Electrical Muscle Stimulation to Develop and Implement ...

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: [email protected]∗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

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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

1052 Journal of Robotics and Mechatronics Vol.33 No.5, 2021


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


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.



(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.


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



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


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,



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]


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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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



2020- Graduate Student, Nara Women’s University





(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.



(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


2020- Graduate Student, Osaka University





(IEICE)


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


2021- Graduate Student, Japan Advanced Institute of Science and

Technology




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


2020- Graduate Student, University of Hyogo




Name:Katsunari Sato

Affiliation:Nara Women’s University


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.


• The Society of Instrument and Control Engineers (SICE)

• Japan Society of Kansei Engineering (JSKE)


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