the foot consists of the medial and lateral longitudinal arches , and the transverse arch of 
 the forefoot ( taf ) .
the arch of the foot works as a shock absorber to attenuate weight 
 loading during the early stance phase of gait .
the arch also works as a rigid lever to 
 propel body mass efficiency during the late stance phase of gait1 , 2 .
clinical 
 measurements of foot arch structures are mainly obtained to evaluate the medial longitudinal 
 arch using the arch height index and the navicular drop test1 , 3,4,5,6 .
several clinical research studies have reported on the relationship 
 between athletic lower extremity disorders and the medial longitudinal arches of the foot . 

knee joint disorders occurred more often in athletes with excessively pronated and supinated 
 feet7 . in long distance runners with a 
 high arch feet ,
ankle joint disorders occur more often than in those without a high medial 
 longitudinal arch , whereas in those with a low longitudinal medial arch , knee joint 
 disorders occur more often8 , 9 .
furthermore , regarding relationships between the medial 
 longitudinal arch and gait , some works of clinical research on the medial longitudinal arch 
 found a correlation between the ground reaction force and structure of a medial arch during 
 gait10 , 11 .
however , the medial longitudinal arch did not have any correlation 
 with plantar pressure and rear - foot motion during gait12 , 13 .
thus , no consensus has 
 been reached about the relationship between the clinical measurements of foot posture and 
 gait .
although the correlation between the clinical measurements of foot posture and gait 
 has not been sufficiently investigated , clinicians assume that there is some correlation 
 between the static measurement of foot posture and gait , and they clinically apply this 
 assumption when treating patients10 , 13 , 14 . clinically , there is much limitation to the evaluation of lateral longitudinal and 
 transverse arches , except the medial longitudinal arch15
. clinical measurements of the forefoot are important , because 
 forefoot deformity is highly correlated with lower leg pain and a risk of falling16 , 17 .
measurements of taf , which is part of the forefoot structure , have 
 been performed using plantar pressure measurements18,19,20 , ultrasonography21 , 22 , and radiographic photography23 , 24 .
recently , a 3-dimensional ( 3d ) foot scanner25 has made it easier to measure taf noninvasively .
however , 
 the relationship between static measurements of taf and gait has not been well investigated . 

it has been reported that taf spreads due to weight bearing placed on the forefoot during 
 gait18 , 19 .
therefore , in adding the morphologic change measurements of taf 
 during weight bearing to the static measurements of taf , the taf becomes more efficiently 
 understood during human activities .
accordingly , the purpose of the present study was to investigate the relationship between 
 the static measurement of taf , using a 3d foot scanner , and kinetics and kinematics of gait 
 parameters on the sagittal plane in healthy subjects .
the results of this study may enable 
 clinicians to more efficiently evaluate the taf results of patients experiencing 
 difficulties during daily activities .
moreover , the evaluation methods of taf may be applied 
 to elderly individuals who experience difficulty during gait .
we hypothesized that static 
 measurements of taf are correlated to gait parameters ( joint angle , joint moment , joint 
 power , and ground reaction force ) .
twenty subjects ( 10 men and 10 women ) participated in this study . they were 22.6  
 2.8  years old ( mean  sd [ standard deviation ] ) and 166.0
we defined the dominant side as the 
 side subjects used to kick a ball .
all subjects in this study provided written informed 
 consent , and the protocol was approved by the ethics committee of the bunkyo gakuin 
 university graduate school ( approval no . : 2014-msj01 ) .
taf was measured using a 3d foot scanner ( infoot ; i - ware laboratory , osaka , japan ) .
three 
 conditions were used to measure taf : sitting ( condition 1 ) , standing ( condition 2 ) , and foot 
 forward and lower leg tilting anteriorly to the maximum ankle dorsiflexion with heel contact 
 ( condition 3 ) ( fig . 1fig .
1.evaluation of foot posture using the 3-dimensional foot scanner ( infoot ; i - ware 
 laboratory , osaka , japan ) under three posture conditions for transverse arch 
 measurements of the forefoota .
evaluation apparatus , b. measured image of the foot , and c. evaluated postures . 

condition 1 ( left ) : sitting , condition 2 ( middle ) : standing , and condition 3 ( right ) : 
 foot forward and lower leg tilting anteriorly to the maximum ankle dorsiflexion with 
 heel contact .
weight bearing of the dominant foot is measured at each condition : 10% 
 body weight in condition 1 , 50% body weight in condition 2 , and 7080% body weight in 
 condition 3.)1 , 5 , 
 6 , 26 .
these conditions of foot posture can be frequently and 
 reproducibly used in human activities , and applied easily in clinical settings .
we confirmed 
 weight bearing under each condition using a scale during the measurements ; condition 1 is 
 10% of body weight , condition 2 is 50% of body weight , and condition 3 is 7080% of body 
 weight on the dominant foot1 , 26 .
furthermore , we confirmed that each subject could carry 
 his / her weight on the forefoot in condition 3 .
we recorded the taf width and height at the level of the 
 metatarsal head for each measurement .
values of the taf width and height were calculated as 
 a mean value of thrice taf measurements . the taf width and taf height
were calculated 
 between condition 1 and condition 2 , and between condition 2 and condition 3 , as the rate of 
 each comparison , i.e. , % width and % height , respectively .
we calculated the rate of the taf 
 width using the following equations : between condition 1 and condition 2 = [ ( taf width of 
 condition 2 ) / ( taf width of condition 1 )  100 ] , and between condition 2 and condition 3 = 
 [ ( taf width of condition 3 ) / ( taf width of condition 2 )  100 ] .
we also calculated the rate 
 of the taf height using the following equations : between condition 1 and condition 2 = [ ( taf 
 height of condition 1  taf height of condition 2 ) / ( taf height of condition 1 )  100 ] , and 
 between condition 2 and condition 3 = [ ( taf height of condition 2  taf height of condition 
 3 ) / ( taf height of condition 2 )  100 ] .
evaluation of foot posture using the 3-dimensional foot scanner ( infoot ; i - ware 
 laboratory , osaka , japan ) under three posture conditions for transverse arch 
 measurements of the forefoot a. evaluation apparatus , b. measured image of the foot , and c. evaluated postures . 

condition 1 ( left ) : sitting , condition 2 ( middle ) : standing , and condition 3 ( right ) : 
 foot forward and lower leg tilting anteriorly to the maximum ankle dorsiflexion with 
 heel contact .
weight bearing of the dominant foot is measured at each condition : 10% 
 body weight in condition 1 , 50% body weight in condition 2 , and 7080% body weight in 
 condition 3 .
body kinematics measurements were performed using eight cameras ( vicon motion systems , 
 ltd . ,
oxford , uk ) at a sampling rate of 100  hz . subjects were clothed in close - fitting 
 t - shirts and shorts .
reflective markers were attached to the body according to the marker 
 position of the vicon plug - in gait full body model by a single investigator .
all data were 
 obtained with a low - pass filter using a fourth - order butterworth filter with a cut - off 
 frequency of 6  hz . a force plate ( amti , watertown , ma , usa )
was used to measure the ground 
 reaction force at a sampling rate of 1,000  hz . subjects were asked to walk at a pace of 110 
 steps / min in bare feet .
the gait performance was determined as successful when the dominant foot 
 completely touched the force plate .
peak values of 
 the joint angles ; joint moments ; joint powers of the hip , knee , and ankle joint ; and ground 
 reaction force in the sagittal plane were calculated using a plug - in - biomechanical modeler 
 ( vicon motion systems , ltd . ) .
values of the joint moment , joint power , and ground 
 reaction force were normalized with regard to a subject s body mass .
the shapiro - wilk test was used to determine whether all data followed a normal 
 distribution .
subsequently , we calculated correlation coefficients between the taf width 
 ( % ) ; taf height ( % ) for each comparison of conditions ; and joint angle , joint moment , joint 
 power , and ground reaction force during gait using the spearman correlation analysis .
the average values of taf height and taf width are shown in table 1table 1.the mean values of taf width and taf height at each condition ( means  
 sd)measurement conditionscondition 1condition 2condition 3taf width ( mm)96.2  6.498.4  6.899.5  7.5taf height ( mm)40.8  4.539.1  4.338.6  4.4taf : transverse arch of the forefoot . condition 1 : sitting , condition 2 : standing , condition 3 : foot forward and lower leg 
 tilting anteriorly to the maximum ankle dorsiflexion with heel contact .
the average change in the taf width and taf height is shown in table 2table 2.the mean change of taf width and taf height between two conditions ( means  
 sd)measurement conditionscondition 1 to condition 2condition 2 to condition 3taf width ( % ) 102.3  0.7100.9  1.2taf height ( % ) 4.4  1.90.84  3.1taf : transverse arch of the forefoot .
condition 1 : sitting , condition 2 : standing , condition 3 : foot forward and lower leg 
 tilting anteriorly to the maximum ankle dorsiflexion with heel contact between condition 1 and condition 2 , and between condition 2 and condition 
 3 .
condition 1 : sitting , condition 2 : standing , condition 3 : foot forward and lower leg 
 tilting anteriorly to the maximum ankle dorsiflexion with heel contact taf : transverse arch of the forefoot .
condition 1 : sitting , condition 2 : standing , condition 3 : foot forward and lower leg 
 tilting anteriorly to the maximum ankle dorsiflexion with heel contact regarding the change between condition 1 and condition 2 , there was no significant 
 correlation between the change in the taf width and taf height , and the gait variables , 
 i.e. , the joint angle , joint moment , joint power , and ground reaction force . regarding the 
 change between condition 2 and condition 3 ,
there were significant correlations between 
 changes in the taf width and the anterior ( r=0.54 ) and posterior component ( r=0.56 ) of the 
 ground reaction forces , and hip joint extension angles ( r=0.40 ) .
additionally , there were 
 significant correlations between changes in the taf height and ankle plantar flexion moment 
 ( r=0.46 ) ( table 3 
 table 3.correlation coefficients between changes of taf width and taf height , and joint 
 angle , joint moment and ground reaction force during gait 
 ) .
this study showed the static measurements of taf were correlated to ground reaction forces , 
 ankle plantar flexion moment , and hip extension angle during gait .
therefore , the results of 
 this study supported our hypothesis . the change in taf between condition 1 ( sitting ) and 
 condition 2 ( standing )
the change in taf 
 between standing ( condition 2 ) and foot forward and lower leg tilting anteriorly to the 
 maximum ankle dorsiflexion with heel contact ( condition 3 ) was statistically correlated with 
 the anterior and posterior component of ground reaction forces , hip extension angle , and 
 ankle plantar flexion moment during gait .
therefore , these results suggest that it will be 
 useful to evaluate changes in taf between condition 2 and condition 3 to assess foot 
 disorders and gait performances .
previous research studies28 , 29 have reported that 
 additional weight bearing causes a change in foot posture
. however , the change in taf 
 between condition 1 and condition 2 seems too small , i.e. , body weight change of only 50% 
 was not large enough to make the morphologic change detectable during an evaluation , or 
 sufficient weight was not placed to the forefoot .
consequently , the change in taf between 
 condition 1 and condition 2 was not significantly detectable during the gait performances . 

although static measurements of the medial longitudinal arch have been obtained clinically 
 using sitting or standing as a measurement position , the current study s results suggest 
 that a sufficient amount of weight bearing is necessary to achieve detectable changes in taf 
 to evaluate arch changes of the foot during gait performance . regarding the relationship between the change in taf and gait parameters , the change in taf 
 between condition 2 and condition 3
was significantly correlated with the anterior and 
 posterior component of ground reaction forces during gait .
the posterior component of the 
 ground reaction force matches the timing of weight bearing and shock absorption during the 
 early stance phase30 , which suggests that 
 the smooth , rapid spreading of taf is important for posture stability in the early stance 
 phase of gait .
moreover , since the anterior component of the ground reaction force increases 
 weight bearing on the forefoot and moves body mass forward30 , the change in taf between condition 2 and condition 3 may be an 
 indicator of the driving force of body mass during gait .
previous works of research have 
 reported that taf spreads during gait due to weight bearing18 , 19 , 31 , and the taf width increases while the taf height decreases due to 
 weight bearing29 .
thus , changes in the 
 taf width and height between condition 2 and condition 3 would be an indicator for the 
 tendency of forefoot spreading with weight bearing in each subject .
furthermore , the change 
 in the taf height between condition 2 and condition 3 was significantly correlated with 
 ankle plantar flexion moment . since ankle plantar flexion moment contributes as a driving 
 force of body mass during the late stance phase32 , 
 33 ,
the lesser change in the taf height 
 between condition 2 and condition 3 suggests a larger driving force of body mass by ankle 
 plantar flexion during the late stance of gait .
when the change in the taf width and height in this study is considered the stiffness of 
 taf , the larger increase in taf means a low stiffness of taf , whereas the lower increase in 
 taf represents a high stiffness of taf .
therefore , when the increase in taf is considered 
 the stiffness of taf , the results of the study indicate that the subjects with a low 
 stiffness of taf walk with low ankle plantar flexion moment and have a large hip extension 
 angle , whereas subjects with a high stiffness of taf walk with high ankle plantar flexion 
 moment and have a small hip extension angle .
previous research studies have reported that 
 individuals with a high arch foot with high stiffness produce greater work of the ankle 
 joint during landing and jogging , whereas individuals with a low arch foot with low 
 stiffness produce greater work of the hip joint to overcome the reduced efficacy of a 
 flexible foot34 , 35 .
the current study s findings showed the same relationships as 
 those reported in previous studies34 , 35 that investigated the relationship between 
 taf stiffness and function of the hip joint and ankle joint during gait .
moreover , elderly 
 people walk with higher hip joint movement36 , so the taf of this population is easily lowered during weight 
 bearing37 .
therefore , the same 
 relationships between taf stiffness and characteristics of gait performance would be 
 indicated in elderly people , as this study demonstrated .
the positive correlation between 
 high stiffness of the taf and ankle plantar flexion moment may partly explain the factors of 
 the medial tibial stress syndrome , as a previous study indicated relationships between high 
 stiffness of the taf and medial tibial stress syndrome38 .
there are some limitations to this study . only healthy subjects participated in this study , 

we only analyzed 
 gait performance in this study , so we did not understand relationships between taf 
 flexibility and sports performances , and other human body motion .
further research with 
 participated elderly individuals and patients with foot deformities should confirm our 
 findings . in summary ,
the static measurement of taf between standing and foot forward and lower leg 
 tilting anteriorly to the maximum ankle dorsiflexion with heel contact was more related to 
 gait parameters than between sitting and standing .
the change in taf between standing and 
 foot forward and lower leg tilting anteriorly to the maximum ankle dorsiflexion with heel 
 contact suggests that increasing taf stiffness was related to the increase in the ankle 
 plantar moment , and decreasing taf stiffness was related to the increase in the hip joint 
 extension angle during gait .
 [ purpose ] to investigate the relationship between the static measurement of the 
 transverse arch of the forefoot , using a 3-dimensional ( 3d ) foot scanner , and kinetics and 
 kinematics of gait parameters in the sagittal plane . 
 [ subjects and methods ] twenty healthy 
 subjects participated in this study . 
 the transverse arch of the forefoot was measured 
 under three conditions as follows : condition 1 , sitting ; condition 2 , standing ; and 
 condition 3 , foot forward and lower leg tilting anteriorly to the maximum position with 
 heel contact . 
 gait parameters were recorded using a 3d motion analysis system and force 
 plate . 
 correlation coefficients between taf for each comparison of conditions and gait 
 parameters were calculated using the spearman correlation analysis . 
 [ results ] rates of the 
 transverse arch of the forefoot width and height between condition 2 and condition 3 were 
 significantly correlated with the anterior and posterior component of ground reaction 
 forces , the hip joint extension angle , and the ankle plantar flexion moment . 
 [ conclusion ] 
 our study s findings indicated that increased stiffness of the transverse arch of the 
 forefoot was related to the increase in ankle plantar moment , and decreased stiffness of 
 the transverse arch of the forefoot was related to the increase in hip joint extension 
 angle during gait . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION