Development of a Proof-of-Concept Portable Electrostimulation

Device for Lower Limbs Blood Flow Enhancement

Ricardo Pinto

, Ana Almeida

, Inês Rocha

, Diogo Carvalho

, Alexander Oks

Miguel Carvalho

, João L. Vilaça

and Vítor Carvalho

2Ai, School of Technology, Polytechnic University Cávado and Ave, Barcelos, Portugal

Klinikum Landkreis Tuttlingen, Tuttlingen, Germany

Riga Technical University, Institute of Architecture and Design, Riga, Latvia

2C2T, School of Engineering, University of Minho, Guimaraes, Portugal

Keywords: Electrostimulation, Blood Flow, Portability, Lower Limbs, Well-Being, Wearable Device, Proof of Concept.

Abstract: This paper presents the design and implementation of a proof of concept of a wearable electrostimulation

device aimed at improving blood flow in the lower limbs. The portable system, integrated into wearable

compression socks, delivers electrical pulses for muscular stimulation in specific areas of the leg, using

conductive yarns in their structure, promoting better blood flow. This device addresses the growing sedentary

lifestyle and the resulting health issues like poor circulation, which can lead to severe complications. It

features Bluetooth Low Energy (BLE) communication for real-time session control via a mobile application.

The preliminary results demonstrate effective electrical stimulation, validated through testing, ensuring the

feasibility of the system.

1 INTRODUCTION

In modern society, sedentary lifestyles are

increasingly prevalent, characterized by prolonged

periods spent sitting, often in front of screens or

during commutes. This lack of physical activity leads

to insufficient stimulation of the lower limb muscles,

resulting in impaired blood circulation. Over time,

this condition can escalate to serious complications,

including chronic venous insufficiency, tissue

damage, and, in severe cases, lower limb failure.

Prolonged lack of circulation, if unaddressed, may

necessitate amputation and could even be fatal

(Higgins, et al., 2022). While physical exercise such

as walking or running is critical for maintaining

healthy blood flow, not everyone can engage in

https://orcid.org/0000-0002-4116-9377

https://orcid.org/0009-0005-6611-2720

https://orcid.org/0009-0009-7960-7748

https://orcid.org/0000-0002-4618-2474

https://orcid.org/0000-0001-6925-1842

https://orcid.org/0000-0001-8010-6478

https://orcid.org/0000-0001-6925-1842

https://orcid.org/0000-0003-4658-5844

regular activity due to professional, medical, or

personal constraints. Consequently, alternative

solutions, including pharmacological interventions

and devices designed to stimulate leg muscles and

enhance blood flow, have gained prominence as

viable approaches to mitigating these risks.

(Ashutosh , Dhaniwala, Dudhekar, Goyal, & Patel,

2023)

Currently, portable stimulation devices are

predominantly designed for the abdominal region,

offering limited applicability to other parts of the

body. For the lower limbs, existing equipment tends

to be large and cumbersome, requiring patients to

remain stationary, often lying on a stretcher, to

receive treatment. This lack of portability and

Pinto, R., Almeida, A., Rocha, I., Carvalho, D., Oks, A., Carvalho, M., Vilaça, J. L. and Carvalho, V.

Development of a Proof-of-Concept Portable Electrostimulation Device for Lower Limbs Blood Flow Enhancement.

DOI: 10.5220/0013396700003911

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 18th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2025) - Volume 2: HEALTHINF, pages 1007-1017

ISBN: 978-989-758-731-3; ISSN: 2184-4305

1007

practicality restricts their usability in daily life or

during routine activities.

In contrast, compression socks are widely used in

sports such as running and walking to improve blood

flow through passive pressure applied by the tightness

of the textile structure. However, these socks provide

only static compression and lack the capability to

actively stimulate lower limb muscles, which is

essential for enhancing venous return and addressing

more severe circulatory deficiencies.

This gap highlights the need for a portable, user-

friendly solution that combines the benefits of

compression socks with active muscle stimulation.

Such a device could be seamlessly integrated into

compression socks to provide dynamic, localized

stimulation, offering a more effective approach to

improving blood flow in the lower limbs. This

innovative approach would be particularly beneficial

for individuals with sedentary lifestyles, athletes

seeking enhanced recovery, and patients undergoing

rehabilitation.

In response to this need, a wearable device was

developed as a proof of concept to improve blood

flow in the lower limbs through targeted and

responsible use. This innovative device delivers

electrical pulses to stimulate specific muscle groups

in the lower legs, enhancing circulation and

promoting venous return.

The wearable system is designed to be compact

and portable, seamlessly integrating with

compression socks that conduct the electrical

stimulation to precise anatomical points. By

combining the passive benefits of traditional

compression with active muscle stimulation, this

device addresses the limitations of existing solutions.

A key feature of the device is its integration of

Bluetooth Low Energy (BLE) communication,

enabling remote control and customization through a

dedicated mobile application. This functionality

allows users to tailor treatment sessions, including

adjusting stimulation intensity and duration, to meet

individual therapeutic or preventative needs.

This paper is organized into five sections. Section

2 provides an overview of the concept of

electrostimulation, its application as a therapeutic

approach for humans, and the associated benefits.

Additionally, existing market solutions are reviewed

to identify gaps and opportunities for improvement in

addressing lower limb blood flow issues. Section 3

introduces the proposed solution, detailing its

development across three core components: hardware,

firmware, and software. This section outlines the

design process, technical specifications, and

integration of these elements to create a functional

and effective wearable device. Section 4 focuses on

validation tests and results. This includes an

evaluation of the device’s performance, a

demonstration of its usability, and a presentation of

the final product, which comprises a compression

sock enhanced with silver-plated textile yarn and the

wearable device with Bluetooth connectivity. Finally,

Section 5 summarizes the challenges, limitations, and

lessons learned throughout the development process.

Potential areas for improvement are discussed, along

with suggestions for future iterations to enhance the

device’s functionality and usability in subsequent

versions of the project.

2 STATE OF ART

Electrostimulation devices are widely available today,

with each system employing its own unique

mechanisms of operation. Muscle electrostimulation

involves the application of an electric current—

typically low or medium frequency—through

electrodes positioned on the skin. This technique can

induce muscle contractions, facilitating functional

movements or enhancing muscle strength to improve

physical performance.

Electrostimulation systems have found extensive

application in both physiotherapy and sports. They

are commonly used for the prevention, treatment, and

management of various disorders affecting the

neuromuscular system. When applied appropriately,

these systems represent a safe and effective method

for promoting neuromuscular function and improving

overall physical health (Sausport, 2024).

2.1 Electrostimulation

The use of electrostimulation dates to ancient times

when electric eels were employed to alleviate pain in

limbs. Over the centuries, advances in understanding

the effects of different waveforms on muscle and

nerve function have allowed for the safe and effective

application of electrostimulation to optimize patient

outcomes in alignment with specific care plans. A

fundamental understanding of the properties of

electricity and current flow is essential for the safe use

of electrostimulation on the human body.

Current flow is governed by its direct

proportionality to voltage and inverse proportionality

to resistance. Biological tissues exhibit varying

electrical properties: the skin, like nerve and muscle

membranes, possesses capacitance, enabling it to

store electrical charges and resist changes in current

flow. Meanwhile, skin and fatty tissues act as

WHC 2025 - Special Session on Wearable HealthCare

1008

resistors, opposing current flow. The current naturally

follows the path of least resistance within the body,

driven by ionic flow—positive and negative charges

attract, while like charges repel (Stillings D., 1975),

(Heidland, et al., 2013).

Figure 1 illustrates the working principle of

electrostimulation. The anode and cathode serve as

points of contact with the skin and carry opposite

charges. At the anode, negative ions migrate toward

the positive pole, resulting in increased acidity,

protein coagulation, and tissue hardening. Conversely,

at the cathode, positive ions migrate toward the

negative pole, causing increased alkalinity, protein

liquefaction, and tissue softening. These processes

contribute to improved circulation as the body strives

to restore homeostasis and maintain a neutral pH level

(College, 2024).

Figure 1: Principle of operation of electrostimulation.

Today, numerous commercial electrostimulation

solutions are available, each offering various control

modes and therapy session options. However, all

these systems are fundamentally based on two core

electrostimulation concepts (Digital, 2024):

• Muscle Electrostimulation (EMS) involves

the application of low-voltage stimuli,

typically with currents ranging from 80 to

100 mA and frequencies between 10 and 100

Hz. EMS primarily targets the motor nerve

fibres of muscles to induce muscle

contractions. This method is commonly used

for muscle strengthening and rehabilitation.

• Transcutaneous Electrical Nerve Stimulation

(TENS) is primarily employed for pain

management by blocking pain signals.

Unlike EMS, TENS uses electrodes placed

on sensitive nerve points rather than motor

nerve fibres. This stimulates the production

of endorphins and provides small electrical

impulses that activate pain-modulating

mechanisms in the body.

In summary, both EMS and TENS deliver

electrical impulses through electrodes placed on the

skin near the target area, but they serve distinct

purposes: TENS aims to alleviate pain, while EMS is

used to relax, strengthen, and improve muscle

function. The repetitive muscle contractions induced

by EMS promote enhanced blood circulation, prevent

muscle atrophy, stimulate muscle growth, aid in

muscle relaxation, and reduce inflammation.

Given the objective of this project—to develop a

device that enhances blood circulation—a Muscle

Electrostimulation (EMS) device was identified as

the most suitable choice due to its direct impact on

improving blood flow through muscle activation.

2.2 Current Solutions and

Standardization

By analysing several commercial models, we

identified several common characteristics, including:

• Wireless operation, powered by compact,

portable batteries.

• Simple electrodes and pads designed for skin

contact.

• Technical specifications, including voltage,

current, and frequency parameters.

In the context of available commercial solutions,

many devices exhibit similarities to the EM49 model

(Beurer, 2023), as shown in Figure 2. This model

exemplifies the standard design and functionality

commonly seen in the market.

Figure 2: Equipment EM49 (Beurer, 2023).

This equipment is manufactured by Beurer and

operates with a maximum voltage of 100Vpp and a

current of up to 200mA. Additionally, OMRON

produces devices such as the HeatTens (HV-F311-E)

(OMRON, 2023), which operates at 70V and can

generate 100µs pulses.

A significant portion of the scientific literature

focuses on the development of human-machine

interfaces, where users can control the activation and

deactivation of electrostimulation signals. However,

the electrostimulation signals themselves are

typically generated and managed by compact

commercial devices, such as power supplies, which

often lack advanced electrical consumption

management (De Almeida, Bertucci Borges, & de

Development of a Proof-of-Concept Portable Electrostimulation Device for Lower Limbs Blood Flow Enhancement

1009

Azevedo Dantas, 2022), (Özgüner, Alaca, Başkurt, &

Akman, 2021). Furthermore, some studies fail to

consider dynamic and user-centred interactions, as

many systems use static signals that cannot be

modified. In many cases, these solutions are

presented as mere proof-of-concept projects rather

than fully developed, functional systems (Velloso,

2005).

3 DEVELOPED WEARABLE

DEVICE

The developed solution consists of three main

components:

• Firmware: This component manages the

control of the electrostimulation waveform,

as well as the reception, processing, and

transmission of messages between the

system and the smartphone.

• Hardware: This encompasses all the

electrical circuits necessary for the system's

operation, including power supply, control

circuits, and actuation mechanisms.

• Software: A mobile application that enables

the creation, editing, and monitoring of

electrostimulation sessions.

Figure 3 illustrates the system architecture,

highlighting the key modules, including the

embedded system responsible for controlling the

electrostimulation of the socks through I/O signals.

The embedded system also facilitates Bluetooth

communication with the mobile application, enabling

seamless interaction and control.

Figure 3: Electrostimulation system architecture.

3.1 Firmware

The ESP32 (Espressif, 2023) was selected as the

microcontroller for the system due to its integrated

Bluetooth Low Energy (BLE) communication

capabilities and dual-core architecture, which allows

for the simultaneous execution of two tasks. The roles

of the two cores are as follows:

• Core 0: Responsible for the initial

configuration of interfaces, services, and

events. Once configured, it handles the

reception of messages and manages

notifications related to BLE characteristics.

• Core 1: Dedicated to processing and

executing the control of the

electrostimulation signal, ensuring proper

modulation and operation of the stimulation.

Figure 4 illustrates the operational workflow of

the electrostimulation module, focusing on the

firmware development and task management across

the two cores.

Figure 4: Configuration and operation of the electro-

stimulation module.

3.2 Hardware

The hardware module developed includes several

blocks, including battery management and signal

modelling.

3.2.1 Battery Management

One of the requirements of the system was to use an

internal lithium battery that could be charged via 5V,

the most common nowadays. The MCP73831-2-OT

(Farnell, 2023), was used to control battery charging

via USB. This is a low-cost and widely used

controller. Figure 5 illustrates the battery charging

circuit designed for the solution.

WHC 2025 - Special Session on Wearable HealthCare

1010

Figure 5: Lithium battery charging circuit.

3.2.2 Electrostimulation Signal Modeling

To model the electrical signal needed to stimulate the

muscle, the following steps are required:

 Raising the electrical voltage: The module's

battery was 3.7V, and it was needed to raise the

voltage (45V in this case).

 Limit current: Control the maximum current to

prevent damage to the user during

electrostimulation, such as electrical

discharges.

 Reverse current direction: To have a two-phase

signal, it was needed to change the current

direction.

In Figure 6, one can graphically see the various

blocks for modeling the electrical signal.

Figure 6: Electrical signal modeling.

Initially, to raise the voltage, were integrated two

booster circuits connected in series. An initial one that

powers up 3.7V to 5V and a second one that powers

up 5V to a maximum of 60V.

The TPS61022RWUR (Instruments, TPS61022 |

Buy TI Parts | TI.com, 2024) was used for the first

regulator, whose main function was to guarantee a

fixed 5V for the next regulator, even if the voltage

supplied by the battery decreases. It also has the

possibility of ON/OFF control, using the Enable pin.

The circuit developed for the first booster is

shown in Figure 7.

Figure 7: Circuit with the TPS61022RWUR.

Connected in series to the TPS61022RWUR is the

TPS55332QPWPRQ1 (Instruments, TPS55332-Q1 |

Buy TI Parts | TI.com, 2024). This booster can adjust

the output voltage up to 60V. Figure 8 shows the

module in the schematic developed.

Figure 8: Circuit with TPS55332QPWPRQ1.

The output voltage is set using the ratio of

resistors between the VREG and VSense pins,

according to the formula on the datasheet

(Instruments, TPS55332-Q1 | Buy TI Parts | TI.com,

2024). However, a potentiometer that has a range of

values within the desired range has been placed, so

fine-tuning is done a posteriori, and with the stability

of the system, the value of the precision resistor to be

placed to replace the potentiometer will be defined.

The voltage configuration circuit used in this project

is shown in Figure 9.

Development of a Proof-of-Concept Portable Electrostimulation Device for Lower Limbs Blood Flow Enhancement

1011

Figure 9: TPS55332QPWPRQ1 output voltage configura-

tion circuit.

In this way, it was possible to obtain a final output

voltage of 45V. Having that assured, it was necessary

to limit the current. It was used a current mirror

circuit, in which two BJT (Bipolar Junction

Transistor) transistors and a resistor guarantee a fixed

and stable current at the output.

Simulation software was used to help with the

development, and it was concluded that a resistance

of 2kΩ is needed to guarantee 20mA at 40V.

A potentiometer operating in the desired range of

values was placed in the module to be adjusted

according to the simulation and guarantee the output

current. The transistors selection was according with

the desired voltages and currents, resulting in the

circuit shown in Figure 10.

Figure 10: Portable module current mirror circuit.

With the voltage and current stabilized, it was

necessary to create a circuit capable of creating a two-

phase pulse. To do this, an H-bridge circuit was

developed. This circuit used mosfets controlled by

signals from the microcontroller. These control

signals were isolated using optocouplers to avoid

damaging the ESP32. All the components were

chosen according to the voltages and currents

circulating in this part of the circuit. The H-bridge

developed is shown in Figure 11.

Figure 11: H Bridge circuit developed.

3.2.3 PCB Layout and Properties

As far as the layout is concerned, all the rules required

by the component datasheets were considered, and

the result is shown in Figure 12.

Note that the components are only in the upper

part, with the lower part only containing the battery

connector.

Looking at Figure 12 one can see:

 Purple (1): USB type-C connector, charging

circuit and selector switch for disconnecting

the battery from the charger or from the circuit.

 Red (2): ESP32 with regulator and surrounding

circuitry (enable pin, boot pin, etc.).

 Orange (3): 3.7V battery to 5V converter.

 Blue (4): Converter from 5V to 45V, with

potentiometer for adjusting the output voltage.

 Green (5): Current limiting circuit, with

potentiometer for adjusting the maximum

current.



Yellow (6): H-bridge circuit with output for the

electrodes.

Figure 12: PCB layout by blocks.

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1012

Table 1 presents the final specifications of the

module.

Table 1: Specifications of the developed module.

Specification Value

Charging voltage 5V

Out

ut volta

e 45V

Batter

volta

e 3.7V

Maximum output

current

20mA

eratin

fre

uenc

–

100 Hz

Pulse width 50 uS

–

100 uS

nal t

e Two-

hase s

uare wave

3.3 Software

As previously referred the mobile application was

developed to act as a remote control for the

electrostimulation system. It includes the following

characteristics:

 Connecting to a Bluetooth Low Energy device.

 Creation of a new electrostimulation session.

 Add electrostimulation programmes to the

session.

 Edit electrostimulation session programs.

 Start and pause the electrostimulation session.

As referred, BLE was used for communication

between the stimulation module and the Smartphone

(Bluetooth Special Interest Group, 2023), which is the

most widely used communication in wearable health

devices. In this work, a service was created with four

characteristics:

 IsRunning – Indicates if a treatment session is

in progress.

 RemainingTime – Indicates the time remaining

until the end of the treatment session in

seconds.

 SendProgram – Characteristic where the

treatment session is sent from the Smartphone

to the electrostimulation module.

 StopProgram – Sending a message to stop the

session.

The mobile application was developed in .NET

MAUI (Microsoft, 2024). Figure 13 shows the

‘treatment session’ pages, which contains the session

created by the user and then sent to the module

(Figure 13 left).

Figure 13: Left: Treatment edition page. Right: Treatment

session page.

In Figure 13 right one can see the page for

selecting the programme to add to the treatment

session, as well as the duration of the session. It also

integrates brief information about the purpose of the

programme to be added.

The application currently has six programs to be

added to the treatment session, as shown in Table 2.

What differs between the programs is the frequency,

pulse length and activation and pause times.

By selecting the program for the

electrostimulation session, the user also sets the

duration.

As the programs are stored in the application, new

programs can be added in the future without having

to change the module's firmware.

Table 2: Electrostimulation programs available on the mobile application.

Program Frequency (Hz) Pulse length(µsecs) Activation time(sec) Pause time(sec)

Train

90 60 1 1

nead

10 100 2 2

assa

e Low

requenc

10 100 2 1

assa

requenc

100 50 4 4

ctivation Lo

requenc

30 100 2 2

ctivation

requenc

90 60 2 2

Development of a Proof-of-Concept Portable Electrostimulation Device for Lower Limbs Blood Flow Enhancement

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4 DEVICE FUNCTIONING

RESULTS

Once the layout had been concluded, the assembly

and respective tests were carried out.

During the tests, the two-phase electrical signal

was validated, as well as the current limitation, since

when the skin was short-circuited, the voltage

remained stable. Sensitivity was also validated on the

skin with gel pads specific for electrostimulation

devices. Figure 14 shows the assembled PCB.

Figure 14: Assembled portable PCB.

In Figure 15 one can see the result of a test

involving biphasic pulses at a frequency of 100Hz,

without the pad being in contact with human skin.

Figure 15: Biphasic pulse at 100Hz.

In Figure 16 one can see the result of another test

at a frequency of 2Hz, now with skin contact, where

a small amount of expected distortion can be

observed.

Figure 16: Biphasic pulse at 2 Hz.

In Figure 17, we can see the device being charged

via USB-C, with the LED signalling charging in

progress.

Figure 17: Charging the device.

In Figure 18 left, one can see an example of an

electrostimulation session in progress and the

application indicating the time remaining. In Figure

18 right, one can see the module running the

electrostimulation session, with the pad in contact

with the skin.

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1014

Figure 18: Left: Electrostimulation session in progress.

Right: Module in operation.

After validating the electronics, we moved on to

the development of the casing and its integration in

the designed compression socks.

The following considerations were considered

when developing the casing and compression socks:

• The module must be easily removable so

that the socks can be washed.

• The electrical pulse from the device to each

muscle must be conducted using textile

conductive threads.

For this reason, a prototype of the compression

sock was built, in which the electrical pulse is

conducted through a silver-plated yarn. Magnetic

snaps were placed at the contact points to attach the

module to the socks, as well as the medical pads for

electro-stimulation.

Figure 19 shows the outer part, with the magnetic

snaps that will allow contact with the module and the

pads, as well as the silver-plated conductive yarns.

Figure 19: Outside of the compression socks.

Figure 20 shows the inside of the socks, which has

been insulated to prevent the conductive yarn from

coming into contact with the skin, making it possible

only at the specific points of the muscle, where the

medical pad is inserted.

Figure 20: Inside of the compression socks.

Tests were carried out to validate the electrical

conduction of the textile, as well as the sensitivity of

the pulse on human skin.

Figure 21 shows confirmation of the textile's

conduction.

Figure 21: Electrical conductivity tests on textile.

Figure 22 shows the sensitivity tests on human

skin, thus validating the functioning of the developed

product.

Figure 22: Final working prototype in a human.

Development of a Proof-of-Concept Portable Electrostimulation Device for Lower Limbs Blood Flow Enhancement

1015

This resulted in the final prototype shown in

Figure 23.

Figure 23: Final prototype

5 CONCLUSION AND FUTURE

WORK

In conclusion, all the objectives of this research have

been successfully achieved. A proof of concept has

been developed for a wireless electrostimulation

device, controlled via a smartphone application. This

device can be connected to socks with specific

characteristics that conduct electric current to

targeted areas of the lower legs, thereby enhancing

blood flow through muscle activation.

During the development process, several

challenges were encountered, such as the issue of

accurately sensing the electrical pulse. This led to an

in-depth investigation into the problem, ultimately

resulting in a clear understanding and an effective

solution.

The Bluetooth Low Energy (BLE)

communication between the smartphone and the

module, as well as the electrical signal delivery to the

electrodes, have been thoroughly validated and

confirmed to be operational. The mobile application

has been successfully compiled and tested on various

Android devices, ensuring compatibility across

different Android versions. Although testing in an

iOS environment was not conducted, it is feasible to

compile the application on iOS using a development

account and an Apple device, without needing to

modify the core code.

In terms of electrical improvements, we identified

the potential for enhancing pulse modulation, which

is currently generated exclusively by hardware, and

current control, which is managed using digital

potentiometers.

From a firmware perspective, further

improvements could be made in battery management,

such as implementing a sleep mode for the ESP32

when no treatment session is in progress, to optimize

power consumption.

Finally, the software component of the system

offers several opportunities for enhancement. The

current mobile application is functional, but its user

interface could be further refined for better aesthetic

appeal and user experience. The application was

initially developed to demonstrate the system's

functionality and control mechanisms, leaving room

for design improvements. Compared to other

equipment on the market, this meets the technical

specifications for EMS equipment and is a good basis

for a commercial version.

Taking advantage of the interactivity between the

device and the smartphone, a potential extension of

this solution, we propose the development of an

online treatment platform that would allow healthcare

professionals, such as doctors and physiotherapists, to

remotely monitor and manage users' treatment

sessions.

ACKNOWLEDGEMENTS

The authors are grateful to FCT for funding under the

programs UIDB/05549/2020, UIDP/05549/2020 and

UID/CTM/00264/2020 and to the company

SANCAR – SANCAR PREMIUM SOCKS, LDA

under the project “TexTechCompress” POCI-02-

0853-FEDER-179821. This work was also funded by

the Innovation Pact HfFP–Health From Portugal, co-

funded from the” Mobilizing Agendas for Business

Innovation” of the ”Next Generation EU” program of

Component 5 of the Recovery and Resilience Plan

(RRP), concerning ”Capitalization and Business

Innovation”, under the Regulation of the Incentive

System ”Agendas for Business Innovation”.

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