Towards Applying Pneumatic Gel Muscles to Augment Plantar
Flexor Muscle Stretching for Children with Cerebral Palsy
Zilan Chen

Sujuan Wang

Swagata Das

Keio University Graduate School ofMedia Design
Yokohama, Japan

Department of Rehabilitation,
Children’s Hospital of Fudan
University
Shanghai, China
sujuanw@163.com

Graduate School of Advanced Scienceand Engineering Hiroshima
University
Higashihiroshima, Japan

Yuichi Kurita

Takashi Goto

Chun Zhai

Graduate School of Advanced Scienceand Engineering Hiroshima
University
Higashihiroshima, Japan

University for Applied Sciences
Hamburg, Germany

Department of Rehabilitation,
Children’s Hospital of Fudan
University
Shanghai, China
joshua_zc@163.com

Lei XuKai Kunze

Department of Rehabilitation,
Children’s Hospital of Fudan
University
Shanghai, China
xuleipaul@foxmail.com

Keio University Graduate School ofMedia Design
Yokohama, Japan
Kai@kmd.keio.ac.jp

Figure 1: Our PGM system being used to help a boy with cerebral palsy stretch his left plantar flexor muscle.

ABSTRACT
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AHs 2022, March 13–15, 2022, Kashiwa, Chiba, Japan© 2022 Copyright held by the owner/author(s).
ACM ISBN 978-1-4503-9632-5/22/03.
https://doi.org/10.1145/3519391.3524179

337

Many children in the world suffer from cerebral palsy (CP), whichis the leading cause of children’s disabilities, affecting their body
movement and muscle coordination [18]. At present, the rehabilitation training of children with cerebral palsy has long relied on thephysical therapist (PT) workforce. Our research wants to empower
parents of children suffering from cerebral palsy to engage in simple

AHs 2022, March 13–15, 2022, Kashiwa, Chiba, Japan

Zilan Chen, et al.

training exercises themselves, supporting the rehabilitation process.
We collaborate with physical therapists of a children’s hospital todesign a system that uses pneumatic artificial muscles (PAMs) tohelp children with cerebral palsy train their plantar flexor muscles(Figure 1). We present an initial experimental prototype validatedwith physical therapists and doctors. We also show a feasibility testwith patients with informed consent from parents and monitoredby the physical therapists.

CCS CONCEPTS• Computer systems organization → Embedded systems; Redundancy; Robotics; • Networks → Network reliability.

KEYWORDS
Home rehabilitation, children with cerebral palsy, soft exoskeleton,
artificial muscles
ACM Reference Format:
Zilan Chen, Sujuan Wang, Swagata Das, Yuichi Kurita, Takashi Goto, Chun
Zhai, Lei Xu, and Kai Kunze. 2022. Towards Applying Pneumatic Gel Muscles
to Augment Plantar Flexor Muscle Stretching for Children with Cerebral
Palsy. In Augmented Humans 2022 (AHs 2022), March 13–15, 2022, Kashiwa,
Chiba, Japan. ACM, New York, NY, USA, 4 pages. https://doi.org/10.1145/
3519391.3524179

1

actuators and soft materials (like the pneumatic gel muscles) as anew, unobtrusive, affordable opportunity for children with cerebral
palsy to help them perform rehabilitation training exercises [8, 29].
We hope that our research will allow more children with cerebral palsy to get opportunities for rehabilitation exercises, liberateparents’ hands in family rehabilitation scenarios, improve family
rehabilitation efficiency, shorten rehabilitation time, and reducerehabilitation costs. This work is an initial step towards a novel
rehabilitation solution, a soft exoskeleton system for children withcerebral palsy applicable in a home setting.
The contributions of this work on cerebral palsy rehabilitation
are: (1) we present a novel soft exoskeleton rehabilitation prototype
based on a low-pressure type PAM called Pneumatic Gel Muscle(PGM) for children with cerebral palsy, (2) we present an experimental protocol applying the prototype to plantar flexor muscle stretching comparing it to a physical therapist stretch. (3) We present an
initial feasibility test with 3 patients (under supervision of 2 doctors
and a physical therapist), as well as discussing future improvements
and potential issues.

2

MOTIVATION

Seventy-three percent of children with cerebral palsy have difficulty
walking, and the situation gets worse with age [11, 16, 18, 23]. Early
rehabilitation training is the only way to recover and is vital totheir future development, preventing walking problems as adults [2,24].The most crucial rehabilitation session for children with cerebral
palsy is physical therapy. The one-to-one physical therapist training,
including muscle stretching and other sessions, is very effective
yet also time-consuming [10, 13, 15]. Rehabilitation practitioners
generally formulate 4-6 family rehabilitation training movements
for each child with cerebral palsy [3, 20]. These contents are usually
expressed in medical professional terms. Then, the rehabilitation
therapists demonstrate each action for the parents of the cerebral
palsy child, and the parents usually record these rehabilitation
actions by taking photos or videos. So in the next three months,
parents would act as rehabilitation therapists and do rehabilitation
training for their children with cerebral palsy. When their children
with cerebral palsy can achieve the goals set by the therapist before,
they return to the hospital for review. Then, the physical therapist
will develop a new rehabilitation plan. There are also some effective
parents community and support efforts [5, 27, 34]. However, themuscle stretching exercises and rehab plans are quite traditional
and the basic processes have not been changed in many years.
There are a couple of efforts using novel therapy approaches, exoskeletons, and other mechanical designs to help the rehabilitation
process, yet most of them are rather large, expensive and requirea large amount of power/air pressure etc. [7, 27, 28, 30, 31]. There
are also a lot of works using lower-limb exoskeletons and artificial
muscles for rehabilitation purposes [1, 4, 9, 12, 17, 19, 22, 25, 26, 32].
In our research, we work towards novel rehabilitation solutions
for cerebral palsy and want to support the process on several scales
in the hospital and at home. Especially, we investigate wearable

338

APPROACH AND ETHICALCONSIDERATIONS

Since we are interested in the complexity of cerebral palsy rehabilitation exercises, we conducted ethnography research, including
observations of cognitive assessment, cerebral palsy screening, rehabilitation course observation, expert interviews, cerebral palsy
rehabilitation-related documents, and review of rehabilitation aids.
Before starting the research to inform the design, we went to ourpartner children’s hospitals and observed daily rehabilitation training for three months to insight research opportunities. We observed
different rehabilitation courses to understand clinical rehabilitation,
focusing on the interaction between cerebral palsy children andrehabilitation experts during rehabilitation training, including theuse of equipment, the time of each rehabilitation action, and how
to attract the child to complete a certain action.
Our hospital rehabilitation observation found that plantar flexor
muscle stretching is essential for most children with cerebral palsy [11,14]. So we decided first to focus on applying pneumatic gel muscles (PGMs) to rehabilitate the ankle movement. Another difficultyis that when parents recover their children at home, they cannot
achieve accurate rehabilitation actions like a therapist. Therefore,
the accuracy of rehabilitation training is what we are exploringand solving with PGM equipment. As a background, we described
the rehabilitation process from the perspective of multiple rehabilitation experts who make rehabilitation plans for children withcerebral palsy. We have observed the rehabilitation treatment ofchildren with cerebral palsy and analyzed which muscle training isessential to better provide information for designing our artificial
muscles’ system. A major concern for conducting experiments is
not to interfere with the rehabilitation process of the children andto ensure the safety of the children when using our research prototypes. To this end we discussed potential experimental setups with
doctors and ethical board members at all institutions involved. Our
Ethics proposal containing the experimental design and the PGM
system description have been approved by the ethics committees

PGMs for Cerebral Palsy Rehabilitation

AHs 2022, March 13–15, 2022, Kashiwa, Chiba, Japan

Figure 2: PGM foot cover and Knee pad. "L1" and "L2" are the longer PGMs, "S1" and "S2" are the shorter ones.
from both the partner hospital and university as well as external
engineering and medical advisors.

