balance is the ability to maintain one s center of gravity with minimum shaking within the 
 basal plane , while postural balance is the ability to continuously maintain equilibrium 
 within the basal plane according to one s center of mass ( com ) and maintain postural control 
 to cope with diverse motions and external swaying1 .
balance abilities are complicated functions derived from 
 integration of the nervous and musculoskeletal systems that involve diverse functional 
 factors such as integration of the stimuli emanating from the visual , hearing , and 
 vestibular organs ; proprioceptors and sensory receptors in the central nervous system ; 
 visual spatial cognitive ability ; muscle tone that responds to environmental changes both 
 quickly and accurately ; muscular endurance ; and joint flexibility2 . mental practice , which is frequently used to improve balance ability ,
was recently 
 presented in diverse areas for the purpose of mastering motor skills and improving motor 
 learning3 .
mental practice is a motor 
 learning method that imparts and improves motor skills and involves imagining movement 
 scenes without making any body movements .
gerardin et al.4 reported that imagining movement scenes and performing exercises 
 identically activated the frontal lobe .
although diverse studies on mental practice have 
 been conducted to date , most addressed improving the upper limb functions of stroke 
 patients , while few have examined mental practice as an approach to improving balance 
 ability .
therefore , the purpose of the present study was to examine the effects of mental 
 practice on the balance abilities of normal individuals .
thirty subjects were randomly assigned to an experimental or control group ( n=15 each ) .
the 
 selection criteria utilized were as follows : no history of orthopedic surgery on a lower 
 limb , never taken any drug due to a neurologic problem , and no musculoskeletal system 
 disease .
the general characteristics of the study subjects are summarized in table 1table 1.general characteristics of the study subjects ( n=30)characteristiceg ( n=15)cg ( n=15)age ( years)21.8 ( 2.0)22.6 ( 1.3)height ( cm)166.5 ( 5.4)169.7 ( 3.3)weight ( kg)60.2 ( 8.1)62.2 ( 6.5)eg : experimental group ; cg : control group .
values are expressed as mean ( sd ) .. the research ethics committee of eulji university hospital approved the 
 study , and all subjects provided informed written consent prior to participating .
participants in both groups performed balance training in a seated position on a gym ball 
 for 20 minutes per session , five sessions per week , for 4 weeks .
participants in the 
 experimental group also completed a mental practice regimen for 10 minutes before each 
 balance training session .
the gym ball exercises included maintaining proper posture in a seated position on a gym 
 ball , laterally moving one s body weight , and moving one s body weight back and forth .
for 
 the mental practice sessions , the subjects were allowed to maintain a comfortable seated 
 position on a chair and the laboratory environment was kept dark and as quite as possible . 

the subjects listened to a voice file describing the imaginary act of maintaining balance in 
 a seated position on a gym ball . during the warm - up stage ,
muscle relaxing training was 
 implemented for 2 minutes to ensure psychological stability . in the recordings ,
the 
 first - person viewpoint was used as described by the classification methods presented by 
 mahoney and avener5 . during the mental 
 practice exercises ,
each subject was allowed to maximally feel the sole pressure and 
 proprioceptive sensory information from the ankles , knees , and hip joints when carrying out 
 the weight shift training ; the mental practice was performed for 6 minutes .
the cooling down 
 stage was used to direct the subject back to reality and become psychologically stabilized . 

after the intervention , balance measuring equipment ( good balance , metitur , finland ) was 
 used to quantitatively measure each subject s balance ability . to measure balance function , 
 the subject was instructed to stand on a triangle platform and maintain a symmetrical 
 posture with the feet shoulder width apart .
a visual fixed point was located in front of the 
 subject to minimize head movements .
the subject s arms were placed comfortably at the hip 
 joints and the center of pressure ( cop ) was measured for 30 seconds in the standing posture 
 with the eyes open .
. 
 means and standard deviations were calculated for all variables . before the intervention , 
 group differences in general characteristics were compared using the independent t - tests and 
  tests .
intragroup comparisons of variables before and after training were 
 conducted using paired sample t - tests .
intergroup comparisons of pre- and post - test 
 differences in variables were performed using the independent t - test .
intergroup effect 
 sizes were calculated using the cohen d coefficient6 , where an effect size < 0.2 reflected a negligible mean 
 difference ; 0.20.5 , a small difference ; 0.50.8 , a moderate difference ; and > 0.8 , a 
 large difference .
the statistical analysis was performed at the 95% confidence level , and p 
 values < 0.05 were considered significant .
table 1 provides a summary of the subjects 
 clinical and demographic features ( n=30 ) .
the characteristics of the two groups before and 
 after intervention are shown in table 
 2table 2.pre- versus post - test balance variables in the experimental and control 
 groupseg ( n=15)cg ( n=15)pre - testpost - testpre - testpost - testmediolateral ( mm / s)135.24 ( 35.62)110.25 ( 36.58)137.69 ( 30.24)130.85 ( 20.31)anteroposterior ( mm / s)195.21 ( 38.21)182.62 ( 40.21)193.26 ( 40.13)187.84 ( 41.74)index of balance function ( score)75.43 ( 12.12)82.64 ( 8.56)74.23 ( 7.32)79.35 ( 6.24)time ( s)22.72 ( 3.52)13.52 ( 2.54)23.74 ( 3.62)18.45 ( 2.45)eg : experimental group ; cg : control group .
values are presented as mean 
 ( sd ) . * significant difference from pre - test , p<0.05 .
the experimental group showed significant increments in the mediolateral , 
 index of balance function , and time variables compared to the pre - intervention results 
 ( p<0.05 ) .
in addition , the control group showed significant increments in the index of 
 balance function and time variables compared to the pre - intervention results ( p<0.05 ) . 

significant intergroup differences were observed for post - training gains in the 
 mediolateral , index of balance function , and time variables ( p<0.05 ) .
the effect sizes of 
 the gains in the experimental and control groups were high for the index of balance function 
 and time variables ( effect sizes=1.12 and 0.86 , respectively ) .
mental practice could be described as  imagining movements for body activities without any 
 gross motor activity6 .
mental practice 
 enhances motor skills by facilitating the imagining of proprioceptive senses such as visual , 
 auditory , tactile , motor , olfactory , and taste without any external stimuli .
theories that explain the mechanism of mental practice include paivio s theory7 , the psychoneuromuscular theory8 , and the cognitive  symbolio learning 
 theory9 .
paivio s theory proposes that visually imagining the carrying out of movements promotes 
 cognitive function and motivation7 , 
 whereas the psychoneuromuscular theory purports that practicing tasks to be performed in 
 advance using imagination reinforces the neurological pathways necessary to conduct the 
 required movements , thus enhancing one s ability to perform the movements8 . on the other hand , the cognitive 
symbolio 
 learning theory proposes that imagining movements provides opportunities to practice their 
 order and enables advanced planning , thus improving efficiency when the movements are 
 actually carried out9 .
weiss et al.10 reported that excitation 
 was observed in the same brain regions during mental practice and physical training , 
 especially the supplementary motor area of the brain during mental practice .
based on the results of previous studies , it can be said that the neuromuscular responses 
 that appear when movement performance is imagined are similar to those observed when the 
 movements are actually performed .
therefore , imagining the movements that are used to carry 
 out a task reinforces the neurological pathways required to actually perform the movements , 
 thereby improving one s ability to perform them .
the results of the present study suggest 
 that balance ability is improved in accordance with the psychoneuromuscular theory . the limitations of the present study are that it was difficult to evaluate whether the 
 imagining practice learning level was appropriate and the intervention period was too short 
 to generalize the results . in addition , subjects could not be controlled after the 
 experimental period and the number of subjects was small .
therefore , in future studies , if 
 the experimental intervention period is extended and environmental factors are more 
 thoroughly addressed , positive generalizable results might be obtained .
in addition , if 
 visual and perceptive sources of stimuli were applied with the auditory stimulus , the 
 effects of the mental practice exercise might be further enhanced .
 [ purpose ] this study aimed to examine the effects of mental practice on the balance 
 abilities of normal individuals . 
 [ subjects and methods ] thirty subjects were randomly 
 assigned to an experimental or control group ( n=15 each ) . 
 participants in both groups 
 performed balance training in a seated position on a gym ball for 20 minutes per session , 
 five sessions per week , for 4 weeks . 
 members of the experimental group also performed 
 mental practice for 10 minutes before the balance training . 
 after the intervention , 
 balance measuring equipment ( good balance , metitur , finland ) was used to quantitatively 
 measure balance ability . 
 [ results ] significant post - training gains were observed in the 
 mediolateral , index of balance function , and time variables of participants of the 
 experimental group . 
 [ conclusion ] the application of mental practice with balance training 
 positively affected balance ability . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION