foot misalignment ( flatfoot and high arch ) is one of the common orthopedic issues in 
 pediatric health1,2,3 and it causes many injuries 
 in the foot , knee , and lower back3,4,5 . 

almost all children are born with flatfoot and normal foot posture develops during the first 
 decade of life6 , 7 . however , some children have misaligned feet even after10  years of 
 age .
if normal foot posture does not develop created during the 
 elementary school period , foot misalignment continues to during adolescence and into 
 adulthood .
flatfoot and high arch are caused by many factors such as neurological disorders , 
 congenital conditions , and structural anomalies1 , 
 3 .
however , flatfoot and high arch can 
 also be found in otherwise healthy individuals , and in the absence of injury , they can be 
 caused by structural issues such as ligament tension and muscle strength1 , 3 . 

ligament laxity typically improves as bones lengthen with age , and the majority of children 
 develop an arch in the first decade of life11 . in early childhood
, the intrinsic and extrinsic foot muscles are 
 usually strengthened through walking and running . however ,
if the intrinsic and extrinsic 
 foot muscles are not used enough in early childhood , they remain weak .
therefore , improving 
 muscle strength in the foot is one method of treating foot misalignment .
toe grip 
 strength is the strength of the toe flexor muscles , such as the flexor hallucis longus and 
 flexor digitorum longus .
hashimoto et al.s study revealed that toe grip strength training can increase the foot arch 
 in adolescents12 .
toe grip strength is 
 related to foot posture in adolescents13 . 
 however , it is not known if the same relationship between toe grip strength and foot posture 
 is present in children .
the authors hypothesized that there was a relationship between toe 
 grip strength and foot posture in children .
the demonstration of a relationship between foot 
 posture and toe grip strength would highlight the importance of toe grip strength in 
 creation normal foot posture during childhood .
therefore , the authors investigated the 
 relationship between toe grip strength and foot posture in this study .
a total of 619 children ( boys , n = 311 , age = 11.2  0.7  years ; girls , n = 308 , age = 11.3 
  0.7  years ; age expressed as mean  sd ) participated in this study . signed consent was 
 obtained from the principals of five elementary schools in nara prefecture in japan for 
 inclusion of their schools in the study .
demographic data were collected from the returned 
 consent forms , as were the inclusion ( age 1012  years ) and exclusion ( no history of foot 
 surgery or congenital disorders ) criteria . the purpose and methods of the current study were 
 explained to the participants and elementary school teachers in detail in a verbal statement 
 and document .
foot posture was measured using a foot printer ( bauerfeind co. ltd , germany ) .
a static 
 footprint was obtained as each child stood barefoot on the foot printer , with weight 
 normally distributed between both feet .
the dominant foot was identified as that preferred 
 for kicking a ball and we used the posture of the dominant foot in the analysis .
children 
 stood with their feet shoulder width apart and placed their foot at whatever angle they 
 preferred .
the width of the foot at the arch and the width of the heel were measured .
the 
 arch index for each foot was calculated by dividing the former number by the latter , as 
 described by staheli et al14 .
toe grip strength was measured using a t.k.k.3362 toe - grip dynamometer ( takei scientific 
 instruments , niigata , japan ) ( fig .
the protocol for measuring toe grip strength was as described in the studies by 
 uritani et al15 , 16 .
participants sat upright on a chair without leaning on the 
 backrest throughout the toe grip strength measurements .
both of the hips and knees were 
 flexed at about 90 and the ankles were placed in a neutral position and fixed with a strap . 

the first proximal phalanx was positioned at the grip bar , and the heel stopper was adjusted 
 to fit the heel of each participant .
the bar was then gripped with the toes using maximal 
 effort , for about 3 seconds .
toe grip strength of the dominant foot was measured twice . the 
 maximum strength from the two measurements
t.k.k.3362 toe - grip dynamometer at first , participants were classified into flatfoot , normal , and high arch categories , 
 based on the arch index , as measured by their footprint .
an arch index value between 0.44 
 and 0.89 was defined as a normal foot , an index < 0.44 was classified as a high arch , and 
 an index , > 0.89 was classified as a low arch14 .
differences in age , body mass index ( bmi ) , toe grip strength , and 
 gender between the three groups were examined using analysis of variance ( anova ) and a 
  test .
differences in toe grip strength among the 3 groups were examined 
 using analysis of covariance ( ancova ) adjusted for age , bmi and gender .
when a significant 
 effect was found , differences were determined using the turkey - kramer post - hoc test for 
 anova , and the bonferroni post - hoc test for ancova .
statistical analysis were carried out 
 using the spss version 20.0 software package ( spss , chicago , il , usa ) , with a p value < 
 0.05 accepted as significant .
table 1table 1.subject characteristics by foot posture groupall subjects ( n = 619)flatfoot ( n = 110)sdnormal ( n = 468)sdhigh arch ( n = 41)sdage ( yrs)11.10.811.30.711.10.7bmi ( kg / m)17.93.017.42.616.82.3gender ( n boy / % ) 66 / 60.0225 / 48.120 / 48.8the parameters above were analyzed by anova and  test , * p < 0.05 . 
 there were no significant differences between any of these parameters between 
 groups shows the characteristics of the participants .
the anova results showed that 
 there was a significant difference in toe grip strength among the 3 groups ( p < 0.01 ) . 

the values for toe grip strength were 11.0  3.9  kg in flatfoot , 12.6  4.1  kg in normal , 
 and 11.4  3.6 in high arch ( table 2table 2.toe grip strength differences by foot posture groupall subjects ( n = 619)flatfoot ( n = 110)sdnormal ( n = 468)sdhigh arch ( n = 41)sdpost - hoctoe grip strength ( kg)11.03.912.64.111.43.6asignificant differences between flatfoot and normal . * analyzed for anova 
 ( p < 0.01 , post - hoc ; a ) . adjusted for subject age ,
bmi and gender 
 ( anacova ) ( p = 0.01 , post - hoc ; a ) ) . the toe grip strength of the low arch group was significantly lower than the 
 normal group ( p < 0.01 ) and that there was no significant difference between the high 
 arch group and other groups .
in addition , ancova showed a significant difference in toe grip 
 strength among the 3 groups when adjusted for age , bmi , and gender ( f = 5.22 , p = 0.01 ) . 

post - hoc tests indicated that the toe grip strength of the low arch group was significantly 
 lower than in the normal group ( p < 0.01 ) .
the parameters above were analyzed by anova and  test , * p < 0.05 . 

there were no significant differences between any of these parameters between 
 groups significant differences between flatfoot and normal .
* analyzed for anova 
 ( p < 0.01 , post - hoc ; a ) .
adjusted for subject age , bmi and gender 
 ( anacova ) ( p = 0.01 , post - hoc ; a )
our study revealed that toe grip strength was related to foot posture in children and that 
 the toe grip strength of the flatfoot group was weaker than that of the normal group . 

however , there was no significant difference between high arch group and the other groups . 

in addition , toe grip strength was related to foot posture after adjustment for bmi , age , 
 and gender .
foot posture of children is related to bmi , age , and gender17 , 18 , however in this study 
 toe grip strength was related to foot posture , when measurements were adjusted for these 
 factors .
moreover , muscle strength and physique differ with age and gender as children go 
 through their growth period19 , as does 
 the prevalence of flatfoot17 .
foot 
 posture in children is flexible , so the foot arch can easily be decreased by the body weight 
 load .
evan found that foot posture was not related to weight in children20 ; nevertheless , many other studies have 
 identified a correlation between bmi and foot posture17 , 18 , 21 , 22 .
pfeiffer et al.s study 
 revealed that flatfoot was present in 62% of obese , 51% in overweight , and 42% of young 
 children with normal body weight17 . in 
 the present study ,
toe grip strength was related to foot posture adjusted for bmi , age , and 
 gender .
two possible explanations for the relationship between toe grip strength and foot posture 
 are proposed here .
first , toe flexor muscles lift up the navicular and make a medial 
 longitudinal arch .
toe grip strength comes from the toe flexor muscles , such as the flexor 
 hallucis longus and flexor digitorum longus , and these muscles pass under the navicular .
the 
 navicular height is the index of the longitudinal medial arch and by definition , flatfoot 
 children have a diminished or absent longitudinal medial arch .
osseous structures , 
 ligaments , tendons , and muscles create navicular height23 , 24 , and toe grip strength 
 is one of the factors in creating the foot arch .
this is supported by hashimoto s study , 
 which revealed that toe grip strength training increases the foot arch height in 
 adolescents12 .
therefore , toe grip 
 strength is related to foot arch , and toe grip strength is different between flatfoot and 
 normal children .
second , toe flexor muscles are stretched in flatfoot children , so the muscles can not 
 contract with maximal strength .
muscles contraction strength exhibits a length - tension 
 relationship25,26,27 , where optimal 
 contraction occurs when the muscle is at the appropriate length and not overly stretched or 
 compressed . in our study ,
however , subjects who had severe high arch due to neurological 
 disorders were excluded from our study , and no significant differences were seen between the 
 high arch group and the other groups .
this is the second reason why toe grip strength of low 
 arch feet was low .
the present study revealed that there was a significant difference in toe grip strength 
 between flatfoot and normal children . a recent systematic review of current research 
 demonstrated that there is very limited evidence for the efficacy of nonsurgical 
 interventions in children with flatfoot28 .
usually , a shoe or insole is used to treat symptomatic flatfoot in 
 children . however , these treatments can not permanently correct foot alignment1 , 29 . 

flatfoot in children is caused by ligament laxity or foot muscle weakness , and ligament 
 laxity is not changeable after foot posture develops .
however , muscle strength is 
 changeable , so increasing toe grip strength has the possibility to improve flatfoot .
this 
 idea is supported by the present study , which reveals that toe grip strength is related to 
 foot posture in children .
therefore , training to increase toe grip strength during childhood 
 may prevent flatfoot and improve foot posture .
first , this study was a 
 cross - sectional design , so the relationship between cause and effect is unknown .
therefore , 
 further research is needed to reveal whether correlated change in grip strength and foot 
 posture can be seen with individuals .
the foot is a complex structure , so more detailed measurements of foot posture 
 should be evaluated .
third , foot posture is related to genetics and ethnicity , but these 
 factors were not considered . despite these limitations , the findings from the present study 
 provide valuable information and illustrate the importance of toe grip strength .
 [ purpose ] this study investigated the relationship between toe grip strength and foot 
 posture in children . [ subjects and methods ] a total of 619 children participated in this 
 study . 
 the foot posture of the participants was measured using a foot printer and toe grip 
 strength was measured using a toe grip dynamometer . 
 children were classified into 3 
 groups ; flatfoot , normal , and high arch , according to staheli s arch index . 
 the 
 differences in demographic data and toe grip strength among each foot posture group were 
 analyzed by analysis of variance . 
 additionally , toe grip strength differences were 
 analyzed by analysis of covariance , adjusted to body mass index , age , and gender . 
 
 [ results ] the number of participants classified as flatfoot , normal , and high arch were 
 110 ( 17.8% ) , 468 ( 75.6% ) , and 41 ( 6.6% ) , respectively . 
 the toe grip strength of flatfoot 
 children was significantly lower than in normal children , as shown by both analysis of 
 variance and analysis of covariance . 
 [ conclusion ] a significant difference was detected in 
 toe grip strength between the low arch and normal foot groups . therefore , it is suggested 
 that training to increase toe grip strength during childhood may prevent the formation of 
 flat feet or help in the development of arch . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION