although the feet occupy only 5% of the areas of the human body , they control postures 
 through afferent information obtained through the sense of the soles , provide stability for 
 maintenance of balance , and absorb impacts1 .
the deformation into flatfoot is induced when the medial longitudinal arch ( mla ) has 
 descended because the arch had been excessively relaxed to the extent that the arch can not 
 be maintained and causes the feet to be excessively pronated compared to normal feet so that 
 heel eversion appears and the weight load is shifted inward to compress the mla2 , 3 . 

when the mla has descended or has been completely lost leading to structural or functional 
 deformation , the ability to absorb impacts will decrease and the sense of balance will be 
 lost so that stability decreases during walking or running leading to walking difficulties 
 and endurance decreases4 , 5 .
foot wedges are clinically applied for correction of diverse foot diseases and for 
 maintenance of balance6 , and customized 
 insoles are used for correction of pronated feet7 .
insoles widen the contact surface of the sole to improve stability 
 during weight bearing , reduce turning actions when the foot has been pronated or supinated , 
 and can be applied to the medial longitudinal arch of the foot to increase the sensory 
 inputs of the sole8 .
study results have 
 been reported indicating that the conservative intervention methods of foot orthotics using 
 support for the arch of the foot improve malformations of the foot , are effective for leg 
 alignment and pain control , and improve gaits to become normal7 .
the previous reported that sole stimulation could improve the motor sensation and postural 
 movements to maintain proper postures9 . 

sensory - motor training applies the proprioceptive feedback of the body to activate the 
 abductor pollicis muscle and the flexor hallucis brevis muscle , which are the intrinsic 
 muscles of the feet important for maintenance of the mla , to help the formation of the arch 
 and the maintenance of the balance of the body10 .
in addition , sensory - motor training delivers proprioceptive 
 sensory signals to the sensory cortex area of the brain and affects even the motor area to 
 improve the asymmetric muscle tone of the sole and draw appropriate new movements thereby 
 improving the motor sensation and postural disturbance to help maintaining the balance and 
 stability of the body9 , 11 .
reported that sensory stimulation 
 training was helpful for flatfoot patients to form and support the arch12 . among exercise methods to improve flatfoot , toe bending exercises or towel - curl exercises 

mainly mobilize the extrinsic muscles of the foot such as the flexor digitorum longus 
 muscle13 .
however , short foot exercises 
 ( sfe ) are sensory - motor training that activates the intrinsic muscles of the foot and 
 actively forms the longitudinal arch and the horizontal arch14 , 15 .
although studies 
 utilizing foot orthotics such as therapeutic footwear , wedges , and insoles to improve the 
 mla of flatfoot have been mainly conducted , studies for improvement of flatfoot that 
 compared foot orthotics with sensory - motor training such as sfe are insufficient .
therefore , the present study is intended to improve the mla of flatfoot and investigate the 
 effects of the improvement on the dynamic balance of the feet and the lower limbs to 
 identify effective application methods .
the subjects of the present study were 14 university students ( males 10 , females 4 ) aged 21 
 to 26  years sampled from among students in the health college of s university in asan - si , 
 chungcheongnam - do and the experiments were conducted from october to december 2015 . before 
 the experiments , the overall details of the purpose and procedure of the present study were 
 explained to all subjects pursuant to the ethical standard of the declaration of helsinki 
 and the subject voluntarily agreed to participate in the experiments .
the subjects that 
 participated in the experiments were randomly assigned to an sfe group of seven subjects and 
 an arch support insoles ( asi ) group of seven subjects .
the selection criteria for participating subjects regarded the foot used to kick balls as 
 the dominant foot to select subjects with flatfoot .
navicular drop tests ( ndt ) were 
 conducted to select those that had flexible flatfoot with a 10  cm or larger difference in 
 the navicular tuberosity heights and those that were performing lower limb exercises 
 separately , or had any foot hypoesthesia , fracture , dislocation , skin disease , or vascular 
 disease were excluded .
the subjects 
 general characteristics are as shown in table 
 1table 1.general characteristics of the subjectssfe group ( n=7)asi group ( n=7)gender ( male / female)6/14/3age ( years)24.0  1.924.1  1.5height ( cm)172.2  6.9167.0  6.7weight ( kg)68.2  12.963.3  17.6mean  sd . and the sfe group s mean age , height , and weight were 24.0  1.9  years , 172.2 
  6.9  cm , and 68.2  12.9  kg respectively .
the asi group s mean age , height , and weight were 
 24.1  1.5  years , 167.0  6.7  cm , and 63.3  17.6  kg respectively .
sfe was implemented as sensory - motor training for improvement in the flatfoot of the 
 experimental group . before the intervention ,
thereafter , each subject was instructed to sit 
 on a height - adjustable chair and bend the hip joint , knee joints , and ankle joints to 90 
 and a towel was placed below the feet .
thereafter , the subject was instructed to pull the 
 head of the first metatarsal bone toward the heel without bending the toes and maintain the 
 state for 20 sec to form the mla . during the exercise , to prevent the forefoot and the heel 
 from being lifted off the ground and smoothly induce the flexion of the head of the 
 metatarsal bone , the measurer gently held the instep and the heel15 .
the posture was maintained for 10 sec followed by 5 sec 
 and this process was implemented for 30 minutes per time , three times per week for a total 
 of five weeks . as a method for improvement in the flatfoot of the control group ,
insoles were applied as 
 medial arch support structures . to make the insoles , the foot shape of each subject was 
 sketched on 3.2  mm thick aquaplast - t ( sammons preston rolyan , usa ) , which is a 
 thermoplastic material .
thereafter , the aquaplast - t was cut out using scissors , 
 wetted with 100  c water , and attached to the sole of the subject to copy the foot and the 
 height of the arch .
thereafter , the mla was made with a shore value of 20 and a height of 
 at least 15 mm16 .
the insoles made as 
 such were given to the subjects and the subjects were instructed to put the insoles into 
 their running shoes and walk on flatlands for 30 minutes per time , three times per week for 
 a total of five weeks .
ndts were conducted to measure changes in the height of the mla . in the ndt ,
each subject 
 was instructed to sit on a chair with the knee joint bent to 90 and align the second toe 
 and the knee so that the subtalar joint was placed on the neutral position and under a 
 non - weight bearing condition , the distance from the ground to the navicular tuberosity was 
 measured and marked .
thereafter , the distance from the ground to the navicular tuberosity 
 was measured in a standing position with the feet place at shoulder width and weight bearing 
 by the two feet . using a plastic ruler and a 35 index card ,
the difference in the height of 
 the navicular tuberosity between the non - weight bearing(sitting position ) position and the 
 weight bearing ( standing position ) position was measured three times repeatedly and the 
 average value was used .
y - balance tests ( ybt ) ( move2perform , evansville , in , usa ) were conducted to measure the 
 dynamic balance ability of the leg .
the y - balance test ( ybt ) kit consists of three 
 directional ( anterior , posteromedial , posterolateral ) pvc pipe graduated rulers .
each 
 subject stood on the platform located on the center on the ybt kit with the bare foot of the 
 leg to be measured and pushed the reach indicator placed on the pvc pipe graduated ruler 
 with the other leg and the maximum reached distance was measured .
the pvc pipe graduated 
 ruler has 0.5  cm grades and thus the distance was recorded in 0.5  cm units . during the 
 measurement , considering the reaching ability depending on leg lengths , the leg length of 
 each subject
was measured and normalized and to minimize learning effects on measurement , 
 reaching was practiced two times in each direction before measurement .
the measurement was 
 performed in the same order of directions and each distance was measured two times and the 
 average value was calculated .
normalized composite reach distance was computed for each leg 
 as the sum of the maximum reach distances ( in centimeter ) in the 3 directions , divided by 3 
 times the limb length , and then multiplied by 10017 .
the general 
 characteristics of the subjects were presented as means and standard deviations using 
 descriptive statistics ( table 1 ) .
independent 
 t - tests were conducted to compare the amounts of changes between the two groups and paired 
 t - tests were used to measure differences before and after experiment in each group .
changes in the ndt and ybt of the sfe group and the asi group are as shown in table 2table 2.comparison of changes in navicular drop height and dynamic balance between the 
 groupsvariablesfe groupasi grouppre - testpost - testpre - testpost - testnavicular drop test ( mm)11.4  1.67.7  1.1*12.2  1.810.5  1.7y balance test ( % ) 74.3  8.382.4  7.472.4  7.174.2  7.2mean  sd . * significant differences between the sfe and the asi groups 
 ( p<0.05 ) .
significant differences between pre- and post - tests ( p<0.05 ) . according to the results on inter - group ndt comparisons , the values of
the 
 sfe group significantly decreased after intervention compared to the asi group and according 
 to the results of ybt comparisons , the values of the sfe group significantly decreased after 
 intervention compared to the asi group ( p<0.05 ) . in intra - group ndt comparison between 
 before and after intervention , whereas the sfe group showed significant decreases , the asi 
 group showed no significant difference and in intra - group ybt comparison , both the sfe group 
 and the asi group showed significant increases ( p<0.05 ) .
in the case of flatfoot , as the pronated state of the heel is maintained , the talus bone is 
 moved to the inside of the sole leading to the disappearance of the medial longitudinal arch 
 so that the ability to accommodate and distribute the weight is reduced compared to normal 
 persons3 .
structural deformation of the 
 feet leads to lesions in the ankle joint and the feet and problems in lower limb joints , 
 results in early fatigue and pain due to the excessive compensating actions of the intrinsic 
 muscles and the extrinsic muscles , and causes problems in the stability and balance of the 
 feet during gaits18 . to improve these 
 flatfoot conditions , methods that correct the mla using foot orthotics or therapeutic 
 footwear are universally used15
other 
 intervention methods include sfe for strengthening the intrinsic muscles and extrinsic 
 muscles of the foot through sensory - motor training .
presented sfe as the most 
 positive method among methods of correcting the eversion of the subtalar articulation19 .
the sfe induces the head of the 
 metatarsal bone to approach the heel without bending the toes in a state where the weight is 
 borne15 . in the present study
, attempts were made to improve flatfoot conditions through changes in 
 the height of the mla by applying sfe for six weeks . according to the results of measurement 
 using ndt , the descending distance of the navicular bone decreased from 11.4  1.6  mm before 
 intervention to 7.7  1.1  mm after intervention indicating that sfe was effective .
however , 
 in the asi group , changes in the medial longitudinal arch were not significant . in a study 
 conducted by allen & glasoe , the mean descending distance of the mla
this indicates that a 
 flexible flatfoot can form ab arch close to that of normal feet through exercise through sfe 
 for six weeks .
reported that towel - curl exercises implemented for four weeks as 
 foot intrinsic muscle strengthening exercises were effective21 and jung et al . reported that when toe curl exercises and arch 
 formation exercises were applied , the rear foot angle significantly decreased while foot 
 intrinsic muscle strength was improved15 .
reported that changes in the structure of the arch of the sole affected 
 balance ability and gait ability7 . in the 
 present study ,
when dynamic balance was measured using ybt , both the sfe group and the asi 
 group showed significant improvement between before and after intervention within each 
 group .
this is considered attributable to the fact that short foot exercises improved the 
 functions and activity of the abductor pollicis muscle that plays the role of bearing the 
 weight and pushing the body forward during push off in gaits and the flexor hallucis brevis 
 muscle that maintains the mla during the terminal stance in gaits to maintain foot 
 stability10 .
the reason why dynamic 
 balance ability was significantly improved in the group applied with arch support insoles is 
 considered to be the fact that the support for the medial longitudinal arch reduced maximum 
 load reactions to improve leg stability thereby brining about dynamic biomechanical 
 effects11 . in the present study
, short foot exercises and arch support insoles were applied to improve 
 flatfoot conditions and it could be seen that as the medial longitudinal arch was improved , 
 dynamic balance ability was improved .
in addition , it could be seen that sensory - motor 
 training such as short foot exercises was more effective than conservative treatment methods 
 such as arch support insoles .
in addition , it could be seen that the intervention period of 
 six weeks was not sufficient to improve the medial longitudinal arch using arch support 
 insoles .
detailed comparison studies combining sensory - motor training of the foot and arch 
 support insoles with more sufficient intervention periods are necessary .
 [ purpose ] the purpose of the present study is to apply short foot exercises and arch 
 support insoles in order to improve the medial longitudinal arch of flatfoot and compare 
 the results to identify the effects of the foregoing exercises on the dynamic balance of 
 the feet and the lower limbs . 
 [ subjects and methods ] fourteen university students with 
 flexible flatfoot were selected by conducting navicular drop tests and randomly assigned 
 to a short foot exercise group of seven subjects and an arch support insoles group of 
 seven subjects . 
 the intervention in the experiment was implemented for 30 minutes per 
 time , three times per week for five weeks in total . 
 [ results ] in inter - group comparison 
 conducted through navicular drop tests and y - balance tests , the short foot exercise group 
 showed significant differences . among intra - group comparisons , in navicular drop tests , 
 
 the short foot exercise group showed significant decreases . 
 in y - balance tests , both the 
 short foot exercise group and the arch support insoles group showed significant increases . 
 
 [ conclusion ] in the present study , it could be seen that to improve flatfoot , applying 
 short foot exercises was more effective than applying arch support insoles in terms of 
 medial longitudinal arch improvement and dynamic balance ability . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION