stroke and other cerebrovascular diseases caused by cerebral vascular blockage or bleeding 
 cause loss of normal blood circulation in the affected area and anoxia , resulting in 
 irreversible brain damage which manifests as functional impairments in consciousness , 
 movement , senses , recognition , comprehension , and language .
common mobility impairments 
 include : lateral muscle weakness , abnormal lateral muscle tension , abnormal postural 
 control , abnormal coordination , abnormal movement sequencing and loss of joint coordination . 

these are all factors which contribute to problems with postural control , thereby affecting 
 standing balance ability1 .
postural control evaluation and training are important 
 contributors to the rehabilitation of balance , walking ability and other daily living 
 activities performed by stroke patients3 , 4 .
the modern theory of movement control and movement learning holds that in humans all 
 intentional movements are task - specific5 , 
 i.e. the response is specific to the environment or situation .
however , 
 rehabilitation therapies involving task - specific actions often have better effects than 
 traditional non - task - specific rehabilitation therapies6 . according to barclay - goddard , stevenson , poluha , et al.7 , through traditional treatment
, stroke 
 patients can increase standing symmetry when using a force plate for treatment .
van peppen , 
 kortsmit , lindeman , et al.8 concluded that 
 stroke patients using visual feedback with traditional treatments showed greater 
 improvements than patients receiving standard treatment only in standing symmetry , postural 
 sway movement with the eyes open and closed , and walking speed9 .
dynamic balance ability is the ability to change postural without 
 losing one s balance10 .
limits of 
 stability ( los : the maximum center of gravity displacement possible without loss of balance ) 
 are also reduced in stroke patients .
damage to the central nervous system function directly 
 affects posture , movement , and thus , balance ability . reduced muscle strength and mobility 

the hemiparesis that often results from stroke tends to 
 force patients to complete movements using a compensation strategy , e.g. fixing the affected 
 part and using the healthy part to complete the target movement
. this behavior will decrease 
 the free movement factors in the central nervous system and reduce the complexity of 
 movement choice , making it easier to complete the intended action .
however , this behavior 
 does not require postural control , so nervous impulses to the affected side reduce , which 
 further hinders functional recovery of the affected side in rehabilitation12,13,14 .
this means that techniques which oblige 
 stroke patients to practice centralized postural and balance control on the affected side 
 will have considerable impact on the stroke patients recovery of balance , walking and other 
 mobility - related functions . in this study ,
a device to enable stroke patients to learn better movement control during 
 rehabilitation than relying on traditional rehabilitation therapies was tested .
the device 
 uses two force plates to measure right and left side centers of foot pressure ( cop ) , and 
 visual feedback with different side reaction ratios to prompt movements of the affected side 
 while the non - affected support base remains in a fixed position .
a schematic diagram of the device and task used in this study is shown in fig . 1fig .
patients stand on the signal capture device ( dual force plate ) , and are prompted 
 with a task from the interactive game through a monitor .
the patient then changes the body 
 center to move an object as prompted by a task shown on the monitor .
all of these physical 
 actions are used to execute balance training and task assessment .
system schematic diagram this study used a cop capture device consisting of a load cell , signal transmitter and an 
 analog / digital converter with a universal serial bus ( usb ) interface .
weight distribution 
 data collected from the foot plantar stress center are displayed in a two - dimensional plane 
 and entered into the game for coordination .
figure 1a shows the cop capture device which 
 consists of two plates ( 30  245  10 mm , 304 stainless steel ) , one for each foot .
the 
 bottom displays an equilateral triangle ( width 165 mm ) consisting of three load cells acting 
 as a unit ( fig .
the center of this 
 equilateral triangle is the geometric center of the stepping zone .
the user needs to step on 
 the center of the stepping zone to align the geometric center of the plantar area and the 
 center of the load cell as closely as possible .
figure 
 1c and 1d show how movements are captured 
 when the cop capture device has been set up .
the load cell retrieves signals from the right 
 and left feet of the user , and the movements of foot pressure center are post - processed to 
 construct the center distribution figure .
if the region d is located in the two - dimensional coordinate system , which is the density 
 function (x , y ) , region d is further divided into left and right sides , sub - regions 
 dl and dr .
the overall weight of 
 the system is the subject s weight on both feet , which is calculated using the 
 formula : the center of gravity of the system is calculated using the formula : the three vertices of a subject s plantar force on the region dl(dr ) , 
 have force and moment arm values li ( ri ) and 
 xli , 
 yli 
 ( xri , 
 yri ) ; for i = 13 , respectively . 
 figure 2fig . 2.the relationship between the force and the moment arm shows the relationship between the force and the moment arm diagram , and the center of 
 gravity is be derived as follows : the relationship between the force and the moment arm figure 3fig .
a signal transmitter is used to provide the 
 operational voltage to the load cell and amplify the signal for transmission to the 
 analog / digital converter .
converted data is saved in a buffer zone and 
 transmitted when the software requests it .
after acquisition by the analysis software , data is 
 processed by a finite impulse response filter ( to a low - pass filter , 10  hz ) and organized in 
 chronological sequence .
the software was written in microsoft visual c # , for ( 1 ) setting the 
 function of the analog / digital converter with the usb interface ; ( 2 ) processing load cell data 
 tables ; ( 3 ) processing vector parameters ; ( 4 ) center distribution plots after vector 
 processing ; ( 5 ) a graphic user interface to display raw data and center distribution plots 
 after vector processing ; and ( 6 ) a graphic user interface to set vector processing and system 
 parameters .
schematic diagram of the capture device the game engine was developed using the microsoft .net framework .
microsoft visual c # with 
 xna game studio was used to build this engine with ( 1 ) an event processing queue ( 2 ) a graphic 
 engine ( 3 ) a user interface ( 4 ) a database interface ( fig . 

4.architecture of the game engine ) . architecture of the game engine the cop capture device of this system used the proportion , single load cell value : whole load 
 cell value = single foot center point distribution value : single foot center point reflect 
 plane boundary , to reflect the collected weight distribution in the virtual plane .
the six 
 distribution values are then merged to become the pressure centers of the right and left feet 
 and the whole cop in the virtual plane of the game engine using this rule : healthy side : 
 affected side = 1 : n ( n is decided by the medical staff based on the patient s diagnosed 
 medical condition : n=1.5 for case a , and 4 for case b in this study ) . if the cop values are over the boundary the display is locked to that boundary . in this study 

the task for patients was to use cop to aim an arrow and to shoot it at a target , when the sum 
 value of the healthy side load cell is less than 20% of the value for the load cell unit as a 
 whole , red warnings were displayed on the monitor to tell the patient to move their cop to the 
 other side .
the formula 
 controlling movement of the target is given by : horizontal boundary bh= vertical boundary bv=1,000 ( unit)moving 
 velocity v : 1v10 ( unit / fps ) moving velocity changing rate n : 10n100 ( fps ) the target moved randomly throughout the game .
the user was considered to have located the target when the angle formed by the target 
 and the monitor center ( the location of the camera ) and the difference was less than 5. at 
 this point , the arrow was shot at the target . the time taken to locate the target
the experiments in this study were approved by the human ethics committee , taipei medical 
 university hospital , taiwan .
inclusion criteria were stroke with hemiplegia , and an age 
 between 25 to 60  years .
this study reports the results of two subjects who used the device for movement control 
 training of the affected side .
training sessions consisted of following the randomly moving target as described 
 above , with one five - minute break in the middle of the session .
baseline performance was measured before the start of training , and performance was measured 
 again at the end of the training period .
the tools used to evaluate performance were : the berg balance scale ( bbs)15 , 16 , 
 14 balance tasks scored on a five - point ( 04 ) scale with 0 representing the poorest 
 performance ; the motor assessment scale ( mas)17 which evaluates motor function on a seven - point ( 06 ) scale , in this 
 study , only items relevant to standing balance were used ; and the newly - developed device was 
 used to evaluate the cop distribution .
the evaluation included the cop motion distribution of 
 the left and right feet and whole body while standing with the eyes open for one minute , and 
 standing with the eyes closed for one minute .
the effect on balance performance training using the device was assessed using two 
 patients .
the side ratio n was 1.5 for case a ( the reaction in the game was 60% on the 
 affected side and 40% on the non - affect - side ) , and 4 for case b ( affected - side 80% , 
 non - affected - side 20% ) .
table 1table 1.basic information the two cases in this studysubjectabgendermalemaleage ( years)4939height ( cm)167168weight ( kg)8272bmi29.425.51main symptomsstrokestrokeonset period6 months11 monthsdominant side / affected sideright/ rightright / rightother illnessesasthma , hypertension , aphasianohabits and customsstopped drinking and smoking ( about a year)exercise at least one 
 hour a daystopped smoking ( 8 months)exercise one to two hours a day summarizes patient data .
5.the cop distribution of case a shows the cop distribution for patient a : before training in the eyes open condition 
 ( fig .
. 6d ) . the cop numerical 
 distribution is shown in fig . 7fig .
the cop distribution of case a the cop distribution of case b cop distribution before and after training baseline and post - training balance assessments using the bbs showed that neither patient a 
 nor patient b regressed on the items for which performance at baseline was already at a 
 ceiling .
the bbs improvement of case a was 19.44% and that of case b was 11.9% , showing that 
 the interactive game used in this study can help stroke patients improve their balancing 
 ability on the stroke affected side .
detailed results are presented in table 2table 2.balance ability assessment with bbssubjectbbs sub taskbefore trainingafter trainingprogressasit to standwith hand assistancewithout hand assistancesignificantstanding unsupported with eyes closedunstablemore stablesignificantstand unsupported with feet togetherwith hand assistancewithout hand assistance and longer standing timeaveragereaching forward with outstretched armsome reachlonger reachaveragepick up object from the floor from a standing 
 positionno changenonturn to look behind over left and right shoulders while 
 standingcant look behind over affected sidecan look behind over affected sidesignificantturn 360low speedfaster speed ( but the score not enough to next 
 level)weakplace alternate foot on bench or stool while standing 
 unsupportedcould not step on a stoolstepped on the stool twice without any supportsignificantstand unsupported with one foot in frontnot able to standunsupported with one foot in front for 8 ssignificantstanding on one legcould not stand on the affected side , short term on the healthy 
 sidestill could not stand on the affected side , but more 
 time on the healthy sideaveragebstand unsupported with feet togetherstand for a long time , but need assistance to drew the feetdrew the feet by himselfsignificantplace alternate foot on bench or stool while standing 
 unsupportedtook 24 sonly took 12 ssignificantstand unsupported with one foot in frontnot able to standstood for 20 ssignificantreaching forward with outstretched arm18 cm19 cmweakpick up object from the floor from a standing 
 positionno changenonturn to look behind over left and right shoulders while 
 standingno changenonturn 360took 13 stook 12 sweakbbs scorecase acase bbefore / after / rate of progress36 point / 43point /19.44%42 point / 47 point /11.9% . table 2
shows that the progress of patient a 
 was not sufficient on some of the bbs items to elicit an improvement in score , although 
 there was some evidence of progress .
we speculate that additional training time would have 
 elicited larger gains in performance . on items such as  reaching forward with an 
 outstretched arm ,  and  picking up an object from the floor from a standing position , 
there 
 were no obvious changes in performance , presumably because these items involve upper limb 
 movement .
patient b was tested after a longer recovery period and was in better physical condition , 
 and his baseline balance performance was better than that of patient a. among the items 
 which were worst at baseline , items involving upper limb movement showed little change after 
 the training , but items related to standing balance showed obvious improvement .
table 3table 3.balance ability assessment with massubjectmas sub taskbefore trainingafter trainingprogressabalance sittingcould maintain sitting , but the weight of two body side was 
 unevenimproved . could look around and touch the side floor 
 but not the front floor.averagesitting to standingcould complete independ- ently , but the weight was uneven.the uneven situation was improved but the speed was 
 rather slow.averagewalkinghad to have assistance all the time for walking.could walk steadily without assistance device but still 
 slow.averagebbalance sittingnormal performancesome progressweaksitting to standinggood performancebetter performancesignificantwalkinggood performancewalking speed was obviously fastersignificantmas scorecase acase bbefore / after / rate of progress6 point/12 point /100%16 point /17 point /6.25
the test program 
 included seated balance and transitions from sitting to standing and walking .
the cop distribution data is shown in table 
 4table 4.cop distributionsubjectcenter point average positionaverage value of the center pointdrifting position and 
 the center point of the average distanceoe ( before / after)ce ( before / after)oe ( before / after)ce ( before / after)a(16.20 , 1.97 ) / ( 2.55 , 0.36)(13.80 , 3.35 ) / ( 13.48 , 22.41)13.39 / 4.9214.78 / 10.39cop distribution change : position moved to right side 
 ( affected side ) from left side ( healthy side).progress : oe : 63.25% , ce : 29.70% drift 
 area of center point ( before / after ) : oe : 1,284.90 / 543.50 ( progress 57.70% ) ce : 
 1,673.30 / 1,238.10 ( progress 26%)b(27.10 , 93.99)/ ( 22.89 , 56.71)(12.23 , 76.06 ) / ( 23.42 , 59.19)6.92 / 5.1214.03 / 14.82cop distribution change : moved from the upper side to 
 the center ( the virtual center of the center point on mapping plane)progress : oe : 26.01% , ce : 5.63% drift 
 area of center point ( before / after ) : oe : 767.20 / 574.30 ( progress 25.14% ) ce : 
 1599.90 / 873.20 ( progress 45.42% ) .
after training , the cop distribution of patient a shifted towards the right 
 ( affected side ) ; presumably because the patient habitually supported standing with the 
 healthy side .
the affected side showed smaller effort during the game , so the patients were 
 forced to use their healthy side to finish the game . over time they became used to having 
 their affected side absorb the weight when standing on the force plate .
the data of the 
 center point drift and the average value of the center point of the average distance showed 
 that there was considerable improvement in the eyes open condition .
this may be because the 
 patients knew they could find a datum point and maintain that datum point .
in fact , the average value for the center 
 position distance in the eyes closed condition indicated a slight deterioration in 
 performance .
patient a showed a 19.44% improvement in performance on the bbs and 100% improvement in 
 performance on the mas following training using the device and interactive game . although 
 patient a used his healthy side to support his body weight in a standing position , under 
 certain circumstances he could switch to using the affected side .
patient a showed 
 considerable improvement in static standing balance control with his eyes open .
patient b 
 showed much smaller improvements in performance : an 11.9% improvement in performance on the 
 bbs , and a 6.25% performance on the mas . in center point plane performance , there was no 
 significant change in the center point position ; and there was no detectable change in 
 average drift extent , even though the center point drift area was smaller .
it is our opinion , that the difference in the effectiveness of the training for the two 
 patients was due to differences in the length of recovery .
case b was tested after an 11 
 month recovery period and had already achieved considerable gains in mobility , most of which 
 were persistent .
this persistence was derived from functional use of the movements in the 
 course of daily life .
the 
 training produced a considerable improvement in static center point drift but no obvious 
 improvement in center point position .
it is our opinion , that patient a made significant 
 progress in all aspects of balance because testing occurred after a shorter recovery period , 
 and patient a had not recovered as much mobility as patient b , leading to larger training 
 effects . in summary , an interactive game with dual force and different side ratio developed for this 
 study can help stroke patients train their balance on their stroke affected side , but this 
 method is only effective for patients who have recently experienced stroke and offers little 
 benefit to patients who have recovered a significant degree of mobility .
we were unable to 
 determine the level of baseline mobility at which training ceases to be effective as this 
 study assessed only two cases .
future research should investigate the effects of our 
 rehabilitation protocol in stroke patients with hemiplegia with varying recovery periods , 
 e.g. 6 to 11 months , bbs score below a certain threshold , e.g. 42 , or mas scores below a 
 certain threshold , e.g. 16 to provide further evidence regarding its efficacy .
 [ purpose ] stroke and other cerebrovascular diseases are major causes of adult mobility 
 problems . because stroke immobilizes the affected body part , balance training uses the 
 healthy body part to complete the target movement . 
 the muscle utilization rate on the 
 stroke affected side is often reduced which further hinders affected side functional 
 recovery in rehabilitation . [ subjects and methods ] this study tested a newly - developed 
 interactive device with two force plates to measuring right and left side centers of 
 pressure , to establish its efficacy in the improvement of the static standing ability of 
 patients with hemiplegia . 
 an interactive virtual reality game with different side reaction 
 ratios was used to improve patient balance . 
 the feasibility of the proposed approach was 
 experimentally demonstrated . 
 [ results ] although the non - affected - side is usually used to 
 support the body weight in the standing position , under certain circumstances the patients 
 could switch to using the affected side . a dramatic improvement in static standing balance 
 control 
 was achieved in the eyes open condition . 
 [ conclusion ] the proposed dual force 
 plate technique used in this study separately measured the affected and non - affected - side 
 centers of pressure . based on this approach 
 , different side ratio integration was achieved 
 using an interactive game that helped stroke patients improve balance on the affected 
 side . 
 only the patient who had suffered stroke relatively recently benefited 
 significantly . 
 the proposed technique is of little benefit for patients whose mobility has 
 stagnated to a certain level . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION