***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: & NA ; Transcutaneous electrical nerve stimulation ( TENS ) is a frequently applied therapy in chronic pain although evidence for effectiveness is inconclusive . Several types of TENS , based on different combinations of frequency , pulse duration and intensity , exist . The precise mechanism of action and the relevance of combinations of stimulus parameters are still unclear . To compare the effectiveness of three types of TENS we conducted a r and omized , single blinded crossover trial . Patients received two times a 2‐week period of daily TENS treatment , separated by a washout period of 2 weeks . In total , 180 chronic pain patients were r and omized into three groups . In group 1 , high frequency , low intensity TENS ( HFT ) was compared with high frequency , high intensity TENS ( HIT ) . In groups 2 and 3 , HFT and HIT were compared with a control TENS ( COT ) . The order of applying the different modalities of TENS in each group was also r and omized . Primary outcome was the patient 's overall assessment of effectiveness and pain reduction ( VAS ) . No differences were found in patient 's assessment or pain reducing effect between the three groups , indicating no superiority of one type of TENS . In total , 56 % continued TENS after the 2‐week treatment period . At 6 months , 42 % of all patients still used TENS . We concluded that there were no differences in effectiveness for the three types of TENS used in this study . Because no placebo group was included , no definite conclusions on effectiveness of TENS in general in the treatment of chronic pain could be made Objective : To investigate the hypoalgesic effects of transcutaneous electrical nerve stimulation ( TENS ) upon low back pain ( LBP ) in people with multiple sclerosis ( MS ) . Design : A r and omized double-blind placebo controlled clinical pilot study . Subjects and setting : Fifteen people with MS were recruited and r and omly allocated to one of the following groups under double blind conditions ( n = 5 per group ) : TENS 1 ( 4 Hz , 200 µs ) , TENS 2 ( 110 Hz , 200 µs ) , placebo TENS . Interventions : Treatment was applied for 45 minutes three times a week for six weeks with a four-week follow-up . Outcome measures : The following outcome measures were taken at weeks 1 , 6 , and 10 : visual analogue scale ( VAS ) ( for current LBP , right leg pain , left leg pain ) ; Leeds Multiple Sclerosis Quality of Life Question naire ; Rol and Morris Disability Question naire ; Short Form-36 ( SF-36 ) Version 1 ; and the McGill Pain Question naire ( MPQ ) . VAS for current LBP , right and left leg pain were also taken before and after treatment , and once a week during the follow-up period . Results : Analysis showed no statistically significant effects for any of the data . However , both active treatment groups showed a trend of improvement in the majority of the outcome measures . Conclusion : Active TENS was more effective than placebo TENS in decreasing VAS scores following each treatment although results were not statistically significant . Further work in this area is warranted and should include a larger number of participants in the form of a r and omized controlled clinical trial to determine the efficacy of this modality OBJECTIVES A preliminary examination of NMES and combined NMES/TENS for the management of  chronic back pain .  DESIGN Double-blind , placebo-controlled , r and omized repeated measures . SUBJECTS AND SETTING Consecutive sample of 24 chronic back pain patients ( 16 women and 8 men ) attending an outpatient pain clinic ( mean age 51.67 years , mean pain duration 3.83 years ) . All treatments were administered at home . INTERVENTIONS Subjects self-administered NMES , combined NMES/TENS , TENS , and placebo treatments . Each treatment had a duration of 5 consecutive hours per day over 2 consecutive days , with a 2-day hiatus between treatments to minimize carryover effects . MAIN OUTCOME MEASURES Pain reduction was assessed through pretreatment to posttreatment differences on the Present Pain Intensity ( PPI ) scale , and a visual analogue scale of Pain Intensity ( VAS-I ) . Posttreatment pain relief was assessed using a visual analogue scale of Pain Relief ( VAS-R ) . RESULTS Combined treatment , NMES , and TENS each produced significant pretreatment to posttreatment reductions in pain intensity as measured by both the PPI and VAS-I ( p < .05 ) . Combined treatment was superior to placebo on pain reduction ( p = .001 , p = .016 ) as well as pain relief ( p < .001 ) . Combined treatment was also superior to both TENS and NMES for pain reduction and pain relief ( p < .01 ) . NMES and TENS were superior only to placebo for pain relief ( p < .001 ) . CONCLUSIONS Combined NMES/TENS treatment consistently produced greater pain reduction and pain relief than placebo , TENS , or NMES . NMES alone , although less effective , did produce as much pain relief as TENS . Although preliminary , this pattern of results suggests that combined NMES/TENS may be a valuable adjunct in the management of chronic back pain . Further research investigating the effectiveness of both NMES and combined NMES/TENS seems warranted Objective This study was design ed to investigate the hypoalgesic effects of self-applied transcutaneous electrical nerve stimulation ( TENS ) on chronic low-back pain ( LBP ) in a multiple sclerosis ( MS ) population . Methods Ninety participants with probable or definite MS ( aged 21 to 78 y ) presenting with chronic LBP were recruited and r and omized into 3 groups ( n=30 per group ) : ( 1 ) low-frequency TENS group ( 4 Hz , 200 μs ) ; ( 2 ) high-frequency TENS group ( 110 Hz , 200 μs ) ; and ( 3 ) placebo TENS . Participants self-applied TENS for 45 minutes , a minimum of twice daily , for 6 weeks . Outcome measures were recorded at weeks 1 , 6 , 10 , and 32 . Primary outcome measures included : Visual Analog Scale for average LBP and the McGill Pain Question naire . Secondary outcome measures included : Visual Analog Scale for worst and weekly LBP , back and leg spasm ; Rol and Morris Disability Question naire ; Barthel Index ; Rivermead Mobility Index ; Multiple Sclerosis Quality of Life-54 Instrument , and a daily logbook . Data were analyzed blind using parametric and nonparametric tests , as appropriate . Results Results indicated a statistically significant interactive effect between groups for average LBP ( P=0.008 ) ; 1-way analysis of covariance did not show any significant effects at any time point once a Bonferonni correction was applied ( P>0.05 ) . However , clinical ly important differences were observed in some of the outcome measures in both active treatment groups during the treatment and follow-up periods . Discussion Although not statistically significant , the observed effects may have implication s for the clinical prescription and the use of TENS within this population In 23 patients with pancreatitis , daily pain for at least 3 months , and no abuse of alcohol , the pain-relieving effect of electroacupuncture ( 13 patients ) or transcutaneous electric nerve stimulation ( TENS ) ( 16 patients ) was studied . In two prospect i ve studies with a cross-over design , active acupuncture was compared with sham acupuncture , and TENS of the segmental points of the pancreas with sham treatment . Neither electroacupuncture nor TENS brought about pain relief that could substitute for or supplement medical treatment 
    Output:
    
We were therefore unable to conclude with any confidence that , in people with chronic pain , TENS is harmful , or beneficial for pain control , disability , health-related quality of life , use of pain relieving medicines , or global impression of change .