an important role of footwear is to prevent injury by decreasing fatigue in the foot and 
 lower extremity while walking1 .
the 
 characteristics of the footwear material are closely related to muscle and joint movements 
 of the lower extremities2 , and contact 
 between the body and the supporting surface may potentially influence balance and the risk 
 of falls3 .
rain boots made of rubber and 
 waterproof shoes are worn in the rainy spells in the summer as fashion items by younger 
 women . however , due to the hard and flat soles of the footwear , the entire foot is used 
 during walking , which focuses pressure on the heels and reduces surface contact ; this may 
 significantly influence impact absorption of the joints in the lower extremities4 .
the maintenance of balance is a crucial requirement in one s daily living , work , and sports 
 activities5 .
balance and postural 
 control are maintained through environmentally - related factors and the dynamic integration 
 of internal and external forces6 .
this is 
 a specialized , complex process that includes various sensory and motor components and 
 requires accurate afferent and efferent output from the associated joints and muscles7 .
the maintenance of balance relies on influx 
 from the visual , vestibular , and somatosensory systems8 , while fatigue of the postural muscles generated during postural 
 maintenance affects the systems responsible for maintaining balance , damaging postural 
 control7 .
fatigue refers to the 
 reduction in efficiency and muscle capacity generated by energy , due to exposure to 
 continuous activities9 .
neuromuscular 
 fatigue is a specific condition resulting from an inability to maintain a given degree of 
 strength , and fatigue is the basis for some widely known changes , such as reduced capacity 
 during functional activities and sport activities .
moreover , fatigue includes central 
 mechanisms originating proximally from the motor neurons as well as from peripheral 
 mechanisms originating distally from the neuromuscular junction , which includes contractile 
 components within the muscles10 .
muscle 
 fatigue is an inevitable phenomenon of the workings of the central nervous system during 
 daily physical activities , as well as the inability to produce expected power according to 
 power output .
it has a negative effect on the proprioceptive receptors by reducing the 
 activity of muscular mechanoreceptors or decreasing muscular function7 .
according to previous studies that analyzed the effects of flat and high - heeled shoes 
 frequently worn by women on the spine and joints , it was found that the maximum pressure on 
 the heels was increased more by flat shoes than by shoes with 3  cm - high and 7  cm - high 
 heels11 .
moreover , a study of the 
 dynamic equilibrium according to the shoe characteristics in young adults and the elderly 
 reported that stiff shoes , rubber tread soles , and high heel - collar shoes did not improve 
 stability during walking3 . additionally , 
 according to the results of a pilot study on sensory integration and balance training , based 
 on the visual feedback of performed actions with older adult subjects , balance ability with 
 the eyes open improved both the anteroposterior ( ap ) sway and the mediolateral ( ml ) sway ; 
 however , only ml sway was improved with the eyes closed12 .
the field of vision plays an overriding role before sensory 
 orientation brings the appropriate adjustment of posture7 , and muscle fatigue has been proven to be a major component in the 
 impairment of the proprioceptive senses and postural control5 .
although there have been numerous research studies regarding the 
 visual information responsible for postural control and muscle fatigue of the lower 
 extremities and relevant research on functional shoes and high heels , research on rain boots 
 worn with regard to the particular characteristics of the material in special circumstances 
 is insufficient .
thus , the purpose of this study was to investigate the effects of muscle 
 fatigue of the lower extremities , generated while walking in rain boots of different shaft 
 lengths , on balance abilities according to visual feedback .
the subjects of this study included twelve healthy female students in their 20s enrolled at 
 a university in cheonan , republic of korea .
those with medical conditions that could affect 
 the study , such as neurological and musculoskeletal conditions ( or other medical 
 conditions)13 , pregnancy , knee 
 injuries , and those who had undergone lower extremity surgeries were excluded9 . regardless of whether they wore glasses or 
 not , those with normal vision were selected14 . the subjects comprehended the purpose and content of the 
 experiment before providing voluntary written consent to participate in the research .
the 
 physical characteristics of the subjects participating in the study are shown in table 1table 1.characteristics of the subjects ( n = 12)characteristicmsdage ( years)20.50.5height ( cm)159.15.0weight ( kg)51.47.3msd : mean  standard deviation .
this study was approved by the namseoul university research 
 ethics committee ( nsu-141006 - 1 ) .
msd : mean  standard deviation the experimental design of this study was a one - way repeated - measures test , in which one 
 subject performed walking exercises wearing the three types of rain boots ( table 2table 2.general characteristics of the rain bootsboot typeheight ( cm)weight ( kg)long401.6middle291.3short170.8 ) , and the subjects were divided into long , middle , and short groups according 
 to the length of the rain boot shaft .
there were three types of shoe groups and a 24-hour 
 rest period15 . before the experiment , 
 body composition analyzers ( inbody 720 , biospace , seoul , republic of korea )
were used to 
 identify the physical characteristics of the subjects . in order to determine the ability to 
 balance before fatigue ,
a professional balance assessment and training platform ( bt4 , hur 
 labs oy , tampere , finland ) were used , while romberg s test was applied and the limits of 
 stability were measured . to induce fatigue in the lower extremity muscles , treadmill walking 
 ( sns care m-400 m , sns care co. , ltd . , goyang , republic of korea ) was performed while wearing 
 each pair of rain boots .
then , the ability to balance was measured immediately after the 
 exercise in order to determine the ability to balance after fatigue16 .
treadmill walking for inducing muscle fatigue was performed for 30 minutes at a constant 
 speed and a normal pace17 . in this study , 

treadmill walking was performed at a speed of 4  km / h , a normal pace18 , with a 5-minute rest to avoid the fatigue effects . in 
 order to determine the balance ability of the subjects before and after fatigue ,
romberg s 
 test according to visual feedback , with eyes opens ( eo ) and closed ( ec ) , and limits of 
 stability were measured . in romberg s test , the subjects were asked to bend one leg along 
 the anterior - posterior axis of the balance platform at a 30 angle , stand on the opposite 
 leg , and maintain as stable a stance as possible19 for a 60-second . in the limits of stability test ,
the subjects 
 feet were aligned along the heel and medial malleolus landmarks printed on the top of the 
 platform .
the subjects were then instructed to shift their body weight ( using their ankle 
 joints as the primary axis of motion , without changing the feet position ) in different 
 directions ( one direction at a time ) as quickly as possible following the appearance of a 
 target on the monitor .
each direction of the target was randomly selected by the researcher 
 and displayed for 8 seconds only once20 . 

the measured directions were left ( lt ) , right ( rt ) , forward ( fw ) , backward ( bw ) , and total 
 directions in this study . the data for this study were analyzed using the statistical program spss version 18.0 for 
 windows .
levene s f - test was used to verify the homogeneity of the data , and the 
 kolmogorov - smirnov test was used to prove the normal distribution .
multivariate analysis of 
 variance ( manova ) was used to compare the balance of the groups ( long , middle , short ) 
 according to timing ( before and after exercise ) in each walking condition .
if results of 
 manova indicated significant differences in the groups , scheffe s test was used as a post 
 hoc analysis .
when a significant difference in time was indicated , the dependent t - test was 
 used .
as a result of romberg s test comparison of the ability to balance according to the shaft 
 length of the rain boots , the changes in the balance ability with the eyes open are shown in 
 table 3table 3.rombergs test comparison according to shaft length ( eyes open)bootspre - testpost - testcog area * * ( mm)long18.9213.7959.3385.21middle18.9213.7970.9269.29short18.9213.79101.75128.55cog length * * ( mm)long5.420.998.394.03middle5.420.998.285.29short5.420.997.833.57cog velocity * * ( mm / s)long0.260.490.350.13middle0.260.490.330.14short0.260.490.320.15cog length / cm ( mm / cm)long50.3345.6833.2325.00middle50.3345.6846.3063.89short50.3345.6819.9222.93values are mean  sd ; cog : center of gravity ; * p < 0.05 ; * * p < 0.01 ; 
 p < 0.05 : compared with post - test , and changes in the balance with the eyes closed are shown in table 4table 4.rombergs test comparison according to shaft length ( eyes closed)bootspre - testpost - testcog area ( mm)long21.6630.5529.2434.63middle21.6630.5553.00120.45short21.6630.5559.3382.30cog length * ( mm)long5.251.246.844.32middle5.251.247.696.23short5.251.247.343.39cog area velocity * ( mm / s)long0.250.670.320.10middle0.250.670.320.25short0.250.670.350.16cog length / cm * ( mm / cm)long80.2073.2752.3745.35middle80.2073.2745.4631.81short80.2073.2735.1135.49values are means  sd ; cog : center of gravity ; * p < 0.05 ; * * p < 0.01 ; 
 p < 0.05 : compared with post - test .
there were neither interactions between the groups and time , nor the main 
 effects of the groups , however , in terms of the main effects of the time , there were 
 statistically significant differences between the pre - test and post - test for eo - cog area , 
 -cog length , -cog velocity , and for ec - cog length , -cog velocity , -cog 
 length / cm . as a result of the dependent t - test , in the long group , there were 
 statistically significant differences in the eo - cog area and -cog velocity ; in the middle 
 group , there were statistically significant differences in the eo - cog area ; and in the short 
 group , there were statistically significant differences in the eo - cog area , eo - length , and 
 eo - velocity , and the ec - cog length / cm also showed a statistically significant 
 difference .
values are mean  sd ; cog : center of gravity ; * p < 0.05 ; * * p < 0.01 ; 
 p < 0.05 : compared with post - test values are means  sd ; cog : center of gravity ; * p < 0.05 ; * * p < 0.01 ; 
 p < 0.05 : compared with post - test the results of the limits of stability comparison of balance ability according to the shaft 
 length of the rain boots are shown in table 
 5table 5.limits of stability comparison of ability to balance according to rain boot shaft 
 lengthbootspre - testpost - testleft**long634.01,803.96,990.22,161.0middle634.01,803.98,368.62,209.3short634.01,803.98,465.32,209.3right**long5,760.51,689.26,400.22,409.2middle5,760.51,689.27,323.91,554.5short5,760.51,689.26,990.11,332.0forward**long7,853.23,008.39,925.93,376.5middle7,853.23,008.310,497.82,291.5short7,853.23,008.311,141.72,292.5backlong3,970.91,177.34,224.82,880.8middle3,970.91,177.35,077.02,113.3short3,970.91,177.34,313.81,887.9total**long12,102.53,384.513,390.94,404.8middle12,102.53,384.515,574.92,723.6short12,102.53,384.514,807.13,512.4values are means  sd ; * p < 0.05 ; * * p < 0.01 ; p < 0.05 ; compared 
 with post - test .
the interaction of the groups and time and the main effects of the groups 
 were not significant .
the main effects of time showed statistically significant differences 
 between the pre - test and post - test values in the lt , rt , fw , and total directions .
the 
 dependent t - test results of the long group did not show statistically significant 
 differences between the pre - test and post - test ; in the middle group , there were 
 statistically significant differences in the lt , rt , fw , and total directions between the 
 pre - test and post - test ; and in the short group , there were statistically significant 
 differences in the pre - test and post - test values in the lt , fw , and total directions .
values are means  sd ; * p < 0.05 ; * * p < 0.01 ; p < 0.05 ; compared 
 with post - test
the postural control system is a dynamic feedback control system that incorporates visual , 
 vestibular , and somatosensory information and also integrates the motor system and central 
 nervous system .
muscle fatigue has been identified as a factor having detrimental effects on 
 balance control21 .
the post - fatigue 
 impairment in balance control is often attributed to deficits in neuromuscular control 
 resulting from altered somatosensory inputs22 ; overall muscle fatigue and local muscle fatigue may restrict 
 balance control output23 .
this study sought to determine the effects of lower - extremity muscle fatigue on balance 
 while walking in three types of rain boots with different shaft lengths in healthy young 
 adults . as a result of the comparative analysis of the romberg s test , there were 
 significant differences for time in eo - cog area , -cog length , -cog velocity and in the 
 ec - cog length , -cog velocity , -cog length / cm . as a result of the analysis of the 
 changes in each group pre - test and post - test , according to visual input , there were 
 significant differences in the eo - cog area and -cog velocity in the long group ; eo - cog area 
 in the middle group ; and eo - cog area , -cog length , -cog velocity , and ec - cog 
 length / cm in the short group . in a previous study on young healthy adults ,
it was reported that as a result of analyzing 
 the effects of visual and proprioceptive sensory information on the muscle activity of the 
 ankle joints in maintaining static balance , the workings of the ankle muscle became 
 diversified through sensory deprivation or changes .
this is because visual perception helps 
 to maintain the standing posture and directional orientation the conscious and unconscious 
 correction of posture is made possible through visual input .
these results show the 
 importance of visual perception in the mechanism of proprioception in the body by 
 emphasizing its importance in postural control24 . as a result of analyzing the changes in the angle of the joints 
 and the position of the upper extremities , due to fatigue induced in the ankle joints and 
 the plantar flexors in which the visual information was removed , the participants upper 
 extremities moved forward while their pelvises moved to the rear , and the flexion in the 
 ankles , knees , and waist increased .
this refers to the negative effects of fatigue and 
 compensation for the deficiency of visual information in terms of postural adjustment .
this 
 strategy could increase the role of the muscles that are not fatigued and could be utilized 
 to optimize the use of all of the associated joints in a one - leg stance25 . in another prior study , in which a group wearing unstable 
 footwear was compared to a control group , there were no significant difference in the hip 
 joint , but there were significant differences in the joints of the ankle and knee . 

compensation for postural sway was shown to be more in the distal joints than that in the 
 proximal joints ; the increased joint excursion of the ankle and knee while wearing the 
 unstable shoes in a standing sway was reported to be a compensatory mechanism in response to 
 the displacement of the center of pressure ( cop ) and the center of mass 
 ( com ) . in this study , using the romberg s test , it was determined that there were differences in 
 the eo - cog area , length , and velocity and in the ec - cog length , ec - cog velocity , ec - cog 
 length / cm , due to the effects of fatigue on the muscles of the lower extremity 
 induced by walking in rain boots , leading to the impairment of the ability to balance . due 
 to muscle fatigue
, visual information could not be received and it caused impairment of the 
 balance ability . because of the impairment of the balance ability , leading to a failure to 
 perform the unconsciousness adjustment of posture necessary for maintaining balance .
the 
 results of the changes according to time showed significant differences when subjects 
 performed the treadmill walking wearing the three types of rain boots ( long , middle , short ) 
 with the eyes open . with the eyes
closed , there was a significant difference in the short 
 group in the cog length / cm , which may be explained by the fact that the muscle 
 fatigue induced by walking reduced the ability to balance , and the relatively short shaft 
 length of the rain boots increased the movement of the ankle joints .
therefore , the workload 
 of the joints in the lower extremity increased as a compensatory mechanism due to the lack 
 of visual feedback when the visual information was eliminated . as a result of the increased 
 work of the distal joints , the shift in the cop and com caused the cog to shift in the 
 standing balance , bringing about a significant difference in the ec - cog 
 length / cm . in this study of the results of the comparative analyses of the limits of stability 
 according to time
, there were significant differences in pre - test and post - test values in 
 the lt , rt , fw , and total directions .
however , the results of the analysis regarding the 
 changes in each group before and after testing showed no significant differences in the long 
 group while there were significant differences in the lt , rt , fw , and total directions in 
 the middle group and in the lt , fw , and total directions in the short group . in a study 
 analyzing the effects of plantar flexor fatigue on posture control , it was determined that 
 localized plantar flexor muscle fatigue caused major impairment to sagittal postural 
 control . when compared to the postural coordination without fatigue , plantar flexor fatigue 
 caused a higher than average threshold sway27 . in previous studies , it was determined that a higher response to 
 ml sway training , with regard to rearward fall , was related to specific fundamental defects 
 in the ml balance .
these results are due to the inherent structural mechanisms of the ankle 
 and hip joints . in contrast , a study that reported that the postural sway in healthy 
 individuals was larger in the ap direction compared to that in the ml direction showed that 
 when compared to that in the ap direction , the risk of falling brought about a higher sway 
 threshold in the ml direction12 . in the 
 unstable shoe group , both the young adult and
such results have resulted in longer reaction times when 
 unstable shoes are worn in terms of response to the rearward sway , due to the flexing of the 
 ankle joints and the hip joints , in which the cop has been moved forward over the forefoot 
 because of changes in the ankle and hip joints .
these differences in increased distal joint 
 excursion and reaction time are responses to the backward sway , such as in a fall , which can 
 result in increased instability26 . 
 although physical balance improved when the shaft length of the shoes was increased3 , according to the results of a study on the 
 effects of shoes and shoe soles on the lower extremities and the subjects discomfort , the 
 shoes and the shoe soles affected discomfort of the lower extremities during a long 
 prolonged stance28 . accordingly , as a result of the comparison of the changes in the limits of stability in 
 this study , it was determined that muscle fatigue induced by walking , when compared to that 
 in a non - fatigued state , brought about increases in postural sway , causing an impairment of 
 postural control and reducing the ability to balance , in turn causing significant 
 differences according to time in the lt , rt , fw , and total directions . in terms of time , the 
 results of the analysis of the changes in each group before and after showed that there were 
 no significant differences in the long group while there were significant differences in the 
 lt , rt , fw , and total directions in the middle group ; and the lt , fw , and total directions 
 in the short group . in the long group ,
the relatively long shaft of the rain boots affected 
 the movement of the joints and did not cause a reduction in the balance ability ; thus , there 
 were no significant differences in the limits of stability .
there were significant 
 differences in the lt and rt directions in the middle group and the lt in the short group 
 due to the reduced ability to balance as a result of muscle fatigue , as well as a basic 
 balance defect in the ml direction due to the risk of a backward fall , causing the ml sway 
 to increase .
moreover , there were significant differences in the forward direction in both 
 the middle and short groups due to increased muscle fatigue - induced instability .
as a 
 response to the rearward sway , the relatively shorter shaft of the rain boots caused flexion 
 of the ankle and hip joints to increase the shifting of the cop forward .
therefore , it was 
 determined that instability with regard to falling caused fear , bringing about no 
 significant differences in the rear direction of all three groups . in conclusion , this study sought to determine the effects of muscle fatigue on the lower 
 extremities induced by walking , wearing three types of rain boots with different shaft 
 lengths , on balance .
( 1 ) the 
 changes in the romberg s test scores , the interactions of the groups and time , and the main 
 effects of the groups did not appear to be significant .
however , the main effects of time 
 showed to be significant in the eo - cog area , eo - cog length , and eo - cog velocity as well as 
 in the ec - cog length / cm .
there were significant differences in the eo - cog area 
 and eo - cog velocity in the long group ; the eo - cog area in the middle group ; and the eo - cog 
 area , eo - cog length , eo - cog velocity and ec - length , ec - velocity , ec - length / cm in 
 the short group .
( 2 ) the changes in the results of the limits of stability , the interaction 
 of the groups and time , and the main effects of time did not appear to be significant .
the 
 main effects of time were not significant in the lt , rt , fw , total directions , and there 
 were no significant differences in the all directions in the long group . however , there were 
 significant differences in the lt , rt , fw , and total directions in the middle group and in 
 the lt , fw , and total directions in the short group .
these results showed that muscle 
 fatigue in the lower extremities was induced by walking in rain boots and affected the 
 joints and the postural control muscles .
the compensatory mechanism due to the visual 
 feedback and the length of the shoe shaft affected the motion of the distal joints more than 
 it did the proximal joints and caused an impaired ability to balance .
thus , these results , 
 in which muscle fatigue induced by the shoe soles and the shaft length of the shoes affected 
 the ability to balance , are expected to aid in future research with regard to postural 
 control , according to visual feedback and the shoe - related ability to balance .
 [ purpose ] effects of muscle fatigue on lower - extremity balance were evaluated in 12 
 healthy young women in their 20s while they walked on a treadmill wearing rain boots of 
 different lengths . 
 [ methods ] the rain boots were divided into three groups based on the 
 shaft length ( long , middle , short ) . 
 romberg s test was applied and limits of stability 
 were measured before and after treadmill walking . [ results ] romberg s test showed a 
 significant main effect for time . 
 there were significant differences between the center of 
 gravity area , length , and velocity when the eyes were open and the center of gravity 
 length , velocity , and length / cm2 when the eyes were closed . 
 changes in the 
 limits of stability also showed a significant main effect of time . 
 there were significant 
 differences in pre - test and post - test values in the left , right , forward , and total 
 directions . 
 [ conclusion ] it was found that muscle fatigue in the lower extremities 
 generated by walking in rain boots affected the joints and the adjuster muscles , depending 
 on shaft lengths . 
 compensation due to visual feedback and the length of the boot shaft 
 affected movement of the distal joints , resulting in a reduced ability to balance . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION