***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Acupuncture-like transcutaneous electrical nerve stimulation ( ALTENS ) was compared with a placebo treatment in altering acute electrical pain thresholds .  Ten pain-free subjects underwent , on different days , an acclimatization session , an ALTENS treatment , and a placebo treatment in a cross-over design . Electrical sensation and pain thresholds were measured from the tip of the index finger bilaterally at 15-minute intervals twice before , once during , and three times after a 30-minute treatment session . The ALTENS treatment was given at 4 Hz at an intensity just below pain threshold delivered to acupuncture points in the h and and wrist . The placebo treatment was similarly delivered , except that the intensity of stimulation was just above sensation threshold . Neither the ALTENS treatment nor the placebo treatment produced a significant change in pain threshold . There was no correlation between initial pain threshold and change in pain threshold . Implication s for the modulation of pain are discussed It is known that stimulation of thin cutaneous nerve fibers can induce long lasting analgesia through both supraspinal and segmental mechanisms , the latter often exhibiting restricted receptive fields . On this basis , we recently developed a new method , termed cutaneous field stimulation ( CFS ) , for localized stimulation of A delta and C fibers in the superficial part of the skin . In the present study , we have evaluated the effects of CFS on non-nociceptive and nociceptive skin senses . We compared the effects of CFS with those of conventional transcutaneous electrical nerve stimulation ( TENS ) , known to preferentially activate coarse myelinated fibers . A battery of sensory tests were made on the right volar forearm of 20 healthy subjects .  CFS ( 16 electrodes , 4 Hz per electrode , 1 ms , up to 0.8 mA ) and TENS ( 100 Hz , 0.2 ms , up to 26 mA ) applied either on the right volar forearm ( homotopically ) , or on the lower right leg ( heterotopically ) were used as conditioning stimulation for 25 min . The tactile threshold was not affected by either homo- or heterotopical CFS or TENS . The mean thresholds for detecting warming or cooling of the skin were increased by 0.4 - 0.9 degrees C after homo- but not heterotopical CFS and TENS . Regarding nociceptive skin senses , homo- but not heterotopical CFS , markedly reduced CO2-laser evoked A delta- and C fiber mediated heat pain to 75 and 48 % of control , respectively , and mechanically evoked pain to 73 % of control . Fabric evoked prickle , was not affected by CFS . Neither homo- nor heterotopical TENS induced any marked analgesic effects . It is concluded that different qualities of nociception can be differentially controlled by CFS OBJECTIVE To determine if interferential current ( IFC ) or transcutaneous electric nerve stimulation ( TENS ) alters C and A delta fiber-mediated thermal perception thresholds . DESIGN Single-blind , r and omized controlled trial . SETTING Laboratory . PARTICIPANTS One hundred forty healthy women volunteers ( mean age + /- st and ard deviation , 20.6+/-2.7 y ) . INTERVENTIONS Subjects were r and omly and exclusively assigned to 1 of 7 groups ( n=20 in each ) : 0 , 5 , and 100 Hz of IFC ; 5 and 100 Hz of TENS ; placebo and control stimulation . Stimulation was applied through 2 electrodes placed over the median nerve . Warm sensation , cold sensation , hot pain , and cold pain perception thresholds were measured from the thenar eminence by using a quantitative sensory testing device and a method of limits algorithm . MAIN OUTCOME MEASURES Warm sensation , cold sensation , hot pain , and cold pain thresholds ( degrees C ) before , during , and after stimulation . RESULTS There was a statistically significant effect of time for all 4 thermal perception thresholds ( separate 2-way analyses of variance with repeated measures , all P<.001 ) . There were no statistically significant differences between experimental groups , nor any interaction effects ( all P>.05 ) . CONCLUSIONS Neither IFC nor TENS altered C and A delta fiber-mediated thermal perception thresholds . The results suggest that any analgesic mechanisms with these modalities are likely to be complex The analgesic efficacy of various pulse patterns of transcutaneous electrical nerve stimulation ( TENS ) were assessed in 84 normal healthy subjects using the cold pressor pain technique .  Burst , modulation , r and om and continuous TENS all significantly elevated ice pain threshold .  Continuous ( 80 Hz ) TENS produced the greatest mean elevation in threshold but the response to r and om TENS showed the least inter-subject variation . Ice pain tolerance was increased by all modes of TENS , continuous TENS producing the greatest magnitude of response , although these changes did not reach statistical significance . Increasing the size of electrodes reduced the effect of continuous TENS . The clinical implication s of these findings are discussed OBJECTIVES To evaluate quantitatively the effectiveness and clinical relevance of various parameters of electrical stimulation used to relieve acute and chronic pain and to further knowledge of the mechanisms that may underlie the physiologic response produced by the transcutaneous application of each type of current . DESIGN A nociceptive flexion reflex ( RIII reflex ) elicited in the lower limb by electrical stimulation of the sural nerve at the ankle was studied before , during , and after application of the following conditioning stimuli : ( 1 ) non-noxious transcutaneous electrical nerve stimulation (TENS)--low-intensity ( 2mA ) , short- duration ( 0.1 msec ) , and high-frequency ( 100Hz ) rectangular pulses ( TENS1 ) ; ( 2 ) noxious TENS -- high-intensity ( 20mA ) , long- duration ( 2 msec ) , and low-frequency ( 3Hz ) rectangular pulses ( TENS2 ) ; ( 3 ) noxious piezo-electric current (PEC)--high-voltage , low-charge , low-intensity , and low-frequency rectangular pulses delivered by a piezo-electric ceramic device ( PECs1 ) ; ( 4 ) a sham PEC situation in which the piezo-electric device did not produce any electric current ( Sham PEC ) . Each conditioning stimulus ( TENS1 , TENS2 , PECs1 , Sham PEC ) was applied for a 2-minute period either segmentally on the sural nerve itself or heterotopically on the skin overlying the first interosseous space of the contralateral h and . PARTICIPANTS Twenty-four healthy volunteers ( 14 women , 10 men , 19 to 52 years of age ) , who were briefed and familiarized with the experimental procedure . During the experimental sessions , subjects were prone in bed to ensure muscular relaxation . MEASURES Value of the nociceptive RIII reflex before , during , and after application of conditioning stimuli in the four procedures described above . This reflex was selected because it has been shown to be an objective and physiologic correlate of pain . RESULTS Non-noxious TENS1 stimulation applied segmentally produced inhibitions of the RIII reflex only during the 2-minute conditioning period . When given segmentally , the noxious TENS2 stimulation produced a facilitatory effect during the 2 minutes of application , followed by significant inhibitory after-effects . The administration of TENS2 heterotopically result ed in inhibitions of the RIII reflex both during and after the 2-minute conditioning period . Application of PECs1 , whether segmentally or heterotopically , produced powerful and long-lasting inhibitory after-effects , especially with the heterotopic paradigm . These effects were associated with long-lasting local changes to the skin of the neurogenic inflammation type , which were well tolerated by all subjects . Application of Sham PEC did not result in significant modification of either the RIII reflex or the skin . CONCLUSIONS These data are discussed in terms of possible spinal and supraspinal mechanisms involving inhibitory descending controls and underline the potential clinical use of PECs1 in the treatment of pain OBJECTIVE To investigate to what extent a single 60-minute session of transcutaneous electrical nerve stimulation ( TENS ) would modify chronic clinical pain , acute experimental pain , and the flexion reflex evoked in chronic low back pain patients . STUDY DESIGN Thirty young subjects with chronic low back pain were r and omly allocated to two groups , receiving either TENS or placebo stimulation to the lumbosacral region for 60 minutes . The flexion reflex was elicited by an electrical stimulation applied to the subject 's right sole and recorded electromyographically from the biceps femoris and the tibialis anterior muscles . MAIN OUTCOME MEASURES Subjective sensation of low back pain and the electrically induced pain were measured by two separate visual analog scales , termed VAS(LBP ) and VAS(FR ) , respectively . Data obtained before , during , and 60 minutes after TENS and placebo stimulations were analyzed using repeated measures ANOVA . RESULTS The VAS(LBP ) score was significantly reduced to 63.1 % of the prestimulation value after TENS ( p<.001 ) , but the reduction was negligible after placebo stimulation ( to 96.7 % , p = .786 ) . In contrast , no significant change was found in the VASFR score ( p = .666 ) and the flexion reflex area ( p = .062 ) during and after stimulation within each group and between the two groups ( p = .133 for VASFR and p = .215 for flexion reflex area ) . CONCLUSIONS The same TENS protocol had different degrees of antinociceptive influence on chronic and acute pain in chronic low back pain patients Transcutaneous electrical nerve stimulation ( TENS ) is commonly used for pain relief . However , little robust research exists regarding the combination of parameters required to provide effective doses . This study investigated the hypoalgesic effects of different parameter combinations , applied simultaneously at two sites ( segmental and extrasegmental ) , on pressure pain threshold ( PPT ) in pain‐free humans . Two‐hundred and eight volunteers ( median age 22 years , range 20–26 ) were r and omized to eight groups : six active TENS groups , placebo and control . Parameter combinations were such that frequency always differed at each site ( 110Hz or 4Hz ) , but intensity could be either the same or different levels : high ( to tolerance without pain ) or low ( strong but comfortable ) . TENS was administered to the forearm over the radial nerve and the ipsilateral leg below the fibular head for 30min with monitoring for 30 further minutes . PPT measurements were taken bilaterally from the mid‐point of first dorsal interosseous muscle , by an independent blinded rater , at baseline and at six subsequent 10‐min intervals . Log‐transformed data were analysed using repeated‐ measures analysis of covariance ( baseline values and gender as covariates ) . Those groups using high‐intensity stimulation at the segmental stimulation sites showed significantly greater hypoalgesia  than placebo ( p<0.025 in each case ) . The largest hypoalgesic effect was for simultaneous high‐intensity stimulation at segmental and extrasegmental sites , using different frequencies . These results reaffirm that high‐intensity stimulation ( regardless of frequency ) is of fundamental importance in effective dosage & NA ; Transcutaneous electrical nerve stimulation ( TENS ) is a popular form of electrostimulation . Despite an extensive research base , there remains no consensus regarding the parameter selection required to achieve maximal hypoalgesic effects . The aim of this double blind , sham‐controlled study was to investigate the relative hypoalgesic effects of different TENS parameters ( frequency , intensity and stimulation site ) upon experimentally induced mechanical pain . Two hundred and forty participants were recruited in order to provide statistical analysis with 80 % power at & agr;=0.05 . Subjects were r and omised to one of the six TENS groups , a control , and a sham TENS group ( n=30 , 15 males , 15 females , per group ) .  TENS groups differed in their combinations of stimulation ; frequency ( 4 or 110 Hz ) , intensity ( ‘ to tolerance ’ or ‘ strong but comfortable ’ ) and stimulation site ( segmental – over the distribution of the radial nerve or , extrasegmental – over acupuncture point ‘ gall bladder 34 ’ , or a combination of both segmental and extrasegmental ) . Pulse duration was fixed at 200 & mgr;s . Stimulation was delivered for 30 min and subjects were then monitored for a further 30 min . Mechanical pain threshold ( MPT ) was measured using a pressure algometer and taken from the first dorsal interosseous muscle of the dominant h and , ipsilateral to the stimulation site . MPT measures were taken , at baseline , and at 10‐min intervals for 60 min . Difference scores were analysed using repeated measures and one‐way ANOVA and relevant post hoc tests . Low frequency , high intensity , extrasegmental stimulation produced a rapid onset hypoalgesic effect , which increased during the stimulation period ( P<0.0005 control and sham ) and was sustained for 30 min post‐stimulation ( P<0.0005control , P=0.024sham ) . Whilst high frequency , ‘ strong but comfortable ’ intensity , segmental stimulation produced comparable hypoalgesic levels during stimulation , this effect was not sustained post‐stimulation . Stimulation at a combination of the two sites did not produce any greater hypoalgesic effects . These results may have implication s for the clinical use of sensory stimulation This study compared the effects of high intensity , low frequency transcutaneous electrical nerve stim 
    Output:
    
Conventional TENS has overall conflicting evidence of efficacy , this is derived from " strong " evidence of efficacy ( generally consistent findings in multiple high- quality RCTs ) on pressure pain but strong evidence of inefficacy on other pain models . "
Limited " evidence ( positive findings from 1 RCT ) of hypoalgesia exists for some novel parameters .
Low-intensity , low-frequency , local TENS has strong evidence of inefficacy .
Inappropriate TENS ( using " barely perceptible " intensities ) has moderate evidence of inefficacy .
DISCUSSION The level of hypoalgesic efficacy of TENS is clearly dependent on TENS parameter combination selection ( defined in terms of intensity , frequency , and stimulation site ) and experimental pain model .