flat foot is a disease that is either congenital or acquired , having characteristics such 
 as talus medial rotation , decreased medial arch height , and forefoot supination and 
 abduction1 .
flat foot also causes 
 excessive movement to be pronated and shock absorption to be decreased . in general , a normal 
 foot experiences a pressure 1.5 times body weight when in contact with the ground , whereas 
 people with flat feet feel more fatigue because of the problem of shock absorption . 

flat foot is a 
 dysfunction of the posterior tibial tendon , one of the important supporters of the medial 
 arch , a dysfunction of the spring ligament2,or an injury to the plantar fascia3 .
it can also result from obesity increasing the load on the feet 
 during the stance phase , causing abnormal foot movement4 .
most previous studies have been causal analyses of flatfoot and studies of treatment 
 effectiveness through sugery .
few studies have investigated the extent to which dynamic 
 activities , such as gait , affect the lower extremities of flat - footed people .
gait is a 
 natural action in daily life , and there is great diversity in individual gait patterns , 
 especially at different gait velocities5 , 6 . because the human foot has evolved for 
 standing and upright movements , such as gait , the alignment of the foot and ankle joints 
 plays an important role in supporting weight during gait .
thus , the human foot uniquely 
 contacts the ground , supplying the momentum for movement via the ground reaction force and 
 playing an important role in the weight - bearing function of subtalar movement7 .
ultimately , gait is possible through 
 interactions that link the human calcaneus , the sole of the foot , and the tips of the toes , 
 and this is why we have conducted this study , to determine the difference between flat feet 
 and the normal feet at different gait velocities using emg and foot pressure analysis .
people with normal feet ( n = 15 ) and people with flat feet ( n = 15 ) , all of whom have no 
 neurological history and were between the ages of 21 and 30 , participated in this study . 
 age , weight , and height were measured to determine the body characteristics of the subjects . 

flat foot was confirmed by posture analysis ( gps400 , redbalance , italy ) . as described by 
 clarke8 , strake
strake s line passes from the forefoot s medial line to the 
 rearfoot s medial line , and marie s line passes from the center of the 3 
 metatarsal bone to the center of the rearfoot .
if the line of the medial sole falls outside 
 marie s line , it is confirmed as a normal foot . if the line of the medial sole falls inside 
 marie s line , it is confirmed as a flat foot .
all the subjects received explanation of the research and provided their consent to 
 participation . a treadmill ( ac5000 m , scifit , uk ) was used to analyze kinematic features 
 during gait , using a slope of 0% with gait velocities of 1.101.25 m / s9 .
the average gait velocity of the average man at slow , 
 normal , and fast rates are 3 , 4 , and 5  km / h , respectively , and those of the average woman 
 are 2.7 , 3.7 , 4.7  km / h , respectively10 . 

subjects walked for about one minute to determine their natural gait velocity before the 
 experiment began .
then all subjects walked barefoot for five minutes on the treadmill , 
 looking forward .
muscle activity data were collected and analyzed using a wireless surface electromyograph 
 ( telemyo 2400 t , noraxon co. , usa ) .
the electrode diameter was 11.4  mm , and the distance between the 
 electrodes was 20  mm .
the sampling rate for the emg signal was set at 1000  hz , the bandwidth 
 was set between 20450  hz , and the notch filter was set at 60  hz .
emg was performed after 
 depilating the electrode - attachment areas with a razor , removing the horny layer with sand 
 paper , and cleansing the areas with an alcohol swab . to measure muscle activations in the 
 lower extremities during gait
, electrodes were attached to the abductor hallucis , tibialis 
 anterior , peroneus longus , medial gastrocnemius , lateral gastrocnemius , vastus medialis , 
 vastus lateralis , and biceps femoris muscles .
the frequency range of the emg signal was 
 band - pass filtered between 20 and 500  hz , and the sampling frequency was 1024  hz . we 
 normalized the signal of each muscle to the maximal voluntary isometric contraction ( mvic ) . 

data on the change of foot pressure was collected using a foot pressure analyzer ( fsa , vista 
 medical , canada ) .
the pressure measurement pad is 0.88  mm thick , and it has 128 numbered 
 resistance sensors ( 916  mm each ) arranged in a 816 grid .
we used a sampling rate of 
 3,072  hz , and measurement range of 030 psi .
the sizes of the pressure measurement mats were 
 230100  mm , 250100  mm , and 270100 mm , and they were fitted to subjects insoles according 
 to their foot size . in this study ,
the foot was divided into eight areas for analysis according to foot 
 regions : two toe regions ( 1st toe region and 2nd5th toe region ) , three forefoot regions 
 ( 1st metatarsal region , 2nd3rd metatarsal region , and 4th5th metatarsal region ) , the 
 midfoot region , and two heel regions ( medial heel region and lateral heel region)11 .
the average pressure of each region was 
 measured during the experiment . the general subject characteristics ( age , height , and 
 weight )
data were analyzed by 
 repeated anova in spss for windows ( version 17.0 ) , and the differences between groups at the 
 different gait velocities were examined with the independent t test .
eg : experimental group ; cc : control group * p<0 .05 , eg : experimental group ; cg : control group rf : rectus femoris ; vm : vastus medialis ; vl : vastus lateralis ; ta : tibialis anterior ; 
 pl : peroneus longus ; mg : medial gastrocnemius ; lg : lateral gastrocnemius ; ah : abductor 
 hallucis * p < 0.05 ; eg : experimental group ; cg : control group t1 : toe1 ; t2 : toe25 ; f1 : 1st metatarsal ; f2 : 2~3rd metatarsal ; f3 : 4~5th metatarsal ; 
 m : midfoot ; h1 : medial heel ; h2 : lateral heel the general characteristics of the subjects are shown in table 1 . muscle activities ( excepting that of the rectus femoris ) 
 of the flat - footed subjects were significantly different from those of the normal - footed 
 subjects at all of the different gait velocities ( p < 0.05 ) , especially those of the 
 vastus medialis and abductor hallucis muscles ( p < 0.05 ) ( table 2 ) .
significant differences in pressure were also detected 
 on the forefoot , midfoot , and the medial area of the hindfoot ( p < 0.05 ) .
table 3 shows a significant difference in the 
 2nd3rd metatarsal area ( p < 0.05 ) .
nakajima et al.12 studied the 
 relationship between the foot s arch height and the shock effect on the knee .
they concluded 
 that a correlation exists between the height of the foot s arch and the shock on the knee . 

thus , we know that the adduction moment of the knee joint of flat - footed subjects is higher 
 than the adduction moment of sunjects with normal feet .
this is due to higher muscle 
 activation of the vastus medialis muscle in flat - footed people .
furthermore , muscle 
 activation of the abductor hallucis muscle in flat - footed people decreases relative to the 
 changes in velocity compared to people with normal feet is relatively lower according to the 
 changes in velocity .
thus , we can conclude that , compared to subjects with normal feet , the 
 medial longitudinal arch of flat - footed subjects does not work well as a dynamic 
 stabilizer .
fiolkowski et al.13 confirmed that the 
 abductor hallucis muscle affects the height of the navicular bone in a tibial nerve block 
 study , and that foot pressure changed with gait velocity .
we confirmed the weight of flat 
 foot was not moved onto the toe until the terminal stance phase , and that the weight of flat 
 footed subjects was focused on the 2:3rd metatarsal area .
we also confirmed that hindfoot 
 eversion of a flat foot is higher with increasing gait velocity , and the foot pressure of a 
 flat foot is higher on the medial side of foot in the terminal stance phase .
we suppose the 
 load of moving the lower extremity increases with velocity and ability of medial 
 longitudinal arch of flat foot is less than normal foot resulting in pressure being focused 
 on 2:3rd metatarsal area in the stance phase .
   [ purpose ] this study determined the difference between flat feet and normal feet of 
 humans at different gait velocities using electromyography ( emg ) and foot pressure 
 analysis . [ subjects ] this study was conducted on 30 adults having normal feet ( n = 15 ) and 
 flat feet ( n = 15 ) , all of whom were 21 to 30  years old and had no neurological history or 
 gait problems . [ methods ] a treadmill ( ac5000 m , scifit , uk ) was used to analyze kinematic 
 features during gait . 
 these features were analyzed at slow , normal , and fast gait 
 velocities . 
 a surface electromyogram ( telemyo 2400 t , noraxon co. , usa ) and a foot pressure 
 analyzer ( fsa , vista medical , canada ) were used to measure muscle activity changes and 
 foot pressure , respectively . 
 [ results ] the activities of most muscles of the flat feet , 
 except that of the rectus femoris , were significantly different from the muscle activities 
 of the normal feet at different gait velocities . 
 for example , there was a significant 
 difference in the vastus medialis and abductor hallucis muscle . 
 likewise , flat feet and 
 normal feet showed significant differences in pressures on the forefoot , midfoot , and 
 medial area of the hindfoot at different gait velocities . 
 finally , comparison showed there 
 were significant differences in pressures on the 2nd3rd metatarsal area . 
 [ conclusion ] 
 because muscle activation has a tendency to increase with an increase in gait velocity , we 
 hypothesized that the lower extremity with a flat foot requires more work to move due to 
 the lack of a medial longitudinal arch , and consequently pressure was focused on the 
 2nd3rd metatarsal area during the stance phase . 