the foot plays an essential role in human movement , as it is the only part of the body that 
 provides contact with the supporting surface during weight bearing activities such as 
 standing , walking , hopping , jumping , and running .
it is responsible for absorbing shock , 
 adapting to irregular surfaces , and generating momentum for forward propulsion during 
 gait1 .
unfortunately , any changes to the 
 foot posture may eventually impair its function and make it prone to injury during physical 
 activities2 . in older adults , changes in the foot structure may be related to the wear and tear 
 processes that progress over the years .
for instance , due to the normal aging process , 
 muscle properties decline about 3050% between the ages of 40 and 80  years old ; this decline 
 may result in reduced range of motion ( rom ) , reduced muscle strength , and diminished plantar 
 tactile sensation leading to alteration in plantar loading responses3 .
these changes may affect the foot posture and , in turn , 
 limit its ability to withstand any perturbation to balance control .
generally , there are three types of foot posture : neutral or normal , pronated , and 
 supinated .
the neutral foot has a normal anatomical structure with strong ligaments and 
 normal height of one transverse and two longitudinal arches , providing a better postural 
 stability .
the pronated foot presents with flattening of the medial arch , calcaneal 
 eversion , forefoot valgus , and a hypermobile midfoot4 . as a result of this posture ,
these alterations may stretch the spring ligament and tendon of the 
 tibialis posterior muscle , potentially leading to increased dropping of the medial 
 longitudinal arch ( mla ) and greater demand on the neuromuscular system to stabilize the foot 
 and maintain an upright stance .
however , the pronated foot is able to unlock the mid - tarsal 
 region during ambulation due to its loose - packed characteristics , allowing it to act as a 
 shock absorber .
a study has shown that a pronated foot may eventually cause mechanical 
 problems at the waist , hip , and knee joints including excessive calcaneal extroversion of 
 about 2 to 3 degrees6 that may further 
 lead to overuse injury7 .
in contrast , the 
 supinated foot , which is also known as a high - arched foot , presents with excessively high 
 mla , calcaneal inversion , and forefoot varus .
the supinated foot is vulnerable as it may not 
 adequately adapt to the underlying surface , increasing the demand on the surrounding 
 musculoskeletal structures to maintain postural stability and balance due to its hypomobile 
 midfoot4 . as a result
, it may not be 
 able to distribute the weight bearing evenly along the metatarsal heads and lateral side of 
 the foot5 , exposing it to decreased 
 plantar sensory input and a significantly larger center of pressure excursion than other 
 foot postures8 .
however , unlike the 
 pronated foot , the supinated foot may provide a rigid lever for propulsion but is not 
 efficient as a shock absorber .
previous studies have reported that 23 to 60% of subjects 
 with a supinated foot experienced foot pain9 , 10 . among athletes with high - arched feet , 
 increased arch height was associated with decreased mediolateral control of single - limb 
 stance11 , potentially increasing the 
 risk of lower limb injury .
both the supinated and pronated foot are at a greater mechanical disadvantage than a 
 neutral foot , especially for maintaining balance while performing activities in weight 
 bearing .
the aim of this study was to compare the lower limb joint rom of the hip , knee , and 
 ankle joints and lower limb muscle length ( ml ) of the hamstrings , quadriceps , gastrocnemius , 
 and soleus between different types of foot postures ( normal , pronated , and supinated ) in 
 older adults .
additionally , this study also aimed to determine the correlation of rom and ml 
 with balance performance .
a total of 90 community - dwelling older women aged 60  years and above were recruited for 
 this cross - sectional study .
the gpower 3 software was used to calculate the sample size , and 
 indicated that 26 participants were sufficient to detect an effect size of 80% power and 
 alpha of 0.05 . anticipating a patient withdrawal rate of 20 to 30% during assessment ,
the participants were divided into three 
 different groups based on their foot posture using the foot posture index ( fpi ) : normal foot 
 ( n=30 ) , pronated foot ( n=30 ) , and supinated foot ( n=30 ) .
participants were included in the 
 study if they met these criteria : community - dwelling , aged 60  years old or above , and able 
 to walk about 10 meters without using walking aids .
meanwhile , the participants were 
 excluded if they presented with other foot symptoms such as pain , swelling , or loss of 
 sensation ; bmi more than 30  kg / m ; a chronic orthopedic condition such as 
 rheumatoid arthritis ( ra ) or severe osteoarthritis ( oa ) pain in the lower limb or fracture ; 
 a vestibular problem ; or visual or peripheral sense disturbances .
the ethics approval was 
 obtained from the university s research ethics committee , and all participants signed 
 written informed consents .
participant details such as age ( year ) , body weight ( kg ) , and height ( m ) were recorded .
the 
 body weight and height were used to calculate the body mass index ( bmi ;  kg / m ) 
 for each participant .
all measurements were performed by three research assistants who were 
 graduates of the physiotherapy degree program .
the fpi was used to classify the participants foot postures using a six clinical 
 criteria12 .
the participants were 
 required to stand with both feet shoulder width apart while the assessor observed their foot 
 from the frontal plane , sagittal plane , and posterior aspect .
the fpi six scoring system 
 includes the following six components : palpation of the talar head , palpation of the supra- 
 and infra - lateral malleolar curvature , calcaneal frontal plane position , prominence in the 
 region of the talonavicular joint , congruence of the mla , and abduction or adduction of the 
 forefoot on the rearfoot .
the summation of the 
 scores obtained was calculated to classify the participants into their respective groups 
 ( normal [ 0 to + 5 ] , pronated [ + 6 to + 9 ] , and supinated [ 1 to 4 ] ) .
the researcher chose to 
 use the fpi as this index is able to evaluate the foot in various planes and has been shown 
 to be valid in various clinical settings13 .
the fpi was developed to provide better foot measurements12 due to the lack of validated methods to 
 categorize or quantify variations in foot postures in the clinical area2 .
the measurements of joint rom were taken using a standard goniometer at the lower limb 
 joints including the hip ( flexion , extension ) , knee ( flexion , extension ) , and ankle 
 ( plantarflexion , dorsiflexion , inversion , eversion ) joints .
both sides of the limb were measured , each measurement was 
 performed three times , and the average score was recorded for analysis .
muscle length measurements were taken from the major muscles of the lower limb including 
 the hamstrings , quadriceps , gastrocnemius , and soleus .
the hamstring length was determined by measuring the straight - leg 
 raise using a goniometer .
the quadriceps length was determined by measuring the quadriceps 
 femoris muscle angle during passive knee flexion with the subject in the prone position .
the 
 gastrocnemius and soleus ml were measured with the patient in the prone position with the 
 knee straight and the knee flexed ( 90 ) , respectively .
both sides of the muscles were 
 measured three times each , and the average was recorded as the final score . balance performance was measured using the functional reach test ( frt)16 . the researchers chose the frt as it demonstrates the 
 maximal distance a person can reach forward beyond arm s length while maintaining a fixed 
 based of support in standing position ; the frt also serves as an index of fall risk17 .
participants were instructed to stand 
 with their feet shoulder distance apart , make a fist , and raise their arm to be parallel 
 with the floor .
the assessor took an initial reading on the yardstick , using the knuckle of 
 the third metacarpal as the landmark .
the participants were instructed to reach forward 
 along the yardstick without moving their feet .
the assessor took a reading on the yardstick 
 of the farthest reach attained by the participant without taking a step .
a score of less than six inches 
 indicates a balance limitation , while a score of more than 10 inches indicates adequate 
 balance for older adults .
the four square step test ( fsst ) was also used to measure balance performance ; this test 
 assesses the participants ability to step over objects forward , sideways , and 
 backwards18 .
we suggest that the fsst 
 is more challenging than the frt , as the fsst requires the participants to lift up the leg 
 and coordinate their movements as fast as possible .
the participants were instructed to step 
 over four canes setup like a cross on the floor with the tips of the canes facing together . 
 at the start of the test
, the participants stood on the upper left square ( in square one and 
 facing square two ) .
then the participants started stepping in a clockwise pattern as 
 follows : square one , square two , square four , square three , and finally returning to square 
 one with both feet .
next , participants continued stepping counter - clockwise in the following 
 pattern : square three , square four , square two , and ending in square one with both feet .
the 
 assessor demonstrated the procedure once and allowed the participants to perform one 
 practice trial prior to administering the test .
the participants performed two trials , and 
 the better time ( measured in seconds ) was taken as the score .
descriptive analysis was 
 conducted to determine the means , standard deviations , and p values for age and body mass 
 index .
the normality test indicated that all variables of interest were not normally 
 distributed ; thus , the non - parametric tests were used for further analysis .
the 
 kruskal - wallis test was used to compare the mean ranks for each variable .
the correlation 
 analysis was done to measure strength of relationship between rom , ml , and dynamic balance 
 among the three different types of foot posture .
there 
 were no significant differences in age ( p>0.05 ) between the normal ( 65.2  4.6  years ) , 
 pronated ( 66.3  4.5  years ) , and supinated ( 67.9  5.7  years ) foot groups .
similarly for 
 body mass index , no significant differences were found between the normal ( 25.9  
 3.9  kg / m ) , pronated ( 23.7  6.6  kg / m ) , supinated ( 24.9  
 2.8  kg / m ) foot groups(f = 1.2 , p>0.05 ) .
the mean rank comparisons for rom , ml , and balance performance for all types of foot 
 posture are shown in table 1table 1.mean rank comparisons using the kruskal - wallis test for range of motion , muscle 
 length , and balance performancevariablesnormal ( n=30)mean rankpronated ( n=30)mean ranksupinated ( n=30)mean rankromhip flexionright42.9 44.449.6left40.2 44.951.4hip extensionright47.545.143.9left45.349.441.7knee flexionright45.144.546.9left41.9 45.848.8knee extensionright42.946.1547.5left44.945.1546.5ankle dorsiflexionright*55.545.735.3left*55.147.4 34.0ankle plantarflexionright40.349.746.4left41.947.8 46.8ankle inversionright51.643.741.2left52.646.837.1ankle eversionright44.544.547.5left44.943.048.5mlhamstringright40.943.851.7left42.145.049.3quadricepsright39.3743.853.4left43.0344.7 48.8gastrocnemiusright45.549.941.1left46.751.937.9soleusright41.949.7044.9left42.653.2240.7balancefrt49.341.6745.6fsst39.654.4242.5*p<0.05 .
rom : range of motion , ml : muscle length . in terms of rom ,
the only variables that showed a significant difference were 
 the right and left ankle dorsiflexion with the most limited rom measured in the supinated 
 foot ( p<0.05 ) .
there were no significant differences found between the hip , knee , ankle 
 plantar flexion , ankle inversion , and ankle eversion rom among different types of foot 
 posture . similarly for ml and balance performance ( fsst and frt ) , there were no significant 
 differences among the foot posture groups ( all p>0.05 ) . * p<0.05 .
rom : range of motion , ml : muscle length the results of the relationships between rom , ml , and balance performance are shown in 
 table 2table 2.spearmans rank - order correlation of rom and ml with balance performancevariablesfoot posturebalance performance ( rs)frtfsstright limbleft limbright limbleft limbromhip flexionnormal0.10.10.20.2pronated0.10.20.00.1supinated0.20.20.20.1hip extensionnormal0.4**0.3*0.00.0pronated0.00.10.20.1supinated 0.20.10.00.2knee flexion normal 0.20.00.10.1pronated0.20.10.10.0supinated 0.10.10.20.1knee extension normal 0.3*0.3 * 0.20.2pronated 0.20.30.3*0.2supinated 0.10.10.20.0ankle dorsiflexionnormal0.30.20.20.2pronated0.10.10.5**0.4*supinated0.4 * 0.5**0.10.1ankle plantarflexionnormal 0.10.10.4*0.2pronated 0.20.30.20.4*supinated 0.3 * 0.10.10.1ankle inversionnormal 0.10.20.20.1pronated 0.20.10.10.1supinated 0.6**0.6**0.00.1ankle eversionnormal 0.10.20.10.1pronated 0.20.30.00.1supinated 0.4**0.5**0.20.2mlhamstrings normal 0.10.10.4**0.5**pronated0.20.20.00.0supinated0.10.10.10.2quadriceps normal 0.20.20.10.0pronated 0.10.4*0.3 * 0.2supinated 0.00.10.20.0gastrocnemiusnormal 0.00.20.00.0pronated 0.10.10.20.2supinated 0.5**0.4 * 0.20.3*soleus normal 0.10.3 * 0.20.2pronated 0.20.20.20.0supinated 0.20.10.20.1*p<0.05 , * * p<0.01 .
rom : range of motion , ml : muscle length . for the normal foot ,
the frt was significantly correlated with the rom of 
 right and left hip extension as well as right and left knee extension ; the fsst was 
 significantly correlated with the rom of right ankle plantarflexion and the ml of the right 
 and left hamstring ( all p<0.05 ) . *
rom : range of motion , ml : muscle length for the pronated foot , the frt was significantly correlated with the ml of the left 
 quadriceps ; the fsst was significantly correlated with the rom of right knee extension , 
 right and left ankle dorsiflexion , and the right quadriceps ml ( all p<0.05 ) . in the supinated foot ,
frt was significantly correlated with the rom of right and left 
 ankle dorsiflexion , right and left ankle inversion , right and left ankle eversion , and the 
 ml of the right and left gastrocnemius ; fsst was significantly correlated with the ml of 
 left gastrocnemius ( all p<0.05 ) .
previous studies have shown that an excessively pronated foot19 or a highly supinated foot8 may alter standing balance in healthy young adults , but limited 
 evidence has been reported regarding whether similar findings exist for older adults . 

therefore , in this study , we present a few interesting results on range of motion , muscle 
 length , and balance performance in older adults with different types of foot posture . 
 uniquely , in this study we used the fpi to reliably identify the participants foot posture . 

previously , menz et al.20 , have used the 
 fpi in their study on foot and ankle characteristics associated with impaired balance and 
 functional ability in older adults . however , in the current study we used the frt and fsst 
 as the measures for balance performance . the most striking result to emerge from the data is that participants with a supinated foot 
 had limited ankle dorsiflexion rom in comparison with the normal and pronated foot .
this 
 finding provides evidence that shortening of the achilles tendon will result in limited 
 ankle dorsiflexion rom .
gajdosik et al.21 
 highlighted that the decrease of calf muscle length , operationally defined by decreased 
 ankle dorsiflexion rom with the knee extended , is associated with normal aging in both men 
 and women .
a previous study by burns and crosbie9 that concluded ligament shortening , bones of the foot crowding 
 together , and an increase in the longitudinal arch were brought about due to the increased 
 activity of the muscles .
in addition , the extreme tendon loads on the short achilles tendon , 
 for example , as well as heightening of the medial longitudinal arch may cause shortening of 
 the plantar fascia in subjects with a supinated foot22 . in this study
, we measured the muscle length of the gastrocnemius 
 and soleus separately , which differs from the methods used by burns and crosbie9 ; according to these authors , the compliance 
 of the calf muscles ( the gastrocnemius and soleus ) can be reflected by the length of the 
 achilles tendon and measured using the modified lunge test that is usually performed by 
 athletes . unfortunately , this test may not be suitable for older adults due to its potential 
 risk of postural instability .
interestingly , it is also apparent from the current results that the pronated foot 
 presented with the highest mean rank for gastrocnemius and soleus muscle length when 
 compared to a supinated and normal foot ; however , the differences were not significant 
 ( p>0.05 ) .
elderly women aged more than 65  years were found to have more pronated feet , 
 especially during ambulation , leading to a higher risk of foot problems than men23 .
increase in gastrocnemius and soleus 
 muscle lengths may contribute to the alteration of plantar pressure during gait , further 
 increasing postural instability among the elderly .
however , there is no clear evidence 
 regarding changes in foot architecture that may contribute to the changes of the 
 gastrocnemius and soleus ml with aging ; accordingly , no significant differences were found 
 between ml among different types of foot posture ( p>0.05 ) .
the current findings also revealed that among the pronated foot group a decreased rom 
 resulted in slower completion of the fsst , indicating poor balance performance .
similarly , 
 the shorter the quadriceps ml the lower the score for the frt .
this is expected as a larger 
 rom and longer ml may prolong the time to complete the fsst as the foot may perform less 
 forceful movements due to weakness or hypermobility of certain joints . according to kawakimi 
 et al.24 , in order for force
to be 
 exerted more effectively during a motion , the gastrocnemius and soleus muscle need to 
 operate with limited variation in length and force .
the results of the present study also suggest a positive correlation between ankle plantar 
 flexion and fsst which indicates that the larger the rom ( hypermobility ) , the longer the 
 time to complete the fsst .
similarly , an increase in the plantarflexion as well as an 
 increase in the muscle length of the quadriceps muscles may reduce balance performance ; 
 however , an increase in the ankle plantar flexion may increase balance performance ( fsst ) . 
 the hypermobility of the pronated foot may result in flattening of the mla ; this alteration 
 would place greater demand on the neuromuscular system to stabilize the foot and uphold a 
 proper posture4 leading to poor balance 
 performance . for the supinated foot , a smaller rom of ankle dorsiflexion , plantar flexion , inversion , 
 and eversion corresponded with a shorter frt time and vice versa .
the 
 current findings indicate that older adults with reduced rom and muscle length may be at 
 risk of poor balance performance ; this may be due in part to the aging process .
this is 
 because the supinated foot may not adequately adapt to the underlying surface , and , as a 
 result , increase the demand on the surrounding musculoskeletal structures to maintain 
 postural stability and balance4 . 

furthermore , limitation in ankle dorsiflexion may influence standing and walking balance as 
 there is a reduction in the available range of the body s center of mass within the base of 
 support25 .
finally , we can conclude that a reduction in rom , especially in the ankle joint , is more 
 commonly found in the supinated foot .
it shows that reduced ankle dorsiflexion in the 
 supinated foot is associated with shortening of the calf muscle .
alterations of foot posture may cause 
 further changes to the musculoskeletal properties and joint flexibility , leading to 
 increased risk of injuries and falls , especially among the older population .
based on this 
 conclusion , a few recommendations can be suggested regarding healthcare practices . a 
 thorough assessment of the foot and ankle should be included when assessing older adults 
 being referred for fall prevention management or those with a history of falls .
this is 
 important as different types of foot postures may present with different limitations in the 
 musculoskeletal properties .
for example , an older person with a pronated foot may require 
 strengthening exercises to certain muscles of the foot , while those with a supinated foot 
 may need more stretching exercises in order to preserve their mobility and prevent 
 falls . the generalizability of these findings is subject to certain limitations .
firstly , the 
 small sample size has prevented us from using a parametric statistical analysis .
another 
 important limitation is that the participants of this study were only women who presented 
 with good mobility and no painful symptoms of the lower limb or foot.thus , the findings are 
 less generalizable to individuals with other problems as a result of foot deformities . a 
 final source of weakness in this study is the use of tools such as a goniometer and tape 
 measure , which could have affected the measurements of joint range of motion and muscle 
 length .
these tools require the assessor to be highly skilled , especially in terms of their 
 observation ; in light of this , we only utilized one assessor for the score observation .
a 
 few confounding factors may have also influenced the results of the current study .
these 
 factors may include the nature of the subjects previous job or activities , the types of 
 footwear worn , and changes in the body weight of subjects throughout the course of their 
 life .
it is also not known whether some of the deformities were solely due to congenital or 
 aging processes .
further research could explore how muscle strength is affected with the different types of 
 foot posture and whether muscle strength does influence balance performance .
in addition , it 
 would be interesting to assess the effect of fatigue on muscle function and gait kinematics 
 in different types of foot posture .
 [ purpose ] to compare the lower limb joint range of motion and muscle length between 
 different types of foot posture , and determine the correlation of range of motion and 
 muscle length with balance performance . 
 [ subjects and methods ] ninety individuals ( age , 
 65.24.6  years ) were assessed using the foot posture index to determine their type of foot 
 ( normal [ 0 to + 5 ] , pronated [ + 6 to + 9 ] , and supinated [ 1 to 4 ] ; n=30 per group ) . 
 the 
 range of motion ( goniometer ) , muscle length ( goniometer and tape measure ) , and balance 
 performance ( functional reach test and four square step test ) were measured for each 
 participant . 
 data were analyzed using the kruskal - wallis test and spearman s rank - order 
 correlation . 
 [ results ] no significant differences were found in range of motion , muscle 
 length , and balance performance among different types of foot posture , except for right 
 and left ankle dorsiflexion range of motion . 
 balance performance was significantly 
 correlated with selected muscle length and range of motion , especially in the supinated 
 foot . 
 [ conclusion ] range of motion and muscle length of the lower limb may be associated 
 with balance performance in older adults with foot deformities . 
 these findings may guide 
 physiotherapists in choosing intervention based on specific assessments for older adults 
 with foot deformity . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION