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Journal of Back and Musculoskeletal Rehabilitation 28 (2015) 19–24
DOI 10.3233/BMR-140482
IOS Press
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Upper trapezius relaxation induced by TENS
and interferential current in computer users
with chronic nonspecific neck discomfort:
An electromyographic analysis
Adriano Alexandre Acedoa, Ana Carolina Luduvice Antunesa, André Barros dos Santosa,
Cintia Barbosa de Olveiraa , Claudia Tavares dos Santosa, Gustavo Lacreta Toledo Colonezia,
Felipe Antonio Medeiros Fontanaa and Thiago Yukio Fukudab,∗
a
Physical therapist staff, Centro Universitário São Camilo, São Paulo SP, Brazil
Department of Physical Therapy, Irmandade da Santa Casa de Misericórdia de São Paulo, Centro Universitário
São Camilo, São Paulo SP, Brazil
b
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Abstract.
BACKGROUND: Recent studies have shown that a transcutaneous electrical nerve stimulation (TENS) and interferential current
(IFC) application reduces pain in subjects with musculoskeletal disorders. However there are no clinical trials evaluating or
comparing the muscle relaxation generated for these devices.
PURPOSE: To compare the muscle relaxation of the upper trapezius induced by the application of TENS and IFC in females
with chronic nonspecific neck discomfort.
METHODS: Sixty-four females between 18 and 40 years of age and a history of nonspecific neck discomfort were randomly
assigned to a TENS or an IFC group. The women in the TENS (N = 32; mean age 22 years) and IFC (N = 32, mean age
23 years) group were submitted to current application during 3 consecutive days and were assessed by electromyography (EMG)
in different times aiming to quantify the muscular tension of the upper trapezius. A visual analogue scale (VAS) was used as pain
measure at baseline (before TENS or IFC application) and at the end of the study.
RESULTS: At baseline, demographic, pain, and EMG assessment data were similar between groups. Those in the IFC group
had a significant trapezius relaxation after 3 IFC applications when compared to baseline and intermediate evaluations (P <
0.05). In contrast, the same analysis showed no significant difference between all assessments in the TENS group (P > 0.05). In
relation to pain relief, both groups showed an improvement at the end of the study when compared to baseline (both, P < 0.05).
The between-group analysis showed no difference for the subjects who received such IFC as TENS application (P < 0.05).
CONCLUSION: IFC induced the upper trapezius relaxation after 3 sessions in females with neck discomfort, but the TENS
application did not change the muscular tension. However, these results should be carefully interpreted due to the lack of differences between groups. A significant pain decrease was found in the subjects of both groups, however, only the IFC application
presented a clinically important improvement.
Keywords: Electrical stimulation, transcutaneous electrical nerve stimulation, muscle relaxation, electromyography, neck pain
1. Introduction
∗ Corresponding author: Thiago Yukio Fukuda, Physical Therapy Department, Avenida Nazaré, 1501, 04263-200, São Paulo SP,
Brazil. E-mail: [email protected].
The stress level of the population has increased,
leading to a compensatory muscle tension, and therefore, several musculoskeletal disorders [1]. These disorders may affect specially the postural muscles, because they are the most requested during functional ac-
c 2015 – IOS Press and the authors. All rights reserved
ISSN 1053-8127/15/$35.00 A.A. Acedo et al. / Upper trapezius relaxation induced by TENS and IFC in computer users
(n = 32) and an IFC group (n = 32). All volunteers
were informed about the procedures for the study and
signed informed consent written in accordance with
the National Health Council, resolution 196/96. This
study was approved by the Research Ethics Committee
of Centro Universitário São Camilo (CUSC), Brazil.
Females between 18 and 40 years old were included
if they had a history of chronic nonspecific neck discomfort with a visual analog scale (VAS) score over
3/10, if they use computer for at least 14 hours per
week or 2 hours daily, and if they had pain during
trigger point palpation of the neck area. For this evaluation, the trigger point was considered active if the
subject presented local pain during a moderate digital
pressure in the middle third of the upper trapezius. The
participants were recruited from the college students of
the university by a single physical therapist with more
than 10 years of clinical experience in spine rehabilitation.
Females were excluded if they had musculoskeletal disorders, physical therapy in the last 6 months, referred or irradiated pain, body mass index over 28, previous surgery involving the upper extremities, if were
pregnant or using corticosteroids or anti-inflammatory
medication, as well as other traditional TENS or IFC
contra-indications [1,7]. A standard cervical clinical
examination was performed to rule out concomitant
pathology of the upper extremities.
The assignment of subjects in the two groups was
performed randomly using opaque and sealed envelopes containing the names of the groups: TENS and
IFC. The envelopes were picked by an individual not
involved in this study. Three therapists were trained in
delivering the device protocols used for the study and
provide all treatment.
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tivities [2,3]. The muscles of the neck and shoulder are
the most affected in workers of different occupations,
especially those that involve repetitive movements as
typing in a computer for a long time [4,5]. This pattern
of muscle tension is found mainly in the upper fibers of
the trapezius muscle, and for this reason, it is an area
much investigated in the literature by electromyography [1,4,6].
Thus, the vicious cycle involving stress, repetitive
activities, and tension in the trapezius also leads to
greater difficulty in returning to basal muscle activity
after a workday [5]. It is usual in the clinical practice finding subjects with muscular discomfort in the
neck area, even without a clear diagnosis of disc herniation, radiculopathies, spine injuries or degenerative
processes.
There are several modalities used in physical therapy focusing on pain relief and muscle relaxation such
as physical agents for cooling, heating, electrical stimulation, and others [7]. The transcutaneous electrical
nerve stimulation (TENS) and the interferential current
(IFC) are noninvasive methods used for analgesia, but
there is a lack of consensus in the literature regarding
the muscle relaxation effects [8]. TENS has been described as a device that generates alternating electrical
current of low-frequency, acting at the sensory level
by closing the spinal cord gates, releasing endorphins,
and helping in tissue repair [9]. On the other hand, the
IFC is the application of alternating medium-frequency
(4.000 Hz) amplitude modulated at low frequency, presenting a higher tissue penetration and less discomfort
when compared to TENS [8,10].
The analgesic effects of the these currents are already well established in the literature, however, there
are no studies comparing the muscle relaxation by lowand medium-frequency currents on a sensory level, i.e.,
using current intensity (mA) only in the sensory threshold. Therefore, the aim of the present study was to
compare the muscle relaxation of the upper trapezius (primary outcome) and pain relief (secondary outcome) induced by the application of TENS and IFC in
females with chronic nonspecific neck discomfort.
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2. Methods
2.1. Participants
Sixty-four women with chronic nonspecific neck
discomfort participated in the study and were randomly assigned to one of two groups: a TENS group
2.2. Intervention
The TENS and IFC applications and electromyographic (EMG) registration were performed on each
subject in a standardized protocol with duration of 5
days. On the first day, subjects remained at rest in
the supine position for 30 minutes before the first assessment. We then analyzed the RMS value of the
EMG signal of both sides of the upper trapezius muscle. This first registration (initial evaluation) was performed with the subject seated on a standardized chair
with the forearms supported.
After the initial evaluation, the subjects of both
groups (TENS and IFC) were submitted to the current
application by self-adhesive silicone electrodes, with
A.A. Acedo et al. / Upper trapezius relaxation induced by TENS and IFC in computer users
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(“lab effect”). Although it was not the main purpose of
the study, we performed a pain assessment by visual
analogue scale (VAS) at initial and final evaluation.
The 0–10 cm VAS, where 0 represented “no pain” and
10 represented “worst imaginable pain”, was used to
assess cervical pain intensities. The VAS has reported
a minimal clinically important difference (MCID) of
2.0 cm (± 0.3 cm at a 95% confidence interval) [11].
2.3. Instrumentation and EMG
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The TENS (Quark
, TensVif 993) equipment was
used in the Burst mode, with a frequency of 100 Hz and
pulse duration of 150 µs. The IFC (KLD Biosistemas,
Endophasys) equipment had a carrier frequency of
4.000 Hz, an amplitude modulated frequency (AMF)
of 100 Hz, a variation frequency (ΔF) of 60 Hz, and
a slope of 6/6. The intensity (mA) in both devices was
set at the tactile sensation threshold.
The EMG equipment utilized in this study was the
portable CS400/EMG System with eight channels. The
EMG rectified signals of the trapezius muscle were obtained by surface Ag/AgCl (10 × 20 mm) differentialtype electrodes with inter-electrode capture distance of
20 mm and a pre-amplification of 20-fold, and send to
the amplifier (frequency range: 20–500 Hz; noise signal rate: 3 µV RMS; CMMR: 100 dB), which has a
gain of a factor of 50, achieving a gain of 1.000 fold
for the EMG signal.
The capture electrodes were positioned at the midpoint between the spinous process of the C7 vertebra
and the acromion bilaterally according to SENIAM –
European Recommendations for Surface Electromyography criteria [12]. The reference electrode was positioned in right lateral malleolus. Before the electrodes
were positioned, we shaved the exposed area, followed
by sterilization with hydrated 70% ethyl alcohol. Afterwards, an EMG signal capture was performed in the
predetermined condition for 30 seconds. The first and
last 5 seconds were removed. Thus, the raw EMG signal was rectified and the RMS values were calculated
during the intermediate 20 seconds.
Fig. 1. Consort flow chart.
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the bipolar technique, i.e., 2 electrodes on each side of
the upper trapezius for 30 minutes. In each side, one
electrode was placed laterally on the C7 spinous process, and the other on the supraspinatus fossa. The intensity (mA) was raised according to the subject’s tolerance, remaining in the sensorial level. Soon after this
application, another EMG registration was performed
at the same condition mentioned before (evaluation 1).
On the second day, the patients received only the
TENS or IFC application on the upper trapezius muscle bilaterally for 30 minutes. On the third day, the patients were initially assessed in relation to the EMG
registration (evaluation 2), followed by TENS or IFC
application. After this application, we performed the
EMG registration again (evaluation 3). There were no
activities or analysis on the fourth day.
On the fifth day, only the EMG registration (final
evaluation) was performed (Fig. 1). The same procedure prior to the analysis was performed in the evaluation 2 and final evaluation, i.e., the subjects remained
at rest in the supine position for 30 minutes to avoid
or minimize possible tensions due to the test situation
2.4. Statistical analysis
Data were analyzed with SPSS Version 13.0. (SPSS,
Chicago, IL, USA). Descriptive statistics for demographic data and all outcome measures were expressed
as averages and standard deviations. Comparison between the dominant and non-dominant side was performed using dependent T test. The data for the RMS
A.A. Acedo et al. / Upper trapezius relaxation induced by TENS and IFC in computer users
Table 1
Demographic data of the TENS and IFC groups
Age (y)
Body mass (kg)
Height (m)
Body mass index
(kg/m2 )
Duration of symptons
(months)
TENS∗
22.0 ± 3.0
60.4 ± 3.6
1.59 ± 0.3
23.6 ± 3.1
IFC∗
23.0 ± 3.0
61.3 ± 2.6
1.60 ± 0.2
24.4 ± 2.9
P value
0.770
0.698
0.924
0.801
2.1 ± 1.7
2.8 ± 0.9
0.621
Abbreviations: TENS, Transcutaneous Electrical Neural Stimulation; IFC, Interferential Current. ∗ Values are mean ± SD, there were
no differences between groups (P > 0.05).
value of the EMG signal were analyzed using separate
2 × 5 (group by time) mixed model ANOVAs. The
factor group had 2 levels (TENS and IFC) and the repeated factor time had 5 levels (initial, 1, 2, 3, and final
evaluations).
3. Results
There was no statistically significant difference
(P > 0.05) for age, height, body mass, and duration of
symptoms between the participants in the TENS and
IFC groups (Table 1). There was no statistical difference between the dominant and non-dominant side in
the intra-group analysis (TENS, P = 0.5 and IFC, P =
0.6). For this reason, both sides were considered together for the comparison between groups. There was
also no statistically significant difference (P = 0.4) between groups for the studied variables (EMG data and
VAS) at baseline (initial evaluation) (Table 2).
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3.2. EMG registration and pain
4. Discussion
This randomized interventional study aimed to compare the muscular relaxing effects of the upper trapezius induced by TENS and IFC application in females
who used a computer daily and presented chronic unspecific neck discomfort. The results of EMG evaluation showed that IFC can reduce the trapezius muscle
tension; however, three sessions are needed to achieve
this effect. On the other hand, there was no relaxation
effect using the TENS application. Both groups presented a decrease of the pain level. It is important to
highlight that there was no difference between groups
for all assessments.
The assessment of muscle activity can be performed
by EMG [13], since the RMS value is a tool of quantifying and processing the EMG signal, showing a linear relationship with muscle tension at rest and during
functional tasks [14].
Previous studies have linked the TENS and IFC application as a tool to provide pain relief and muscle relaxation [8,15,16]. There is also hypothesis about effects of increasing blood flow and excitation of large
diameter afferent fibers (Gate theory) [9,17,18]. However, there is a lack of clinical studies using quantitative assessment for muscle relaxation induced by
TENS and IFC.
The results of the present study demonstrate that a
decrease in muscular activity can be observed at sensorial level stimulation in medium-frequency current,
ie., using current intensity (mA) only in the sensory
threshold. However, this relaxation appears to be more
related to cumulative rather than immediate effect, because we observed that there was significant relaxation
in the final evaluation when compared to initial assessment for the subjects who received IFC application. This information corroborates the data from recent meta-analysis conducted by Fuentes et al. [15]. A
hypothesis for the lack of effect using TENS applica-
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3.1. Baseline data
The analysis of differences between groups at evaluations 1, 2, and 3, as well as final evaluation showed
no difference for the subjects who received such IFC as
TENS application (P < 0.05). There was also no difference in the between-group analysis for VAS (P >
0.05).
It is important to highlight that we controlled the use
of any anti-inflammatory, muscular relaxant, or analgesic medication; and no subject reported performing
physical activity during this period.
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There was a statistically significant group-by-timeinteraction for the 2-by-5 mixed-model ANOVA for
muscle tension and pain assessment measures (P <
0.01). Planned pairwise comparisons for the RMS
value of the EMG signal indicated that the subjects in
the IFC group had significant muscle relaxation at final
evaluation when compared to baseline (initial evaluation), evaluations 1, 2, and 3 (P < 0.01, P < 0.02, and
P < 0.05, respectively). The same analysis showed no
significant difference between all assessments in the
subjects of the TENS group (P > 0.05). In relation to
pain relief, both groups showed an improvement at final evaluation when compared to baseline (both, P <
0.05).
A.A. Acedo et al. / Upper trapezius relaxation induced by TENS and IFC in computer users
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Table 2
Outcome measures for the TENS (n = 32) and IFC (n = 32) groups
TENS∗
IFC∗
Initial
10.5 ± 1.7
(9.9, 11.1)
11.2 ± 2.5
(10.3, 12.1)
RMS value of the EMG signal (µV) – trapezius muscle
Evaluation 1
Evaluation 2
Evaluation 3
11.4 ± 3.8
10.8 ± 1.9
10.5 ± 1.9
(10.0, 12.8)
(10.1, 11.5)
(9.8, 11.2)
10.5 ± 1.4
10.5 ± 1.7
10.2 ± 1.1
(10.0, 11.0)
(9.7, 10.4)
(9.8, 10.6)
Final
10.3 ± 1.8
(9.6, 10.9)
9.7 ± 0.8
(9.4, 10.0)
VAS (0–10 cm)
Initial
Final
4.2 ± 1.3
2.9 ± 0.5
(3.7, 4.7)
(2.7, 3.1)
4.6 ± 1.9
2.4 ± 0.5
(3.9, 5.3)
(2.2, 2.6)
ate muscle relaxing. This proceeding was also used in
previous studies [26,27].
The present study contributed to the literature because this is the first clinical study investigating immediate and cumulative muscle relaxation by surface
EMG in subjects with chronic discomfort in the cervical area. Further research is needed to relate other
IFC and TENS parameters such as modulated or carrier frequency, duty cycle, intensity, and time. In addition, these findings need to be correlated with clinical
evaluations of local microcirculation in subjects with
chronic diseases, neck, and superior limb disorders, as
well as in spastic muscles of neurological patients.
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tion is that this device provide a low-frequency current, suffering a high tissue resistance, leading to a peripheral vasodilatation, and consequently, insufficient
to promote the trapezius relaxation [9,10,16,19].
Hou et al. [20] postulated that electrical stimulation
can lead to physiological suppression of sympathetic
fibers of small arterioles in the muscle belly, reducing
sympathetic tonus, and thereby, increasing local blood
flow. This mechanism has been suggested as the main
cause of increased tissue oxygen and, consequently,
providing a clinical reduction of the pain-spasm-pain
cycle [21–23].
Based on this information, one factor should be
taken into account when utilizing this equipment aimed
at muscle relaxation. It is necessary to receive IFC
for a long time in each session, since the subjects
of the present study have received applications for
30 minutes. Some authors have shown that electrical stimulation applications for a short time (approximately 20 minutes) are not sufficient to promote therapeutic effects [19]. As a secondary outcome, both
groups showed significant pain reduction at the final
evaluation when compared to initial evaluation. However, Farrar et al. [24] and Forouzanfar et al. [25]
showed that the minimal clinically important difference (MCID) for VAS is approximately 2 points.
Therefore, only the IFC group presented a mean improvement in pain that superpassed the MCID (2.2 for
IFC and 1.3 for TENS).
This study presents a limitation due to the lack of
a sham group. However, this bias was minimized because the subjects submitted to IFC and TENS therapy
performed complete rest before the initial EMG evaluation trying to avoid or minimize possible tensions due
to the test situation (“lab effect”). Another justification
is the fact that EMG is a quantitative tool for analyzing
the muscular tension, and therefore was not directly influenced by the placebo effect. Also, we did not perform a normalization of the data in relation to the maximum isometric contraction because we did not find a
rationale for using this kind of normalization to evalu-
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Abbreviations: TENS, Transcutaneous Electrical Neural Stimulation; IFC, Interferencial Current; RMS, Root Mean Square; EMG, Electromyographic; VAS, Visual Analogue Scale. ∗ Values are mean ± SD (95% confidence interval).
5. Conclusion
IFC induced the upper trapezius relaxation after 3
sessions in females with chronic unspecific neck discomfort, but the TENS application did not change the
muscular tension. However, these results should be
carefully interpreted due to the lack of differences between groups. A significant pain decrease was found
in the subjects of both groups, however, only the IFC
application presented a clinically important improvement.
Ethics
The protocol for this study was approved by the
Ethics Committee on Research of the Centro Universitário São Camilo (CUSC).
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