subjects opened both arms to form an angle of 
 about 30 degrees , with the knee joints bent at 90 degrees , and placed the palms on the base . 
 then with the knees and feet shoulder width
the head and the neck were maintained straight with the eyes looking at the 
 ceiling .
the subjects held up the pelvis according to the tester struction of  hold up the 
 buttocks  and maintained the posture for 15 seconds ( contraction ) according to the tester 
 instruction of  maintain the position  and lowered the pelvis to the ground for 5 seconds 
 ( relaxation ) according to the tester instruction of  place down  . at this moment
the tester 
 directed the subjects to draw in the navel in the upper posterior direction ( lumbar 
 direction ) so that the abdominal area slightly subsided .
ten repetitions of this process 
 were considered one set and a total of six sets were conducted3 .
this study employed ultrasonic diagnostic equipment ( mysonou5 , samsung medison , korea ) in 
 order to examine changes in the thicknesses of the trunk and abdominal muscles prior to and 
 after the bridge exercise using an abdominal drawing - in method .
a 12  mhz linear probe was 
 used and the measured area was marked during the first measurement in order to measure the 
 same position .
the subjects relaxed the abdominal area and comfortably lay in a supine position on the 
 testing board .
the probe was transversely placed on the top of the iliac chest , and moved 
 toward the center of abdomen .
the probe was stopped where all of the external obliques , 
 internal obliques , and transversus abdominis were visible .
the thickness of the internal 
 obliques and transversus abdominis was measured at a point 13  mm moved distal from the 
 region where the fascias of the muscles met9 . for the measurement of the multifidus , the subject lay comfortably 
 in the prone position , and the probe was placed perpendicularly on the left transverse 
 process of the fourth lumbar spine . the thickness from the left transverse process to the 
 surface muscles was measured10 .
the 
 subjects were instructed to abstain from talking , laughing , or chewing during the data 
 collection period and all images were captured and measured at maximal inspiration . in order to evaluate static and dynamic lumbar stability prior to and after the bridge 
 exercise using an abdominal drawing - in method , contractibility of the transversus abdominis 

was measured using a pressure biofeedback unit ( pbu ) ( stabilizer , chattanooga group inc .
, 
 hixson , usa)11 . the pbu is an inelastic 
 16.724.0  cm sack that can be inflated is connected to a pressure gauge , and excessive 
 changes in pbu pressure show that movement of the lumbar pelvic area is not being adjusted . 
 for the measurement of static lumbar stability ( sls ) ,
subjects lay in the prone position on 
 hard ground and the pbu was placed below the navel at the midpoint between the bilateral 
 anterior superior iliac spines . at a pbu baseline pressure of 70 mmhg , the subject pulled in 
 their abdomen as maximally as possible for 10 seconds without moving the lumbus or hip 
 joint , relieving pressure in the pbu .
for the measurement of dynamic lumbar stability ( dls ) , the subjects lay in the supine 
 position . at a pbu
was placed 2  cm below the posterior superior iliac spine vertically from 
 the lumbar spine . with the baseline pressure of 40 mmhg , the hip and knee joints of one leg 
 were bent and the foot
was placed on the ground and the hip joint was abducted to about 45 
 degrees .
the changes in pbu were measured and recorded when the subject returned to the 
 starting position12 . in order to minimize 
 the sway of the trunk during measurement ,
spss version 12.0 ( spss , chicago , il , usa ) was used for the statistical analysis of the 
 data . the independent t - test
was conducted in order to compare the general characteristics 
 of the two groups , and the paired t - test was performed in order to compare the muscle 
 thickness and lumbar stability of each group between prior to and after the exercise of each 
 group . the independent t - test
was used in order to compare muscle thickness and lumbar 
 stability between the groups prior to and after the exercise .
* p<0.05 ; sbeg stable bridge exercise group ; ubeg unstable bridge exercise group ; tra 
 transversus abdominis ; io internal obliquus abdominis ; sls static lumbar stability ; dls 
 dynamic lumbar stability according to the comparison of the pre - intervention and post - intervention results of the 
 sbeg and the ubeg , only tra was significantly different in the sbeg ; however , tra , io , sls , 
 and dls were significantly different in the ubeg ( p<0.05 ) ( table 1 ) . according to the comparison of the results
the sbeg and the ubeg at pre - intervention , and 
 post - intervention , and the change between pre- and post - intervention , none of the items were 
 significantly different ( p < 0.05 ) ( table 
 2 ) .
this study compared the effects of bridge exercise using an abdominal drawing - in method on 
 stable and unstable bases of support on the thicknesses of lumbar and abdominal muscles and 
 lumbar stability .
the purpose of spinal stability exercise is to protect spinal joints from repetitive 
 micro - damage caused by the muscles around the spine , pain from spinal instability , and 
 degenerative spinal changes5 .
the 
 abdominal drawing - in method is effective at activating abdominal muscles , in particular , the 
 transversus abdominis4 .
susan et al.12 reported that ultrasonography of the 
 transversus abdominis showed activation of the muscle after abdominal drawing - in exercise . 

stevens et al.5 reported that bridging 
 exercise with the lumbar spine in the neutral position increased activity of the abdominal 
 muscles , but did not significantly increase activity of the multifidus .
this result is 
 consistent with those of the present study which the thickness of the transversus abdominis 
 significantly increased ( p<0.05 ) when the bridge exercise using an abdominal drawing - in 
 method was performed on different bases . on the other hand ,
we consider this is because compensation 
 bridge exercise using the abdominal drawing - in method increased activity of the abdominal 
 muscles and minimizes substitutions , such as through increased lumbar lordosis , relatively 
 reducing action by erector spinae muscles such as the multifidus .
cholewicki and mcgill13 observed that 
 stability indexes of the lumbar spine during performance of different tasks were higher in 
 tasks that placed a lot of load on the lumbar spine
. when instability in the base of support 
 increases , more muscles for stability and balance maintenance , and more load on the lumbar 
 spine increases muscle contraction14 . 

this result is consistent with those of the present study in which bridge exercise on the 
 unstable base significantly increased ( p<0.05 ) dynamic and static lumbar stability 
 relative to bridge exercise on the unstable base .
adjusting the degree of difficulty of the 
 bridge exercise on the unstable base , inducing greater trunk muscle activity , and improving 
 lumbar stability may have resulted in a better exercise effect than exercise on the stable 
 base of support .
lumbar pain triggers fast contraction of the abdominal muscles and impairs muscle function , 
 and compared to healthy subjects , lumbar pain patients muscle recruitment patterns are 
 modified15 resulting in instability 
 between spinal segments .
therefore , in clinical treatment of lumbar pain patients , 
 conducting lumbar stability exercise using an abdominal drawing - in method minimizing 
 compensation by the lumbar spine , should be effective at increasing muscle strength and the 
 spinal instability of the lumbar region .
   [ purpose ] we examined the effects of an abdominal drawing - in bridge exercise using a 
 pressure biofeedback unit on different bases on the thickness of trunk and abdominal 
 muscles , and lumbar stability . [ subjects ] thirty healthy young adults ( 2 males , 28 
 females ) took part in this study . 
 the subjects were randomly and equally assigned to a 
 stable bridge exercise group and an unstable bridge exercise group . 
 [ methods ] the subjects 
 performed bridge exercises using an abdominal drawing - in method on a stable base and on an 
 unstable base , and changes in their abdominal muscle thickness and on the stable and on 
 unstable bases lumbar stability were evaluated . 
 [ results ] after the intervention , the 
 stable bridge exercise group showed a statistically significantly increased muscle 
 thickness in the transversus abdominis , and the unstable bridge exercise group showed 
 significantly increased muscle thicknesses of the transversus abdominis and internal 
 obliques in static and dynamic lumbar stability . 
 the unstable bridge exercise group showed 
 significant increase after performing the exercise . 
 [ conclusion ] lumbar stability 
 exercise , with the compensation of the lumbar spine minimized , using an abdominal 
 drawing - in method on an unstable support of base is effective and efforts to prevent the 
 compensation may induce a greater exercise effect . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION