Shanaham Et Al - TENS x IFC

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ARTICLE IN PRESSPHYST-222; No.of Pages 7

Physiotherapy xxx (2006) xxxxxx

Comparison of the analgesic efficacy of interferential therapy andtranscutaneous electrical nerve stimulation

Christine Shanahan a, Alex R. Ward b,, Val J. Robertson c,d

a School of Physiotherapy, La Trobe University, Vic. 3086, Australiab Department of Human Physiology and Anatomy, La Trobe University, Vic. 3086, Australia

c University of Newcastle, University Drive, Callaghan, NSW. 2308, Australiad North Sydney Central Coast Health Service, Gosford Hospital, Cnr Holden & Racecourse Rds, Gosford, NSW. 2250, Australia

Abstract

Objective To compare the analgesic efficacy of interferential therapy (IFT) and transcutaneous electrical nerve stimulation (TENS) using an

experimental cold pain model.

Design Randomised controlled trial with repeated measures design.

Setting University research laboratory.

Participants Twenty healthy subjects.

Interventions IFT and TENS applied to each subject on different days.

Main outcome measures Cold pain threshold (time), intensity and unpleasantness (visual analogue scales).

Results The mean cold pain threshold with a TENS intervention was higher than that with IFT. A training effect was evident as subjects

responses become more consistent with repeated exposure to stimulation and the testing procedure. Using data from the second testing

sessions, the differences in pain threshold between IFT and TENS for the two during-intervention (T3 and T4) measures were statistically

significant (T3 difference in the means 5.9 seconds, 99% confidence interval 3.1 to 8.7 seconds; T4 difference in the means 6.6 seconds, 99%

confidence interval 3.8 to 9.4 seconds). No significant differences were identified in pain intensity and unpleasantness ratings.

Conclusions TENS is more effective than IFT at increasing cold pain thresholds in healthy subjects, and this effect increases with repeated

exposures. Future trials should include a familiarisation session prior to testing to increase the consistency of subjects responses. The clinical

implications of these effects need investigation.

2006 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.

Keywords: Transcutaneous nerve stimulation; Cold pain; Pain measures; Experimental pain; Electroanalgesia; Hypoalgesia

Introduction

Electrical stimulation is used regularly by physiother-

apists. Indications include pain management, muscle re-

education, strengthening and oedema reduction [1,2]. Ofthese, pain management is the most common use, and the

current types used are interferential therapy (IFT) and tran-

scutaneous electrical nerve stimulation (TENS) [3].

The physical properties of IFT and TENS are quite dif-

ferent. Conventional TENS is a type of low-frequency stim-

ulation, commonly applied at frequencies of 1200 Hz [1].

Corresponding author. Tel.: +61 3 9479 5814; fax: +61 3 9479 5784.

E-mail address: [email protected] (A.R. Ward).

The current is pulsed and the flow of charge is interrupted

rather than continuous. IFT is a type of medium-frequency

alternating current, with carrier frequencies of 110 kHz [4].

Unlike TENS, IFT current is sinusoidal and provides a con-

tinuous flow of charge. IFT is usually delivered in bursts witha frequency in the biological range (1150 Hz) [2]. Despite

the widespread use of IFT and TENS for pain management,

there is a lack of scientificevidence supporting aspects of their

claimed effectiveness. Consequently, in a clinical setting,

selection of the type and parameters of electrical stimulation

is largely based on theoretical or anecdotal evidence [2,4].

The aim of the present study was to compare the analgesic

effectiveness of IFT and TENS. A literature search was con-

ducted using the keywords interferential and/or TENS,

0031-9406/$ see front matter 2006 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.physio.2006.05.008

Please cite this article as: Christine Shanahan et al., Comparison of the analgesic efficacy of interferential therapy and transcutaneous

electrical nerve stimulation, Physiotherapy (2006), doi:10.1016/j.physio.2006.05.008
mailto:[email protected]://dx.doi.org/10.1016/j.physio.2006.05.008http://dx.doi.org/10.1016/j.physio.2006.05.008http://dx.doi.org/10.1016/j.physio.2006.05.008http://dx.doi.org/10.1016/j.physio.2006.05.008mailto:[email protected]


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2 C. Shanahan et al. / Physiotherapy xxx (2006) xxxxxx

and pain or pain threshold (not dental, teeth, anaesthesia

or labour). The search was limited to studies of human sub-

jects, written in the English language, that reported the use

of ITF and/or TENS for treating musculoskeletal pain. The

databases searched were Embase, Medline, Cinahl, Sports

Discus, The Cochrane Library and PubMed (19662005).

Thirty-eight articles were identified.These studies used a range of pain-induction techniques:

cold [58], heat [9], mechanical [10] and ischaemic [11]. The

most consistent analgesic effects were observed with cold-

induced pain [6,7], with more varied results obtained using

other pain-induction techniques [1012].

Most studies examined the hypoalgesic effects of TENS

[7,1118], and a smaller number studied IFT [8,1922]. Only

four of the studies compared the effectiveness of TENS and

IFT directly [6,9,10,23]. Three of these reported that IFT

and TENS were significantly more effective at modulating

pain than sham interventions or control groups (the exception

being Alves-Guerreiro et al.[10]). However, no significant

differences in the analgesic effectiveness of IFT and TENSwere identified in any of the four studies. This was possibly

due to inadequate statistical power as the question addressed

was not do the interventions have an effect? but do the

effects differ? If both interventions had an effect, any differ-

ences could easily be obscured or more difficult to detect.

A common limitation across existing comparisons of

TENS and IFT is small sample sizes, ranging from 7 [6] to 18

[9] subjects per group. Unlessa within-subject design is used,

the risk of a type II error is high. For example, the Johnson

and Tabasam study [6] used seven subjects per group, and

each subject was tested with a single type of stimulation. The

observed difference (i.e. TENS more effective than IFT) wasstatistically insignificant (P = 0.09). However, a calculation

using 10 subjects and the same means and standard devia-

tions produces a P-value of less than 0.05, suggesting that

the group was too small given the effect size, resulting in a

type II statistical error.

The most effective and practical method to compare IFT

and TENS is to use a within-subject repeated measures

design, and to administer both to each subject. This design

eliminates between-subject variation and increases the statis-

tical power of the study. Existing comparative studies did not

use this approach.

The aim of the present study was to compare the analgesic

effectiveness of IFT and TENS using the same experimental

cold pain model as Johnson and Tabasam [6], but with larger

subject numbers and a within-subject design. A secondary

aim was to investigate whether familiarisation with electrical

stimulation and the testing procedure affected the consistency

of subjects responses.

The following hypotheses were tested:

TENS is more effective than IFT at increasing the cold

pain threshold of healthy subjects;

there is no difference in the effectiveness of IFTand TENS

at altering pain intensity and unpleasantness; and

familiarisation with stimulation and the testing procedure

affects the consistency of subjects responses (i.e. there is

a training effect).

Methods

Research design

A single blind randomised controlled trial with a repeated

measures design was used. The design was based on the

method used in previous research (e.g. [6,24]), but was modi-

fied to increase statistical power by using a larger sample size

and a training session identical to the testing session. Each

subject attended on two separate days and IFT and TENS

were given in a pre-determined order. Subjects were blinded

to the treatment modality being administered. The investi-

gator was not blinded as the investigators role was simply

to record the outcome measures as numerical values [mea-

sured time or reported visual analogue scale (VAS) rating],rather than make any subjective assessment or measurement;

thus, the risk of assessor bias being able to influence the

results was minimal. A sham group was not included as the

aim was specifically to compare the effectiveness of two

current types that had previously been shown to be more

effective than sham stimulation [57,9,24]. A single investi-

gator administered the electrical stimulation and recorded all

measurements.

The independent variable was the type of stimulation

administered (IFT or TENS). The dependent variables were

the time to pain threshold (seconds), and pain intensity and

unpleasantness as rated by subjects on two, 10-cm horizontalVASs.Painintensitywas operationally defined as howstrong

the pain in your hand feels, whilst pain unpleasantness was

how uncomfortable the pain in your hand feels.

Subjects

Twenty volunteers (10 males, 10 females) aged between

18 and 32 years (mean age 21.7 years, standard deviation 3.5

years) were recruited into the study. Potential participants

were excluded if their non-dominant arm was affected by

any orthopaedic, neurological or circulatory pathology, or

if the skin in the area under the electrodes was broken or

irritated.Participants were instructednot to takeany analgesic

or anti-inflammatory medication (or apply them as creams or

gels to their non-dominant forearm) in the 12 hours prior to

eachtesting session. No volunteers were excludedwhenthese

criteria were applied.

Apparatus

Electrical stimulation

A Chattanooga Intelect (Intelect Legend Stim, Chat-

tanooga Group Inc., Hixson, TN, USA) was used to deliver

the pre-modulated IFT current, and a Metron Multistimu-


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C. Shanahan et al. / Physiotherapy xxx (2006) xxxxxx 3

lator (Metron Medical Australia Pty. Ltd., Carrum Downs,

Victoria, Australia) was used for TENS. These stimulators,

similar in size and appearance, meant that testing conditions

were kept as uniform as possible for the two interventions.

The display screen and control panels were not visible to

subjects, and subjects were given no indication of which cur-

rent type was being delivered. Stimulation parameters werekept constant throughout the procedure, and only the current

intensitywasadjustedduring the session.Current was applied

via two Stimtrode 50 mm 90 mm rectangular self-adhesive

electrodes (Axelgaard Manufacturing Co. Ltd., Fallbrook,

CA, USA). TENS stimulation used 200-s biphasic pulses

(100-s phaseduration) anda pulse frequency of 100 Hz.Pre-

modulated IFT was applied with a carrier frequency of 5kHz

(100-s phase duration) and a beat frequency of 100 Hz.

Cold pain induction

Cold pain induction required two water baths of uniform

size andshape; onewas maintained at 37 C and the other was

maintained at 0 C with ice and water. A Heidolph heater stir-rer unit (AccurexEquipment,Brunswick, Victoria, Australia)

was used in each bath to ensure that the water temperatures

(both monitored with a thermometer) remained constant.

Procedure

Prior to the first session

Eligibility was confirmed and informed consent was

obtained. Each participant wasallocated at random to a group

by selecting a sealed envelope (marked for male or female)

containing a pre-arranged order of testing conditions. Within

the 10 envelopes designated to each sex, five specified thatIFT would be delivered in Session A and five specified that

TENS would be delivered in Session A. Subjects were not

informed of the group to which they were assigned. The sub-

ject was seated and their non-dominant forearm was cleaned

with an alcohol swab. The two electrodes were then posi-

tioned on the subjects non-dominant forearm, one anterior

and one posterior, with the centre point of the electrode lying

equidistant to the elbow and wrist. The electrode alignment

was standardised between subjects and between sessions.

Cold pain induction

The cold-induced pain cycle is based on a method used

in previous research [68,24]. Six cold pain cycles, each of

10-minutes duration, were conducted sequentially for a 1-

hour test session. The procedure is depicted in Fig. 1. Each

cycle commenced as the subject placed their hand (up to the

distal wrist crease) in a warm water bath. After 5 minutes,

the subject transferred their hand to a cold water bath. The

subject was instructed to focus on the sensations in their

immersed hand until they felt the onset of deep, dull, aching

pain and to then say pain. The time from immersion in cold

water to this point was recorded as the pain threshold (in sec-

onds). The subject was required to leave their hand in the

cold water for a further 30 seconds. Immediately upon with-

Fig. 1. Procedure for (a) one cold pain cycle and (b) one testing session

consisting of six cold pain cycles, based on Johnson and Tabasam [6].

drawal from the cold water, the subject completed a VAS

rating of pain intensity and pain unpleasantness (where zero

represented not intense/unpleasant at all and 10 represented

most intense/unpleasant pain imaginable). The subject then

rested until 10 minutes had elapsed since the beginning of the

cycle, at which time the next cycle was commenced with re-

immersion of the hand in warm water.

Electrical stimulation

At the start of Cycle 3 (i.e. 20 minutes into the session), the

allocated electrical stimulator was turned on. The investiga-tor increased the current intensity, as directed by the subject,

until they experienced a strong but comfortable level of

stimulation. The current intensity was adjusted upon request

to maintain this level, except when the subjects hand was

in the cold water bath. Stimulation continued uninterrupted

for 20 minutes, which constituted two complete pain cycles

(Cycles 3 and 4). Two further pain cycles (Cycles 5 and 6)

were completed once the stimulation was turned off. The pro-

cedure was identical for TENS and IFT delivery. Thus, two

pre-intervention measures, two during-intervention measures

and two post-intervention measures were obtained.

Session B

Session B was conducted no earlier than 12 hours after

Session A to minimise the risk of a carry-over effect. Subject

eligibility was reconfirmed, and the cold-pain-induction pro-

cedure was repeated using the alternative type of stimulation.

All 20 subjects participated in both sessions. After comple-

tion of Session B, subjects were asked in which, if either, of

the two sessions they felt stimulation was more effective and

also more comfortable. Subjects were also given an oppor-

tunity to make any other comments about the stimulation or

testing procedure.




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Data analysis

Data were analysed using SPSS Version 11. For data anal-

ysis purposes, the group who received IFT in Session A and

TENS in Session B were referred to as Group 1, and those

who received TENS in Session A and IFT in Session B were

referred to as Group 2.Results were analysed in two stages. First, descriptive

statistics were obtained for each group (1 or 2; TENS first

or IFT first) and each condition (TENS or IFT), and tests of

normality were made. Data from the first session for each

group were much more scattered than data from the second

session, with standard deviations being approximately dou-

ble in the first session. Consequently, the first session was

considered to be the training/familiarisation session and only

the data from the second session were used for subsequent

analysis.

Data from the second session were analysed using a

two-way repeated measures analysis of variance (ANOVA)

(cycle stimulus type). Where justified by the ANOVA, posthoc tests were performed.

Previous research has shown that both TENS and IFT

elevate the cold pain threshold [6,9,23]. The present sta-

tistical analysis was therefore restricted to testing whether

the two current types had significantly different effects.

Pre-planned comparisons were made to reduce the Bon-

ferroni correction needed when multiple comparisons are

performed and to reduce the risk of a type II error. For sin-

gle comparisons, a 95% confidence interval can be used,

but the confidence interval must be set higher for multiple

comparisons.

Pain threshold data

Pain thresholddata were analysed using changefrom base-

line (seconds)for each intervention. The two pre-intervention

measurements from Cycles 1 and 2 (T1 and T2) were aver-

aged to give a baseline for each session, which was then

subtracted from the pain threshold measurements taken dur-

ing Cycles 3 (T3), 4 (T4), 5 (T5) and 6 (T6). Resulting data

were subjected to preliminary analysis by calculating means

and standard deviations, and performing tests of normality.

An ANOVA was conducted using the data from the sec-

ond session, which clearly had greater consistency due to

subjects familiarisation and practice. Finally, comparisons

of the change in pain threshold at T3 and T4 were con-

ducted; the change from baseline data for IFT was compared

with that for TENS at these points. The rationale for this

was that Johnson and Tabasam [6] first noticed a differ-

ence between IFT and TENS at T3, which reached a peak

at T4 before returning to baseline. The choice of only two

statistical comparisons meant that with a Bonferroni cor-

rection, a 97.5% confidence interval ( = 0.025) could be

used to assess the significance of any TENS versus IFT

differences.

Pain intensity and unpleasantness data

Pain intensity and unpleasantness ratings were compared

in terms of change from baseline in the same manner as

the pain threshold data. Similarly, ANOVAs were conducted

using data from Session B alone. Post hoc testing was not

justified by the ANOVAs.

Subjects comments

The frequencies of subjects comments regarding the

effectiveness and comfort of the interventions were calcu-

lated and compared.

Results

One of the 20 subjects failed to reach a pain threshold

within the allocated 5-minute time period in 11 of the 12

measurement cycles. As such, this setof results was excluded,

leaving 19 data sets for analysis.

Pain thresholds

Fig. 2 shows the mean change in pain threshold with

electrical stimulation intervention (Cycles 3 and 4) and fol-

lowing intervention (Cycles 5 and 6) for the second set of

measurements (Session B, post-familiarisation). Thresholds

increasedwhen stimulation was applied, and the increase was

greater with TENS than with IFT. The difference between the

two current types was greatest at T4, near the end of stimu-

lation; the increase in pain threshold for TENS was nearlytwice that for IFT. A two-way ANOVA (cycle stimulus

type) using data from Session B found that between-cycle

differences were significant [F(3,1) = 3.88, P = 0.033] and

between-stimulus type effects were, on average, insignifi-

Fig. 2. Mean change in pain threshold (seconds) using data from the second

(post-familiarisation)testingsession.Error barsare standarddeviations. IFT,

interferential therapy; TENS, transcutaneous electrical nerve stimulation.




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cant [F(1,3) = 2.13, P = 0.164], but a significant interaction

effect (cycle stimulus type) was observed [F(1,3) = 4.36,

P = 0.023]. The significant interaction effect indicates the

possibility that there is a between-stimulus type effect, which

is only evident at particular cycles. Inspection of Fig. 2

suggests that there may be a between-stimulus type effect

at T3 and T4 but not at T5 and T6. At T3, the meanTENS threshold change was 6.25 seconds, compared with

0.35 seconds for IFT. At T4,when thedifference was greatest,

the mean TENS threshold change was 9.75 seconds, com-

pared with 3.15 seconds for IFT. The differences between

pain thresholds at T3 and T4 were significant at the

P = 0.01 level (T3 difference in the means = 5.9 seconds,

99% confidence interval 3.1 to 8.7 seconds; T4 difference

in the means= 6.6 seconds, 99% confidence interval 3.8

to 9.4 seconds). Ninety-nine percent confidence intervals

were used to meet the need for Bonferronis correction

and to further minimise the risk of a type I statistical

error.

Pain intensity

As with the threshold data, the pain intensity results

showed a much greater scatter in Session A than in Session B.

Standard deviations for Session A were typically 30% greater

than those for Session B. Fig. 3 compares Session B results

for pain intensity. Both IFT and TENS decreased the pain

intensity ratings but to a similar extent. There is the sugges-

tion that TENS is more effective but that the difference is not

significant.

A two-way ANOVA (cycle stimulus type) was con-

ducted using data from Session B. This indicated thatbetween-cycle differences were significant [F(1,3) = 3.64,

P = 0.04], but between-stimulus type effects were not

[F(1,3) = 0.195, P = 0.67] and there was no significant inter-

action effect [F(1,3) = 0.32, P = 0.81].

Fig.3. Mean change in painintensity [visual analoguescale (VAS)]showing

averageddata for the second (post-familiarisation)testing session.Error bars

are standard deviations. IFT, interferential therapy; TENS, transcutaneous

electrical nerve stimulation.

Fig. 4. Mean change in pain unpleasantness [visual analogue scale (VAS)]

showing averaged data for the second (post-familiarisation) testing session.

Error bars are standard deviations. IFT, interferential therapy; TENS, tran-

scutaneous electrical nerve stimulation.

Pain unpleasantness

Fig. 4 shows the results for pain unpleasantness, compar-

ing results from Session B. Both TENS and IFTdecreased the

pain unpleasantnessratings but to a similar extent. A two-way

ANOVA (cycle stimulus type) was conducted using results

from Session B. Between-cycle differences were insignifi-

cant [F(1,3) = 0.66, P = 0.59], as was the between-stimulus

type effect [F(1,3) = 0.014, P = 0.91]. There was no signifi-

cant interaction effect [F(1,3) = 0.39, P = 0.76].

Subjects comments

Comfort of stimulation

Twelve subjects (63%) reported that IFT was more com-

fortable than TENS, and four subjects (21%) reported that

TENS was more comfortable than IFT. Three subjects (16%)

reported no difference.

Effectiveness of stimulation

The effectiveness ratings were exactly the same as the

comfort ratings, i.e. 12 subjects (63%) reported that IFT was

more effective than TENS at altering their response to the

cold pain. Only four of the 19 subjects (21%) reported that

TENS was more effective than IFT. The remaining three sub-

jects reported no difference in perceived effectiveness. Thus,

a clear majority thought that IFT was more effective and also

that it was more comfortable than TENS.

Discussion

Training effect

Training had a major impact on the consistency of sub-

jects responses, as demonstrated by the decrease in standard

deviations across all outcome measures from Session A to




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Table 1

Pain threshold (time to pain onset) changes during (T3 and T4) and after (T5 and T6) interventions [interferential therapy (IFT) or transcutaneous electrical

nerve stimulation (TENS)]

IFT threshold changes (seconds)

T3 T4 T5 T6

Mean (S.D.), Group 1 (IFT first) 3.8 (9.6) 1.5 (4.7) 0.0 (6.8) 1.3 (6.1)

Mean (S.D.), Group 2 (IFT second) 0.4 (3.6) 3.2 (3.7) 3.6 (5.0) 4.1 (4.0)

TENS threshold changes (seconds)

T3 T4 T5 T6

Mean (S.D.), Group 2 (TENS first) 0.3 (9.4) 2.4 (9.9) 7.0 (8.6) 1.3 (12.2)

Mean (S.D.), Group 1 (TENS second) 6.3 (7.9) 9.8 (7.7) 2.6 (4.2) 3.8 (3.9)

Standard deviations (S.D.) were much reduced in the second experimental session.

Session B (Table 1). The effect of repeated exposures to the

test conditions was not reported in existing comparisons of

IFT and TENS, and may have contributed to the absence of

significant findings [5,6,9]. The present study highlights the

importance of familiarising subjects prior to testing so thatresponses are more consistent. Future evaluations should,

ideally, use three sessions per participant; one for training

or familiarisation with either type of stimulator and two for

testing.

The presence of a training effect also suggests that, in

a clinical context, the desired results of electrical stimula-

tion for pain management may not be achieved in an initial

application. The efficacy of stimulation may improve with

subsequent exposures, so treatment may be more effective

when used repeatedly. Clinically, this suggests that at least

two trials of electrical stimulation are needed to determine

the effectiveness of pain management reliably. This is con-sistent with a clinical finding that the effectiveness of IFT

for treatment of arthritic knee pain increased over an 8-week

treatment period [21].

Pain thresholds

The present study identified that TENS was significantly

more effective than IFT at increasing the experimental cold

pain threshold of healthy subjects, and that the difference

between the two current types was greatest during a 20-

minute period of stimulation (Fig. 2). AtT3 and T4, the mean

pain threshold increases were greater with TENS than IFT.

The difference was significant at the 99% confidence level.

Contrary to these findings, IFT is used clinically in prefer-

ence to TENS in the majority of physiotherapy departments

[3]. The present findings, however, suggest that IFT is less

effective butperhaps more comfortableand perceived as more

effective than TENS, as reported by Johnson and Tabasam

[23]. The choice of IFT or TENS in a clinical context depends

on the relative importance of effectiveness and patient com-

fort/acceptance. Unless patient acceptance or tolerance is a

major issue, the findings suggest that TENS should be the

clinical modality of choice and IFT should be used as a fall-

back alternative.

The properties of clinical pain, however, may differ from

those of experimental pain in healthy subjects. Healthy sub-

jects know that experimentally induced pain is strictly tempo-

rary, so the psychological impact may be different. Similarly,

the neurophysiological aspects of the pain, i.e. the originand pattern of neural activity, are also different. This means

that future trials using a clinical population are necessary to

progress this matter. If TENS is also shown to be more effec-

tive in clinical trials, it should be adopted in preference to

IFT unless comfort and acceptance are an issue.

Pain intensity and unpleasantness

The results for painintensityand unpleasantnesswere very

similar. Although both IFT and TENS apparently decreased

pain ratings to lower than baseline levels, the difference

between the effects of the two types of stimulation was notstatistically significant. These results are consistent with find-

ings from previous research usingthe samevariables [6,9,24].

This calls into question whether pain intensity and unpleas-

antness ratings are useful tools for measuring the effect of

electrical stimulation, as these measures do not show change

and they require an extension of the period of painful stimu-

lation after onset.

Subjects comments

The majority of subjects reported that IFT was their pre-

ferred type of stimulation, for both comfort and perceived

effectiveness, despite results indicating that TENS is actually

more effective at increasing the pain threshold. The subjects

preference for IFT warrants further investigation.

Conclusion

The effectiveness of TENS at increasing pain threshold

was greater than that for IFT. This difference in effectiveness

of the two current types was statistically significant when

the training effect was taken into consideration. The present

study established that repeated exposures to stimulation and




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cold-induced pain have a significant effect on the consistency

of subjects responses. Consequently, it is recommended that

future studies should include familiarisation sessions prior

to testing to allow for a training effect. The training effect

may also have clinical implications, and multiple uses may

be needed prior to evaluating effectiveness in a patient.

Neither TENS nor IFT was more effective at altering painratings of intensity and unpleasantness. This result is con-

sistent with the existing literature and raises questions about

whether the continued useof these outcome measures is justi-

fied in laboratory-based studies, particularly considering the

increased discomfort that they impose on participants.

The pain threshold results in the present study support the

use of TENS in preference to IFT for the treatment of pain.

This is contrary to current clinical practice,whichfavours IFT

despite TENS machines being considerably cheaper, more

portable, andmore practical for home use. Thepresent results

challenge existing beliefs and clinical practices, and indicate

the need for clinical trials.

Ethical approval: Faculty Human Ethics Committee, Faculty

of Health Sciences, La Trobe University, Victoria, Australia.

Funding: The Schools of Physiotherapy and Human Bio-

sciences, La Trobe University, Victoria, Australia.

Conflicts of interest: None.

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Shanaham Et Al - TENS x IFC