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Electrical Muscle Stimulation to Develop Menstrual Simulator System
Paper:
Electrical Muscle Stimulation to Develop and ImplementMenstrual Simulator System
Chihiro Asada∗1, Kotori Tsutsumi∗1, Yuichi Tamura∗2, Naoya Hara∗3,
Wataru Omori∗4, Yuta Otsuka∗5, and Katsunari Sato∗1
∗1Nara Women’s University
Kitauoyanishimachi, Nara 630-8506, Japan
E-mail: chihiro.asada.mmg@gmail.com∗2Konan University
8-9-1 Okamoto, Higashinada-ku, Kobe, Hyogo 658-8501, Japan∗3Osaka University
1-1 Yamadaoka, Suita, Osaka 658-8501, Japan∗4Japan Advanced Institute of Science and Technology
1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan∗5University of Hyogo
7-1-28 Minatojimaminamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
[Received April 3, 2021; accepted August 27, 2021]
Menstrual symptoms and cycles are complex, and the
associated discomfort is difficult to quantify. There-
fore, men, and some women, do not completely un-
derstand them. Here, we propose a system that
simulates menstruation-like cramps through electri-
cal muscle stimulation (EMS). We conducted an ex-
periment to compare and evaluate the natural and
electrically stimulated menstrual cramps. The results
show that menstrual cramps using EMS can repro-
duce the nature of periodic dull pain. However, in this
study, the position where the pain occurred was shal-
low. Furthermore, we constructed a demonstration
system based on the proposed method. From the exhi-
bition, we confirmed that this experience can help ver-
balize menstrual-related discomfort and allow people
to better understand menstrual symptoms. In other
words, this experience will help eliminate negative per-
ception of menstruation.
Keywords: electrical muscle stimulation, menstrual
cramps, virtual reality, pain sensation, pain reproduction
1. Introduction
Owing to the complexity of the menstrual cycle and its
symptoms [1, 2], menstruation-related discomfort is sub-
jective and varies among individuals. Therefore, individ-
uals find it difficult to verbalize and quantify the inconve-
nience of menstruation symptoms. Typically, men do not
understand the discomforts of menstrual symptoms. Fur-
thermore, some women do not completely understand the
menstrual symptoms experienced by other women.
To solve this problem, it is necessary to overcome phys-
ical barriers in different body structure. These differences
make it impossible for everyone to experience menstrual
symptoms. Therefore, we aimed to create a virtual reality
(VR) system that reproduces menstrual symptoms.
Menstrual cramps are dull pain in the abdomen that
occurs intermittently during the menstrual period due to
contractions of the uterus. Here, a system that utilizes
electrical muscle stimulation (EMS) is proposed to enable
users to experience menstrual cramps. Through EMS,
users of this system can experience menstrual cramps in
their abdomen while performing daily movements. As a
result, men will be able to overcome the physical barri-
ers of different bodily structures to experience menstrua-
tion in their own bodies and understand the daily incon-
veniences associated with it. Women will be able to com-
pare their own menstrual cramps with the pain caused by
electrical stimulation and evaluate the cramps objectively.
In this way, the system will help eliminate the perceptions
of menstruation as “inexpressible, subjective, and diffi-
cult to communicate.” This will contribute to achieving
Sustainable Development Goal 3 (“Ensure healthy lives
and promote well-being for all at all ages”) and Goal 5
(“Achieve gender equality and empower all women and
girls”) [a].
Accordingly, experiments will be conducted to investi-
gate the reproducibility of menstrual cramps using EMS.
Also, a demonstration system based on the proposed
method is constructed and the usefulness of reproducing
menstrual cramps is confirmed through two exhibitions.
Journal of Robotics and Mechatronics Vol.33 No.5, 2021 1051
https://doi.org/10.20965/jrm.2021.p1051
© Fuji Technology Press Ltd. Creative Commons CC BY-ND: This is an Open Access article distributed under the terms of
the Creative Commons Attribution-NoDerivatives 4.0 International License (http://creativecommons.org/licenses/by-nd/4.0/).
Asada, C. et al.
2. Related Work
2.1. Experiment Pain and VR
VR technology enables users to navigate through
highly immersive VR spaces and experiences. It is partic-
ularly effective in treating various psychiatric disorders,
such as anxiety disorders and phobias [3], and in reduc-
ing anxiety during painful treatments such as burns and
cancer [4–6]. Therefore, it is used in various clinical
fields [7, 8]. Several studies have confirmed the effec-
tiveness of VR in clinical settings by exposing healthy
participants to simulated pain (experimental pain) [9–17].
Consequently, it was discovered that VR can increase pain
tolerance and thresholds as well as reduce pain intensity
and discomfort.
Also, VR technology can share various physical bur-
dens with others. For example, CHILDHOOD [18] al-
lows adults to share the physical constraints of children
by experiencing the small hands and low perspective of
children. Some studies have investigated the effect of
children’s sense of body ownership, which was repro-
duced by VR technology such as head mount display, on
adults’ perception [19, 20]. Mommy Tummy [21] sim-
ulates the physical burden of pregnancy. The Urinary
Incontinence Experience Device1 allows people to share
their experiences of urinary incontinence. Ozaki et al. [b]
proposed a “Menstrual Machine” that simulated the av-
erage five-day menstrual process and bleeding in women
through blood distribution systems and electrical stimu-
lation. Peck et al. [22] and Maister et al. [23] used VR
technology to understand body ownership and study its
effects on racial bias and social cognition. Some studies
have investigated the use of VR technology to immerse
oneself in the body of another person and observed its
consequences [24, 25]. Woebken et al. [c] proposed a sys-
tem that helps users understand nature and its phenomena
by recreating the perspective of insects and animals.
However, these works did not attempt to quantify pain
by recreating and sharing it based on an actual user’s
experience. Also, these works could not facilitate mu-
tual understanding and verbalizing of subjectively experi-
enced discomfort. Effectively reproducing pain and dis-
comfort is a promising way to facilitate mutual under-
standing and enable the quantification of pain and discom-
fort caused by various diseases, which is often subjective.
2.2. Pain Sensation Types
In this section, we describe the types of pain sensations
with reference to previous studies [26, 27]. Pain can either
be “somatic,” which is mainly felt in the skin or muscles,
or “visceral” such as menstrual cramps. Somatic pain is
further classified into superficial pain, which is experi-
enced on the skin surface, and deep pain, which is sensed
in the muscles and joints. The perceived location of deep
and visceral pain is unclear. Moreover, pain is divided into
first and second pain, according to its nature. First pain is
1. https://urealabyrinth.wixsite.com/incontinence [Accessed September 24,2021]
a sharp, pricking pain that travels up the Aδ fibers of the
peripheral nerves. Meanwhile, second pain is a deep and
visceral pain that travels up the C fibers of the peripheral
nerves.
EMS has been used to generate muscle contractions by
applying electricity to the muscles. Typically, it causes
dull pain when the muscle is contracted. In particular,
dull pain is caused by strong muscle contraction, which
compresses blood vessels; thus, causing muscle ischemia
and the release of pain-producing substances [28].
2.3. Pain Sensation and Mechanism in Menstrual
Cramps and EMS
Menstrual cramps (primary dysmenorrhea) are known
to have a high prevalence in younger women [29] and are
a pain in the uterus that arises without organic cause [30].
This pain is characterized by dull pain that lasts for
some time. These pains are caused by prostaglandins,
which cause the uterus to contract. Higher levels of
prostaglandins trigger stronger contractions [31]. Strong
uterine contractions reduce blood flow in the uterus, caus-
ing it to become hypoxic (ischemic). The mechanism of
uterine muscle contractions causes menstrual cramps.
Here, we aim to reproduce the dull pain that appears
and disappears with uterine contractions using EMS.
EMS can cause dull pain due to muscle contraction, and
the characteristics of EMS pain are similar to those of
menstrual cramps. Therefore, we hypothesized that mus-
cle contraction induced by electrical stimulation could re-
produce the pain of menstrual cramps with similar char-
acteristics. However, the extent to which EMS can re-
produce menstrual cramps and the appropriate EMS tech-
nique to be utilized for this purpose remain unclear.
3. EMS-Based Menstrual Experience System
An experiment was conducted to evaluate the similar-
ity between actual and EMS-induced menstrual cramps.
The participants were 33 female university students aged
between 18 and 30 years of age. The experiment
was approved by the Ethics Review Committee of Nara
Women’s University. The period during which the partic-
ipants did not have strong symptoms of menstrual cramps
was avoided.
3.1. Stimulation Method
Figure 1 shows the proposed EMS system. This system
consisted of a control board, an Arduino, a power supply,
and two electrode pads.
(a) Power supply
The power supply used was P4K36-1 (Matsusada Pre-
cision Inc., Japan) with voltage control. The voltage was
set to be updated every 0.1 s using the supplied SDK and
Unity to change the strength of electrical stimulation. The
maximum current was set to 20.7 mA while assuming the
human body resistance to be 1 kΩ. A DC form setting
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Electrical Muscle Stimulation to Develop Menstrual Simulator System
Fig. 1. Proposed EMS system.
Fig. 2. Frequency and pulse width of electrical stimulation.
was used. Also, the current control program had built-in
safety measures, such as overcurrent protection, to protect
the participant. Furthermore, if the participant could not
handle the pain, the experience could be terminated.
(b) Arduino
Arduino Uno Rev3 was used to control the timing of
electrical stimulation. The updated rate was 100 Hz.
A voltage was alternately applied to the two electrode
pads (Fig. 2). The pulse width was 0.01 s, and the fre-
quency of stimulation was 50 Hz. The parameters that
made up the EMS, such as the DC form, update rate, fre-
quency, and pulse width, were determined from prelim-
inary experiments. These experiments were conducted
using conventional EMS systems by two female partici-
pants.
(c) Two electrode pads
The two electrode pads and their attachment procedure
are described as follows:
1. To reduce the electrical resistance of the skin [32],
the skin surface of the participant’s abdomen was
wiped with wet tissue.
2. Participants were asked to tighten their abdominal
muscles, and a female experimenter palpated them
to determine the location of their lower rectus abdo-
minis muscle. This was because the position of the
rectus abdominis muscle is different for each indi-
vidual.
3. Two electrode pads (Axelgaard Manufacturing Co.,
Ltd.) were attached to the participants’ bodies in the
lower part of the rectus abdominis. The surface area
of each electrode pad was 45 cm2. The electrode
pads were positioned on the lower part of the rectus
abdominis muscle (identified by palpation) and sym-
metrical with the participant’s navel in between.
4. The electrode pads were fixed from the outside using
an elastic belt.
As an additional safety measure, the participants could
disconnect the electrode pads from the control board with
a power supply at the electrode connections.
3.2. Change Stimulation Strength
The EMS’s strength was varied over time to reproduce
a menstrual cycle’s pain.
A preliminary experiment was conducted on two fe-
male participants to evaluate the electrical stimulus that
caused the strongest sensation of dull pain associated with
muscle contraction. As a result, one participant chose a
stimulus with a voltage varying at 2 V/s, and the other
chose a stimulus with a voltage varying in a sinusoidal
function. Based on these results, we hypothesized that
the differences in the rate of change in the strength of
the electrical stimulus would affect the sensation of pain.
Specifically, we inferred that the larger the change rate,
the stronger the sensation of deep pain and the greater the
reproducibility of menstrual cramps.
In the experiment, three types of electrical stimulations
were used to explore the effect of the change rate on pain
sensation (Fig. 3).
• “wave 1” changed by 1 V/s. This stimulus had
the smallest rate of change among the three stimuli
types.
• “wave 2” varied by 2 V/s, which was twice the
change rate of wave 1.
• “wave 3” varied following a sine function. The
change rate was not constant: it changed rapidly in
the middle of the increase.
3.3. Experimental Procedures
i) Table 1 presents the questionnaire items. In the sub-
jective evaluation of menstrual cramps, the period
during which the participant felt the worst menstrual
cramps was specified. This was because it was nec-
essary to consider individual differences in the du-
ration and intensity of menstrual cramps. The word
groups listed in Tables 1-Q2 and 2-Q4, were selected
and presented since they were thought to be neces-
sary for evaluating menstrual cramps [33].
ii) Using wave 1, we adjusted the maximum current
value to suit the participants so that the pain they felt
did not exceed their own menstrual cramps. In the
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Asada, C. et al.
Fig. 3. Presented electrical stimulation.
Table 1. Questionnaire before the experiment (NRS: numeric rating scale).
Question Evaluated methods
Q1: How painful are your menstrual cramps in general? 11-step NRS: 0 = “no pain,” 5 = “painful,” and 10 = “excruciating pain.”
Q2: Please select the type of pain of menstrual cramps
that applies to you from the word group.
(Multiple answers are possible.)
Select multiple words from the following groups:
“stabbing pain,” “sharp pain,” “scalding pain,” “aching pain,” “penetrat-
ing pain,” “cramping pain,” “pain felt from deep within the body,” “dull
pain,” “pricking pain,” and “throbbing pain.”
Table 2. Questionnaire (NRS: numeric rating scale).
Question Evaluated methods
Q1: How painful was the electrical stimulation, com-
pared to your normal menstrual cramps?
11-step NRS: 0 = “less than half,” 5 = “approximately the same amount
of pain as usual,” and 10 = “more than twice.”
Q2: Where was the location stimulated by the electrical
stimulation?
11-step NRS for depth: 0 = “shallower than usual, superficial to the skin,”
5 = “where menstrual cramps are usually felt,” and 10 = “deeper than
usual, deep to the body.”
3-step NRS for height: above, same, or below navel.
Q3: Does the presented electrical stimulus resemble
normal menstrual cramps?
11-step NRS: 0 = “not menstrual cramps” and 10 = “similar to usual
menstrual cramps.”
Q4: Please select the type of pain that corresponds to
the presented electrical stimulus.
(You may choose multiple answers.)
Select multiple words from the following groups:
“stabbing pain,” “sharp pain,” “scalding pain,” “aching pain,” “penetrat-
ing pain,” “cramping pain,” “pain felt from deep within the body,” “dull
pain,” “pricking pain,” and “throbbing pain.”
experiment, we prepared five settings for the maxi-
mum current: 4.1 mA, 8.2 mA, 12.4 mA, 16.6 mA,
and 20.7 mA. Also, presenting the electrical stimuli
before the experiment reduced the effect of the order
because it caused habituation to the electrical stim-
uli.
iii) One type of electrical stimulus was applied to the
participants for two consecutive cycles. When the
participants requested an additional stimulus presen-
tation, the same type of stimulus was presented for
one cycle.
iv) Participants were asked to evaluate the stimuli. Users
completed another questionnaire (see Table 2).
Processes iii) and iv) were repeated for the three types
of electrical stimulation which were presented in random
order.
4. Results and Discussion
4.1. Questionnaire Items
Figure 4(a) shows the results of the participants’ re-
sponses to the degree of their own menstrual cramps. The
results showed a mean value of 4.97. Also, when some
participants responded to the question, the following com-
ment was obtained: “I was unaware of how painful my
menstrual cramps were.” Based on these responses, we
concluded that the question was effective in guiding the
participants to recognize how painful their natural men-
strual cramps were.
Figure 4(b) shows the number of participants per max-
imum allowable current value. Owing to missing data,
we considered a total of 32 participants. Table 1-Q1 pro-
vides the correlation coefficient between the results of the
answers, and the number of participants per maximum al-
lowable current value as 0.39. This weak positive cor-
relation indicated that participants who experienced men-
strual cramps tended to have a higher pain threshold when
experiencing electrically stimulated menstrual cramps.
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Electrical Muscle Stimulation to Develop Menstrual Simulator System
(a) Participants’ evaluation
of the level of pain of nat-
ural menstrual cramps.
(b) Number of participants
per maximum allowable
current value.
(c) Participants’ evaluation of the degree of pain induced by
varying electrical stimulation.
(d) Results showing the location of the electrically stimulated
pain.
(e) Comparison of the similarity between the presented elec-
trical stimuli and menstrual cramps.
(f) Descriptions and number of responses indicating they are common to both natural and electrically stimulated menstrual
cramps (low and high).
Fig. 4. Evaluation results.
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Asada, C. et al.
Next, the results from Tables 2-Q1 to 2-Q4 were ana-
lyzed by grouping the participants according to their usual
degree of pain from menstrual cramps. The following two
categories were used: low group, participants marked 0–4
in Table 1-Q1, and high group, participants who marked
5–10 in Table 1-Q1.
Figure 4(c) shows the results of the participants’ eval-
uation of the degree of pain induced by EMS. The mean
values for the low and high groups were 5.02 and 4.04,
respectively. Two one-sided tests (TOST) were con-
ducted on the results of each evaluation in Table 2-Q1
and dummy data with a value of five, which is a scale
of pain equivalent to usual menstrual cramps, at a sig-
nificance level of 5% and an equivalence margin of 2.0.
Equivalence was observed in the results of all types of
electrical stimulations in both the low and high groups.
These results demonstrated that the pain induced by the
three electrical stimuli was comparable to actual men-
strual cramps. This indicated that the reproducibility of
the degree of pain in menstrual cramps using electrical
stimulation was high.
The results plotted in Fig. 4(d) indicate the location
where the electrical stimulation was felt. The mean values
for the low and high groups were 2.67 and 3.14, respec-
tively. TOST was conducted on the results of each evalu-
ation in Table 2-Q2 and dummy data with a value of five,
which was a scale equivalent to the depth of feeling usual
menstrual cramps, at a significance level of 5% and an
equivalence margin of 2.0. Equivalence was not observed
in the results of any electrical stimulation in either the low
or high groups. This indicated that the location where the
participants felt the electrical stimulation was more super-
ficial than the location of actual menstrual cramps.
Figure 4(e) shows the similarities between the pre-
sented electrical stimuli and menstrual cramps based on
a comparative evaluation. The mean values for the low
and high groups were 4.69 and 5.68, respectively. The
results indicated that the similarity induced by electrical
stimuli was approximately half of that caused by natural
menstrual cramps.
The correlations between the answers to each question
regarding EMS were evaluated. The correlation coeffi-
cients for each element in Tables 2-Q1 and 2-Q3 were
−0.17, 0.44, and 0.54 for waves 1, 2, and 3, respectively,
in the low group; and 0.62, 0.46, and 0.64 for waves 1, 2,
and 3, respectively, in the high group. The correlation co-
efficients for each element in Tables 2-Q2 and 2-Q3 were
−0.71, 0.33, and 0.82 for waves 1, 2, and 3, respectively,
in the low group; and 0.65, 0.56, and 0.60 for waves 1, 2,
and 3, respectively, in the high group. Interestingly, the re-
sults in Table 2-Q1, regarding the painfulness of the elec-
trical stimulation compared to natural menstrual cramps,
had a lower correlation with the results of Table 2-Q3,
compared to Table 2-Q2. Therefore, the factor related to
the reproducibility of menstrual cramps by electric stimu-
lation was the location of pain and not its degree.
Furthermore, we conducted a two-factor analysis of
variance (ANOVA) to investigate the effect of the types
of electrical stimulation on each question. These factors
were the group of participants (between-participants fac-
tor) and the three types of electrical stimulation (within-
participants factor). The interaction was significantly
different (F(2,62) = 3.18, p = 0.049), (see Table 2-
Q1). Furthermore, the results of multiple comparisons
(Ryan’s method) revealed a significant difference be-
tween the types of electrical stimulation in the low group
(F(2,62) = 5.82, p = 0.048). Moreover, a significant dif-
ference was observed between the degree of pain induced
by waves 1, 2, and 3 (Fig. 4(c)).
Figure 4(f) graphs the results obtained for Tables 1-Q2
and 2-Q4. The most common response related to actual
menstrual cramps was “dull pain” with 11 participants in
the low group and 14 participants in the high group not-
ing it. This result suggested that menstrual cramps were
essentially dull pain, which was the characteristic of vis-
ceral pain. Also, 11 participants in the high group selected
“pain felt from deep within the body.”
As for the selection of the quality of the pain of the
electrical stimulation, “dull pain” was selected by more
than six participants in the high and four participants the
low groups. These results implied similarities between
dull pain caused by muscle contraction and that caused
by uterine contraction.
Meanwhile, the number of participants who chose
“pricking pain” in the EMS evaluation was 13, 17, and
16 for waves 1, 2, and 3, respectively. Also, there were
more participants who felt “penetrating pain” and “cramp-
ing pain” compared to their own menstrual cramps. We
considered that these pains were sharp pain caused by the
electric sensation perceived on the skin. Since this pain
was unique to electrical stimulation from the skin sur-
face, it made the perceived location of pain shallow. Also,
because of the different nature of electrical stimulation-
specific pain, it might have interfered with the perception
of dull pain due to muscle contraction.
In the free description column, the participants com-
mented that, “the original menstrual cramps exhibit more
intense variations, and the duration of the strong contrac-
tion sensation is much longer than that in the menstrual
cramps reproduced by this system.”
4.2. Overall Discussion
From the experimental results, the menstrual cramps
using EMS were comparable to the degree of pain, but
the perceived location of the pain was shallow. Moreover,
the dissimilarity in stimuli-induced pain and normal men-
strual cramp-induced pain was an unresolved issue. We
considered that the low reproducibility of the perceived
location of EMS-induced pain reduced its similarity to its
natural counterpart. Also, dull pain using EMS shared
this common property with the pain caused by uterine
contractions. From these results, menstrual cramps using
EMS reproduced the nature of periodic dull pain; how-
ever, deepening the pain location remained a challenge.
The major problem in reproducing menstrual cramps us-
ing EMS was the electrical sensation perceived on the skin
surface. This sensation lowered the reproduction of pain
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Electrical Muscle Stimulation to Develop Menstrual Simulator System
using EMS because it caused the perceived position to be
shallower and the difference in the quality of the pain was
felt more strongly. By reducing the effect of electrical
stimulation on the skin surface in the future, it would be
possible to achieve an EMS system that better reproduces
menstrual cramps. For example, a previous study [32] in-
dicated that variations in skin impedance caused electrical
pain sensation. Therefore, real-time feedback of the skin
impedance of the abdomen could reduce pain, as proposed
in a previous study [34]. Also, using high-frequency elec-
trical stimulation of 10 kHz to 100 kHz to stabilize the
skin impedance [35], electrode pads that better adhere to
the skin than the current ones should be considered.
Before the experiment, it was hypothesized that the dif-
ferences in the rate of change in the strength of the elec-
trical stimulus would affect pain sensation. The results of
the verification showed that the rate of change in strength
affected only the degree of pain. Especially in the low
group, the result of wave 1 was significantly higher, and
the degree of pain was more painful than that of menstrual
cramps. The rate of change in the strength of wave 1 was
the smallest among the three types of electrical stimula-
tion. This prolonged the participants’ perception of pain,
which might have caused them to feel a stronger degree
of pain than their own menstrual cramps. Based on these
results, it was suggested that waves 2 and 3, which had
mean values close to five, were more likely to reproduce
the degree of pain. Furthermore, because there were no
significant differences between Tables 2-Q2 or 2-Q3 and
the three types of stimuli, the rate of change in strength
did not affect the perceived location or similarity of the
electrical stimuli. In the future, the method of electrical
stimulation to reproduce more natural menstrual cramps
through EMS will be reviewed. Also, in future studies it
needs to be verified whether participants’ perceptions of
menstruation have changed through this experience.
Also, our study had four other limitations that will be
addressed in future research.
1. Order of presenting electrical stimuli affected the sen-
sation.
Three types of electrical stimuli were presented in ran-
dom order because the effect of the order could affect
the impression of the electrical stimulus. To understand
this effect, we conducted a two-factor ANOVA, in which
the between-participants factor was the group of partici-
pants, and the within-participants factor was the order of
presentation of the electrical stimuli (without distinguish-
ing the three types of electrical stimuli). For the order
of presentation of the electrical stimuli, there were sig-
nificant differences and tendencies between the results of
Table 2-Q2 (F(2,62) = 3.52, p = 0.036) and Table 2-Q3
(F(2,62) = 2.82, p = 0.067), respectively. Fig. 5 shows
the results of multiple comparisons (Ryan’s method). The
rating at the first presentation of Table 2-Q2 was signifi-
cantly lower, indicating that the participants strongly felt
the pain acting on the skin surface. It was believed that
this was the reason why the evaluation at the first pre-
sentation of Table 2-Q3, which represents the similarity
Fig. 5. Tables 2-Q2 and 2-Q3 results of the analysis of
variance for presentation order.
of the electrical stimuli, was significantly lower. Further-
more, the participants in the high group were considered
to be not sufficiently accustomed to the electric stimulus
at the first presentation in the experiment. However, be-
cause three types of electrical stimuli were presented in a
random order, the effect of the order was reduced in this
experiment.
2. The electrical stimulation was weaker than the actual
menstrual cramps experienced by some participants.
For safety reasons, the maximum current was limited to
20.7 mA. However, participants whose usual evaluation of
menstrual cramps was close to “10” evaluated the electric
stimulation of 20.7 mA as “almost painless compared to
actual menstrual cramps.” This was seen in the “0” rating
Journal of Robotics and Mechatronics Vol.33 No.5, 2021 1057
Asada, C. et al.
for each question. Therefore, the maximum current of
the current system should be set higher in the future to
achieve a better evaluation. However, to raise this upper
limit of the current, it will be necessary to introduce a finer
setting for safety reasons.
3. Individual differences in participants’ menstrual symp-
toms were not fully considered.
Several participants opined in the free descriptions and
comments that “evaluation is difficult during menstrual
cramps because back pain, not abdominal pain, is strongly
expressed.” This was consistent with a previous study [1]
in which abdominal and back pain were cited as the main
unpleasant symptoms during menstruation. Here, the
characteristics of participants were divided by the degree
of pain of actual menstrual cramps, but it was impossi-
ble to say whether individual differences were sufficiently
considered in the evaluation. In the future, it would be
necessary to add factors that consider more detailed indi-
vidual differences, such as the perceived location of men-
strual cramps and the intensity of symptoms of back and
abdominal pain, to evaluate electrical stimulation.
4. The electrode pad could not be attached to the correct
location.
The experimenter confirmed the location of the lower
part of the rectus abdominis muscle by palpation to at-
tach the electrode pads on it. However, this method had
the problem that it depended on the experience of the per-
son conducting the experiment. Furthermore, we found
that the individual differences in the location of the rec-
tus abdominis muscles were larger than expected. There-
fore, we thought that there was a possibility that the par-
ticipants could not sense the expected stimulus through
the experiments. In other words, some participants could
not perceive the expected stimulus because of incorrect
placement of the electrode pads. Thus, to reduce the influ-
ence of various individual differences, we should confirm
whether the electric stimulus is correctly presented to the
lower part of the rectus abdominis muscle.
5. Exhibiting the Menstrual Experience
System
5.1. Configurating the Exhibition System
An exhibition system was developed using an EMS
that allowed visitors to experience menstrual symptoms
(Fig. 6(a)).
Menstrual symptoms include not only the physical an-
noyance of menstrual cramps and the sensation of men-
strual blood leakage, but also having normal behaviors
restricted by menstrual symptoms. This means feeling
anxious about certain activities (such as sitting, walk-
ing, or standing) that might worsen menstrual leakage or
cramps. Thus, menstrual symptoms and discomfort asso-
ciated with menstrual symptoms are so complex that it is
difficult to verbalize and share their inconvenience.
(a)
(b)
Fig. 6. (a) System configuration of demonstration system.
(b) Actual experience in exhibition.
Our system allowed users to experience not only the
physical annoyance of menstrual cramps and the sensa-
tion of menstrual blood leakage, but also the mental an-
noyance of having their activities restricted by menstrual
symptoms. Therefore, though the reproducibility of the
electrical stimulation was partial, it was highly effective
as a demonstration to comprehensively understand the an-
noyance of menstrual symptoms.
Through electrical stimulation, this system reproduced
menstrual cramps in users’ abdomens during their daily
activities. A warm sensation was presented using a Peltier
device to reproduce the sensation of menstrual bleeding.
Also, electrical stimulation and warm sensations were
presented to reproduce the discomfort of behavioral re-
striction based on the posture of the user obtained from a
posture detection sensor.
〈 Bleeding sensation by thermal display 〉
Several studies have proposed using a Peltier device
for thermal displays [36, 37]. Here, heated Peltier devices
were used to convey the sensation of blood dripping onto
the inner thigh. The users wore three Peltier devices with
an elastic band that adhered to the skin on the inside of
their legs. They experienced the sensation of dripping
blood as each Peltier device was heated from the top to
the bottom of the leg. All the Peltier devices were 16 cm2
in size. To convey the sensation of slowly dripping blood,
1058 Journal of Robotics and Mechatronics Vol.33 No.5, 2021
Electrical Muscle Stimulation to Develop Menstrual Simulator System
the times at which the current was applied to each Peltier
device were different.
〈 Attitude detection sensor 〉
A Polhemus magnetic sensor was used to monitor the
state of the users. The magnetic sensor acquired their
position and posture, and the stimuli corresponding to
their current situation were applied through the EMS and
Peltier devices.
5.2. Menstrual Experience Flow
i) Explaining the experience and consent requisition:
The participants received an explanation of the safety
of the experiment and completed a consent form.
ii) Completing the questionnaire before the experience:
The participants completed a questionnaire about
menstruation.
iii) Attaching the device: Fixing the electrode pads us-
ing an elastic belt to prevent the electrode pads from
shifting owing to participants’ movement. Moreover,
Peltier and Polhemus sensors were attached to the
legs.
iv) Adjusting the maximum current value for each par-
ticipant: This process was performed to avoid any
mental/physical discomfort. The adjustment started
with a maximum current of 8.2 mA; if it could be tol-
erated without inconvenience, the maximum current
was increased gradually. For participants who could
not tolerate 8.2 mA, a lower output value adjustment
was made. If the participant felt that they could not
tolerate the current beyond a certain point, it was set
as the maximum current for electrical stimulation.
v) Experiencing menstrual symptoms in different sit-
uations: The participants experienced menstrual
symptoms for daily activities, such as standing, sit-
ting, and moving back and forth in a crowded train
(Fig. 6(b)). As train-related behaviors were the same
for everyone, it was possible to intuitively under-
stand the impact of menstrual symptoms. In par-
ticular, standing in a crowded urban train is diffi-
cult for anyone because the number of passengers
is considerably high; people are usually squeezed in
close proximity or rocked by the train. By combin-
ing a crowded train situation with a device that re-
produced menstrual cramps, the discomfort caused
by menstruation in situations that could not be con-
trolled was better understood.
vi) Completing the questionnaire after the experience:
The participants completed a questionnaire after par-
ticipation. This questionnaire and pre-experience
questionnaire helped participants understand the
changes in how they perceived menstruation.
5.3. Demonstration Exhibit
We demonstrated the use of this system at domestic
exhibitions.2,3 This study included 10 women and 41 men.
The female participants commented that the experience
was “realistic” and “more similar to the sensation of men-
struation than they imagined.” One female participant was
surprised at the individual differences in menstrual symp-
toms because she felt stronger cramps from the electri-
cal stimulation than her own menstrual cramps. Based
on these responses, it was believed that it was possible
to bridge the gap in perceptions regarding individual dif-
ferences in menstrual symptoms. The male participants
confessed, “I can’t believe that the pain and symptoms
I experienced will last for about a week,” and “it is dif-
ficult for me to endure this pain in a crowded train, and
I would like to give up my seat to a woman the next time
I ride a train”; this indicated that the experience changed
their perception of menstruation.
From these participants’ reactions, we concluded that
this experience could help verbalize menstrual cramps
and allow people to better understand menstruation. Si-
multaneously, the system created an opportunity to dis-
cuss individual differences in menstrual symptoms and
cramps. Also, by viewing the experiences of other users,
people understood their reactions and developed an inter-
est in the topic of menstruation. In other words, through
this experience, both men and women had the opportunity
to change their current perception of menstruation.
6. Conclusion
Here, a system was proposed that enabled users to ex-
perience menstrual cramps through an EMS. To reveal the
reproducibility of menstrual cramps induced by electri-
cal stimulation, natural menstrual cramps and electrically
stimulated menstrual cramps were compared. The results
showed that menstrual cramps using EMS could repro-
duce the nature of periodic dull pain, although there is
room for improvement in reproducing the depth at which
the pain occurs. Also, the experiment revealed some is-
sues with the current system. Furthermore, studies have
shown that reproducing menstrual cramps could help ver-
balize menstrual cramps and allow people to better under-
stand menstruation. In other words, this experience will
help eliminate negative perceptions of menstruation.
In the future, we plan on improving the system to in-
crease the reproducibility of menstrual cramps and stan-
dardize the experimental conditions so that more appro-
priate evaluations can be made.
Acknowledgements
We would like to express our sincere gratitude to Mr. Azuma,
Mr. Ishida, Mr. Goda, and Mr. Asahi of the IVRC2019 menstru-
ation experience team of Konan University for their cooperation
2. http://ivrc.net/2019/ [Accessed September 24, 2021]3. https://www.konan-u.ac.jp/front/front/wp/wpcontent/uploads/
ScienceFairPoster3.pdf [Accessed September 24, 2021]
Journal of Robotics and Mechatronics Vol.33 No.5, 2021 1059
Asada, C. et al.
in developing this study since 2019. This work was supported by
JSPS KAKENHI Grant Numbers JP17H01956 and JP21H00807.
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1060 Journal of Robotics and Mechatronics Vol.33 No.5, 2021
Electrical Muscle Stimulation to Develop Menstrual Simulator System
Name:Chihiro Asada
Affiliation:Major in Human Centered Engineering, Grad-
uate School of Humanities and Sciences, Nara
Women’s University
Address:Kitauoyanishimachi, Nara 630-8506, Japan
Brief Biographical History:2016-2020 Undergraduate Student, Konan University
2020- Graduate Student, Nara Women’s University
Main Works:• International Collegiate Virtual Reality Contest (IVRC 2019), the
Special Judge’s Award
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
• The Institute of Electronics, Information and Communication Engineers
(IEICE)
Name:Kotori Tsutsumi
Affiliation:Major in Human Centered Engineering, Grad-
uate School of Humanities and Sciences, Nara
Women’s University
Address:Kitauoyanishimachi, Nara 630-8506, Japan
Brief Biographical History:2016-2020 Undergraduate Student, Konan University
2020- Graduate Student, Nara Women’s University
Main Works:• International Collegiate Virtual Reality Contest (IVRC 2019), the
Special Judge’s Award
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
• The Institute of Electronics, Information and Communication Engineers
(IEICE)
Name:Yuichi Tamura
Affiliation:Professor, Department of Information and Infor-
matics, Konan University
Address:8-9-1 Okamoto, Higashinada, Kobe 658-8501, Japan
Brief Biographical History:1995- Sumitomo Electric Industries, Ltd.
1998- National Institute for Fusion Science
2008- Konan University
Main Works:• “Haptization on Numerical Simulation of Plasma,” IEEE Trans. on
Plasma Science, Vol.38, No.10, pp. 2974-2979, 2010.
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
• The Institute of Electronics, Information and Communication Engineers
(IEICE)
• The Japan Society for Simulation Technology (JSST)
• The Institute of Electrical Engineers of Japan (IEEJ)
• Association for Computing Machinery (ACM)
Name:Naoya Hara
Affiliation:Department of Bioinformatics, Graduate School
of Information Science and Technology, Osaka
University
Address:1-1 Yamadaoka, Suita, Osaka 658-8501, Japan
Brief Biographical History:2016-2020 Undergraduate Student, Konan University
2020- Graduate Student, Osaka University
Main Works:• International Collegiate Virtual Reality Contest (IVRC 2019), the
Special Judge’s Award
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
• The Institute of Electronics, Information and Communication Engineers
(IEICE)
Journal of Robotics and Mechatronics Vol.33 No.5, 2021 1061
Asada, C. et al.
Name:Wataru Omori
Affiliation:School of Knowledge Science, Japan Advanced
Institute of Science and Technology
Address:1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
Brief Biographical History:2017-2021 Undergraduate Student, Konan University
2021- Graduate Student, Japan Advanced Institute of Science and
Technology
Main Works:• International Collegiate Virtual Reality Contest (IVRC 2019), the
Special Judge’s Award
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
Name:Yuta Otsuka
Affiliation:Graduate School of Simulation Studies, Univer-
sity of Hyogo
Address:7-1-28 Minatojimaminamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
Brief Biographical History:2016-2020 Undergraduate Student, Konan University
2020- Graduate Student, University of Hyogo
Main Works:• International Collegiate Virtual Reality Contest (IVRC 2019), the
Special Judge’s Award
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
Name:Katsunari Sato
Affiliation:Nara Women’s University
Address:Kitauoyanishimachi, Nara 630-8506, Japan
Brief Biographical History:2008- JSPS Research Fellow (DC1), The University of Tokyo
2011- JSPS Research Fellow (PD), Keio University
2013- Nara Women’s University
Main Works:• “Presentation of Rapid Temperature Change using Spatially Divided Hot
and Cold Stimuli,” J. Robot. Mechatron., Vol.25, No.3, pp. 497-505, Jun.
2013.
Membership in Academic Societies:• The Virtual Reality Society of Japan (VRSJ)
• The Society of Instrument and Control Engineers (SICE)
• Japan Society of Kansei Engineering (JSKE)
1062 Journal of Robotics and Mechatronics Vol.33 No.5, 2021
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