the ankle joints play an important role in gait . the structure of foot is adapted for 
 locomotion and the alignment of the foot and ankle plays an important role in standing and 
 gait1 , and supporting weight during 
 gait2 .
the proper functioning of the 
 ankle joint is necessary for daily life , recreation and sports activities3 , and it is important in ambulation and 
 functional gait in terms of its mechanical properties4 . the strength of the muscles around the ankle is related injuries 
 from sports activities3 , and this strength 
 is essential for the prevention of falls5 . 
 the passive torque gained through the tension of muscular tissue and the stiffness of the 
 tissues adjacent to joints like ligaments or tendons is required for the development of an 
 appropriate strategy for the ankle joint . the central nervous system , which controls the 
 spontaneous physical response to the external events , and stretches and contracts the 
 muscles , generates the active torque . the active torque that is gained through the central 
 nervous system is also required for the development of an appropriate strategy for the ankle 
 joint6 .
postural control involves an 
 adequate stepping strategy and the appropriate use of the muscles attached to the hips and 
 ankles7 .
the primary functions of the 
 ankle joints are the provision of balance adjustment in response to postural disturbance , 
 absorption of shock during gait , and movement of the lower extremity8 .
the maintenance of balance is a complex prcess , and it is influenced by a range of several 
 sensorimotor functions , including muscular strength , proprioception , and the visual and 
 vestibular sensory systems9 .
the central 
 nervous system uses ascending motor pathways that receive information from the feet to 
 control the position of the body and coordinate posture in relation to the surrounding 
 environment10 .
the ankle joint has the 
 function of balance control , responding to the ground reaction force , it contracts muscles 
 such as the gastrocnemius , the soleus and the tibialis anterior6 .
the plantar flexor and dorsiflexor play a central role in 
 maintaining balance during single - limb support and bilateral - limb support , and the 
 gastrocnemius and soleus play a significant role in postural correction11 .
muscular strength and muscle activation are required for 
 balance , to keep the center of gravity within the base of support12 . in one study ,
subjects performed short - term isometric and isotonic exercise , and isometric 
 exercise increased muscular strength significantly at the low speed of 60/sec , while 
 isotonic exercise did the same at the higher speeds of 120/sec and 180/sec13 .
another study analyzed how the function 
 and muscular strength of the lower limbs are influenced by isotonic and isokinetic exercise 
 in a closed kinetic chain type exercise for 6 weeks , and reported that muscular strength , 
 muscle power and muscle endurance of the knee joint extensors and flexors did not show any 
 statistically significant differences14 . 

also , a study of a muscle strengthening program , including isometric and isotonic 
 contractions and stretching exercises , performed by elderly women for a period of 12 weeks , 
 reported that increased muscular strength improved their balance15 .
another study analyzed the isokinetic torque and the 
 absolute peak torque of the invertor and evertor muscles of females with functional ankle 
 instability who performed eccentric contraction and concentric contraction at the respective 
 speeds of 60/sec and 120/sec .
deficits in eccentric invertor strength contributed to 
 symptoms of functional ankle instability , and it was noted that eccentric contraction 
 decrease of the invertor had a significant impact on the results16 .
another study analyzed the equilibrium and emg 
 ( electromyography ) activity of a sports player using a single - limb stance on four different 
 unstable surfaces and reported that the emg activities of the peroneus longus , extensor 
 digitorum longus , and tibialis anterior muscle were greater on a small wood board than on to 
 hemi - cylindrical and large plastic wood boards17 .
the calf muscle - tendon unit of the ankle plays an important role in basic human movement 
 activities18 , such as balance control 
 while standing19 , and the enhancement of 
 the effectiveness of walking20 . in spite 
 of the fact that the ankle joint is of such importance
, most studies have performed 
 exercises on the knee joint muscle rather than on the ankle joint and analyzed the variables 
 of muscular function such as muscle strength and muscle power .
therefore , this study 
 examined the effects of isotonic and isokinetic exercise performed by the essential muscles 
 of the ankle joint , which play an important role in balance and gait .
the purpose was to 
 investigate how the muscle activity and balance were affected by isotonic and isokinetic 
 exercise .
in addition , the effects of isotonic and isokinetic exercise on the tibialis 
 anterior , which is responsible for dorsiflexion , and on the peroneus longus and 
 gastrocnemius , which are responsible for ankle plantarflexion were investigated .
twenty students ( 10 men , 10 women ; 18 right dominant , 2 left dominant ) attending namseoul 
 university in cheonan - si , republic of korea , volunteered for this study .
they were clearly 
 informed of the purpose and experimental procedures before providing their written consent . 

none of the subjects had impairments of the musculoskeletal or neurological systems , and 
 none had a history of athletics or had received any training for muscle strengthening within 
 the past 6 months21 .
two types of 
 exercises were performed and 10 subjects each were randomly assigned to the isotonic and 
 isokinetic exercise groups . a body composition analyzer ( inbody720 .
biospace o. ltd , seoul , korea ) was used to measure 
 subjects physical characteristics . a functional rehab system ( primus rs , bte tech . , 

hanover , usa ) was used to asses maximal voluntary isometric contraction and to perform 
 isotonic and isokinetic exercise . a free emg system ( free emg , bts inc .
, milan , italy ) was 
 used to measure muscle activity . a computerized balance platform ( hur bt4 , burlabs , tampere , 
 finland )
prior to the commencement of this experiment , the subjects were informed of the contents of 
 the experiment and were allowed to participate in the experiment only after submitting their 
 written consent .
the subjects were placed in either the isotonic exercise group or the 
 isokinetic exercise group with 10 individuals in each group .
the subjects were ordered to 
 kick a ball on the ground , and the side they used to kick the ball was considered to be 
 their dominant side22 .
surface electrodes 
 were then attached to the bilateral tibialis anterior , the peroneus longus and the medial 
 gastrocnemius of each participant .
the subjects were seated on a dynamometer with their hip 
 joint and knee joints fixed in the mid - positon with a brace belt .
the rotation axis of the 
 equipment was then adjusted to match the line that links the medial malleolus , and the foot 
 was fixed for the isokinetic exercise23 . 

no movement was possible , and the exercise was performed on the non - dominant side24 . balance was measured immediately after 
 completion of the exercise protocol11 . 
 all exercises and measurements were performed with the subjects barefoot to prevent any 
 potential confusion being caused by different shoe types or heel heights18 . for surface electromyography , electrodes were attached to the muscle at maximum static 
 contraction to prevent any technical difficulties from influencing the experiment25 .
the skin was abraded with sandpaper and 
 shaved , then cleaned with an alcohol - soaked cotton swab , to reduce the electrical impedance 
 of the skin to less than 5 k. active electrodes ( carbon electrode , 3 m , usa ) were placed 
 2  cm apart , in parallel with the muscle fibers , on the tibialis anterior , the peroneus 
 longus and the medial gastrocnemius26 . 
 during the electromyography measurements ,
the electromyography signals were recorded at a 
 sampling rate of 1 khz , bandpass - filtered between 20 and 500  hz . the root mean square value 
 was calculated from the raw emg data27 . 
 the emg data of balance measures was processed after excluding the first and last 5 seconds . 

the subjects performed a series of 5 submaximal contractions as a warm - up to familiarize 
 themselves with the dynamometer28 .
the highest peak torque of 3 maximum voluntary isometric 
 contractions ( mvics ) was used in this study30 . in the isotonic group ,
the istonic group performed 
 dorsiflexion and plantar flexion 10 times for 3 sets and had a 1-minute rest between sets to 
 prevent fatigue13 . in the isokinetic 
 group ,
the angular velocity of 60/sec that is generally used for muscle strengthening 
 exercises for healthy adults and athletes was chosen from among the angular velocities of 
 60/sec , 180/sec and 300/sec , which are appropriate for isokinetics33 . in the isotonic group ,
the ankle was placed in the 
 neutral position34 , and subjects 
 performed dorsiflexion and plantarflexion in a non - painful range of motion 10 times for 3 
 sets , for a total of 30 times35 , and had 
 a 1-minute rest between sets to prevent fatigue24 .
the one - leg standing 
 test with eyes open was performed on a computerized balance platform35 . during the trials , the subjects had to stand barefoot on 
 one leg for 30 seconds with their eyes open36 , while the other leg was held off the surface with a knee flexion 
 of 30 degrees along the anterior - posterior axis of the foot plate35 , and with both arms in a relaxed state at the sides . for 
 visual information ,
the subjects were asked to stand in as stable a position as possible , 
 watching a point on a monitor that was 65  cm in front of them during experimental 
 testing37 . for visual information 
 directions ,
a reverse countdown was started from 4 before beginning the measurements , and 
  stop  was said after the measurements had been taken .
the 
 measurements were taken twice , and the mean value of the two measurements was 
 calculated .
the dependent variables were tested 
 for normality using the kolmogorov - smirnov test , and for homogeneity of variance using 
 levene s test .
manova ( multivariate analysis of variance ) was used to examine the 
 significance of differences in balance and compare emg and the balance of the tibialis 
 anterior , the peroneus longus and the medial gastrocnemius between the groups ( isotonic and 
 isokinetic exercise ) and time ( pre - exercise and post - exercise ) .
this study was approved by the institutional review board of namseoul university 
 ( cheonan , korea , nsu-140528 - 1 ) .
twenty healthy adults took part in this study , and their physical characteristics are 
 presented in table 1table 1.subject characteristicsgroupnage ( years)height ( cm)weight ( kg)bmi ( kg / m)msdmsdmsdmsdisotonic1020.31.7170.29.970.014.623.92.6isokinetic1020.21.8165.59.965.820.223.64.8msd : meansstandard deviation , bmi : body mass index . the results of the comparison of muscle electromyography between pre - test and 
 post - test by group are shown in table 
 2table 2.comparison of muscle electromyography between pre- and post - test ( mv)variablegrouppre - testpost - testmsdmsdnon - dominant tibialis anterior*isotonic0.350.300.330.14(support by non - dominant side)isokinetic1.471.521.180.83dominant tibialis anterior*isotonic0.160.130.420.64(support by non - dominant side)isokinetic0.620.590.710.52dominant gastrocnemius*isotonic0.570.591.372.14(support by dominant side)isokinetic2.351.622.422.25dominant peroneus longus*isotonic0.620.581.010.83(supported by dominant side)isokinetic1.400.901.871.23*significant difference , p<0.05 . statistical analysis
revealed that both the isotonic exercise and isokinetic 
 exercise groups showed neither an interaction effect between group and time as , nor a main 
 effect of time . a main effect of group
was found in the non - dominant tibialis anterior , the 
 dominant tibialis anterior , the dominant gastrocnemius and the dominant peroneus longus 
 ( p<0.05 ) .
the changes in balance between pre - test and post - test by group are shown in 
 table 3table 3.comparison of balance between pre- and post - test ( mm)variablegrouppre - testpost - testmsdmsdsway area(support by non - dominant 
 side)isotonic435.0139.1615.1244.1*isokinetic389.3215.6515.6277.7 * * significant difference , p<0.05 . statistical analysis
revealed that both the isotonic exercise and isokinetic 
 exercise groups showed neither an interaction effect between group and time , nor a main 
 effect of group .
a main effect of time was statistically significant for the sway area when 
 support was provided by the non - dominant side in both groups ( p<0.05 ) .
msd : meansstandard deviation , bmi : body mass index * significant difference , p<0.05 * significant difference , p<0.05
loss of balance is caused by the center 
 of foot pressure leaving the limits of stability of the base of support38 .
the sensory process of balance is interaction among the 
 somatic senses , which include proprioception , visual sense , and stereotactic input from the 
 vestibular system40 .
the lower limb 
 activity sequence is an important factor for the neuromuscular function of the ankle 
 joint41 , and the sway is related to the 
 postural variable , which provides important information about stability and postural 
 control .
fatigue increases the sway36 and 
 analyzing the sway is essential for understanding of the postural control mechanisms and the 
 treatment of patients with balance dysfunction42 . in this study
, healthy adults performed isotonic and isokinetic 
 exercise for the ankle joint , and how the respective exercises influenced muscle activity 
 and balance was investigated . when muscle activity was compared between pre - test and 
 post - test by group , both the dominant tibialis anterior and the non - dominant tibialis 
 anterior presented significant differences when support was provided by the non - dominant 
 side , and the dominant gastrocnemius muscle and the dominant peroneus longus presented 
 significant differences when support was provided by the dominant side .
razaeimanech and farsani43 reported that 
 performance of isotonic exercise for the lower limb for 6 weeks increased emg and improved 
 the muscle strength of volleyball players .
onambele et al.38 reported that in both elderly and young adults , emg of the tibialis 
 anterior was higher than that of the gastrocnemius when their eyes were closed .
they also 
 reported that the tibialis anterior emg of the elderly was higher than that of the 
 gastrocnemius , but the gastrocnemius emg of the young adults was higher than the tibialis 
 anterior emg their eyes were open . in this study ,
the dominant tibialis anterior showed a 
 significant increase when support was provided by the non - dominant side , and the dominant 
 gastrocnemius muscle and dominant peroneus longus showed a significant increase when support 
 was provided by the dominant side .
thus , our present study s results are similar to those of 
 previous studies .
kennedy et al.44 
 studied neuromuscular fatigue caused by isometric contraction of the plantar flexor and 
 dorsiflexor , and reported that central fatigue could be determined by comparing the level of 
 voluntary activation of the dorsiflexor and plantar flexor between pre - fatigue and 
 post - fatigue .
however , the two muscle groups had different characteristics of fatigue 
 mechanism and recovery , and because the mechanisms of the two muscle groups were not 
 similar , they might not be influenced by the same method .
they also reported that it took 7 
 minutes for the plantar flexor to recover from fatigue , while it took only 1 minute for the 
 dorsiflexor .
in addition , the possibility of compensation between muscles was higher in the 
 plantar flexor than in the dorsiflexor , which is mainly composed of the tibialis anterior , 
 contrary to that of the plantar flexor , which is composed of synergistic muscle .
so we 
 conjecture the reason why both sides ( regardless of dominant or non - dominant side ) of the 
 tibialis anterior had a better recovery speed than the plantar flexor ( as indicated by the 
 significant difference in this study ) is due to compensation among muscles .
berger et 
 al.45 reported that the emg of the 
 exercised tibialis anterior decreased in their study of the bilateral effects of unilateral 
 lower limb muscle fatigue on emg .
they reported that the fatigued muscle activity was 
 related to passive tension increase , and to resist increasing the stretch of the fatigued 
 muscle , the decrease of the exercised tibialis anterior emg might restrict tension and 
 increase the risk of injury to the fatigued triceps surae .
thus , the reason why the 
 non - dominant tibialis anterior showed a significant difference when support was provided by 
 the non - dominant side , in this study , can be attributed to the fact that the muscle tension 
 was influenced by the fatigue of the non - dominant tibialis anterior . in this study , the dominant gastrocnemius muscle and
the dominant peroneus longus showed 
 significant differences when support was provided by the dominant side .
south and 
 george46 studied the effect of fatigue 
 of the peroneus muscle on proprioception and reported that fatigue of the peroneus muscle 
 did not affect ankle position sense after inducing muscle fatigue using an isokinetic 
 dynamometer .
mcloda et al.47 concluded 
 that muscles around the ankle other than the peroneal muscle are able to compensate for 
 fatigue of the peroneal muscle as they are less fatigued than the peroneal muscle and can 
 process the sensory information .
they also reported that only 5 out of 12 muscles passing 
 through the ankle , are restricted by the ankle joint .
giulio et al.48 suggested that the tibialis anterior is not always the 
 best muscle for preventing postural sway , and that the triceps surae is not always an 
 agonist of ankle muscles .
they also suggested that these roles are dynamic and can change 
 according to the location of the center of gravity relative to the ankle joint .
paillard et 
 al.49 studied the impairment of 
 postural control in the contralateral ( non - exercised ) lower limb after stimulation and 
 voluntary contraction of the ipsilateral ( exercised ) lower limb .
they observed a cross - over 
 fatigue effect after the sensory stimulus , and suggested that voluntary contraction might 
 impair postural control , since the sway area showed a significant difference after fatigue 
 of the lower limbs had been induced by voluntary contraction and electrical stimulus .
it is 
 also known that the effect of one leg balance training can be transferred to the untrained 
 contralateral side by the cross - education effect50 .
accordingly , we consider the dominant gastrocnemius and peroneus 
 longus showed a significant difference in the current study due to the fact that fatigue 
 induced by exercise being transferred to the dominant tibialis anterior by the cross - over 
 fatigue effect , and the non - exercised muscle transmitting the sensory information , because 
 the location of the center of gravity changed during the one leg stance . in this study ,
the sway area showed a significant difference between pre - test and post - test 
 by group when support was provided by the non - dominant side .
boyas et al.11 studied postural control impairment after 
 muscle fatigue induced by isokinetic exercise of the ankle joint in healthy adults .
they 
 reported that the sway area during the one - leg stance with eyes open was greater when the 
 plantar flexor and ankle dorsiflexor were exercised simultaneously than when the two muscles 
 were exercised separately11 .
yaggie and 
 mcgregor51 conducted a study in which 
 they examined the balance maintenance and postural limits after inducing muscle fatigue by 
 isokinetic exercise of the ankle joint at 60/sec in healthy and young adults .
they reported 
 that fatigue of the ankle plantar flexor and ankle dorsiflexor significantly affected the 
 sway and the range of posture control .
bisson et al.52 studied the acute effects of fatigue on the plantar flexor and 
 reported that postural sway increased as fatigue increased , especially during the one - leg 
 stance .
boyas et al.36 studied postural 
 changes related to postural control impairment due to fatigue of the plantar flexor during 
 the one - leg stance and reported that the sway area was greater during the post - fatigue 
 period than during the pre - fatigue period , showing that fatigue of the plantar flexor is 
 directly connected to changes in the postural sway
. the results of our present study show 
 that fatigue of the lower limb , induced by isotonic or isokinetic exercise , significantly 
 affected the mechanism of postural control and the sway area .
hence , we consider the results 
 of our present study are similar to those of previous studies in that the sway area showed a 
 significant difference between pre- and post - fatigue . in conclusion , this study was conducted to examine how the balance of the lower limbs and 
 the muscle activities of the tibialis anterior , the medial gastrocnemius and the peroneus 
 longus are influenced by isotonic and isokinetic exercise of the ankle joint .
the subjects 
 of this study were healthy adults in their 20s , and the following results were obtained .
( 1 ) 
 the changes in muscle activities between pre- and post - test in both the isotonic and 
 isokinetic exercise groups did not show an the interaction effect between group and time , 
 and a main effect of time was not shown by either of the groups .
a main effect was shown by 
 in the non - dominant tibialis anterior , the dominant tibialis anterior , the dominant 
 gastrocnemius muscle and the dominant peroneus longus .
( 2 ) the changes in balance between 
 pre - test and post - test in both exercise groups did not show an the interaction effect 
 between group and time , and a main effect was not shown by either of the groups .
a main 
 effect of time was shown by both the isotonic and isokinetic exercise groups for the sway 
 area when support was provided by the non - dominant side .
the two exercise groups showed 
 significant differences in muscle activities , and the group performing isokinetic exercise 
 showed higher muscle activities .
in terms of balance , there was no difference between the 
 groups , but there was a significant difference between the pre - test and the post - test 
 results .
the results of this study may help in the selection of exercises for physical therapy , 
 because they demonstrate that muscle activity and balance vary according to the type of 
 exercise .
 [ purpose ] this study was performed to examine how the balance of lower limbs and the 
 muscle activities of the tibialis anterior ( ta ) , the medial gastrocnemius ( gcm ) , and the 
 peroneus longus ( pl ) are influenced by isotonic and isokinetic exercise of the ankle 
 joint . 
 [ subjects ] the subjects of this study were healthy adults ( n=20 ) , and they were 
 divided into two groups ( isotonic=10 , isokinetic=10 ) . [ methods ] isotonic group performed 3 
 sets of 10 contractions at 50% of mvic and isokinetic group performed 3 sets of 60/sec . 
 
 muscle activity was measured by emg and balance was measured by one - leg standing test . 
 
 [ results ] for muscle activity , a main effect of group was found in the non - dominant ta , 
 and the dominant ta , gcm and pl . for balance , 
 a main effect of time was found in both 
 groups for the sway area measured support was provided by the non - dominant side . 
 
 [ conclusion ] in terms of muscle activity , the two groups showed a significant difference , 
 and the isokinetic group showed higher muscle activities . in terms of balance 
 , there was a 
 significant difference between the pre - test and the post - test . 
 the results of this study 
 may help in the selection of exercises for physical therapy , because they show that muscle 
 activity and balance vary according to the type of exercise . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION