functional balance is defined as the ability to maintain a position and to adjust posture 
 during functional movement and mobility , such as the movement from one postural position to 
 another or moving from one location to another1 .
the maintenance of balance is a complex phenomenon , and it is 
 influenced by a range of several sensorimotor functions , including muscular strength , 
 proprioception , and the visual and vestibular sensory system2 , 3 .
a standing posture has a high center of gravity ( cog ) which is maintained over a relatively 
 small base of support4 .
previous studies 
 have identified two discrete strategies of postural control , and ankle and hip strategies 
 have often been used to describe maintenance of postural control through specific actions at 
 those two joints4 , 5 .
strength of the ankles has been found to correlate with postural 
 stability and functional tests6 , 7 .
several studies have also demonstrated the importance of 
 foot and ankle musculature in the optimal performance of functional motor tasks , such as 
 walking , running , and jumping8 , 9 .
however , to date , most studies associated with strength 
 training and balance for the lower limbs have been limited to the hip or knee joint13,14,15 , and little is known about the effects of 
 balance after isokinetic training for the ankles . in general , an efficient way to increase 
 balance ability is resistance training for the hip and knee joint10,11,12 .
the purpose of this study was to investigate the changes in the anterior - posterior 
 stability index ( apsi ) , medial - lateral stability index ( mlsi ) , and overall stability index 
 ( osi ) in one - legged standing balance of the ipsilateral lower limb following unilateral 
 isokinetic strength training for the ankle .
thirty healthy and physically active subjects were recruited as volunteers for this study . 
 the subjects were randomly assigned to a training ( n=15 ) or control group ( n=15 ) .
the 
 baseline demographic characteristics of the subjects enrolled in the study were as follows . 

each group consisted of five male and 10 female subjects . the mean age , height , weight , and 
 foot length of subjects in the control group were 23.6  2.35  years , 162.9  8.24  cm , 56.1  
 12.66  kg , and 241.7  16.65  mm , respectively , and those of the training group were 23.4  
 2.03  years , 165.5  5.71  cm , 55.5  6.37  kg , and 245.7  14.05  mm , respectively .
the 
 subjects had not participated in a resistance training program for at least six months . 

subjects were excluded if they had ; a diagnosed neurologic disease or disorder ; acute back 
 or lower - limb musculoskeletal problems , such as strain , sprain , surgery , or fracture ; or 
 neurologic or vestibular impairment that prevented single - limb stance .
all the subjects 
 understood the purpose of this study and provided their written informed consent prior to 
 their participation in the study in accordance with the ethical standards of the declaration 
 of helsinki .
unilateral training was performed using the biodex 3 pro system ( biodex , inc . , shirley , ny , 
 usa ) for strength training of ankle dorsiflexion and plantar flexion , and inversion and 
 eversion . subjects in the training group received training five times per week for four 
 consecutive weeks .
isokinetic exercise were performed on the right side in five sets of 10 
 repetitions at the angular velocity of 60/s with a rest period of 2  min between sets . 

subjects who complained of ankle pain during the training period were excluded from this 
 study .
subjects in the control group attended health education programs , such as fall 
 prevention , balance , exercise , and were given general information regarding health promotion 
 for one hour each week .
for balance testing , we used a commercial balance device , the biodex stability system ( bss ) 
 ( biodex medical systems , shirley , ny , usa ) , a movable balance platform providing up to 20 
 of surface tilt in all directions .
measures of postural stability include the stability 
 indexes of apsi , mlsi , and osi . these indices are standard deviations of fluctuations around 
 the zero point rather than around a group mean .
one - legged stance between the training and 
 control group was assessed at level 10 ( level 12 is the most stable , 1 is the least stable ) 
 stability of the bss for a period of 20 s. the stability indexes were calculated from the 
 degree of tilt deviation from horizontal and were averaged over three evaluations . for this 
 test , subjects were instructed to fold their arms across the chest and look straight ahead , 
 lift the untrained knee from the floor and flex it to 90at the start of the assessment , and 
 maintain the position as accurately as possible .
balance measurements using bss of the 
 training and control group were performed before and after the four - week intervention 
 period .
statistical analyses were performed using spss version 18.0 software . the independent 
 t - test
was used for analysis of differences between the training and control groups , in 
 terms of the baseline data for age , height , weight , and foot length .
all data were evaluated 
 using separate univariate analyses of variance , and two - way anova with repeated measures 
 ( groups : training group , control group )  2 ( test sessions : pre - test , post - test ) on the two 
 dependent variables .
apsi ( anterior - posterior 
 stability index ) , mlsi ( medial - lateral stability index ) , osi ( overall stability index ) . 

nm ( newton meter ) no significant differences in terms of distributions of gender , age , height , weight , and 
 foot length were observed between the two groups .
table 
 1 shows the parameters of ankle strength ( dorsiflexion , plantarflexion , eversion 
 and inversion ) and stability parameters ( alsi , mlsi and osi ) at the pre- and post - tests of 
 the two groups . in terms of the parameters of ankle strength ( dorsiflexion , plantarflexion , 
 eversion and inversion ) and stability parameters ( alsi , mlsi and osi ) , two - way anova with 
 repeated measures showed significantly large main effects of group ( p<0.05 ) , time 
 ( p<0.05 ) , and group - by - time interaction ( p<0.05 ) .
in addition , changes in pre - test and 
 post - test values were significant in the training group ( p<0.05 ) . however , there were no 
 significant differences in the control group ( p>0.05 ) .
these data indicate that the 
 training group achieved significant improvements in ankle strength and stability over the 
 4-week intervention period .
in the current study , we attempted to investigate the effect of unilateral isokinetic 
 strength training for the ankle on the one - legged standing balance of the ipsilateral lower 
 limb .
we acknowledge that no studies have been conducted to investigate the effect of ankle 
 training with isokinetic exercise on the one - legged standing balance of the ipsilateral 
 lower limb .
our findings show there were significant improvements in ankle strength 
 ( dorsiflexion , plantarflexion , eversion and inversion ) and in the apsi , mlsi and osi 
 stability indexes of the ipsilateral lower limb in one - leg standing balance in the training 
 group , compared to the gender- and age - matched control groups . in order to support the whole body ,
muscle action around the ankle is important , because it 
 is responsible for control of this joint8 , 9 .
one of the most common interventions for 
 improving postural stability is physical exercise , such as ioskinetic exercise and 
 progressive resistance exercise16 , 17 .
these findings are in agreement with those 
 of several previous studies , which suggested that strength exercise targeting the lower limb 
 muscles improves balance ability12,13,14 . 

we think that balance improvement may be a result of better coordination of the muscles 
 around the ankle after isokinetic training .
in addition , increase in balance ability may be 
 related to promotion of the proprioceptive senses , due to strength exercise , since 
 proprioceptive function is an important factor of balance ability18 .
strength exercise can activate proprioceptive functions , 
 which might provide feedback to the joint , increase stimulation of the mechanoreceptors , 
 such as the muscle spindle , golgi tendon organ and ruffini nerve endings around the 
 joint19,20,21 .
hilberg et al.19 used isometric muscular strength training 
 for knee joints , and reported improved performances in the one - legged standing test and 
 proprioceptive function after exercise by a training group , compared with control group . on 
 the basis of these results , we think that balance improvement is influenced by activation of 
 motor coordination and proprioceptive sense in the ankle joint due to the strength 
 training .
previous studies have reported that the relation between strength training exercise and 
 balance is a good indicator of dynamic stability in healthy and older adults .
our findings 
 emphasize that ankle strengthening exercise can be considered as a form of exercise that may 
 assist individuals in improvement of balance .
however , in this study , it is possible that 
 the training for ankle strength may have simultaneously influenced the activation of the 
 muscles around the knee joint , which is the joint closest to the ankle , as well as the 
 muscles around ankle .
in addition , the results of our study should be interpreted with 
 consideration of potential limitations .
if the intervention were carried out for a longer period of time , the result 
 would possibly show more significant improvements .
second , conduct of a study with older 
 subjects is needed in order to investigate the therapeutic efficacy of isokinetic strength 
 training , because older subjects may have a greater need for balance improvement than 
 younger subjects with regard to the prevention of falls .
   [ purpose ] the purpose of the current study was to investigate the changes in one - legged 
 standing balance of the ipsilateral lower limb following unilateral isokinetic strength 
 training . 
 [ subjects and methods ] thirty healthy adult volunteers were randomly assigned to 
 either a training group or a control group , so that each group included 15 subjects . 
 
 subjects in the training group performed unilateral ankle isokinetic exercises of the 
 dominant leg using the biodex 3 pro system for a period of four weeks . 
 ipsilateral 
 one - legged standing balance was evaluated before and after the intervention with three 
 stability indexes of balance using the biodex system : anterior - posterior stability index 
 ( apsi ) , medial - lateral stability index ( mlsi ) , and overall stability index ( osi ) . 
 
 [ results ] comparison of pre- and post - test data revealed significant improvements in 
 strength values ( dorsiflexion , plantarflexion , eversion , and inversion ) and stability 
 indexes ( apsi , mlsi , osi ) . 
 [ conclusion ] these results suggest that ankle strengthening 
 exercise can be considered as a form of exercise that may assist individuals with 
 improvement of balance . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION