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Paper text:
ankle sprains are one of the most common injuries caused by physical activity during sports 
 or activities of daily living1,2,3 .
they usually occur 
 during dynamic movement , and over 50% of all ankle injuries involve ligament damage4 . chronic ankle instability ( cai )
is defined 
 as a subjective feeling of the ankle giving way , which results from a pattern of instability 
 involving an initial ankle sprain followed by repeated ankle sprains5 .
cai can be defined as the state caused by the experience of 
 multiple ankle sprains , with instability resulting from restricted joint range of motion 
 ( rom ) and limited movement6 .
in addition , 
 stability of the ankle can have a positive effect on standing balance , and even influence 
 the stability of such movements as walking and jumping7 .
cai can occur as a result of inappropriate treatment following an initial injury and pain 
 in the lateral part of the ankle joint is reported to be the most common cause5 , 8 , 9 .
due to instability and discomfort during 
 sudden changes of direction or stopping actions , patients with cai report reduced balance 
 control . therefore , when ankle injury occurs , the mechanical receptors in the joint become 
 damaged , leading to functional instability10 .
although the precise mechanisms of functional ankle instability 
 have not been elucidated , the condition presents with ligament damage , reduced muscle 
 strength , delayed muscle response time , and proprioceptive deficits in the ankle11,12,13 .
ankle injuries can be divided into acute 
 and chronic injuries . in the case of cai , because dynamic movement is restricted and balance 
 and gait abilities are impaired , conservative treatment via rehabilitation exercise is 
 thought to be important5 , 8 , 14 , 15 .
the aim of active conservative treatment after an exercise - related injury is to promote 
 functional recovery to a level equivalent to or better than the pre - injury level , through 
 the use of appropriate treatments and exercises , thereby enabling the patient to return to 
 the field or to daily life .
hence , this study aimed to construct an integrated 
 rehabilitation exercise program that could improve functional measures , such as muscle 
 strength and dynamic coordination , in order to prevent chronic pain and improve functional 
 impairment caused by ankle injury or re - injury .
the study subjects were 26 male soccer players who required functional strength exercises 
 due to repeated ankle injuries .
the subjects had a mean age of 23.2  1.4  years , a mean 
 height of 179.8  4.8  cm , and a mean body weight of 75.4  6.0  kg .
all the subjects 
 understood the purpose of this study and provided their written informed consent prior to 
 participation in this in the study in accordance with the ethical principles of the 
 declaration of helsinki .
rehabilitation exercise was performed for a total of 12 weeks , two sessions per week , 80 
 minutes per session , with the aim of alleviating cai , strengthening in this by muscles of 
 the ankle and the dynamic coordination of the lower limb .
the rehabilitation exercise 
 program consisted of three phases : the initial exercise phase ( weeks 12 ) , the functional 
 improvement phase ( weeks 310 ) , and the functional maintenance phase ( weeks 1112 ) ( table 1table 1.rehabilitation exercise programprogramintensitytimewarm up walking and cycling no pain10main exercise ( 12 weeks)1 ( 12 week)[initial] rom exercise of the ankle joint focused on pf / df & in / ev  no pain rpe 1113 circuit 
 ex. increase ex. repetition ex.602 ( 310 week)[improvement] rom exercise of the ankle joint  band exercise ( red & green 
 bands) weight ( focused on the lower extremity)3 ( 1112 week)[maintenance] plyometric & pnf training focused on pf / df & in / evcool down static stretching ( mat exercise )  no pain10 ) .
the program focused on joint rom for dorsiflexion ( df ) , plantarflexion ( pf ) , 
 internal rotation , and external rotation in order to strengthen the muscles of the ankle . 

these exercises were combined with band training , weight training , plyometrics , and 
 exercises to improve proprioception in order to develop stable , coordinated , functional 
 ability .
measurements were performed before and after participation in the 12-week program 
 in order to evaluate the degree of improvement in muscle strength and dynamic coordination . 

the humac norm testing & rehabilitation system ( computer sports medicine , inc . , 

stoughton , ma , usa ) was used to measure the isometric muscle strength of the ankle , 
 considering the functional movements of df , pf , inversion ( in ) , and eversion ( ev ) .
the torque of the joint was aligned 
 with the rotation axis of the dynamometer , and the axis of movement was aligned with the 
 anatomical position of the joint .
measurements were made of each subject , and were converted 
 into a digital format using a computer program . in order to evaluate ankle muscle strength , 
 peak torque ( nm ) and the ipsilateral muscle strength ratio ( % ) of df , pf , in , and ev were 
 measured 30/s .
the y balance test ( functional movement systems , chatham , va , usa ) , which was developed to 
 improve dynamic coordination , was used in this study .
this test not only allows subjects to 
 gain stability , but also contributes to gradual improvement in muscle strength and 
 flexibility .
the y balance test is a method of testing lower limb muscle strength and 
 coordinated functions in dynamic stability , and was adapted from the star excursion balance 
 test , using three directions instead of eight16 .
the 
 subject stands on one leg at the center , and the maximum distance that he / she can stretch 
 the other leg is measured for each of the three directions . here , the three directions 
 corresponded to the anterior , posteromedial , and posterolateral axes .
three measurements 
 were made of each leg , and the average of these measurements was used in the analysis . means and sds were calculated for all the measured data . the paired - sample t - test was used 
 to compare isometric muscle strength and dynamic coordination before and after the 12-week 
 program .
data were analyzed using spss version 23.0 ( spss inc . , chicago , il , usa ) , and 
 values of p<0.05 were considered statistically significant .
following 12 weeks of rehabilitation exercise , there were statistically significant 
 improvements in bilateral pf strength , the ipsilateral muscle strength ratio , isometric in 
 strength , and isometric ev strength ( p<0.05 ) .
over 70% of patients who experience ankle sprains report additional symptoms resembling 
 cai , such as re - injury or functional abnormalities17 .
moreover , cai has been reported to be associated with several 
 important functional impairments , such as reduced muscle strength and proprioception , as 
 well as loss of both neuromuscular and postural control5 .
it is presumed that cai is caused by complex functional 
 deterioration , including reduced proprioception and weakening of the ankle evertors18 .
it has also been reported that 
 proprioceptive and muscle strengthening exercises are important for the rehabilitation of 
 ankle instability6 , 9 , 19 , 20 . in this study ,
isometric muscle strength was compared between before and after 
 participation in the 12-week rehabilitation exercise program aimed at alleviating cai .
the 
 results show there were significant improvements in df and pf strength , as well as in the 
 ipsilateral muscle strength ratio , demonstrating an overall improvement in ankle muscle 
 strength ( p<0.001 ) .
these results are consistent with those of a previous study , which 
 evaluated eight weeks of strategic resistance training performed by 22 subjects diagnosed 
 with functional ankle injury21 . in 
 another study of the strength , balance , and functional ability of functionally unstable 
 ankles22 , significant differences in pf 
 strength at 30/s , 60/s , and 120/s , and in peak isometric pf force at 30/s
were reported 
 ( table 2table 2.isokinetic strength at 30/sec ( nm)pre - testpost - testpeak torque(nm)pfr98.4  25.5107.8  28.1l105.4  25.9114.8  28.1dfr22.2  5.034.5  5.8l37.7  5.046.0  5.9ratio ( % ) r21.7  7.038.1  15.0l34.5  8.946.8  15.9values are mean  sd .
pf : planterflexion ; df : dorsiflexor , r : right ; l : left . * * * p<0.001 ) .
these findings indicate that it is likely that improvement in ankle muscle 
 strength improves functional stability and prevents injury .
pf : planterflexion ; df : dorsiflexor , r : right ; l : left . * * * p<0.001 compared with the general population , soccer players show reduced evertor muscle strength 
 and stiff invertor muscles due to repeated training , overuse , and soft tissue damage2 .
these differences lead to a tendency of the 
 in angle to be larger than in typical individuals , which has been reported to cause cai due 
 to weakening of the lateral muscles , and development of a supination foot deformity23 .
the results of the present study show the 
 exercise program increased in and ev strength , and there were significant increases in right 
 ev ( p<0.05 ) , left ev ( p<0.001 ) , and left in ( p<0.01 ) ( table 3table 3.isokinetic strength at 30/sec ( nm)pre - testpost - testpeak torque(nm)inr42.3  9.743.7  12.4l54.3  9.962.2  12.9evr27.1  4.330.3  7.9l34.6  4.540.8  7.7ratio ( % ) r67.2  18.173.4  21.3l65.8  14.967.9
pf : planterflexion ; df : dorsiflexor , r : right ; l : left .
similarly , a meta - analysis of the relationship between ankle instability and 
 balance impairment demonstrated that weakening of the ankle evertors was associated with 
 functional ankle instability24 .
it is our 
 opinion the the significant increases in ev and in strength after exercise in this study 
 were due to the active rehabilitation exercise preventing weakening of the evertor muscles . 
 additionally , the significant difference in ev strength is essential for the athletic 
 performance of soccer players .
our finding is consistent with previous studies reporting 
 that continual strengthening of the evertors helps to protect against injury by preventing 
 damage to the lateral ankle ligament and reducing tibial slope25 , 26 .
generally , 
 when evaluating isometric strength , lower limb muscle strength and the balance ratio are 
 used to evaluate the isometric strength of individual muscles , and to predict the relative 
 risk of certain injuries27 .
pf : planterflexion ; df : dorsiflexor , r : right ; l : left .
* p<0.05 , * * p<0.01 , * * * p<0.001 when standing erect , ankle stability can have a positive effect on standing balance , and 
 even influence the stability of such movements as walking and jumping7 , 28 . in this study
, 
 the y balance test was used as an index of functional balance ability .
the y balance test 
 uses three directions of the star excursion balance test and it has been shown in previous 
 studies to have a high reliability ( cronbach s =0.91 ) in assessments of patients with 
 cai29 . in a previous study of 
 functional rom in cai8 , improvements from 
 75.06  5.19% to 78.71  4.97% in the anterior direction , 93.3  10.37% to 97.47  11.20% in 
 the posteromedial direction , and 85.92  11.97%
to 93.09  12.96% in the posterolateral 
 direction were reported , but they were not statistically significant . however , a comparison 
 1 week later showed results , which were consistent with those of our present study ( table 4table 4.functional ability as measured by the y balance test ( cm)pre - testpost - testa61.8  4.462.0  5.7rightpm95.7  8.797.6  10.9pl106.8  8.9106.9  7.1a63.5  5.863.8  4.2leftpm99.1  8.8100.5  10.9pl110.6  6.9111.3
the results cited above indicate there was improved functional balance 
 ability , including muscle strength , flexibility , and proprioception in the lower limb , after 
 only 1 week of repeated training .
therefore , in order to improve function in the major 
 joints of the lower limb , namely , the knee and ankle , participation in an exercise program 
 that can improve muscle strength , flexibility , and proprioception is essential .
values are mean  sd . a : anterior ; pm : posteromedial ; pl : posterolateral active protocols that can reduce pain , and restore normal joint rom , muscle strength and 
 endurance , and functional ability will need to be developed .
[ purpose ] the aim of the present study was to construct an integrated rehabilitation 
 exercise program to prevent chronic pain and improve motor ability in cases of ankle 
 injury and re - injury . [ subjects and methods ] twenty - six male soccer players who required 
 functional strength exercises due to repeated ankle injury were the subjects . 
 a 12-week 
 rehabilitation exercise program was constructed with the aim of improving muscle strength 
 in the ankle and dynamic coordination of the lower limb . 
 muscle strength and dynamic 
 coordination were evaluated using the y balance test , and isokinetic muscle strength of 
 ankle dorsiflexion , plantarflexion , inversion , and eversion were measured before and after 
 the 12-week program . 
 [ results ] following 12 weeks of rehabilitation exercise , there were 
 statistically significant improvements in the ratios of dorsiflexor strength to 
 plantarflexor strength , eversion strength , and inversion strength on the left side . 
 the 
 other variables showed no significant changes . 
 [ conclusion ] the rehabilitation exercise 
 program for chronic ankle instability helped to reduce pain , and to restore normal joint 
 range of motion , muscle strength and endurance , and functional ability . 
 active protocols 
 to improve complex functions need to be developed to complement these results .