stroke is a disease that causes sudden local neurological deficit symptoms due to a 
 cerebrovascular accident1 .
stroke may 
 decrease postural control and balance ability due to sensory disability , motor disturbance , 
 muscular weakness , and asymmetric postures resulting from central nervous system damage2
. reduced postural control and balance 
 ability decreases overall physical function , making independent activities of daily living 
 difficult for stroke patients , and increases the risk of falls .
therefore , improving stroke 
 patients balance ability is an important therapeutic objective3 . with regard to this issue
, a recent cross - sectional study 
 revealed that stroke patients trunk control ability was correlated with balance , gait , and 
 functional abilities4 .
exercises intended to improve stroke patients trunk control have been extensively studied 
 in recent years .
verheyden et al.2 
 reported that a group of stroke patients that performed trunk exercises on plinths showed 
 better improvement in trunk control than a group that received only conventional physical 
 therapy .
pereira et al.5 conducted trunk 
 flexion and extension , and compared trunk muscle activities measured by semg on the affected 
 and unaffected sides of stroke patients .
karthikbabu et al.6 studied the effect of exercise using swiss balls on the improvement 
 of trunk muscles .
although many exercise programs for trunk control have been implemented , 
 there are few programs that can improve subjects balance while maintaining their interest . 

after the first horse riding studies were performed with patients with neurological damage , 
 hippotherapy was used only to treat children with neurological disorders , mainly cerebral 
 palsy , to improve their postural control and promote their normal development and functional 
 recovery7 , 8 .
the horse s gait is repetitive and rhythmic , and 
 causes the center of gravity to move in anterior - posterior , lateral , and upward - downward 
 directions .
since the patterns of these movements are similar to those of the movements of 
 the trunk and pelvis during human gait , such exercise is expected to make the subjects feel 
 as if they were walking9 .
hippotherapy is 
 effective in terms of psychological motivation because it arouses subjects interest in 
 participating in the therapy9 , 10 , and helps in the recovery of many physical functions . 

hippotherapy increases the range of joint motion , strengthens muscles , and improves muscle 
 tone , postural control , and balance and equilibrium ability .
improvements in postural 
 control and balance ability are achieved through stimulation of the upper motor neurons 
 through proprioceptive sensory stimulation inputs11 , 
 12 . despite these therapeutic effects , 

no studies have been conducted on the changes in muscles related to stroke patients 
 stability and balance after hippotherapy . in this study , the improvement in stroke patients 
 trunk control and changes in abdominal muscle thicknesses after horse riding simulation 
 training were examined .
the purpose of this study was explained to patients diagnosed with stroke at d general 
 hospital in busan , south korea .
patients willing to participate in the study were recruited , 
 and those who satisfied the selection criteria were randomly assigned to a control or 
 experimental group ( 15 patients per group ) .
subject selection criteria were as follows : patients with hemiplegia and no previous 
 experience with hippotherapy who could follow verbal instructions , sit and walk 
 independently ( regardless of the use of walking aids ) , and had no restriction in the range 
 of joint motion .
then , the 
 experimental group performed horse riding simulation training , while the control group 
 performed trunk exercises using swiss balls .
training was performed for 30  min per session , 
 three sessions per week for a total of eight weeks10 .
subjects general characteristic ( n = 30)groupcontrol group(n = 15)experimental group(n = 15)age ( years)56.57.555.16.1height ( cm)163.38.2165.18.5weight ( kg)63.58.565.49.8sex ( male / female)8 / 77 / 8cause of brain damage(cerebral hemorrhage /cerebral 

infarction)8 / 76 / 9affected side ( right / left)9 / 610 / 5data are mean  sd . all subjects agreed in writing to participate in this study after receiving a detailed 
 explanation of the experimental procedure , and possible side effects of the intervention . 
 the experiment was conducted after receiving approval from the human subjects research 
 ethics committee of dong - eui medical center ( demcirb-2013 - 1001 ) .
the horse riding simulator ( eu6441 core muscle trainer ; panasonic , japan ) used is designed 
 to simulate the effects of horse riding exercises in an indoor environment using 
 three - directional movements ( anterior - posterior , lateral , upward - downward ) , and has three 
 different programs and nine levels of exercise intensity .
a therapist and an assistant 
 monitored each subject during horse riding training . a balance ability measuring and training system ( an analysis system with biofeedback , 
 ap1153 ; biorescue , france ) was used to evaluate subjects balance ability .
static balance 
 ability ( center of pressure [ cop ] path length and cop travel speed ) was measured while 
 subjects stood for 60  s with their eyes open .
the subjects were prevented from seeing the 
 monitor to avoid visual feedback , and the position of the feet was maintained during 
 repeated measurements to eliminate errors resulting from changes in foot positions .
all 
 tests were performed three times , and average values were calculated . ultrasonic imaging equipment ( sonoace x4 ; medison , korea )
subjects were instructed to bend their knees to 90 and to maintain a 
 comfortable posture in a supine position .
linear probes were positioned on both sides , 
 midway between the bottom of the rib cage and the top of the iliac crest .
the 
 thicknesses of the external oblique , internal oblique , and transversus abdominis muscles 
 were measured three times and their average values were calculated .
the paired t - test was conducted to 
 compare the results before and after the intervention within each group and the independent 
 t - test was used to compare the exercise and control groups before and after the experiment . 

the experimental but not the control group showed statistically significant differences 
 ( p<0.01 ) between the cop path lengths of before and after the intervention .
the 
 differences between the two groups were not significant before the experiment , but were 
 statistically significant ( p<0.05 ) after the intervention ( table 2table 2 .
changes in static balance following horse riding simulation traininggrouppre - testpost- testcenter of pressure path length ( cm)control14.55.914.45.8experimental15.95.112.24.3 center of pressure travel speed ( mm / s)control0.70.30.70.2experimental0.70.30.60.2   different superscripts within the same columns indicate significant 
 differences ( p<0.05 ) ) .   different superscripts within the same columns indicate significant 
 differences ( p<0.05 ) the experimental , but not the control group , showed statistically significant differences 
 ( p<0.05 ) between the speeds of the cop travel of before and after the intervention .
there 
 was no significant difference between the control and the experimental group before the 
 experiment , but the speed of cop travel decreased more in the experimental group than in the 
 control group after the experiment , and this difference was statistically significant 
 ( p<0.05 ; table 2 ) .
changes in abdominal muscle thicknesses after training were observed in the experimental 
 group . before training , tra and io did not show any significant differences between the 
 affected and unaffected sides .
in contrast , eo showed significant differences : 5.71.6  mm on 
 the unaffected side and 4.71.4  mm on the affected side ( p<0.05 ) .
after eight weeks of 
 training , tra , io , and eo on the unaffected side did not show any changes compared to before 
 the training .
tra and io on the affected side did not show any changes after training , but the eo 
 thickness significantly increased from 4.71.4  mm to 5.21.6  mm .
total abdominal muscle 
 thickness differed significantly before training between the affected and unaffected sides 
 ( 13.52.7  mm and 14.33.0  mm , respectively ) .
after eight weeks of training , both sides 
 showed slight increases , with final values of 14.12.9  mm on the affected side and 
 14.35.8  mm on the unaffected side , but these differences were not statistically significant 
 ( p>0.05 ; table 3table 3 .
changes in abdominal muscle thickness following horse riding simulation training 
 ( experimental group ; n = 15)sidepre - testpost - testtraa2.50.82.70.9na2.50.62.60.6ioa6.30.156.31.6na6.00.166.11.8eoa4.71.4 5.21.6na5.71.65.71.4totala13.52.7 14.12.9na14.33.014.35.8a , affected side ; na , non - affected side ; abdominal muscle thicknesses unit :  mm . 

different superscripts within the same columns indicate significant differences 
 ( p<0.05 ) ) . a , affected side ; na , non - affected side ; abdominal muscle thicknesses unit :  mm . 

this study examined the effects of horse riding simulation training on the improvement of 
 balance ability ( which is an important issue for stroke patients ) , and the changes in 
 abdominal muscle thicknesses of stroke patients . the distance and speed of center of gravity 
 movements
were measured using a biorescue system , and changes in abdominal muscle 
 thicknesses were observed by ultrasonography .
the cop path lengths of before and after the intervention were similar in the control group 
 ( p>0.05 ) , but significantly decreased in the experimental group after horse riding 
 training .
the changes in the speed of cop travel showed that body sway remarkably decreased 
 in the experimental group after training in comparison with the control group .
these changes 
 presumably occurred because the trunks of the subjects became more stable as a result of 
 horse riding simulation training , reducing body sway and shaking .
regarding abdominal muscle thicknesses , eo was thinner before training on the affected side 
 than on the unaffected side , resulting in a difference in total abdominal muscle thickness 
 on the affected and unaffected sides .
this is consistent with the results of the study by 
 english et al.14 , which measured the 
 abdominal muscles of stroke patients ( 65  years old or older ) at rest .
although the mean age 
 of the subjects in our present study was somewhat lower ( 55.16.1  years ) , similar results 
 were obtained .
even 
 though eo is mainly mobilized during trunk rotation movements , pereria et al.5 reported that eo was activated when stroke 
 patients performed exercises that involved lifting of both legs , and this reportedly 
 occurred to compensate for the inactivity of the rectus abdominis .
similarly , in our present 
 study the eo muscle may have activated more to compensate for the weakness of the rectus 
 abdominal muscles on the affected side of the stroke patients .
another reason for higher eo 
 activation on the affected side could be that it is located closer to the surface layer than 
 tra and io , which would affect thickness changes because horse riding simulation exercises 
 induce multi - directional movements .
although diverse balance training programs for stroke patients have been reported , 
 therapeutic approaches using horse riding have rarely been studied with stroke patients as 
 subjects .
some studies have been conducted with persons with neurological disorders , in 
 particular children with cerebral palsy7 , 8 . therefore , comparison of our 
 present results with those of previous studies was difficult .
future studies of horse riding 
 simulation may lead to an improvement in stroke patients balance ability .
horse riding 
 simulation training can be fun and interesting for patients , which may increase their 
 motivation to actively participate in exercise program and thus enhance the improvement of 
 neurologic functions9 , 10 .
second , ultrasonic measurement was conducted in a steady state in a supine 
 position .
third , since the damaged sites and symptoms differed among subjects , standard 
 subjects could not be selected .
therefore , in future studies , the effects of hippotherapy 
 on stroke patients should be examined with a more efficient control and the selection of a 
 wide range of subjects .
additional information should be provided by comparison ( during 
 ultrasonic measurement ) of the degrees of contraction on the affected and unaffected 
 sides . in conclusion ,
horse riding simulation training may reduce the distance and speed of the 
 center of gravity movements of stroke patients and reduce the asymmetry of the abdominal 
 muscles . to improve stroke patients balance ability , diverse uses of horse riding 
 simulation training should be considered .
   [ purpose ] the purpose of this study was to assess the effects of horse riding simulation 
 training on changes in balance ability and abdominal muscle thicknesses of stroke 
 patients . 
 [ subjects ] thirty stroke patients with hemiplegia were recruited , and they were 
 randomly assigned to a control or experimental group . [ methods ] the experimental group 
 performed horse riding simulation training , whereas the control group performed trunk 
 exercises for 8 weeks . 
 balance ability was measured using a biorescue system . 
 the 
 thicknesses of subjects external oblique , internal oblique , and transversus abdominis 
 muscles were measured by ultrasonic imaging . [ results ] in the experimental group , balance 
 ability 
 was significantly improved after training . 
 similarly , the thickness of the 
 abdominal muscles on the affected side changed after training in the experimental group , 
 whereas the control group showed no statistically significant changes . [ conclusion ] 
 we 
 suggest that horse riding simulation training is more effective than trunk exercises at 
 reducing the center of pressure path length and travel speed and improving the asymmetry 
 of the abdominal muscles of stroke patients . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION