chronic stroke patients commonly experience decreased balance control , which dramatically impacts their ability to perform activities of daily living ( adls ) , or purposeful activities , and maintain independent gait . decreased balance may be due to cognitive changes , decreased muscle power , limited range of motion , abnormal muscle tone , uncoordinated movements , or sensory integration alterations . spasticity , which is the major cause of decreased balance and gait , has commonly been reported in patients with stroke , multiple sclerosis , spinal cord injury , and traumatic brain injury . moreover , spasticity causes spastic movement disorder , slowed gait , and disturbances in voluntary movement . in addition , passive and active range of motion , functional ability , and dynamic balance are affected . passive movement , passive stretching , prostheses , and electrical stimulation   have been employed in efforts to decrease spasticity . electrical stimulation has been used in the rehabilitation of chronic stroke patients , and functional electrical stimulation by neuromuscular electrical stimulation and transcutaneous electrical nerve stimulation ( tens ) have been used for pain and sensory stimulation . tens and functional electrical stimulation have been shown to increase muscle power and movement function , and decrease spasticity . however , functional electrical stimulation induces more powerful muscle contraction and a wider range of motion than does tens , and the repetitive movement and sensory information that results from functional electrical stimulation effectively improve gait speed and increase muscle power in chronic stroke patients . use of tens for inhibition of spasticity , antagonist stimulation , agonist stimulation , and dermatome stimulation on spastic muscle   has been reported . the combination of tens and task - oriented movement was demonstrated to improve functional ability relative to the placebo tens group , and tens with bobath treatment resulted in decreased spasticity , compared to the use of bobath treatment group , have been reported . for chronic hemi - neglect patients , application of tens on the paretic neck muscle resulted in increased postural control and spatial improvement , while normal participants who received tens showed decreased postural sway when standing . however , previous studies used tens independently or with an exercise program for a short period of time . therefore , in this study , we examined the effects of a tens exercise program on spasticity , balance , and gait in chronic stroke patients to determine whether exercise with tens increases patients exercise function . the patients were randomly allocated to either tens group or placebo tens group in a ratio 1:1 . one hundred participants were initially recruited from 4 rehabilitation hospitals in seoul , south korea . participants were included if they had been diagnosed with hemiplegic stroke more than 6 months previously ( to exclude natural recovery ) and were able to walk 10 m independently . exclusion criteria included cognitive impairment indicated by scoring higher than 24 on the mini - mental state examination , other orthopedic disease , and visual or auditory disorders . thirty quadriplegic patients , 29 patients who could not walk 10 m independently , 4 patients with orthopedic disorder , and 3 patients with cerebellar disease were excluded from the study . thirty - four eligible participants provided written informed consent after receiving an explanation of the study ( figure 1 ) . the sample size was calculated using the mean difference in modified ashworth scale ( mas ) for spasticity between the experimental and control groups . 3.1 ) founded on pilot study results , we set the effect size at 0.992 . when a 2-tailed test with a test power of =0.8 and significance level of =.05 was applied . four additional participants were recruited in anticipation of a dropout rate of approximately 15% during the study . seventeen participants received tens plus therapeutic exercise ( tens group ) , and 17 participants received placebo tens plus therapeutic exercise ( placebo tens group ) . participants in the 2 groups engaged in the same 30-min therapeutic exercise 5 days per week for 6 weeks . the exercise comprised a one - to - one rom exercise ( 10 min ) , a functional mat exercise ( 10 min ) , and a gait exercise ( 10 min ) , which were each performed at a difficulty level appropriate for the patient . in order to minimize differences between the present and previous interventions , the exercise program was performed according to the pre - set principles , once 1 week before the experiment , and 6 times during the experiment ; thus , there were 7 education and practice sessions in total . education was provided to resolve problems occurring during the exercise program , and to teach performance of exercise program according to the established principles . two - channel tens ( tens-7000 , koalaty products inc . , usa ) was used . tens electrodes ( 5 cm ) were placed on the affected lower extremity on the lateral and medial quadriceps and gastrocnemius . a frequency of 100 hz and a pulse width 200 s were used . participant pre - stimulation threshold was measured from 0.01 ma and stimulated by 90% amplitude using the sub - sensory threshold . two - channel tens was used in the same manner as in the tens group . however , stimulation was not applied and patients were informed that the treatment would be imperceptible . the intra - rater credibility was.57 and inter - rater credibility was.62 . to perform the mas , the patient s ankle is passively extended from maximal plantar flexion to the painless range and the examiner assigns a score that ranges from 0 to 4 ( 0 , 1 , 1 + , 2 , 3 , and 4 ) : 0 indicates normal or very low muscle tone , and 4 indicates that passive extension is not possible . the examiner repeats the measurement 3 times while covering the patient s calf with 1 hand to ensure that the knee does not bend while the patient is lying supine , and dorsiflexion of the patient s ankle with the other hand . for measurement of static balance , the good balance ( metitur ltd , finland , 2008 ) device was used . this device , which comprises a portable triangular foot plate and a scale on the foot plate for foot placement , is widely used for measuring balance in elderly persons and chronic stroke patients . participants stood with eyes open on the foot plate with their second toe and heel over the scale lines and maintained the position for 30 s ; measurements were performed 3 times , maintaining for 30 s with eyes closed . the average of the measurements was used as an indicator of anterior - posterior and medial - lateral postural sway , speed , and speed moment . the timed up and go ( tug ) test was used to assess dynamic balance in the patients . this test measures the time required for a patient to stand up from a 46-cm - high chair , at the cue of start and walk 3 m in front of them , and return to the chair . optogait , microgate s.r.l , italy , 2010 ) was used to test the gait pattern of patients and quantity of gait analysis . the gait analyzer was 3 m in length and had 2 transmitting bars and a webcam ( logitech webcam pro 9000 ) . the distance between the 2 bars was 1 m , bars were 1 cm from each other , and were continuously receiving signals from a light - emitting diode in the transmitter . participants gait was sensed and transmitted through the infrared ray sensor , temporal and spatial variables were collected , and participant walking order was stored in the webcam and later synced with the perception error for accurate gait measurement . collected data were processed using optogait , version 1.5.0 . 0 software ( microgate s.r.l , italy , 2010 ) . to ensure data collection accuracy , the device was calibrated before the test . in order to minimize muscle fatigue , a 1-minute break was provided between measurements ; measurement was repeated 3 times , and the average was used . for data analysis , spss ver . data normality was tested using shapiro - wilk test , and all variables showed normal distribution . the patients were randomly allocated to either tens group or placebo tens group in a ratio 1:1 . one hundred participants were initially recruited from 4 rehabilitation hospitals in seoul , south korea . participants were included if they had been diagnosed with hemiplegic stroke more than 6 months previously ( to exclude natural recovery ) and were able to walk 10 m independently . exclusion criteria included cognitive impairment indicated by scoring higher than 24 on the mini - mental state examination , other orthopedic disease , and visual or auditory disorders . thirty quadriplegic patients , 29 patients who could not walk 10 m independently , 4 patients with orthopedic disorder , and 3 patients with cerebellar disease were excluded from the study . thirty - four eligible participants provided written informed consent after receiving an explanation of the study ( figure 1 ) . the sample size was calculated using the mean difference in modified ashworth scale ( mas ) for spasticity between the experimental and control groups . 3.1 ) founded on pilot study results , we set the effect size at 0.992 . when a 2-tailed test with a test power of =0.8 and significance level of =.05 was applied . four additional participants were recruited in anticipation of a dropout rate of approximately 15% during the study . seventeen participants received tens plus therapeutic exercise ( tens group ) , and 17 participants received placebo tens plus therapeutic exercise ( placebo tens group ) . participants in the 2 groups engaged in the same 30-min therapeutic exercise 5 days per week for 6 weeks . the exercise comprised a one - to - one rom exercise ( 10 min ) , a functional mat exercise ( 10 min ) , and a gait exercise ( 10 min ) , which were each performed at a difficulty level appropriate for the patient . in order to minimize differences between the present and previous interventions , the exercise program was performed according to the pre - set principles , once 1 week before the experiment , and 6 times during the experiment ; thus , there were 7 education and practice sessions in total . education was provided to resolve problems occurring during the exercise program , and to teach performance of exercise program according to the established principles . two - channel tens ( tens-7000 , koalaty products inc . , usa ) was used . tens electrodes ( 5 cm ) were placed on the affected lower extremity on the lateral and medial quadriceps and gastrocnemius . a frequency of 100 hz and a pulse width 200 s were used . participant pre - stimulation threshold was measured from 0.01 ma and stimulated by 90% amplitude using the sub - sensory threshold . two - channel tens was used in the same manner as in the tens group . however , stimulation was not applied and patients were informed that the treatment would be imperceptible . the exercise comprised a one - to - one rom exercise ( 10 min ) , a functional mat exercise ( 10 min ) , and a gait exercise ( 10 min ) , which were each performed at a difficulty level appropriate for the patient . in order to minimize differences between the present and previous interventions , the exercise program was performed according to the pre - set principles , once 1 week before the experiment , and 6 times during the experiment ; thus , there were 7 education and practice sessions in total . education was provided to resolve problems occurring during the exercise program , and to teach performance of exercise program according to the established principles . tens electrodes ( 5 cm ) were placed on the affected lower extremity on the lateral and medial quadriceps and gastrocnemius . a frequency of 100 hz and a pulse width 200 s were used . participant pre - stimulation threshold was measured from 0.01 ma and stimulated by 90% amplitude using the sub - sensory threshold . two - channel tens was used in the same manner as in the tens group . however , stimulation was not applied and patients were informed that the treatment would be imperceptible . the mas is a subjective method used for the measurement of spasticity . the intra - rater credibility was.57 and inter - rater credibility was.62 . to perform the mas , the patient s ankle is passively extended from maximal plantar flexion to the painless range and the examiner assigns a score that ranges from 0 to 4 ( 0 , 1 , 1 + , 2 , 3 , and 4 ) : 0 indicates normal or very low muscle tone , and 4 indicates that passive extension is not possible . the examiner repeats the measurement 3 times while covering the patient s calf with 1 hand to ensure that the knee does not bend while the patient is lying supine , and dorsiflexion of the patient s ankle with the other hand . for measurement of static balance , the good balance ( metitur ltd , finland , 2008 ) device was used . this device , which comprises a portable triangular foot plate and a scale on the foot plate for foot placement , is widely used for measuring balance in elderly persons and chronic stroke patients . participants stood with eyes open on the foot plate with their second toe and heel over the scale lines and maintained the position for 30 s ; measurements were performed 3 times , maintaining for 30 s with eyes closed . the average of the measurements was used as an indicator of anterior - posterior and medial - lateral postural sway , speed , and speed moment . the timed up and go ( tug ) test was used to assess dynamic balance in the patients . this test measures the time required for a patient to stand up from a 46-cm - high chair , at the cue of start and walk 3 m in front of them , and return to the chair . optogait , microgate s.r.l , italy , 2010 ) was used to test the gait pattern of patients and quantity of gait analysis . the gait analyzer was 3 m in length and had 2 transmitting bars and a webcam ( logitech webcam pro 9000 ) . the distance between the 2 bars was 1 m , bars were 1 cm from each other , and were continuously receiving signals from a light - emitting diode in the transmitter . participants gait was sensed and transmitted through the infrared ray sensor , temporal and spatial variables were collected , and participant walking order was stored in the webcam and later synced with the perception error for accurate gait measurement . collected data were processed using optogait , version 1.5.0 . 0 software ( microgate s.r.l , italy , 2010 ) . to ensure data collection accuracy , a 1-minute break was provided between measurements ; measurement was repeated 3 times , and the average was used . the mas is a subjective method used for the measurement of spasticity . the intra - rater credibility was.57 and inter - rater credibility was.62 . to perform the mas , the patient s ankle is passively extended from maximal plantar flexion to the painless range and the examiner assigns a score that ranges from 0 to 4 ( 0 , 1 , 1 + , 2 , 3 , and 4 ) : 0 indicates normal or very low muscle tone , and 4 indicates that passive extension is not possible . the examiner repeats the measurement 3 times while covering the patient s calf with 1 hand to ensure that the knee does not bend while the patient is lying supine , and dorsiflexion of the patient s ankle with the other hand . for measurement of static balance , the good balance ( metitur ltd , finland , 2008 ) device was used . this device , which comprises a portable triangular foot plate and a scale on the foot plate for foot placement , is widely used for measuring balance in elderly persons and chronic stroke patients . participants stood with eyes open on the foot plate with their second toe and heel over the scale lines and maintained the position for 30 s ; measurements were performed 3 times , maintaining for 30 s with eyes closed . the average of the measurements was used as an indicator of anterior - posterior and medial - lateral postural sway , speed , and speed moment . the timed up and go ( tug ) test was used to assess dynamic balance in the patients . this test measures the time required for a patient to stand up from a 46-cm - high chair , at the cue of start and walk 3 m in front of them , and return to the chair . a gait analyzer ( optogait , microgate s.r.l , italy , 2010 ) was used to test the gait pattern of patients and quantity of gait analysis . the gait analyzer was 3 m in length and had 2 transmitting bars and a webcam ( logitech webcam pro 9000 ) . the distance between the 2 bars was 1 m , bars were 1 cm from each other , and were continuously receiving signals from a light - emitting diode in the transmitter . participants gait was sensed and transmitted through the infrared ray sensor , temporal and spatial variables were collected , and participant walking order was stored in the webcam and later synced with the perception error for accurate gait measurement . collected data were processed using optogait , version 1.5.0 . 0 software ( microgate s.r.l , italy , 2010 ) . to ensure data collection accuracy , a 1-minute break was provided between measurements ; measurement was repeated 3 times , and the average was used . for data analysis , spss ver . 16.0 was used for averages and standard deviations . data normality was tested using shapiro - wilk test , and all variables showed normal distribution . five participants dropped out : 2 participants from the experimental group and 3 participants from the control group ( figure 1 ) . participants in the tens group and the placebo tens group were the same with regard to general characteristics . the tens group showed more reductions of mas than the placebo tens group ( p<.05 ) ( table 2 ) . on the static balance test , a significant difference in eyes closed and opened , anterior posterior , medial lateral postural sway velocity , and velocity moment was observed in the tens group before and after the test ( p<.05 ) , and in mean difference from pre- and posttest between the 2 groups ( p<.05 ) ( table 3 ) . in tug of the dynamic balance test , a significant difference in before and after the test was observed in the tens group ( p<.05 ) and the tens group was more improved than the placebo tens group ( p<.05 ) ( table 2 ) . on the gait analysis test , significant differences in velocity , cadence , and step length and stride length of the paretic side were observed in the tens group before and after the test ( p<.05 ) , but in the placebo tens group , only velocity showed a significant difference before and after the test ( p<.05 ) and the tens group showed more improvements of cadence , step length of the paretic side , and stride length of the paretic side than the placebo tens group ( p<.05 ) ( table 4 ) . our results suggest that the combination of tens and exercise improves spasticity , balance , and gait in chronic stroke patients . in previous studies using motor level stimulation threshold , application of tens resulted in decreased spasticity in patients with spinal cord injury   and chronic stroke patients , and decreased h - reflex size and spasticity in patients with hemiplegia . robbins et al .   reported that motor level stimulation has to be far above threshold for attainment of muscle contraction related to proprioception feedback in skin , muscles , and joints ; and that sensory - level stimulation has to affect the afferent fibers of skin with no muscle contraction . reported that sensory - level stimulation of a lower threshold stimulates skin or proprioceptors to increase skin or proprioception to increase standing posture stability . dickstein et al .   reported that use of tens led to an increase in somatosensory flow from the lower extremity . in this study , after tens and exercise , a greater decrease in mas was observed in the tens group relative to the placebo tens group . in this study , sensory level tens was applied on the gastrocnemius and quadriceps , and exercise was performed to decrease spasticity . decreased spasticity led to improved asymmetric alignment , decreased extremity function , and ( possibly ) effective energy consumption . proprioceptive sensory damage causes postural control difficulties because it alters one s perception of changes in body orientation in the environment ; various types of sensory stimulation , such as proprioception , induce development of minimum muscle contraction and activation of the cortex and cerebellum , which affects balance . this evidence demonstrates that exercise with tens promotes activation of the network that mediates proprioception and balance . reported that standing on 1 foot decreased postural sway in elderly individuals who received electrical stimulation , and prennou et al .   reported a decrease in postural sway in stroke patients who received tens on the cervical area . in this study , tens was applied to chronic stroke patients at 100 hz below threshold on the gastrocnemius to decrease postural sway ; the results were the same as those of previous studies . this result is the same as that of a study reporting that tens improved somatosensory function in the lower extremity . this study conducted an exercise program with tens to improve standing postural control , and maintenance on quadriceps and gastrocnemius increased somatosensory function in the lower extremity . the improvement in balance might have been due to changes in the distance of cadence or step length on the affected side . gait is a complex movement consisting of balance , coordination , proprioception , and integrated harmony between joints and muscles . ng and hui - chan   applied tens on acupuncture points and reported improved gait speed and endurance . chen   applied sensory electrical stimulation on the achilles tendon and gastrocnemius 6 times per week for 1 month , and reported significantly increased gait speed in stroke patients . the tens group showed improved gait speed , step length , and cadence in the affected leg during gait , compared with the placebo tens group . previous studies used tens for measurement of balance , but not gait , or did not report significant improvements in gait ; however , correlations were observed between balance and gait function . most chronic stroke patients have an asymmetric gait pattern , resulting in decreased speed , increased double stance , and short step length . in this study , the combination of exercise and tens effectively improved proprioception to each muscle , resulting in increased body orientation . second , the sample size was small , which limits the generalizability of the data . given the findings of this study , we can logically assume that exercise therapy with tens improves spasticity , balance , and gait in chronic stroke patients and could be actively used in clinic settings as an adjunct to conventional physical therapy .
backgroundtranscutaneous electrical nerve stimulation ( tens ) is a useful modality for pain control . 
 tens has recently been applied to decrease spasticity . 
 the purpose of this study is to determine whether the addition of tens to an exercise program reduces spasticity and improves balance and gait in chronic stroke patients.material/methodsthis was a single - blinded , multicenter , randomized controlled trial . 
 thirty - four ambulatory individuals with chronic stroke participated and were randomly allocated to the tens or placebo group . 
 the tens group performed therapeutic exercise with tens while the placebo ( non - stimulation ) tens group performed therapeutic exercise with placebo tens . 
 participants in both groups followed the same 30-min exercise regimen 5 times per week for a period of 6 weeks . 
 spasticity ( modified ashworth scale ) , static ( balance system ) , and dynamic balance ( timed up and go test ) , and gait ability ( gait analyzer ) were measured at 1 week before and 1 week after the intervention.resultssignificant differences were observed between the 2 groups . 
 spasticity improved by 0.80 points in the tens group . 
 anterior - posterior and medial - lateral sway velocity among static balance parameters and dynamic balance showed significant differences between the tens and placebo tens groups ( p=.000 ) . 
 gait speed and cadence were enhanced significantly in the tens group ( p=.000 ) . 
 step and stride length on the paretic side showed a significant difference in the tens group ( p=.000 ) , while only velocity showed a significant difference in the placebo tens group ( p=.004).conclusionsa combination of therapeutic exercise and tens may reduce spasticity and improve balance , gait , and functional activity in chronic stroke patients .