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men when polarized currents are used, and there is a risk of skin lesion because of their high thresholds.
muscular stimulation, especially at the sensory [1] and
motor [2] levels. The term threshold is applied to
denote the energy required to promote presynaptic
excitation of the neuronal membrane, which produces
tensity can be applied in the cases of chronic pain. In
addition, adequate intensities are required to produce
analgesia [5], thus characterizing a dose-dependent
response.
The current frequency, expressed in hertz (Hz), is
(20
sensory (sensory threshold) or motor response (motor
Introduction
Electrical stimulation, when applied with percuta-
neous electrodes, is a noninvasive therapeutic proce-
dure useful in clinical practice. It has been often used
in rehabilitation in several areas of health care, such
as analgesia, tissue repair, circulation, and neuro-
The combination of physical parameters (ie, pulse
duration, intensity, frequency) characterizes the
different types of electrical currents, thus producing
several therapeutic effects. Overall, higher frequencies
in association with sensory threshold intensity [4] are
used in the cases of cicatrization or acute pain, whereas
low frequencies in association with motor threshold in-
Conclusion: Age and gender interfere directly with ES. These v
indicate that electrical stimulation in elderly women should be
ariables should be considered during rehabilitation because they
carefully performed, as they have lower thresholds than elderly
occurred only in male subjects at 5 Hz.
Rinaldo Roberto de Jesus Guirro, PhD, Elaine Caldeira de Oliveira Guirro, PhD,
Natanael Teixeira Alves de Sousa, PT
Abstract
Background: Transcutaneous electrical stimulation (ES) is a therapeutic procedure used in rehabilitation. However, the effec-
tiveness of it depends on sensory responses to pain and motor control in neuromuscular recruitment, considering the differences
related to gender and age of the subjects treated, as well as the intensity and frequency of ES.
Objective: To determine the threshold of sensory perception (TSP) and the threshold of motor response (TMR) in young and
elderly individuals of both genders.
Design: Randomized controlled clinical trial.
Setting: General community.
Participants: Eighty volunteers with no history of systemic diseases were selected to participate in the study: 40 men and 40
women were subdivided by convenience sampling and age group into young male and female (age 21.6 � 2.4 years) groups as well
as into elderly female and male groups (age 72.6 � 6.1 years).
Interventions: The participants received electrical stimulation (ES) at 5 and 50 Hz, with pulse durations of 20, 100, 400, 1000, and
3000 ms applied on the flexor muscle bellies of the wrist and fingers.
Main Outcome Measures: TSP was identified as the first sensation of increased current intensity and TMR as the minimum
muscle contraction detected. The results were submitted to analysis of variance, followed by the Tukey’s test, with a significance
level of 5%.
Results: TSP was lower than TMR for all pulse durations, regardless of gender and age. In women, TSP was lower than that in young
and elderly men at both frequencies. However, TSP was higher in elderly subjects than in younger subjects at 50 Hz for both
genders. Age also affected the TMR, presenting higher thresholds in elderly subjects of both genders at 50 Hz; however the same
Original
Sensory and Motor Threshold
Stimulation Are Influen
PM R 7
threshold) [3].
1934-1482/$ - see front matter ª 2015 by the American Academy of Physi
http://dx.doi.org/10.1016/j.pmrj.2014.07.004
search
of Transcutaneous Electrical
ed by Gender and Age
15) 42-47
www.pmrjournal.org
an important parameter, as it exerts a direct influence
cal Medicine and Rehabilitation
on the electrical resistance of the tissues [6,7]. The
frequency-dependent response refers to the level of
skeletal muscle contraction, as it may be either non-
tetanic (low frequency) or tetanic (frequencies >30
Hz) [2]. Besides the parameters of electric current,
there is evidence that other factors, such as age and
gender, may influence the responses of sensory and
motor thresholds [3,8,9]. As the stimulation of sensory
and motor nerves can influence the rehabilitation
process, one can obtain a better understanding of the
influence of age and gender on the response thresh-
olds, which may enable therapeutic interventions to
be applied more effectively on a safer and more
effective basis.
The physiological aging has a major impact on the
sensory-motor processing due to reduced cerebral blood
Methods
The study was approved by the local ethics commit-
tee according to protocol number 64/05. All participants
signed an informed consent form in accordance with the
Declaration of Helsinki.
Eighty volunteers with no history of systemic diseases
were selected to participate in the study: 40 men and 40
women. The subjects were subdivided by age and
gender groups as follows: young males (n ¼ 20), young
females (n ¼ 20), elderly males (n ¼ 20), and elderly
females (n ¼ 20) according to the Health Sciences
Descriptors [14], that is, young male and female adults
(aged 21.6 � 2.4 years) and elderly female and male
adults (aged 72.6 � 6.1 years). All of the subjects had
normal mean body mass index (20-25 kg/m2). The
43R.R.d.J. Guirro et al. / PM R 7 (2015) 42-47
flow and structural and functional changes in peripheral
and cortical neurons [8,10], thus reducing the number of
cutaneous mechanoreceptors [11] and decreasing the
conduction velocity of the peripheral [12] nerves. To
overcome these deficits, different compensation
methods play a crucial role in maintaining the functional
performance, often correlated with increased brain
activation areas [8,10,13].
There are few studies in the literature focusing on
the sensory and motor responses to ES when gender and
age of the participants are considered. Because of the
various pathological conditions treated by electrical
stimulation, knowledge of the subject becomes rele-
vant, as sensory and motor behaviors are influenced by
sexual hormones that can interfere with the therapeutic
response.
Therefore, this study aimed to investigate the
threshold of sensory perception (TSP) and the threshold
of motor response (TMR) in healthy individuals of both
genders and different ages, considering stimulation
parameters such as frequency and pulse duration.
Figure 1. Chart of volunteer distribut
descriptors are a vocabulary that contains the standard
terminology in health sciences developed by the Latin
American and Caribbean Center for information on
health sciences, considering the aging aspects for
developing countries.
In addition to these, 6 volunteers were excluded for
not having time to complete the 2 ES tests. The
threshold of sensory perception (TSP) and the threshold
of motor response (TMR) were evaluated, as shown in
Figure 1.
The frequency to be used in each session of ES was
randomly chosen for each individual (software research
Randomizer Form v 4.0). A pulse generator was used for
data collection (Dualpex 961; Quark, Piracicaba/SP,
Brazil) at constant current intensity, and the following
parameters were used for current stimulation: square
biphasic wave; pulse durations of 20, 50, 100, 200, 300,
500, 1000, and 3000 ms; and frequency of 5 or 50 Hz.
New silicon-carbon electrodes measuring 5�2 cm
each were attached to the skin with water-soluble gel
(2 mL) and placed over the flexor muscle bellies of the
ion and experimental procedures.
wrist and fingers of the nondominant limb. Placement
followed the longitudinal direction of the muscle fibers,
with the first electrode being placed 4 cm distal to the
medial epicondyle and the second electrode 2 cm distal
to the first electrode, following the same direction.During the procedure, the volunteers remained
seated, with their forearms in supination, resting on the
table surface for 15 minutes in a temperature-
controlled environment (23�C � 2�C) for acclimatiza-
tion. The tests always initiated with 20 ms pulse
duration, increasing in intensity until TSP and TMR. At
this point, the intensity was reset and the procedure
resumed, followed by the next pulse duration, pro-
gressively evolving up to 3000 ms and repeated 3 times
with a 10-minute interval between the tests. According
to Nelson and Hunt [15], this method preserves a sig-
nificant level of interrater and intrarater correlation
and reliability. The procedures were carried out with a
minimum interval of 72 hours for different frequencies.
The volunteers were instructed to describe the first
sensation of the first current, identified as a sensory
perception threshold. Thresholds were defined by the
submitted to analysis of variance followed by the Tukey
test by using SPSS version 20.0 for Windows (IBM
Corporation, Armonk, NY) at a significance level of 5%.
Results
There were significant differences between TSP and
TMR in all groups, with the former always being lower
than the latter, regardless of gender or age. The results
also showed that in both thresholds the ES intensity was
inversely proportional to the pulse duration. With
respect to the gender comparison, young and elderly
men showed TSP lower than that of women at both 5 Hz
and 50 Hz.
With regard to the motor threshold, no definitive
pattern was found between genders. The differences
were found only between young groups of males and
females for pulse duration equal to or greater than 300
ms, with the lower values always being seen among
women (Table 1).
Age affected both TSP and TMR of men and women at
50 Hz, thus demonstrating higher values in elderly than
for
*
,§
A),
rly
44 TENS Thresholds are Influenced by Gender and Age
current intensity in milliamperes (mA). The TMR was set
when there was a slight contraction of the flexor mus-
cles of the wrist and fingers, quantified by an experi-
enced examiner (R.R.J.G.). For the group of young adult
women, special care was taken so that the tests were
not conducted during the premenstrual period or 1 week
before that, as TSP and TMR could be changed [16].
Data were analyzed by a different blinded researcher
who did not perform the acquisition of data. Data were
Table 1
Comparison of the mean values (� SD) of electrical current intensities
Pulse Duration Threshold
5 Hz
YM YF EM
20 (ms) Sensory 32.5 � 7.5 21.5 � 4.8† 34.8 � 9.9
Motor 50.6 � 9.6*,‡ 56.7 � 14*,§ 58.9 � 10.6
50 (ms) Sensory 15.4 � 3 11.3 � 3.3† 17.2 � 5.1§
Motor 22.4 � 4.1*,‡ 25.3 � 6.3* 28.9 � 6.4*
100 (ms) Sensory 9.8 � 2 7.3 � 2.3† 11 � 3.3§
Motor 14 � 2.6*,‡ 15.2 � 3.3* 17.8 � 4.1*
200 (ms) Sensory 5.9 � 1.2 4.8 � 1.5 6.9 � 2§
Motor 9.4 � 1.8*,‡ 10.1 � 2.1* 11.6 � 2.7*
300 (ms) Sensory 4.6 � 0.8 3.7 � 1† 5.7 � 1.5§
Motor 7.7 � 1.7*,†,‡ 8.6 � 1.8*,‡ 9.7 � 2.2*
500 (ms) Sensory 3.7 � 0.7 3.1 � 0.9 4.5 � 1.3§
Motor 6.6 � 1.4*,†,‡ 7.5 � 1.5* 8 � 2.2*
1000 (ms) Sensory 2.5 � 0.6 2.3 � 0.7 3.3 � 0.8§
Motor 5.5 � 1.3*,†,‡ 6.3 � 1.2* 6.5 � 1.8*
3000 (ms) Sensory 2.1 � 0.5 1.7 � 0.6 2.7 � 0.8
Motor 5 � 1.3*,† 5.8 � 1*,§ 5.6 � 1.6*
Values refer to the intensity of the electric current in milliamps (m
seconds (ms).
YM ¼ young male; YF ¼ young female; EM ¼ elderly male; EF ¼ elde
* P < .05, sensory versus motor for the same age, frequency and gender
† P < .05, male versus female for the same age, frequency, and thresho
‡ P < .05, young versus elderly for the same threshold, gender and frequ
§ P < .05, 5-Hz frequency versus 50 Hz for the same threshold, gender a
in young subjects. At 5 Hz, an increase in TMR among
elderly men was observed. By comparing the ES fre-
quencies (5 and 50 Hz), it was found that this variable
had an influence on TSP in both elderly men and women,
with significant difference regarding some pulse dura-
tions as values greater than 50 Hz were observed
(Table 1).
Because 8 pulse durations were used, we opted to
analyze the distribution of the TSP and TMR values, thus
different thresholds, genders, frequencies, and ages (n ¼ 20)
50 Hz
EF YM YF EM EF
19.9 � 4.6†,§ 29 � 8.1‡ 18.3 � 5.3†,‡ 34.7 � 6.4 25.2 � 7.4†
58.6 � 10.4* 47.8 � 10*,‡ 47.6 � 10*,‡ 57.7 � 3.6* 53.4 � 7.9*
11.9 � 6† 16.5 � 4.6‡ 11.5 � 3.2†,‡ 20.8 � 4.3 14.9 � 3.3†
26.1 � 5.1* 24.7 � 4.3*,‡ 26.2 � 7.7* 33 � 6.1* 28.6 � 3.9*,†
6.9 � 2.1†,§ 10 � 2.5‡ 7.2 � 2.2†,‡ 13.5 � 3.3 9.7 � 2.2†
16.3 � 2.8* 15.1 � 2.7*,‡ 16 � 4.5*,‡ 19.9 � 4.2* 18.4 � 2.4*
4.9 � 1.6† 6.2 � 1.5‡ 5 � 1.8 9.1 � 2.3 6.2 � 1.2†
11.2 � 1.8* 9.2 � 2.2*,‡ 9.7 � 2.4*,‡ 12.6 � 3.4* 11.4 � 1.9*
4.1 � 1.1† 5 � 1.3‡ 4 � 1.3‡ 6.9 � 1.8 5.1 � 1.2†
9.4 � 1.4* 7.7 � 1.8*,‡ 8 � 1.9*,‡ 10.2 � 3.1* 9.4 � 1.6*
3.3 � 1.3§ 3.9 � 1‡ 3.2 � 1‡ 5.8 � 1.5 4.2 � 1.2†
8.2 � 1.4* 6.6 � 2*,‡ 6.8 � 1.7*,‡ 8.6 � 2.6* 8.2 � 1.4*
2.5 � 0.8§ 3 � 1‡ 2.3 � 0.8‡ 4.2 � 1.1 3.4 � 1
7 � 1.7* 5.5 � 1.3*,‡ 5.5 � 1.5*,‡ 6.9 � 2* 6.4 � 1.6*
2.1 � 0.7†,§ 2.5 � 1 1.9 � 0.4‡ 2.9 � 1 2.8 � 0.8
6.4 � 1.4* 5.1 � 1.4* 4.7 � 1.2*,‡ 5.8 � 1.8* 5.7 � 1.2*
frequencies expressed in Hertz (Hz), and pulse duration in micro-
female.
.
ld.
ency.
nd age.
characterizing the curves of intensityeduration pulse.
The values of R2 demonstrate that power regression
represents, on average, 96.3% and 91.0% of the values
gathered for sensory and motor thresholds, respectively
(Table 2).
Discussion
R.R.d.J. Guirro et al. /
Table 2
Values R2 refer to the intensity of the electric current for different
thresholds, genders, frequencies, and ages (n ¼ 20)
Thresholds
5 Hz 50 Hz
YM YF EM EF YM YF EM EF
In the present study, we observed that both age and
gender affected the sensory and motor thresholds
during transcutaneous electrical stimulation. The main
findings of the present study were the following: (1)
TSP was always lower than TRM, regardless of gender,
age, and frequency; (2) TSP was lower in women than
in elderly and young men at both frequencies; (3) TSP
and TMR were higher in elderly subjects than in young
subjects at 50 Hz, regardless of gender; (4) at 5 Hz,
TMR was higher in elderly men only; and (5) TSP and
TMR had values of R2 greater than 95% and 98%,
respectively. These results were obtained from the
flexor muscles of wrist and fingers that were very
compromised because of the cutting-contuse lesions in
the upper limb, thus requiring electrical stimulation
for both pain control and neuromuscular rehabilita-
tion, a procedure widely used in daily practice. The
parameters used are within the range of frequency and
pulse duration for clinical use in both elderly and
young subjects, which maximizes the external validity
of the study. The analysis of gender-related differ-
ences for the TSP in young and elderly subjects, both
at 5 and at 50 Hz, showed lower thresholds in females.
These findings corroborate those obtained by Maffiu-
letti et al [3], who demonstrated that the sensory
threshold was lower in women than in men. In addi-
tion, it was suggested that GIRK2, a protein located on
the surface of nerve cells, increases the TSP in male
subjects [17]. It was also reported that the density of
epidermal nerve fibers was found to be lower in men
than in women [18,19], thus demonstrating that the
difference in sensory threshold is strongly related to
morphological changes resulting from the sexual
characteristics. However, other factors such as race/
ethnicity, hormones, and psychosocial interactions can
also influence the TSP [20,21]. Kantor et al [22]
demonstrated that the sensory and motor nerves
Sensory 0.96 0.97 0.96 0.95 0.95 0.97 0.98 0.95
Motor 0.89 0.88 0.92 0.88 0.9 0.92 0.94 0.93
YM ¼ young male; YF ¼ young female; EM ¼ elderly male; EF ¼ elderly
female.
respond in a seemingly identical wayto trans-
cutaneous stimulation and that different waveforms
have no meaningful influence on the responses.
The clinical contextualization of this research area
can be viewed in the study by Hardy et al [23], who
examined the thresholds applied over the dorsiflexors or
plantar flexors of the ankle at 100 ms and 20 Hz. The
authors observed that the results were similar to those
found to reduce spasticity, hyperreflexia, and clonus. In
addition, in a group of young women, mean values of
sensory threshold of 90 mA and 67 mA were found for
plantar flexors and dorsiflexors, respectively. In another
study, conducted to identify the sensorial threshold on
the forearm, greater sensitivity was found in females
compared to males when the same frequency was
applied [24]. However, Galva˜o et al [25] evaluated the
sensory threshold by using different frequencies (5, 250,
and 2000 Hz), reporting no significant differences
despite the significant correlations at 250 and 2000 Hz
frequencies regarding gender and age. Based on the
results found in the present study, it was observed that
TSP can vary according to the frequency of the current
with the same pulse duration.
Another factor to be considered in the response to
electrical responses is the adipose tissue, where lower
sensory thresholds were noted in subjects with greater
skinfold thickness (mainly women), suggesting a link
between mass of subcutaneous adipose tissue and
sensorial excitation [3]. However, in a previous study,
the same author investigated the relationship between
body fat percentage and gender in obese and non-obese
subjects, reporting that the sensory threshold was lower
in women than in men, regardless of the obesity.
Moreover, both sensory and motor thresholds were
found to be higher in obese than in non-obese subjects
[26], thus showing a relationship between adipose tissue
mass and sensory excitability. In the present study, the
differences found in either sensory or motor thresholds
may not be attibuted to this condition, as all the vol-
unteers had BMI values within the normality standards.
The hypothesis applied to the motor threshold was
considered because only a few results were obtained
between men and women, although the subcutaneous
fat thickness might limit the conductivity between
electrode and efferent axons. This may explain, in part,
the results found by comparing the TMR between young
and elderly subjects as a significant difference was
observed in both genders, with higher intensities
observed among elderly subjects that then decreased as
the pulse duration increased (20-1000 ms). Because
elderly subjects tend to have a higher fat percentage in
relation to the muscle tissue, this might cause an in-
crease in the current resistance. Therefore, a higher
electrical tension would be required to achieve the
45PM R 7 (2015) 42-47
motor nerves, which is directly related to the increase
in intensity. The use of different pulse durations in the
present study allowed us to demonstrate, by means of
uen
regression analysis, that the data gathered had indeed a
very uniform behavior, as at least 95% and 88% of the
sensory and motor thresholds, respectively, could be
represented by a regression curve. This fact is clinically
important, because it would be possible to predict the
intensity needed to maintain the same level of neural
excitation at different pulse durations.
There was no significant relationship at 5 Hz when the
TSP between different ages and frequencies were
analyzed. On the other hand, nearly all pulse durations
showed higher thresholds at 50 Hz, in both genders in
elderly subjects. In this context, the influence of fre-
quency on the determination of the sensory threshold in
elderly subjects can also be linked to an expected
decline related to the aging process. Reinforcing this
hypothesis, the results obtained by Brodoehl et al [8]
indicated that, in addition to the overactivation to
compensate for the impaired brain functions, there are
complex mechanisms of modified inhibition and excit-
ability involved in the somatosensory processing in the
aging brain.
In our study, the thresholds were lower at 5 Hz than
at 50 Hz. We also observed differences in TSP in both
elderly men and women. These findings are in accor-
dance with a study that found significantly lower
thresholds at 10 Hz compared to 75 Hz [3]. Neverthe-
less, another study [24] reported a sensory threshold
inversely related to the frequency, a finding diverging
from ours, although the sample assessed by the author
was small. These results may be associated with a
greater perception of painful stimuli in elderly subjects,
since the frequency of 5 HZ excites the afferent fibers
A-d and C, which convey low-frequency stimuli, whereas
afferent fibers A-b convey higher frequencies.
Considering that studies on thresholds have clinical
importance as they provide a better understanding of
the pathophysiology of some diseases [7,27-30],
including the treatment of skeletal muscle injuries and
pain-control palliative care [31,32], our findings play a
preponderant role in achieving clinical success, as the
sensory and motor thresholds are affected by age and
gender.
The comparison between the present study and the
literature indicates a greater number of variables
analyzed, because the relationships between sensory
and motor thresholds regarding frequency and gender
[3], as well as regarding obesity and gender [26], have
already been studied. Our study assessed the relation-
ship between sensory and motor thresholds regarding
frequency, gender, pulse duration, and age, showing
that electrical stimulation in elderly subjects at 50 Hz
with pulse duration of less than 1000 ms should be
carefully applied so as to avoid risk of skin lesions,
because higher thresholds are observed when polarized
46 TENS Thresholds are Infl
currents are used. Future research in this area should
investigate individuals with different levels of subcu-
taneous fat, including some possible interference
caused by pathologies that compromise the peripheral
nervous system or skeletal muscles.
Conclusion
The results of the present study can help practi-
tioners to obtain better sensory or motor responses,
which in turn depend on gender, age, and pulse duration
and are often neglected in clinical practice. Therefore,
we recommend that practitioners consider the
following: (1) TSP will be lower than TMR, regardless of
gender, age, and frequency; (2) TSP may be lower in
women than in elderly and young men at both fre-
quencies; (3) TSP and TMR in elderly subjects may be
higher than in young men and women at a stimulation of
50 Hz with pulse duration of less than 1000 ms; (4) TMR
may be higher in elderly men at 5 Hz; and (5) TSP and
TMR values may be predicted with 90% precision.
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47R.R.d.J. Guirro et al. / PM R 7 (2015) 42-47
Disclosure
R.R.d.J.G. Department of Biomechanics, Medicine and Rehabilitation, Ribeira˜o
Preto Medical School, Universidade de Sa˜o Paulo (USP), Ribeira˜o Preto, SP,
Brazil; and Post-Graduation Program in Rehabilitation and Functional Perfor-
mance, Ribeira˜o Preto Medical School, Universidade de Sa˜o Paulo (USP), Ribeira˜o
Preto, SP, Brazil. Address correspondence to: R.R.d.J.G.; e-mail: rguirro@fmrp.
usp.br
Disclosure: nothing to disclose
E.C.d.O.G. Department of Biomechanics, Medicine and Rehabilitation, Ribeira˜o
Preto Medical School, Universidade de Sa˜o Paulo (USP), Ribeira˜o Preto, SP,
Brazil; and Post-Graduation Program in Rehabilitation and Functional Perfor-
mance, Ribeira˜o Preto Medical School, Universidade de Sa˜o Paulo (USP), Ribeira˜o
Preto, SP, Brazil
Disclosure: nothing to disclose
N.T.A.d.S. Department of Biomechanics, Medicine and Rehabilitation and post-
graduate program in Rehabilitation and Functional Performance, Ribeira˜o Preto
Medical School, Universidade de Sa˜o Paulo (USP), Ribeira˜o Preto, SP, Brazil
Disclosure: nothing to disclose
The present study received financial assistance in the form of a grant from the
Coordination for Improvement of Higher Education Personnel (CAPES) Founda-
tion; and National Council for Scientific and Technological Development (CNPq -
N�:487767/2013-6).
Clinical trial registration number: NCT01876160.
Submitted for publication August 9, 2013; accepted July 6, 2014.
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	Sensory and Motor Thresholds of Transcutaneous Electrical Stimulation Are Influenced by Gender and Age
	Introduction
	Methods
	Results
	Discussion
	Conclusion
	References