postural control is essential in performance of independent activities of daily living in 
 stroke patients1 .
postural control is 
 defined as the ability to maintain the center of mass ( com ) within the base of support with 
 minimal postural sway , and the sensory systems ( visual , somatosensory , and vestibular 
 systems ) , cognitive processing , and movement strategies are needed for maintenance of 
 postural control2 . in general , postural 
 control can be classified according to static and dynamic postural control3
. therefore , evaluation of postural control 
 should be considered for both aspects of static and dynamic postural control . in the clinic 
 or hospital
setting , the berg balance scale ( bbs ) and timed up and go test ( tug ) are used 
 mainly for evaluation of dynamic postural control4 , 
 5 , and measurement of postural sway 
 using a force platform is commonly used for evaluation of static postural control6 .
. a force platform system can provide quantifying data for 
 postural control of subjects by measuring the postural sway7 .
in addition , lajoie et 
 al.9 reported an association of 
 increased postural sway with reduction of dynamic balance ability . on the other hand
, some 
 studies reported that an increase in postural sway is not necessarily an indication of poor 
 dynamic balance ability but simply indicates static balance ability10 , 11 .
thus , the 
 question of whether or not postural sway is associated with dynamic balance is still 
 debatable .
the purpose of the current study was to gain a more comprehensive understanding 
 of the relationship between postural sway and dynamic balance in post stroke patients .
thirty - one stroke patients were recruited on a 
 voluntary basis from an inpatient hospital .
subjects were included if ( 1 ) they had a 
 diagnosis of stroke ( cerebral cortex lesion : ischemic brain injury or intracerebral 
 hemorrhage ) based on magnetic resonance imaging or computed tomography , ( 2 ) they were able 
 to understand and follow simple verbal instructions ( korean version of the mini - mental state 
 examination score > 24 ) , ( 3 ) they had no known musculoskeletal conditions that would 
 affect the ability to stand safely ; and ( 4 ) they had no serious visual impairment or hearing 
 disorder .
the exclusion criteria were ( 1 ) participation in another study or rehabilitation 
 program , ( 2 ) severe heart disease or uncontrolled hypertension and pain , and ( 3 ) any 
 neurologic or orthopedic disease that might interfere with the study .
all subjects 
 participated in conventional rehabilitation programs consisting of physical and occupational 
 therapy during hospitalization .
three of the 34 potential subjects were excluded because 
 they met the exclusion criteria ( participation in another study or uncontrolled 
 hypertension ) . ultimately
, 31 subjects ( 20 men and 11 women ; age 64.25  years ; stroke 
 duration 12.70 months ; mmse - k score 26.35 ) were included in this study .
the subjects were 
 briefed on the experimental procedure , and written consent forms were collected from all 
 subjects prior to conduct of the experiment ; the subjects voluntarily signed informed 
 consent forms .
human subject ethical approval was obtained from the relevant committee of 
 the sahmyook university institutional review board prior to conduct of the experiment . a good balance system ( good balance system , metitur , oy , 
 jyvaskyla , finland ) was used for measurement of postural sway velocity and velocity moment 
 of subjects in the standing posture . according to a previous study , the good balance 
 system has adequate reliability for research and clinical use 
 in stroke patients11 . on the basis of the 
 coordinate values for x and y ,
the following parameters were calculated : ( 1 ) mean speed of 
 movement of the center of pressure ( cop ) in the anteroposterior ( ap ) direction ( mm / s ) ; ( 2 ) 
 mean speed of movement of the cop in the mediolateral ( ml ) direction ( mm / s ) , and ( 3 ) mean 
 velocity moment ( mm / s ) .
postural sway velocity moment is defined as the average 
 horizontal area covered by movement of the center ( ap and ml direction ) of force per second . 

the force platform , which was an equilateral triangle ( 800 mm ) , was connected to a 
 three - channel dc amplifier .
signals from the amplifier were converted into digital form 
 using a 12-byte converter ( sampling frequency=50 hz ) and stored on the hard disk of a 
 personal computer . for measurement of postural sway under the stable surface condition
, 
 subjects stood on the force plate with their legs spread at shoulder width and then looked 
 at a number on a monitor three times for 30 seconds . for measurement of postural sway under 
 the unstable surface condition
, a subject stood on the force plate , which was covered with 
 foam , with their legs spread at shoulder width and then looked at a number on a monitor 
 three times for 30 seconds11 .
three 
 repeats of each measurement were performed , and the average was used in the statistical 
 analysis .
the following 
 instruction was communicated to the subjects in order to ask them to move their bodies as 
 little as possible :  please try your best to stand without swaying .
 the berg balance scale ( bbs ) and timed up and go test ( tug ) were used for measurement of 
 dynamic balance ability .
the bbs is a valid and reliable instrument for measurement of both 
 the static and dynamic aspects of balance in elderly people after a stroke4 .
the tug is measured as the time ( seconds ) 
 required for performance of the following : stand up from a chair , walk 3  m at a normal 
 walking speed , turn around , walk back to the chair , and sit back down on the chair .
all measurements , including postural sway and dynamic balance ( bbs 
 and tug ) , were performed while the patients were in a rehabilitation ward , and the assessor 
 was blinded . the spss ver .
correlations between postural sway 
 under stable and unstable conditions and dynamic balance abilities ( bbs and tug ) were 
 assessed using pearson s correlational coefficient .
general characteristics and data concerning postural sway and dynamic balance ability of 
 the subjects are summarized in table 
 1table 1.general characteristics and dependent variables of the subjects ( n=31)variablesmsd ( % ) gendermale / female ( % ) 20/11 ( 64.5/35.5)paretic sideright / left ( % ) 25/6 ( 80.6/19.4)etiologyinfarction / hemorrhage ( % ) 18/13 ( 58.1/41.9)age ( years)64.24.8height ( cm)165.36.2mass ( kg)63.57.5post stroke duration ( months)12.72.5mmse - k ( score)26.32.2stable conditionap - psv(eo ) ( mm / s)7.12.4ml - psv(eo ) ( mm / s)10.83.4psvm(eo ) ( mm)33.024.8ap - psv(ec ) ( mm / s)9.25.1ml - psv(ec ) ( mm / s)17.08.6psvm(ec ) ( mm)58.664.1unstable conditionap - psv(eo ) ( mm / s)11.54.6ml - psv(eo ) ( mm / s)16.56.6psvm(eo ) ( mm)71.838.2ap - psv(ec ) ( mm / s)20.611.8ml - psv(ec ) ( mm / s)41.243.6psvm(ec ) ( mm)222.6173.7dynamic balancebbs ( score)41.45.2tug ( sec)21.74.1values are expressed as numbers ( % ) or meanssd.mmse-k : korean version of the mini mental state examination .
eo , eyes open ; ec , eyes 
 closed ; ap - psv , anteroposterior postural sway velocity ; ml - psv , mediolateral postural 
 sway velocity ; psvm , postural sway velocity moment ; bbs , berg balance scale ; tug , 
 timed up and go test .. values are expressed as numbers ( % ) or meanssd .
eo , eyes open ; ec , eyes 
 closed ; ap - psv , anteroposterior postural sway velocity ; ml - psv , mediolateral postural 
 sway velocity ; psvm , postural sway velocity moment ; bbs , berg balance scale ; tug , 
 timed up and go test . the correlations between postural sway and dynamic balance in the stable and unstable 
 conditions are summarized in table 2table 2.correlation between postural sway and dynamic balance ( n=31)ap - psv ( eo)mm / sml - psv ( eo)mm / spsvm ( eo)mmap - psv ( ec)mm / sml - psv ( ec)mm / spsvm ( ec)mmstable conditionbbs ( score)0.240.100.200.140.110.07tug ( sec)0.100.010.210.060.070.24unstable conditionbbs ( score)0.46**0.060.200.42*0.230.50**tug ( sec)0.330.080.080.160.050.32psvm , postural sway velocity moment ; ap - psv , anteroposterior postural sway velocity ; 
 ml - psv , mediolateral postural sway velocity ; bbs , berg balance scale ; tug : timed up 
 and go test ; eo , eyes open ; ec , eyes closed .
no significant correlation was observed 
 between postural sway and dynamic balance except for the bbs score and anteroposterior 
 postural sway velocity in the eyes open condition ( r=0.46 , p<0.01 ) , 
 anteroposterior postural sway velocity in the eyes closed condition 
 ( r=0.42 , p<0.05 ) , and postural sway velocity moment 
 ( r=0.50 , p<0.01 ) .
however , in the stable condition , no significant 
 correlation was observed between postural sway and dynamic balance .
psvm , postural sway velocity moment ; ap - psv , anteroposterior postural sway velocity ; 
 ml - psv , mediolateral postural sway velocity ; bbs , berg balance scale ; tug : timed up 
 and go test ; eo , eyes open ; ec , eyes closed .
the current study was conducted in order to investigate the relationship between postural 
 sway and dynamic balance in post stroke patients . according to our main findings , no 
 significant correlation was observed between postural sway and dynamic balance except 
 between the bbs score and anteroposterior postural sway velocity in the eyes open condition , 
 anteroposterior postural sway velocity in the eyes closed condition , and postural sway 
 velocity moment on the unstable surface ( foam ) .
in addition , in the stable condition , no 
 significant correlation was observed between postural sway and dynamic balance .
postural control is defined as a complex skill involving interaction with sensory and motor 
 systems , and postural control is essential and inevitable to maintenance of independent 
 activities of daily living in stroke patients12 , 
 13 .
humans are swayed in several 
 directions for maintenance of standing balance within the base of support , and a force 
 platform is commonly used in assessment of postural sway14 , 15 . through many previous 
 studies3 , 16 , 
 17 , increases in postural sway
have 
 been shown to be associated with a reduction in balnace ability and weight trasfer and to 
 lead to an increased incidence of falls .
chisholm et al.18 reported an association of decreases in postural sway with 
 functional movement .
in addition , niam et al.19 reported negative correlation of postural sway with dynamic balance 
 ( bbs ) in stroke patients .
in contrast , our findings showed no significant correlation between postural sway and 
 dynamic balance . according to previous studies investigating dynamic balance and postural 
 sway10 , 20
increases in 
 postural sway may not be associated with maintenance of dynamic postural stability . in 
 stroke patients with damage to the central nervous system ,
body movements are made as they 
 attempt to control their posture in the standing position and as they try to maintain their 
 center of mass21 .
thus , the results of 
 our study indicate that a decrease in postural sway does not necessarily reflect improvement 
 of dynamic balance ability .
we believe that this finding may be useful in balance 
 rehabilitation for prevention of falls after stroke .
, many factors 
 can affect postural sway including the vestibular , somatosensory , and visual systems .
in 
 particular , postural control can be affected through fatigue in the musculature surrounding 
 the ankles , knees , and hip24 , 25 .
thus , conduct of additional studies will be needed in order to fully understand the 
 relation between postural sway and dynamic balance ability .
 [ purpose ] the purpose of the current study was to investigate the relationship between 
 postural sway and dynamic balance in post stroke patients . [ subjects ] thirty - one stroke 
 patients ( 20 men and 11 women ; age 64.25  years ; stroke duration 12.70 months ; mmse - k score 
 26.35 ) participated in this study . 
 [ methods ] this study applied a cross - sectional design . 
 a good balance system was used for measurement of the postural sway velocity 
 ( anteroposterior and mediolateral ) and velocity moment of subjects under the eyes open and 
 eyes closed conditions in a standing posture . 
 the postural sway of subjects was measured 
 under two surface conditions ( stable and unstable surfaces ) . 
 [ results ] on the unstable 
 surface ( foam ) , no significant correlation was observed between postural sway and dynamic 
 balance except for the berg balance scale ( bbs ) score and anteroposterior postural sway 
 velocity under the eyes open condition , anteroposterior postural sway velocity under the 
 eyes closed condition , and postural sway velocity moment . 
 in addition , in the stable 
 condition , no significant correlation was observed between postural sway and dynamic 
 balance . 
 [ conclusion ] our results indicate that a decrease in postural sway does not 
 necessarily reflect improvement of dynamic balance ability . 
 we believe that this finding 
 may be useful in balance rehabilitation for prevention of falls after a stroke . 
INTRODUCTIONS
SUBJECTS AND METHODS
RESULTS
DISCUSSION