females commonly wear high heels to give an appearance of being taller and to accentuate 
 the appearance of their legs1 . in 
 addition , as they have social and cultural meaning , as well as psychosexual significance , 
 high heels have become a consistent component of fashion trends for females2 .
in fact , it has been reported that 
 fashion - conscious young females can wear high - heel shoes for up to 8 hours per day while 
 performing activities of daily living , such as standing and walking3 .
prolonged wearing of high heels may be a predisposing risk 
 factor for impairments in body alignment , lower limb proprioception , and musculoskeletal 
 injury4 , 5 .
it has been suggested that an interaction between high heels and 
 hormonal factors could explain the 2-fold higher incidence of knee osteoarthritis in 
 females , compared to males6 .
moreover , as 
 they increase the magnitude of torque about the knee during standing and walking , high heels 
 could increase the risk for knee joint injury and degenerative changes due to accumulated 
 fatigue7 .
such degenerative changes 
 could alter knee joint position sense , negatively affecting balance control and leading to 
 lowered capacity for activities of daily living and mobility8 , 9 .
balance control largely refers to the ability to maintain alignment of the body along the 
 line of gravity and lower the amplitude and velocity of sway of the body center of 
 gravity10 , 11 , and is strongly influenced by knee joint position sense .
high 
 heels narrow the base of support and restrict the area within which body sway must be 
 controlled to avoid triggering a fall . compounding
this problem of balance control is the 
 negative effect of high heels on knee joint position sense , which reduces the efficiency of 
 the system to use proprioceptive information to strictly control body sway within the 
 available base of support5 .
the chronic 
 demand on lower limb muscles and soft tissues to manage these changes in proprioception and 
 base of support can eventually lead to inefficient contraction of leg muscles and abnormal 
 muscle lengths12 .
however , the effects of 
 high heels on muscle activity , proprioception , and lower limb alignment have only been 
 evaluated within the context of standing4 , 13 , without consideration of the potentiating 
 effects of walking in high heels .
therefore , the aim of our study was to examine the effects 
 of increased heel height and gait velocity on balance control and knee joint position 
 sense .
all participants were right - foot dominant , 
 naive to high - heel use , and had no previous history of neuromuscular disease , fractures , 
 spine - related diseases , or lower limb surgery .
after being provided with a full explanation of the study procedure , without 
 disclosure of the study purpose , participants gave informed consent .
participants were randomly allocated to the low - heel , low - speed group ( 3  cm , 2  km / h , ll ) , 
 the low - heel , high - speed group ( 3  cm , 4  km / h , lh ) , the high - heel , low - speed group ( 9  cm , 
 2  km / h , hl ) , or the high - heel , high - speed group ( 9  cm , 4  km / h , hh ) , with 10 subjects per 
 group .
the distribution of age , height , and weight within each group is reported in table 1table 1.general characteristics of the study group ( n=40)grouplllhhlhh(n=10)(n=10)(n=10)(n=10)age ( years)21.6  1.921.9  2.222.0  1.922.8  2.0height ( cm)158.4  5.5157.2  5.0158.4  8.0158.5  5.4weight ( kg)56.2  5.057.6  4.356.5  4.257.4
ll(a ) : low - heel low - speed 
 group ; lh(b ) : low - heel high - speed group ; hl(c ) : high - heel low - speed group ; hh(d ) : 
 high - heel high - speed group .
baseline measurements of static and dynamic balance and joint 
 position sense were obtained prior to the experimental session .
participants in the ll and 
 hl groups wore shoes with a 3-cm heel , while participants in the lh and hh groups wore shoes 
 with a 9-cm heel .
all walking trials were performed on a treadmill ( t25 , motus , korea ) , at 2 
 speeds for 20  min : 2  km / h for the low - speed group and 4  km / h for the high - speed group . 
 following the walking trial , participants removed their shoes and completed posttest 
 assessments of static and dynamic balance , and knee joint position sense .
all participants 
 were evaluated under the same experimental conditions , and provided with an adaptation time 
 of approximately 10  min before and after the measurements .
ll(a ) : low - heel low - speed 
 group ; lh(b ) : low - heel high - speed group ; hl(c ) : high - heel low - speed group ; hh(d ) : 
 high - heel high - speed group static and dynamic balance tests were performed using an automatic balance calibration 
 system ( model i balance s , cybermedic co. , iksan , korea ) .
the i - balance system provides a 
 measure of the sway velocity of the center of gravity of the body and the total amplitude of 
 sway , using a force platform equipped with 4 load cells . for static balance testing
, 
 participants stood on the force platform , with feet shoulder - width apart and hands folded 
 across the chest .
participants were asked to look directly in front at a monitor providing 
 feedback of the location of their center of gravity and to maintain the position within the 
 spatial area provided by the program .
static balance was quantified by the length of time 
 ( s ) the reference position of the center of gravity was maintained within the reference 
 spatial area .
for dynamic balance testing , participants assumed the same posture as for 
 static balance testing but were asked to change the position of the center of gravity to 
 match locations presented by the program : anterior , posterior , right , left , and along 
 diagonals relative to their neutral position .
dynamic balance was quantified by the response 
 time along each direction ( s ) .
diagnostic tests using smartphone applications have 
 recently been conducted for clinical and scientific diagnosis , and the reliability of the 
 drgoniometer application has been verified in previous studies15 , 16 .
participants 
 were placed in the prone position , with eyes blindfolded and the torso and thighs stabilized 
 using a belt .
the knee being assessed was passively flexed to 90 and held for 5  s to 
 provide participants with a sensory representation of the reference angle .
participants were 
 then asked to actively flex their knee further to 120 , holding the new end - point position 
 again for 5 s. the learning trial was repeated 3 times to ensure that participants had 
 obtained an accurate sensory representation of 90 and 120 of knee flexion . for testing , 
 the knee was again passively flexed to 90 , and participants were then asked to actively 
 flex their knee further to 120 , telling the experimenter when they felt they had reached 
 the target knee angle .
a total of 6 measurements were completed and the difference between 
 the target angle of 120 and the measured angle calculated .
the assessments were performed under identical experimental 
 conditions for the pre- and posttest , and all tests were performed by the same experimenter . 

the normality of the distribution of variables 
 was evaluated using the shapiro - wilk test , with data transformation used as needed to 
 achieve a normal distribution .
effects of heel height and walking speed were evaluated using 
 a two - way analysis of variance ( anova ) , and statistical significance was set at an -level 
 of 0.05 .
changes in static balance as a function of shoe heel height and gait velocity are reported 
 for each group in table 2table 2.changes of static balance according to shoe heel height and gait velocity 
 ( sec)groupmean  sdprepostll0.34  0.10.39  0.1***lh0.36  0.10.41  0.1***hl0.34  0.10.45  0.2***hh0.34  0.10.53  0.1****p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post . p<0.05 , 
 p<0.01 , p<0.001 , comparison between group .. overall , we identified an increase in sway amplitude as a function of 
 increased heel height and gait velocity , with an increase in sway amplitude of 0.05 in the 
 ll group , 0.05 in the lh group , 0.11 in the hl group , and 0.19 in the hh group .
a 
 significant group time interaction was identified ( p<0.05 ) , with the condition of high 
 heels and high velocity causing the largest increase in sway amplitude .
* p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post .
changes in dynamic balance as a function of shoe heel height and gait velocity are reported 
 for each group in table 3table 3.change of dynamic balance according to shoe heel height and gait velocity 
 ( sec)groupmean  sdprepostll1.69  0.62.23  0.9***lh1.66  0.42.33  0.8***hl1.50  0.42.76  0.9***hh1.60  0.43.89  0.9****p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post .
p<0.05 , 
 p<0.01 , p<0.001 , comparison between group .. sway amplitude increased by 0.54 in the ll group , 0.67 in the lh group , 1.26 
 in the hl group , and 2.29 in the hh group , again indicating that amplitude of sway increased 
 as shoe heel height and gait velocity increased .
a significant group  time interaction was 
 identified ( p<0.001 ) , with the condition of high heels and high velocity causing the 
 largest increase in sway amplitude .
* p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post .
assessment of knee position sense provided evidence of an increased magnitude of error with 
 increasing heel height and gait velocity .
the magnitude of error in joint position sense 
 across the 4 groups , using the reference position of 60 , was as follows : 0.68 for the ll 
 group ; 1 for the lh group ; 0.86 for the hl group , and 4.62 for the hl group ( table 4table 4.change of position sense of knee joint according to shoe heel height and gait 
 velocity ( )groupmean  sdprepostll0.64  3.31.32  2.8lh0.16  5.71.16  2.2hl0.76  3.31.62  3.0hh0.48  3.05.10  4.2*p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post .
again , a significant group  time interaction was identified ( p<0.05 ) , 
 with the condition .
* p<0.05 , * * p<0.01 , * * * p<0.001 , comparison between pre and post .
an improper fitting of the shoe can 
 negatively affect the body alignment and balance19 .
in particular , high - heel shoes can modify the position sense of 
 the knee joint , which itself modifies the responsiveness of the muscles responsible for 
 aligning the trunk and lower limbs along the line of gravity .
these modifications in 
 sensory - motor control can functionally reduce balance capacity and increase the risk for 
 falls20,21,22 , 24 .
balance capacity has been shown to be closely correlated with proprioception , with knee 
 joint position sense being an important component of proprioception influencing balance and 
 walking performance23 .
single - leg balance 
 training on a trampoline has been shown to enhance knee joint position sense , resulting in 
 increased balance capacity , measured by a significant reduction in the amplitude of body 
 sway .
our study contributes novel knowledge on the effects of wearing high heels on balance 
 control .
specifically , we demonstrated that a trial of 20  min of treadmill walking with high 
 heels was sufficient to lower the acuity of knee position sense and to increase the 
 amplitude of body sway under both conditions of static and dynamic balance .
our findings are 
 comparable to previous reports of the effect of high heels in increasing the amplitude and 
 area of sway during static standing4 and 
 reduced dynamic stability during fore - aft walking22 .
similar negative effects of high heels on sensory input were 
 identified by a reduction in two - point discrimination and sensitivity to light tactile touch 
 on the soles of the feet , and lower position sense of the great toe in young females who 
 wore high heels for more than 20  h per week13 .
other studies have reported a decrease in knee joint position 
 sense following high - intensity isokinetic knee exercises26 .
the effects of high heels on knee joint position sense could be 
 mediated by an increase in ankle plantar flexion angle and an associated larger range in 
 vertical displacement of the center of gravity during walking21 , 25 .
another important 
 component of decreased knee joint position sense might be muscle fatigue induced by 
 increased gait velocity , which increases the number of strides per minute26,27,28 .
overall , our results show that higher gait velocity and heel height induce a change in knee 
 joint position sense , which negatively affect static and dynamic posture control .
future 
 studies regarding the effects of heel height on lower limb proprioception and balance 
 capacity are needed to evaluate age effects that would be prognostic of an increased risk 
 for falls .
 [ purpose ] the aim of this study was to examine the effects of increased heel height and 
 gait velocity on balance control and knee joint position sense . [ subjects and methods ] 
 forty healthy adults were randomly allocated to 4 groups : low - heel , low - speed group ( 3  cm , 
 2  km / h ) , low - heel , high - speed group ( 3  cm , 4  km / h ) , high - heel , low - speed group ( 9  cm , 
 2  km / h ) , high - heel , and high - speed group ( 9  cm , 4  km / h ) , with 10 subjects per group . 
 
 static and dynamic balance was evaluated using the i - balance system and knee joint 
 position sense using a goniometer . 
 measurements were compared using a pre- and posttest 
 design . 
 [ results ] increasing heel height and gait velocity decreased knee joint position 
 sense and significantly increased the amplitude of body sway under conditions of static 
 and dynamic balance , with highest sway amplitude induced by the high - heel , high - speed 
 condition . 
 [ conclusion ] increased walking speed in high heels produced significant 
 negative effects on knee joint sense and balance control . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION