gait is the most natural motion performed by humans in their ordinary life and has the 
 highest frequency in human activities .
numerous musculoskeletal muscles and nerves of the 
 lower extremities respond together during gait1 , 2 . during gait
, movement occurs through a 
 series of interactions among the heel bones , the soles , and the ends of the feet .
damages to 
 the feet is associated with impact force , control force , and the distribution of plantar 
 pressure during grounding of the heel bones3 .
flat - arched feet , in particular , have been associated with altered 
 foot function , including prolonged calcaneal eversion , increased tibial internal rotation , 
 increased forefoot abduction , reduced efficiency of gait , and reduced shock absorption4 .
the medial longitudinal arch ( mla ) plays an important role in shock absorbance and energy 
 transfer during walking5 .
although the 
 etiology of this deformity can be arthritic or traumatic in nature6 , it is most commonly associated with posterior tibial tendon 
 dysfunction7 .
load during gait increases the number of steps and the double support time , decreases step 
 length , raises energy consumption , and makes the repulsive force against the earth or the 
 lower extremity joints greater8 , 9 . during gait ,
the kinds or directions of loading change the 
 distribution of pressure delivered to the center of the body and the feet , which may trigger 
 abnormal gait by causing fatigue fracture or affecting muscle activity or postural 
 alignment9 , 10 . based on the fact that individuals with the flatfeet more easily 
 feel muscle fatigue of the lower extremities and have a higher risk of damages to the 
 musculoskeletal system than individuals with normal feet , the aim of this study was to 
 examine differences between flatfeet and normal feet while subjects walked on an ascending 
 slope like when climbing a mountain .
the subjects in the present study , people with normal feet ( n=15 ) or flatfeet ( n=15 ) , were 
 between the ages of 21 and 30
. sufficient explanations of this study s intent and the 
 overall purpose were given , and voluntary consent to participate in this study was obtained 
 from all of the subjects .
all procedures were reviewed and approved by the institutional 
 ethics committee of eulji university hospital .
flatfoot was confirmed by posture analysis 
 ( gps400 , redbalance , italy ) . as described by clarke11
strake s line is the line that passes between the medial border of the forefoot and the 
 medial border of the hindfoot , and marie s line is the line that passes between the center 
 of the 3rd toe and the center of the hindfoot . there is also a bisector line between 
 strake s line and marie s line .
we categorized subjects into the normal foot group if their 
 medial soles passed to the lateral side of marie s line , and we categorized subjects into 
 the flat foot group if their medial soles passed between the bisector line and strake s 
 line .
all subjects received a sufficient explanation about the research and provided consent to 
 participation .
a treadmill ( ac5000 m , scifit , uk ) was used to examine kinematic features 
 during gait .
the average gait velocities of the men at slow , normal , and fast rates are 3 , 
 4 , and 5  km / h using a slope of 10% , respectively , and those of women are 2.7 , 3.7 , 4.7  km / h 
 using a slope of 10% , respectively12 . 

subjects walked for one minute to determine their natural gait velocity before the 
 experiment .
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 conducted after 
 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 , medial gastrocnemius , lateral 
 gastrocnemius , peroneus longus , 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 signals of muscles to the maximal 
 voluntary isometric contraction ( mvic ) .
the general subject characteristics ( age , height , and weight ) were tested for homogeneity 
 using the independent t - test .
data were analyzed by repeated measures 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 . statistical significance was accepted for p 
 values less than 0.05 .
the general characteristics of the subjects are shown in table 1table 1.general characteristics of each group ( meanse)eg ( n=15)cc ( n=15)number of individuals ( male / female)5/106/9age ( years)21.41.322.10.6height ( cm)164.21.6167.42.1body weight ( kg)61.2.357.22.4foot length ( mm)254.24.2257.22.7ankle width ( cm)5.60.36.21.2 .
muscle activities 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 ) ( table 2table 2 .
comparison of variable with different velocity on a 10% slope ( % mvc)groupslownormalfastrectus femoriseg*20.83.224.13.230.63.7cg*21.42.523.73.929.94.7vastus medialiseg*19.92.325.15.838.06.2cg*21.71.624.21.431.84.1vastus lateraliseg*20.51.823.81.629.53.6cg*20.72.424.31.929.13.7tibialis anterioreg*23.40.724.81.430.24.5cg*22.51.825.22.130.03.4peroneus longuseg*20.83.127.02.031.00.7cg*22.11.327.63.432.94.3medial gastrocnemiuseg*32.24.534.24.635.83.2cg*33.31.034.61.337.11.5lateral gastrocnemiuseg*33.41.734.41.636.22.3cg*32.71.234.11.338.71.7abductor halluciseg*14.64.217.34.020.23.6cg*15.23.421.45.026.43.2*p<0.05 , eg : experimental group ; cg : control group ) , especially those of the vastus medialis and abductor hallucis muscles ( p 
 < 0.05 ) ( table 3table 3 .
results of between - subject comparisons of the effects of muscle activation 
 during treadmill gait on a 10% slopetype iii ssdfmsrectus femorisgroup0.210.2error225.2288.0vastus medialis*group23.9123.9error155.7285.5vastus lateralisgroup0.010.0error68.4282.4tibialis anteriorgroup0.410.4error70.7282.5peroneus longusgroup11.6111.6error111.7283.9medial gastrocnemiusgroup6.316.3error311.12811.1lateral gastrocnemiusgroup1.711.7error63.5282.2abductor hallucis*group98.2198.2error381.12813.6*p<0.05 ) .
in the subjects with the flatfeet , the function of their feet may did not activate properly 
 as a result of overuse when conducting activities that put repetitive loads on the feet13 .
when the subtalar joints are excessively 
 pronated , the medial tibia areas of the knees slip backward at a rapid speed , rotate and 
 enter under the medial femoral condyles , which may cause damage to the medial side of the 
 knees6 .
the results of analysis of the 
 muscle activities of the subjects during gait on an ascending slope showed that overall , 
 their muscle activities increased according to the rise in gait speed , and there were 
 significant differences between the two groups in the vastus medialis and abductor hallucis 
 muscles . in the subjects with flatfeet ,
extensor muscles , in particular , the vastus medialis , play a role in 
 lowering speed and absorbing impact through eccentric contraction .
the subjects with 
 flatfeet received more loads on the vastus medialis than those with normal feet due to 
 weakened plantar flexion muscles .
drawing in a slant line of the patellas by the vastus 
 medialis muscles has an important meaning in stabilization and direction of the patellas 
 when they pass or slip through the intercondylar areas of the femurs14 .
the abductor hallucis muscles , which are situated below 
 the medial longitudinal arches of the feet , stop at the sesamoid bones of the distal 
 phalanxes from the heel bones and provide dynamic stability to the medial longitudinal 
 arches15 . in this study ,
the changes in 
 activity of the abductor hallucis muscles according to the changes in speed and gradient 
 were smaller in the subjects with flatfeet than those with normal feet .
this indicates that 
 the abductor halluces muscles of individuals with flatfeet do not properly function as 
 muscles for dynamic stability of the medial longitudinal arches .
the present study verified 
 that in individuals with flatfeet , the abductor hallucis muscles affected descent of the 
 navicular bones by inducing blockage16 
 and fatigue of the tibial nerves17 .
   [ purpose ] this study determined the difference between flatfeet and normal feet in 
 humans on an ascending slope using electromyography ( emg ) . [ subjects ] this study was 
 conducted on 30 adults having normal feet ( n=15 ) and flatfeet ( n=15 ) , all of whom were 21 
 to 30  years old . 
 [ methods ] a treadmill ( ac5000 m , scifit , ) was used to analyze kinematic 
 features during gait . 
 these features were analyzed at slow , normal , and fast gait 
 velocities on an ascending slope . 
 a surface electromyogram ( telemyo 2400 t , noraxon co. , 
 usa ) was used to measure muscle activity changes . 
 [ results ] the activities of most muscles 
 in the subjects with flatfeet were significantly different from the muscle activities in 
 the subjects with normal feet at different gait velocities on an ascending slope . 
 there 
 were significant differences in the vastus medialis and abductor hallucis muscles . 
 
 [ conclusion ] because muscle activation of the vastus medialis in relation to stability of 
 the lower extremity has a tendency to increase with an increase in gait velocity on an 
 ascending slope , we hypothesized that higher impact transfer to the knee joints occurs in 
 subjects with flatfeet due to the lack of a medial longitudinal arch and that the abductor 
 halluces muscles , which provide dynamic stability to the medial longitudinal arches , do 
 not activate well when they are needed in subjects with flatfeet . 