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Paper text:
lateral ankle sprain ( las ) is one of the common injuries experienced in sport .
instability 
 associated with las is classified into three types : structural , functional , and both 
 structural and functional instability1 . 

structural instability ( si ) is a deviation from the normal physiological range of motion . in 
 contrast
, functional instability ( fi ) is instability of ankle joint sprain regardless of 
 si2 .
it has been reported that ankle sprain caused by noncontact damage often occurs during jump 
 landing and direction change3 .
karlsson and peterson reported that fi led to a delay in the muscle 
 reaction time and weakness of the peroneal muscles5 .
furthermore , an increased resting motor threshold might indicate 
 deficits in peroneus longus corticomotor excitability in people with chronic ankle 
 instability ( cai)6 . in our previous study , we assessed whether electrical stimulation of the peripheral nerve 
 for a specific period of time increases the excitability of the cerebral cortex7 .
increases in pinch force and grip strength 
 were observed as a result of by electrical stimulation of the median nerve of healthy 
 subjects8 . in the present study
, we examined the effects of transcutaneous electrical nerve 
 stimulation ( tens ) during a balance exercise on patients with fi of a sprained ankle , 
 including the ability to land after jumping at the center of foot pressure ( cop ) .
the subjects were seven males ( mean age , 20.3  0.8 ) with a history of ankle joint sprain , 
 and a sprained ankle score 80 points on karlson s functional instability test5 .
we 
 performed the anterior drawer and medial subtalar glide ( msg ) tests for their sprained 
 ankles .
patients with 
 positive scores in either test were excluded from the study because of structural 
 instability . it should be noted that subjects were excluded if dorsiflexion was limited in the ankle to 
 be studied .
this study was approved by the institutional research ethics committee of kansai 
 university of health sciences .
the subjects were asked to jump over a 20-cm - high platform sideways for 10 consecutive 
 seconds on a force plate using one leg in a posture with the arms crossed in front of the 
 chest .
the length of the cop was measured for comparison of balance exercise ( ex condition ) 
 and balance exercise with simultaneous tens therapy ( tens condition ) .
the exercise was 
 repeated three times for ten minutes , with a five - minute break , and included the front 
 lunge , side lunge , stepping , squat , and one - leg standing .
it should be noted that the length 
 of the cop was normalized by dividing it by the jump - landing time .
the stimulation conditions were as 
 follows : 4.8  1.5 ma , single - phase square wave , pulse width of 1  ms , burst frequency of 1 
 bp , and pulse frequency of 10  hz for the common peroneal nerve .
tens was administered with 
 an intellect mobile stim ( chattanooga , djo uk ltd . ,
an adhesive pad electrode 
 ( 5  5  cm ) was placed on the lower edge of the head of the fibula , and used as a stimulating 
 electrode .
statistical processing 
 was performed to examine the length of the cop on the sprain side and non - sprain side under 
 the ex and tens conditions using the mann - whitney u - test , and the date were compared before 
 and after the study task using the wilcoxon test .
the length of the cop on the sprain side was significantly larger than on the non - sprain 
 side under both the ex condition and tens condition . under the ex condition ,
the length of 
 the cop on the sprain side showed no significant change , with the values being 585.6  158.9 
 and 562.6  150.6  mm before and after the task , respectively . under the tens condition ,
the 
 length of cop on the sprain side was significantly reduced , with the values being 627.0  
 235.4 and 551.8  172.1  mm before and after the task , respectively ( table 1table1.length of the cop on the force plate ( unit :  mm)sprain sidenon - sprain sidebeforeafterbeforeafterex condition585.6158.9562.6150.6510.8175.4505.8187.2tens condition627.0235.4551.8172.1539.3160.0503.2144.3before : before balance exercise or tens therapy during balance exercise ; after : after 
 balance exercise or tens therapy during balance exercise .
* p<0.05 ; p<0.05 ) . before : before balance exercise or tens therapy during balance exercise ; after : after 
 balance exercise or tens therapy during balance exercise .
our results showed that , in both the ex and tens conditions , the length of the cop during 
 jump landing was significantly longer on the sprained side than on the non - sprained side . 

many authors reported that , in patients with functional instability following ankle sprain , 
 there was altered ankle position sense , slower reaction time of the peroneal muscle group , 
 and worsening of posture control function9 , 10 .
it was also reported that single - limb 
 postural sway was significantly greater in ankles with functional instability than in the 
 contralateral stable joint11,12,13 .
it was further 
 demonstrated that the muscular reaction times of the peroneal muscles in sprained ankles 
 were significantly slower than those in contralateral stable ankles and healthy control 
 ankles .
thus , extension of the length of the cop during jump landing on the sprained side 
 may be due to delay the contraction response of peroneal muscles , a property of functional 
 instability .
the body sway under the tens condition during one - leg standing on the sprain 
 side decreased compared with that under the ex condition .
application of electrical 
 stimulation to the common peroneal nerve had an impact on the dorsal motor area , and the 
 primary motor cortex became more active .
furthermore , the peroneal muscles showed increased 
 activity as a result of common peroneal innervation , which was induced based on the method 
 reported by wu et al7 . in another report , 
 pinch force improved as a result of transcutaneous electrical stimulation of stroke 
 patients .
the bilateral peroneus longus resting motor threshold was higher in participants 
 with cal than in those without cai
. an increased resting motor threshold might indicate 
 deficits in peroneus longus corticomotor excitability in people with cai .
the resting motor 
 threshold and self - reported function were moderately correlated , suggesting that deficits in 
 corticomotor excitability might influence the function6 . as a limitation of the present study
, conclusions can not be made regarding the mechanism of 
 effect of tens in this study , because stimulation of the sensory nerves excites the  motor 
 nerve fibers and is transmitted to the spinal cord ventral root rather than the dorsal 
 root14 and there is a path that passes 
 sensory stimulation to the top line in the motor cortex from the thalamus15 .
it is necessary to examine changes over 
 time because the long - term effect of tens has not been verified .
therefore , it is important 
 to carry out physical therapy in consideration of the influence on the central nervous 
 system even after ankle sprain .
[ purpose ] functional instability leads to a delay in the muscle reaction time and 
 weakness of the peroneal muscles . 
 the present study examined the effects of transcutaneous 
 electrical nerve stimulation during balance exercise on patients with functional 
 instability of the ankles , including the ability to land after jumping at the center of 
 foot pressure . 
 [ subjects ] the subjects were seven males with a history of ankle sprain . 
 
 all had a sprained ankle score of 80 points on karlson s functional instability test . 
 
 [ methods ] they were asked to jump over a 20-cm - high platform sideways for 10 consecutive 
 seconds on a force plate with one leg . 
 the length of the center of pressure was measured 
 for comparison of balance exercise and balance exercise with simultaneous transcutaneous 
 electrical nerve stimulation . 
 [ results ] the length of the center of foot pressure on the 
 sprain side was significantly greater than on the non - sprain side under both conditions . 
 under the balance exercise with simultaneous transcutaneous electrical nerve stimulation 
 therapy condition , 
 the length of the center of foot pressure on the sprain side was 
 significantly reduced , with the values being 627.0  235.4 and 551.8  171.1  mm before and 
 after the challenge , respectively . 
 [ conclusion ] ankle instability on the sprain side was 
 significantly reduced under the balance exercise with simultaneous transcutaneous 
 electrical nerve stimulation therapy condition before and after the challenge . 
 peroneal 
 muscles showed increased activity caused by common peroneal innervation .