the aging process is often associated with biomechanical changes in the foot with effects 
 on lateral deviation of the legs , the plantar arch , and intrinsic muscular strength of the 
 toes1,2,3,4,5 . the most prevalent toe disorder is the 
 hallux valgus , which is characterized by a lateral deviation of the big toe away from the 
 midline of the body6 , 7 . the prevalence of this disorder is 36% in those over 65  years , 
 while the rate in adults is 23%7 . this 
 disorder is often associated with pain , mobility impairment , postural instability , and an 
 increased risk of falls8,9,10 . genetic history , abnormal hind foot kinematics , wearing high - heeled shoes , bony 
 abnormalities , foot muscular dysfunction and imbalance could be associated with the etiology 
 of hallux valgus11,12,13,14,15 . the foot provides a 
 direct source of contact with the ground during standing and walking activitie and with pain 
 and/or structural deformity , it is likely in turn to impair balance and consequently 
 increase the risk of falls . as suggested by menz et al.16 , the foot contributes to maintenance of postural stability in two 
 ways : 1 ) mechanical support for the body via the osteoligamentous arch and the coordinated 
 function of lower limb muscles , and 2 ) sensory information with regard to body position and 
 proprioception from plantar tactile mechanoreceptors . foot posture can be measured objectively by anthropometric approaches as well as by 
 photographs or footprint analysis with digital imaging software ( e.g. , imajej , sapo)16 , 17 . other approaches include use of the manchester scale to assess the 
 level of severity of hallux valgus18 , 19 , x - ray angular measurement20 , 21 , a force plate for balance and force reaction measurements22 , and electromyography or an ultrasound 
 system for measurement of muscular dysfunction of the foot23,24,25 . these last techniques provide both accurate and reliable 
 information21,22,23,24,25 , although they require 
 high - tech equipment and are costly for clinical practice . some evidences has shown that excessively flat feet and highly arched feet impair standing 
 balance in healthy young subjects26 , 27 . also , a significant association was 
 observed in measurements of the ankle range of motion ( rom ) and balance in older 
 subjects28 . based on differences 
 between younger and older subjects in the neuromuscular and bony systems , it would be of 
 interest to perform a comparison of foot posture measurements and balance in an experiment 
 using the same design . the purposes of this study were to 1 ) compare age differences for a 
 broader range of anthropometric posture measurements of the foot and for two main balance 
 parameters on a force platform under two balance conditions ( bipodal and unipodal ) , and 2 ) 
 to determine the relationship between all these measurements in both younger and older 
 subjects . a total of 110 healthy female volunteers ( n=68 older and n=42 younger subjects ) 
 participated in the present study . the mean characteristics of the older subjects were as 
 follows : age 685 yrs , body mass 6311  kg , height 1.520.1 m , and body mass index ( bmi ) 
 274  kg / m . those of the younger subjects were as follows : age 212 yrs , body 
 mass 608  kg , height 1.640.1 , and bmi 223 the inclusion criteria were as follows for older 
 subjects : ( 1 ) age more than 60  years old , physically independent , no falls in the previous 
 year , and a score > 18 on the mini - mental state examination29 . the inclusion criteria for the younger group were age between 18 
 and 30  years and being healthy . general exclusion criteria for both groups were as follows : 
 participation in any physical activity program , neuromusculoskeletal disorders , 
 labyrinthitis , and chronic cardiovascular system diseases . the subjects were informed about 
 the study s experimental protocol , and potential risks and written consent was obtained 
 before their participation . the consent forms were previously approved by the local ethics 
 committee ( cep 276.702 ) . prior to performing all measurements , the subjects were familiarized with the experimental 
 protocol , especially with respect to assessment under two balance conditions on a force 
 platform . foot posture was tested across four domains16 , 17 , 30,31,32,33,34 . for hallux flexion and extension rom , the subjects were in an orthostatic position with the limb to 
 be evaluated placed on a bench ( approximately at 90 of knee flexion ) allowing free 
 movements of the hallux . the first metatarsophalangeal joint ( hallux joint ) was then 
 measured in a non - weight - bearing position with a goniometer while the examiner maximally 
 extended and flexed the hallux32 . three 
 trials of the hallux rom by side ( right foot , r ; left foot , l ) were performed , and the mean 
 was retained . for goniometry measurements , the navicular height was measured in centimeters 
 ( cm ) using an analog pachymeter while the subject was bearing her full weight , and was then 
 corrected for differences in foot size by dividing it by the length of the foot34 , which was measured with a pachymeter . for 
 both measurements ( navicular height and length of the foot ) , three trials were performed for 
 both feet by the examiner , and the mean was computed . the footprints were obtained using a carbon - paper imprint material with the subject 
 standing in a relaxed position under the following standardized conditions : barefoot and 
 arms parallel to their trunk . afterwards , the foot imprint material was analyzed using a 
 computer graphics tablet and the imaging software imagej v.145 ( national institutes of 
 health , bethesda md , usa ) , and the reference footprint parameters ( area of the foot on 
 paper ) were then calculated , as previously detailed by bega31 : the width of the forefoot is the quotient of the total length of 
 the foot ( corrected by height ) divided by three ; the arch index in the transverse plane of 
 the footprint is calculated as the quotient of the width of the forefoot divided by three 
 ( e.g. , defined as high values for flatfeet and low values for arched feet)17 , 31 , and finally , the physiological hallux valgus of the footprint was 
 calculated by multiplying by 2% of the total length of the foot31 . after the foot measurements , the participants stood on a force platform ( biomec400 , so 
 paulo , brazil ) under the following two conditions : ( 1 ) the bipodal condition ( bc : two legs 
 placed on force platform ) during 60-s trials35 ; and ( 2 ) the unipodal condition ( uc : leg preferred on force 
 platform ) during 30-s trials . there was a rest period of approximately 30  s between each 
 trial under both conditions , and the mean was retained for analysis . during all trials , the 
 participants were instructed concerning the following standardized conditions : barefoot , 
 eyes open and looking at a target ( cross ) placed on a wall at eye level 2  m away , and arms 
 at the sides or parallel to the trunk36 . force reaction signals from the platform were collected with a sampling at 100  hz and 
 filtered with a butterworth low - pass second - order filter at 35  hz . signals were then 
 converted through a stabilographic analysis to extract all of the parameters associated with 
 movements of the center of pressure ( cop ) , such as the ellipse area ( 95% ) of the cop ( a - cop 
 in cm ) and mean velocity ( vel in cm / s ) of the cop sway in the anteroposterior 
 ( a / p ) and mediolateral ( m / l ) directions . the test - retest reliability of these main 
 parameters of balance has been shown to be excellent for both groups36 . the 
 student s unpaired t - test was used to assess between - group differences in anthropometric 
 variables , foot posture measurement , and balance parameters . pearson s correlation 
 coefficients were used to assess the relationship between all foot posture measurements and 
 balance parameters under both conditions . the spss software ( version 15 for windows ) was 
 used to perform all statistical analyses , with significance taken at 5% ( p < 0.05 ) . significant differences between groups were found for age , height , and bmi variables , but 
 not for body mass . from goniometry measurements , older subjects presented lower rom values 
 for the hallux than young adults , with significant differences ( p<0.01 ) between groups 
 for all variables ( table 1table 1.goniometry measurement of the hallux in flexion and extensionvariablesolder ( n=68)mean ( sd)young ( n=42)mean ( sd)size effectrom flexion - r ( )54 ( 7)57 ( 7)*0.41rom flexion - l ( )50 ( 6)55 ( 5)*0.81rom extension - r ( )48 ( 8)53 ( 8)*0.61rom extension - l ( )51 ( 9)55 ( 7)*0.45rom , range of motion of the hallux in flexion and extension . * p<0.05 : significant differences between the groups ( older < rom of hallux 
 than young ) . there was a moderately high size , which in itself is clinically 
 interesting . ) . a moderately high size effect was shown , which in itself is clinically 
 interesting . * p<0.05 : significant differences between the groups ( older < rom of hallux 
 than young ) . significant differences between older and younger subjects were found for all variables in 
 the pachymeter ( navicular height and length of the foot ) and footprint ( width of forefoot , 
 arch index , and hallux valgus ) measurements ( table 
 2table 2.foot posture measurements obtained with the pachymeter and footprintvariablesolder ( n=68)mean ( sd)young ( n=42)mean ( sd)size effectpachymeter measurementsnavicular height - r ( cm)7.5 ( 0.7)7.7 ( 0.5)*0.31navicular height - l ( cm)7.5 ( 0.7)7.8 ( 0.5)*0.47length feet - r ( cm)22.1 ( 1.1)22.6 ( 1.0)*0.47length feet - l ( cm)21.9 ( 1.14)22.5 ( 1.1)*0.53footprint measurementswidth of fore feet - r ( cm)8.8 ( 0.8)8.4 ( 0.4)*0.58width of fore feet - l ( cm)8.8 ( 0.5)8.4 ( 0.4)*0.58arch index - r ( cm)3.7 ( 0.9)3.3 ( 0.7)*0.51arch index - l ( cm)3.7 ( 0.9)3.2 ( 0.7)*0.59hallux valgus - r ( cm)0.43 ( 0.1)0.44 ( 0.5)*0.07hallux valgus - l ( cm)0.43 ( 0.1)0.45 ( 0.2)*0.13mean values are shown with the standard deviation ( sd ) in parentheses . pachymeter measurements : navicular height and length of the foot ; 
 footprint measurements : width of forefoot , arch index and hallux valgus . the footprint measurements are also generally moderate but for both hallux 
 valgus measurements , the effect sizes are really weak , even though the values are 
 significant . from a clinical perspective , the hallux measurements are not 
 interesting . ) . for both sides ( r and l ) , older individuals presented lower values than 
 younger adults for navicular height and length of the foot ( pachymeter ) , and for hallux 
 valgus ( footprint ) variables , with a moderate size effect between them . in contrast , high 
 values were found for width of the forefoot and transverse arch index variables in older 
 compared with younger subjects ( table 2 ) , thus 
 characterizing the flatfeet of older people . from the footprint measurements , the size 
 effect was moderate across measurements but for both the hallux valgus , the effect sizes 
 were weak , even when the values were significant . from a clinical perspective , the hallux 
 measurements are not interesting . pachymeter measurements : navicular height and length of the foot ; 
 footprint measurements : width of forefoot , arch index and hallux valgus . * the footprint measurements are also generally moderate but for both hallux 
 valgus measurements , the effect sizes are really weak , even though the values are 
 significant . from a clinical perspective , the hallux measurements are not 
 interesting . poor balance in older people in comparison with younger people was seen only under the 
 unipodal conditions ( uc ) for all cop parameters ( table 
 3table 3.postural balance results under bipodal and unipodal conditions ( bc and 
 uc)variablesolder ( n=68)mean ( sd)young ( n=42)mean ( sd)size effectbipodal conditionbc a - cop ( cm)1.2 ( 0.9)1.1 ( 0.6)0.09bc vel a / p ( cm / s)0.7 ( 0.1)0.6 ( 0.1)0.24bc vel m / l ( cm / s)0.5 ( 0.1)0.5 ( 0.1)0.26unipodal conditionuc a - cop ( cm)9.9 ( 3.7)7.7 ( 2.6)*0.70uc vel a / p ( cm / s)2.9 ( 0.8)2.2 ( 0.5)*1.02uc vel m / l ( cm / s)3.3 ( 0.7)2.4 ( 0.6)*1.20mean values are shown with the standard deviation ( sd ) in parentheses . bc , bipodal 
 balance condition ; uc , unipodal balance condition . a - cop : the ellipse area ( 95% ) of 
 the center of pressure ( cop ) . vel : mean velocity of the cop sway in both directions of 
 movement anteroposterior ( a / p ) and mediolateral ( m / l ) . * p<0.05 : significant 
 differences between groups only under the unipodal condition . under the bipodal 
 condition , a weak effect size was found . under the unipodal condition , a very strong 
 effect size was found . ) . the cop values were significantly higher in older subjects than in younger 
 subjects ( e.g. , a - cop of 9.97 vs. 7.72  cm ) . interestingly , a very strong effect 
 size was found only under the unipodal condition . the correlations between all foot posture 
 measurements and cop parameters varied across groups , from weak to moderate 
 ( r 0.01 to 0.46 ; tables 
 4table 4.pearson coefficient correlation between goniometry measurements 
 and balance cop parametersvariablesgroupsbalance cop parametersbc - acop rbc - velap rbc - velml ruc - acop ruc - velap ruc - velml rrom flx - rolder0.130.120.040.380.030.08young0.290.150.230.010.210.24rom flx - lolder0.030.130.160.290.200.01young0.330.200.340.210.330.16rom ext - rolder0.060.300.260.080.150.10young0.340.160.060.200.020.01rom ext - lolder0.040.060.130.460.170.01young0.310.180.100.030.030.12r , coefficient correlation values and p values in parentheses . a - cop : the ellipse area 
 ( 95% ) of the center of pressure ( cop ) . vel : mean velocity of the cop sway in both 
 directions of movement anteroposterior ( a / p ) and mediolateral ( m / l ) . rom : range of 
 motion of the hallux in flexion ( flx ) and extension ( ext ) . p<0.01 : significant correlation between goniometry measurements 
 and balance cop parameters . and 5table 5.pearson coefficient correlation between foot posture 
 measurements ( pachymeter and footprint measurements ) and balance cop 
 parametersvariablesgroupsbalance cop parametersbc - acop rbc - velap rbc - velml ruc - acop ruc - velap ruc - velml rnav . height - lolder0.110.410.280.180.320.39young0.060.030.090.140.050.08length feet - rolder0.060.010.160.010.210.07young0.030.080.030.250.260.35length feet - lolder0.140.010.210.040.180.12young0.020.100.020.280.250.29width feet - rolder0.230.260.120.120.080.28young0.010.050.110.080.120.12width feet - lolder0.120.080.070.130.020.03young0.020.020.020.260.170.23arch index - rolder0.180.160.010.110.330.09young0.140.060.080.100.100.10arch index - lolder0.140.040.150.230.090.05young0.090.070.180.270.080.09hallux valgus - rolder0.070.020.200.020.210.09young0.070.120.010.270.290.36hallux valgus - lolder0.010.040.290.010.170.05young0.030.100.020.260.250.29r , coefficient correlation values and p values in parentheses . a - cop : the ellipse area 
 ( 95% ) of the center of pressure ( cop ) . vel : mean velocity of the cop sway in both 
 directions of movement anteroposterior ( a / p ) and mediolateral ( m / l ) . p<0.01 : significant correlation between foot posture measurements 
 ( pachymeter and footprint ) and balance cop parameters . ) . no systematic advantage of any one foot posture measurement in relation to 
 cop parameters was found across the groups . the best and most significant correlations were 
 found for the hallux rom ( r 0.046 for rom in extension with a - cop under 
 the unipodal condition ) and navicular height ( r 0.041 for navicular height 
 under the bipodal condition for vel - ap ) with the cop parameters . a - cop : the ellipse area ( 95% ) of 
 the center of pressure ( cop ) . vel : mean velocity of the cop sway in both directions of 
 movement anteroposterior ( a / p ) and mediolateral ( m / l ) . * p<0.05 : significant 
 differences between groups only under the unipodal condition . under the bipodal 
 condition , a weak effect size was found . under the unipodal condition , a - cop : the ellipse area 
 ( 95% ) of the center of pressure ( cop ) . vel : mean velocity of the cop sway in both 
 directions of movement anteroposterior ( a / p ) and mediolateral ( m / l ) . rom : range of 
 motion of the hallux in flexion ( flx ) and extension ( ext ) . a - cop : the ellipse area 
 ( 95% ) of the center of pressure ( cop ) . vel : mean velocity of the cop sway in both 
 directions of movement anteroposterior ( a / p ) and mediolateral ( m / l ) . pachymeter measurements : navicular ( nav . ) height and length of the foot . p<0.01 : significant correlation between foot posture measurements 
 ( pachymeter and footprint ) and balance cop parameters . older and younger people had differences in all foot posture measurements , the older having 
 lower hallux mobility and higher values of forefoot width and transverse arch index than 
 young adults , thus characterizing the flatness of their feet . however , no systematic 
 advantage of any one foot posture measurement ( goniometry , pachymeter , footprint ) in 
 relation to cop parameters was found across groups , although low mobility of the hallux was 
 related to higher cop values ( poor balance ) , especially in older people . to the authors knowledge and based on a literature search on this issue10,15,16,17 , 22 , 26,27,28 , 
 a comparison of older and younger adults in the same study for different foot posture 
 measurements and cop parameters under two conditions , and an examination of the correlation 
 between all these measurements have not been previously reported . with regard to foot 
 posture measurements , age - related differences can be dependent on changes in orthopedic 
 anatomy and/or foot architectural and anthropometric characteristics with the increase in 
 age1,2,3 . older healthy people ( without apparent 
 deformities ) present a lower rom of the hallux and flatfeet compared with young adults16 , 28 , 37 , which support our findings . it is also 
 known that aging is associated with neuro - musculoskeletal alterations and decreased 
 physiological functions , which in turn can lead to problems such as muscular weakness and 
 lack of mobility , as well as other sensory - motor deficits and a consequent loss of 
 balance15,16,17 , 25 , 28 , 29 , which also support our results of poor balance in the elderly . in the present study , these results agree with previous studies for this condition36 , 38 
 but are contrary to those of another study35 , which assessed healthy community - dwelling older adults using a 
 double - leg stance task . no difference was identified under the bipodal condition in our 
 findings , which is also supported by the size effects . an explanation for this could be 
 collection of the data at 30  s , while in previous work , the time series was stopped at 60 or 
 120 s. however , as suggested by parreira et al.38 , differences between older and younger adults are observed with 
 10  s cop time series . at this time , motor control strategies as well as real balance 
 deficits from muscular weakness or sensorymotor impairment become more evident between 
 groups . in this case , we assumed then that a bipodal condition is not adequate to 
 discriminate postural control , since both populations can perform similar short - term 
 postural adjustments . compared with the bipodal condition , the unipodal condition has often 
 been more associated with the prediction of falls as well as fall - related injuries39 . the clinical relevance of foot posture measurements in both older and younger adults is 
 that foot structures have an influence on balance26 , 
 27 . it is suggested that the presence 
 of non - weight - bearing frontal - plane foot postures such as forefoot varus , rearfoot varus , 
 plantar - flexed fifth ray , or ankle joint equinus result in increased compensatory foot 
 pronation during weight bearing , which in turn causes compensatory hypermobility of the 
 subtalar joint and midtarsal joint and consequently can create an unstable base of support 
 that may translate into impaired postural balance . cobb et al.26 , evaluating 32 healthy young adults ( mean age 29 yrs ) in a 
 one - leg stance platform task , showed decreased postural stability in individuals with 
 increased forefoot varus ( > 7 ) . the authors explained their results as being due to a 
 decrease in joint subtalar congruity and increased reliance on soft tissue structures for 
 foot stability . hertel et al.27 , also 
 evaluating young adults ( n=30 , mean age 22 yrs ) , reported an increased cop sway area in 
 individuals with pes cavus foot structures compared with those with pes rectus foot 
 structures . the authors showed no differences in either cop sway area or cop sway velocity 
 between subjects with pes planus foot structures compared with those with pes rectus foot 
 structures . however , both the studies of cobb26 and hertel27 
 collected only limited cop time - series data computed at 5 and 10  s , respectively , during the 
 one - leg stance task . as stated before , a short time series is not enough to accurately 
 discriminate the balance mechanism of postural control in the two different groups38 . in contrast , the present study showed 
 significant differences between older and younger subjects for all variables in the 
 pachymeter ( navicular height and length of the foot ) and footprint ( width of fore foot , arch 
 index and hallux valgus ) measurements and cop measurements in a 30  s time series instead of 
 5 or 10  s time series , which were used by cobb26 and hertel27 . the relationship between hallux rom and cop parameters is in agreement with previous 
 studies16 , 28 , although the experimental protocols were not exactly the same . mecagni et al.28 , evaluating women 
 between 64 and 87 yrs old , showed an association ( in mean r = 0.30 ) of 
 ankle rom with functional balance . menz et al.16 , evaluating 156 older women ( mean age 80 yrs ) , reported a 
 significant association (  weight = 0.226 from multiple regression analyses ) between ankle 
 flexibility and sway functional balance on the floor . the authors pointed out also that this 
 mobility measure and others such as plantar flexor strength can explain 59% of the variance 
 in the balance scores . our results are in agreement with these , at least for the rom of the 
 hallux in relation to with cop parameters . in summary , our results suggest that some foot 
 characteristics can influence in cop sway on force platform measurements . these results have 
 clinical and research implications for balance rehabilitation programs for the elderly as 
 well as for prevention programs linked to musculoskeletal foot postural disorders . foot 
 posture characteristics are of concern , since cutaneous plantar afferent activity is often 
 important in the regulation of postural control37 . if individuals with foot postural disorders receive less afferent 
 input from the plantar cutaneous receptors , they may have less efficient mechanisms of 
 control of their upright posture during a single - leg stance . however , further research is 
 needed on this issue . finally , the results of this study can not necessarily be generalized to all older 
 individuals . toe weakness and deformity , foot posture deformities , ankle mobility , and foot 
 muscular strength were not investigated . a side comparison was not performed , although no 
 significant differences in postural control measurements have been reported between the 
 right and left limbs or dominant and nondominant limbs40 . in conclusion , older people showed poor balance compared with 
 young adults only under the unipodal condition . older individuals have low hallux mobility 
 and high values for the width of the forefoot and transverse arch index compared with young 
 adults , thus characterizing their flatfeet . low mobility of the hallux was significantly 
 related to higher cop values ( poor balance ) under the bipodal condition , and this was 
 especially the case for older subjects under the unipodal condition .
[ purpose ] the aim of this study was to compare age - related differences in balance and 
 anthropometric posture measurements of the foot and to determine any relationship between 
 them . [ subjects and methods ] sixty - eight older and 42 younger adults participated in this 
 study . 
 foot posture was tested for four domains : 1 ) hallux flexion and extension range of 
 motion using a goniometer , 2 ) navicular height and 3 ) length of the foot using a 
 pachymeter , and 4 ) footprint ( width of forefoot , arch index and hallux valgus ) . 
 balance 
 was tested under two conditions on a force platform : bipodal in 60-s trials and unipodal 
 in 30-s trials . 
 the sway area of the center of pressure and velocity in the 
 anteroposterior and mediolateral directions were computed . 
 [ results ] older individuals 
 showed significantly poorer balance compared with younger adults under in the unipodal 
 condition ( center of pressure area 9.97 vs. 7.72  cm2 ) . 
 older people presented a 
 significantly lower hallux mobility and higher values for width of the forefoot and 
 transverse arch index than younger adults . 
 the correlations between all foot posture and 
 center of pressure parameters varied across groups , from weak to moderate 
 ( r 0.01 to 0.46 ) . 
 low hallux mobility was significantly related to 
 higher center of pressure values in older people . 
 [ conclusion ] these results have clinical 
 implications for balance and foot posture assessments .