transcutaneous electrical nerve stimulation ( tens ) is the application of an electric 
 current through the skin to stimulate the nervous system . this type of electrical 
 stimulation activates spinal afferent pathways that connect to spinal gray matter of the 
 dorsal horn modulating sensory afferent traffic . the electric current stimulates the 
 underlying fibers producing painless paresthesias without causing damage to the skin1 , 2 . its application technique varies depending on several parameters and can be divided into 
 high frequency ( 50  hz ) low intensity and low frequency ( 10  hz ) high intensity tens , both 
 of which are used to relieve both acute and chronic pain3,4,5 . acupuncture is also widely used in clinical settings for the relief of pain caused by lower 
 back injury , fibromyalgia , and headache disorders , among others . uniting the technique of 
 acupuncture analgesia with electrotherapy , with certain modifications , has created 
 electroacupuncture which is used as a substitute for conventional acupuncture , and in cases 
 where clinical acupuncture alone has noeffect5 , 6 . low frequency tens is also called acupuncture like tens , because it interacting with the 
 peripheral nervous system eliciting a pricking sensation , that is modulated by the frequency 
 of electrical stimulation , the current intensity and the pulse duration . to present this 
 kind of sensation , the 
 procedure differs from classical electroacupuncture , as it does not use needles , only 
 electrodes with a high intensity of the electrical current7,8,9 . currently , several terms are used to describe the transcutaneous 
 electrical stimulation of acupoint . for example : acu - tens ( tens applied to an acupoint ) and 
 teas ( transcutaneous electric acupoint stimulation ) that involves any electric current 
 applied to acupoints10 . in this study , two different areas of electrodes , 1  cm and 15  cm , 
 te5 ( waiguan ) and pc6 ( neiguan ) acupoints . according to chinese traditional medicine 
 stimulation of the te5 acupoint is indicated for arthritis in the wrist and finger joints , 
 and that of the acupoint pc6 is indicated for pain in the forearm , carpal tunnel , and wrist , 
 median nerve palsy , and pain and contracture in the elbow and arm . this study analyzed 
 whether the areas of electrodes elicit different effects . when tens is applied to acupoints 
 frequency of 10  hz with sufficient intensity to promote muscle jerks . the latency of the 
 pain threshold and its intensity in healthy subjects subjected to cold - induced pain was 
 measured . this was a single - blind , quasi - experimental study with a control and placebo . forty - eight 
 subjects ( convenience sample ) were recruited from the departmental centres of the university 
 federal of pernambuco ( ufpe ) . they were divided into three groups of 16 subjects , composed 
 of both sexes aged between 18 and 30  years . the groups were formed by the allocation of the 
 subjects who were verbally invited to particpate and sent to the laboratory . all of the 
 participants provided their written informed consent . after reading and accepting the terms 
 of the study , subjects were allocated to three groups : the 1  cm electrode group , 
 the 15  cm electrode group , and the placebo group . the subjects were allocated by 
 raffle in blocks of four to each group in succession . during the period of experimentation 
 subjects showed no pathological state in the region subjected to cold - induced pain , did not 
 use allopathic and/or homeopathic drugs , showed no intolerance or phobia at low 
 temperatures , and the female subjects , were not in a state of pre - menstrual tension or 
 menstrual flow . all experiments were performed in the laboratory of electrothermy at the department of 
 physical therapy of the federal university of pernambuco . the first experimental group ( 8 
 males and 8 females ) was stimulated by acupuncture like tens on the te5 and pc6 acupoints 
 with 1  cm electrodes ; the second experimental group ( 9 males and 7 females ) was 
 also stimulated by acupuncture like tens on the same acupoints with 15  cm 
 electrodes ; and the placebo group ( 10 females and 6 males ) were told they were receiving 
 microcurrent stimulation of the deltoid muscle with a 15  cm electrode . the study 
 received approval from the university federal of pernambuco s research ethical committee , 
 under the registration of sisnep fr-294607 , caae-0315.0.172.000 - 9 based on resolution 466/12 
 national health council . the experimental intervention consisted of three stages ( six cycles ) which were termed 
 pretreatment time ( cycles 1 and 2 ) , treatment time ( cycles 3 and 4 ) and post treatment time 
 ( cycles 5 and 6 ) . each cycle lasted ten minutes , making a total of one hour trial . in the first cycle , subjects put their non - dominant hand in a container of warm water 
 ( 37  c ) for five minutes . the temperature was maintained by an electrical water heater and 
 constant measurement by mercury thermometer incoterm - l 212/04 . this procedure aimed to 
 equalize the temperature of the hand of all subjects before the procedure of cold - induced 
 pain . after this , the hands were removed from the container and placed into another with icy 
 water 02c ( control performed by the mercury thermometer incoterm - l 212/04 ) . the time to 
 pain threshold from when the individuals put their hands into the icy water to the moment 
 when they expressed  pain  was measured in seconds by digital stopwatch ( cronobio sw2018 ) . the subjects were asked to keep their hands in cold water for thirty more seconds , during 
 this time ( depending on the tolerance ) they were asked to describe the painful sensation 
 using a visual analog scale ( values from 0 to 10 , where 0 corresponds to no pain and 10 
 refers to the maximum tolerable pain ) to assess pain intensity . after this they were allowed 
 to take their hands out of the icy . after a rest interval , that varied among the individuals , butwas short enough to complete 
 half the period of the last five minutes of the first cycle , the subjects again put their 
 hands for 5 minutes in warm water , beginning the second cycle , followed immersion in cold 
 water . procedure was repeated , completing two cycles of cold - induced pain , with pretreatment 
 time , lasting twenty minutes . in the third cycle after wiring for tens , subjects again put their hands into the warm 
 water for five minutes , and then into the container with cold water . the time to the pain 
 threshold and pain intensity were measured , and the procedure was repeated for a fourth 
 cycle , twenty minutes of tens application in total . acupuncture - like tens ( 10  hz ) was 
 delivered with a balanced , asymmetrical , biphasic pulsed current ( tensys et9771 kld ) of 1  ms 
 ( millisecond ) pulse duration , with sufficient intensity of electric current to cause muscle 
 jerks when placed over the te5 and pc6 acupoints , located two from the wrist crease , on the 
 posterior and anterior forearm , respectively . to standardize electrical stimulation the 
 cathode was placed on the te5 and the anode on the pc6 acupoints . the electrical stimulation 
 of acupuncture - like tens was pervormed with 1  cm and 15  cm 
 electrodes . at the end of the treatment period , the subjects were subjected to two more cycles , the 
 fifth and sixth following the same method described above , to evaluate the effect of tens 
 post - treatment ( tens off ) . in the placebo group , subjects were subjected to the same procedure of the cold - induced 
 pain test ( pre - treatment , treatment and post - treatment ) , but the electrodes were placed on 
 the shoulder ( without connection to any acupoint ) on the belly of the anterior deltoid 
 muscle and the individuals were told that they were receiving a microcurrent treatment , in 
 which they would not feel any sensation . they were told that the microcurrent works with 
 very low intensities , was imperceptible , and had a painkilling effect . they were connected 
 to the first channel of the equipment , and the second channel was connected so that the 
 lights on the device certified that the current was supposedly operating . however the data of the latency of the pain threshold are presented as the mean  standard 
 deviation ( sd ) . the results of pain intensity are presented as the average scores on the 
 visual analog scale ( vas ) . the latency of the pain threshold between cycles within each 
 group was examined using repeated measures one - way anova and the post hoc newman - keuls test . 
 for the pain intensity , the analysis between cycles within each group was performed using 
 the friedman test . the groups pain threshold latencies were compared one - way anova followed 
 by , post hoc newman - keuls test , when necessary . the effect size was calculated using cohen s 
 d formula to investigate the clinical significance . a acupuncture - like tens with electrodes with an area of 1  cm showed effects on 
 the pain threshold latency during application , while acupuncture - like tens with 
 15  cm electrodes showed effects after tens application . the placebo group 
 showed no significant changes in any experimental phase ( table 1table 1.the latency threshold ( seconds ) of pain in the different periods of acupuncture 
 tens with electrodes of 1  cm , 15  cm , and placeboelectrodespretreatmenttreatmentposttreatment1 cm30.9  8.945.78  11.8 * 39.5  11.615 cm25.5  7.732.0  12.936.3  13.0*placebo25.2  10.725.2  7.622.4  7.4anova and post hoc newman - keuls . results expressed in mean  sd ( seconds ) * significant difference from pre - treatment the intensity of pain was reduced during tens treatment with 1  cm electrodes 
 both in relation to the time before treatment and after treatment ( table 2table 2.pain intensity in the different periods of acupuncture - like tens with electrodes 
 1  cm , 15  cm , and placeboelectrodespretreatment(mean ranks)treatment(mean ranks)posttreatment(mean ranks)1 cm2.91.1**2.0 * 15 cm1.32.6 * 2.1placebo2.12.11.7friedman test . * significant difference from pre - treatment . * * significant difference 
 from pre - treatment and post - treatment ) . with the 15  cm electrode the sensation of pain increased in 
 relation to the time before treatment . in the placebo group * significant difference from pre - treatment . * * significant difference 
 from pre - treatment and post - treatment table 3table 3.pain threshold latency ( seconds ) of the groupsplacebo1 cm15 cmpre - treatment22.4  7.425.2  10.725.2  7.6treatment39.5  11.6 * 30.9  8.945.8  11.8**post - treatment36.3  13.0 * 25.5  7.732.0  12.9anova and post hoc newman - keuls . * significant difference from the placebo group at 
 pre - treatment . * * significant difference between the 15  cm group and placebo group shows the results of the pain threshold latency times of the groups . during 
 the treatment , the 1  cm electrode group showed a longer pain threshold latency 
 than the other two groups . after treatment the tens groups ( 1  cm and 
 15  cm ) electrodes showed pain threshold latencies longer than the placebo 
 group . * significant difference between the 15  cm group and placebo group the effect size ( cohen s d ) with 1  cm electrodes was d = 0.98 pain and of 
 15  cm was d = 0.88 for the pain threshold latency time and respectively d = 
 0.96 and d = 0.91 post - treatment pain threshold latency time . to induce experimental pain without causing tissue injury we used a model called the cold 
 pressure test , also known as the cold - induced pain test . in this model pain is induced 
 through local hypothermia , since low temperatures ( 04c ) cause to painful sensations 
 through both vasoconstriction11 , 12 and the activation of thermal nociceptors 
 ( a- and c fibers ) that signal potential tissue damage . this information is sent via the 
 peripheral and central pathways to the somatosensory cortex11 . this information of pain has different representations in the 
 cerebral cortex , a sensory version and a psychological one , that might be interpreted in 
 this experiment as the pain threshold latency and pain intensity , respectively13 . this is due to the 
 characteristics of electric current , that has low frequency and high intensity , activating 
 the supra - segmental pathways of -endorphin and met - enkephalin14 . we found that the low frequency , high intensity tens was 
 bearable , and prolonged the pain threshold latency in the acute phase , and that prolongation 
 of the pain threshold latency was dependent on the size of the electrode . a previous study15 demonstrated that 
 analgesia of 80  hz tens for pain induced by mechanical which was measured subjectively by 
 subjects pressure was by increasing the intensity of electrical current . the frequency and pulse duration are 
 also parameters that influence analgesia16 . in our study , it was found that the size of the electrode and its 
 location affected analgesia . initially , a high threshold of stimulation was required for 
 both electrodes at the respective coupled acupoints , that are distal from the muscular motor 
 points of the forearm , and required high intensities to promote muscle twitch and sting 
 sensation . a functional magnetic resonance imaging study of healthy subjects subjected to cold - induced 
 pain , and demonstrated that the periaqueductal gray , the superior frontal gyrus , anterior 
 cingulate cortex , thalamus , left insula , right inferior frontal gyrus and left inferior 
 temporal gyrus were activated17 . these 
 structures are related to the perception of the pain threshold , but not pain intensity . these structures are also activated when stimuli acupoints , by needles or by transcutaneous 
 electrical current18 . as the action of acupuncture - like tens with 10  hz was relatively rapid at prolonging the 
 pain threshold latency , during or after application , it suggests that it acts directly on 
 a- and c fiber , promoting action potentials in them . this would have served as a mechanism 
 of segment concurrence , which is usually seen as fibers a- mediating the stimulation of 
 high frequency tens . when the painful stimulus of low temperature triggered the a- and c 
 fibers they were already receiving electrical stimulus , leaving them less responsive to the 
 cold stimulus . its influence on the pain threshold latency during and after tens 
 application , may be due the concentration of the stimulus in the receptive field of the 
 nerve endings being stimulated by electrical current , the smaller electrode focused on the 
 acupoints , while the larger electrodes encompassed this area and most of the surrounding 
 regions . these acupoints are stimulated by needles , classically , and they have a large 
 concentration of mechanical stimuli in their areas . studies have shown that acupoints 
 located in the areas of dermatomes , myotomes and sclerotomes which are pain afferents , are 
 more effective than acupoints which are distant from them18 , 19 . in the placebo group , 
 which received no electrical stimulation , no statistical differences were observed among the 
 pre- , and during- , and post - treatment periods . table 3 compares the pain threshold latencies 
 of the groups . during tens treatment , the 1  cm electrode group showed 
 significant differences from the other two groups . this result corroborates the hypothesis 
 that the concentration of eletrical stimulus in a small area is more effective than that 
 over larger areas . acupuncture points have intrinsic neuronal properties , as well as increased conductance , 
 low impedance , and high electric potential compared to other locations . it has been 
 suggested that the meridians are more a functional concept than anatomical , a multiple 
 system incorporating the physiological , neurological , endocrine and immune systems9 . the values show that the 1  cm electrode group showed a reduction in pain 
 intensity during the tens treatment compared to pretreatment , while the 15  cm 
 electrode group showed an increase in pain compared to pretreatment . as mentioned above , the 
 pain threshold latency and pain intensity are mediated differently by the central nervous 
 system11 . another study14 applied tens to the li4 
 ( he - gu ) and pc6 ( neiguan ) acupoints of subjects submitted to cold - induced pain with a 
 current intensity of 3 ma , pulse duration of 300 s and frequency of 4  hz , and noted a 
 reduction in pain intensity relative to a placebo group over periods of 30 to 170 seconds of 
 cold - induced pain . some other studies1 , 20 have also reported significant changes in pain intensity with 
 electroanalgesia , while , others11 , 21 , 22 
 have reported that the intensity of pain showed no significant change with the use of tens . items that differed in these works were the experimental pain models , parameters of 
 electrical stimulation , location of the electrodes and the number of subjects involved in 
 each experiment , as well as the recruitment and randomization methods . another controversial 
 point is the measurement of pain using the visual analog scale since , even though it is 
 widely used and accepted , its results tend to be contradictory . the 15  cm electrode group showed an increase in the sensation of pain 
 intensity , rather than a reduction , during the tens treatment , but there was no significant 
 difference in the timeof the pain threshold latency . in the 
 case of the 1  cm electrode , the result was consistent . the intensity of pain is 
 subjective measure which depends on the interpretation and previous experience of each 
 individual . this may cause some confusion at the time of assessment , making it impossible to 
 compare the results of pain intensity between groups . we suggest that as well as the 
 measurement of pain intensity using the vas scale , some objective form of measurement is 
 also used , such as the pain threshold latency , measurement of the conduction velocity of 
 nociceptive fibers . the effect size , as calculated by cohen s d , of the 1  cm electrode group showed 
 a percentage ranging from 88% to 98% when compared to the other groups , indicating that the 
 1-cm group , during the tens treatment , had this percentage of individuals with 
 higher values than their respective control . at post - treatment the percentage was 9196% 
 compared to the placebo group . this demonstrates there was a clinically significant 
 difference between the 1  cm group and the placebo group . in the literature , we 
 could find no other references reporting statistically significant results for this type of 
 treatment . our findings support the view that acupuncture - like tens at 10  hz frequency , applied to pc6 
 and te5 acupoints with the parameters described above , increases the pain threshold latency 
 during tens treatment with 1  cm electrodes and post - treatment with 
 15  cm electrodes . the pain intensity was reduced during tens treatment when 
 applied to the acupoints with an electrode area of 1  cm . the effect size 
 calculations show that tens applied to these acupoints were clinically significant . the 
 combination of acupuncture - like tens and acupoints is a treatment choice for acute pain in 
 the hand region .
[ purpose ] this study assesse the effect of low frequency transcutaneous electrical nerve 
 stimulation ( tens ) of thete5 ( waiguan ) and pc6 ( neiguan ) acupoints on cold - induced pain . 
 [ subjects and methods ] forty - eight subjects were divided by convenience into three groups : 
 tens with electrodes of 1  cm2 area , tens with electrodes of area 
 15  cm2 and a placebo group . 
 the study consisted of three phases : cold - induced 
 pain without electroanalgesia , cold - induced pain with electroanalgesia or placebo , and 
 cold - induced pain post - electroanalgesia or placebo . 
 [ results ] acupuncture like tens 
 increased the pain threshold latency during treatment ( 45.7  11.7s ) compared to 
 pre - treatment ( 30.9  8.9s ) in the tens group with 1  cm2 electrodes . in the 
 tens group with 15  cm2 electrodes , 
 the pain threshold latency increased at 
 post - treatment ( 36.2  12.9s ) compared to pre - treatment ( 25.5  7.4s ) . 
 the placebo group 
 showed no significant changes . 
 the group with 1  cm2 electrodes showed a 
 significantly higher pain threshold latency ( 45.7  11.7s ) than the other two groups . at 
 post - treatment , 
 the pain threshold latencies of both the 1  cm2 ( 39.4  11.5s ) 
 and 15  cm2 ( 36.2  12.9s ) tens group were higher than that of the placebo group 
 ( 22.4  7.4s ) . [ conclusion ] 
 acupuncture like tens applied to pc6 and te5 acupoints 
 increased the pain threshold latency . 
 the pain intensity was reduced by tens with an 
 electrode area of 1  cm2 .