3

PNEUMATIC ARTIFICIAL MUSCLEPROTOTYPE DESIGN

Together with physical therapists, we designed and refined ourfunctional PGM prototype. Before applying it to children, we did
several pre-tests on multiple adults, including a physical therapist,
as well as demonstrations to the parents. Our system uses four
pneumatic gel muscles (PGM) as soft actuators worn by the user
on their leg. Total weight of the system excluding the air pressuresource is around 400g (including four PGMs of weight 86g).
The PGMs we use can be activated with low air pressure andhave been used in related work for soft exoskeletons in training
and other rehabilitation research by Ogawa et al., Takashi et al.
and others [6, 21, 29, 33]. Each PGM is either actuated or deflated
through a dedicated 3/2 solenoid valve, operated in normally-closed
configuration. The solenoid valve used in our device is the SYJ312MSLZD-M3 (SMC) with an operating pressure range of 0-0.7MPa.
Our device does not required to use a stationary air compressor,
instead we can opt for a NTG mini CO2 gas cylinder (with a gas
volume of 74 grams). The cylinder is attached to a regulator used
to maintain an input air pressure of 0.2MPa to the solenoid valves.
One charge can work for up to 500 muscle contractions. Our device
is controlled via a ESP32 microcontroller. The air pressure to the
PGMs can be controlled individually, although in the current setup
we activate them together (only stretch an relax state). Therefore,
the microcontroller can receive instructions over wifi/bluetoothor USB connection and actuates the corresponding channels toenergize or de-energize the solenoid valves. The system also offers
a stand-alone mode, in which the stretching programs can be loaded
directly into the micro-controller (used in the experimental setup).
The program can be started and stopped over a simple button-press.
We tested the prototype under the supervision of the physicaltherapist together with 3 children (aged 3, 6 and 9). The prototype isfunctional and can be adjusted to stretch the plantar felxor muscle
in a similar fashion as the physcial therapist does.
Four PGMs with two different lengths were used in our experiment. We also designed a special foot cover and a knee pad for
fixing the PGMs by Velcro. The function of the two longer PGMs
which are crossed with each other is responsible for the stretching,339

and the two shorter ones are used for safety consideration ( 2). One
side of the longer PGMs is fixed on the knee pad’s upper part, andanother side is fixed on the upper part of the foot cover. One sideof the shorter ones is fixed on the lower part of the knee pad, andanother side is fixed on the lower part of the foot cover. We used
the CO2 gas cylinders to actuate the PGMs and maintained theair pressure at max 0.2MPa to ensure the safety of the experimentusing over-pressure valves.

4

CONCLUSION AND FUTURE WORKWe designed a lower-limb rehabilitation system for children withcerebral palsy to train their plantar flexor muscles by applying
pneumatic artificial muscles. After the initial tests, we will now
move forward to conduct a control experiment on children withcerebral palsy, using PGM to imitate the same movement performedby physical therapists and comparing the rehabilitation effect between the physical therapists and PGM. We hope to show that
PGM stretching can be an effective alternative for cerebral palsy
rehabilitation.

ACKNOWLEDGMENTS
We would like to thank Daiya Industry Co., Ltd. for their providing
PGMs used in our experiments. We also want to thank Minzhi Lee
for providing the circuit engineering support. This work is also
partly supported by JST Presto Grant Number JPMJPR2132.

REFERENCES[1] Wang Biyuan, Takahashi Nobuhiro, and Koike Hideki. 2020. Sensor Glove Implemented with Artificial Muscle Set for Hand Rehabilitation | Proceedingsof the Augmented Humans International Conference. AHs ’20: Proceedingsof the Augmented Humans International Conference (Mar 2020), 1–4. https://doi.org/10.1145/3384657.3384791[2] Bruno Bonnechère, Bart Jansen, Lubos Omelina, Serge Van Sint Jan, et al. 2016.
The use of commercial video games in rehabilitation: a systematic review. International journal of rehabilitation research 39, 4 (2016), 277–290.
[3] Hilde Capjon and Ida Torunn Bjørk. 2010. Rehabilitation after multilevel surgery
in ambulant spastic children with cerebral palsy: children and parent experiences.
Developmental neurorehabilitation 13, 3 (2010), 182–191.
[4] Chia-Yu Chen, Yen-Yu Chen, Yi-Ju Chung, and Neng-Hao Yu. 2016. Motion
guidance sleeve: Guiding the forearm rotation through external artificial muscles.
In Proceedings of the 2016 CHI Conference on Human Factors in Computing Systems.
3272–3276.
[5] Johanna Darrah, Mary C Law, Nancy Pollock, Brenda Wilson, Dianne J Russell,
Stephen D Walter, Peter Rosenbaum, and Barb Galuppi. 2011. Context therapy:
a new intervention approach for children with cerebral palsy. Developmental
Medicine & Child Neurology 53, 7 (2011), 615–620.

AHs 2022, March 13–15, 2022, Kashiwa, Chiba, Japan

Zilan Chen, et al.

[6] Swagata Das, Yusuke Kishishita, Toshio Tsuji, Cassie Lowell, Kazunori Ogawa,and Yuichi Kurita. 2018. ForceHand glove: a wearable force-feedback glove withpneumatic artificial muscles (PAMs). IEEE Robotics and Automation Letters 3, 3(2018), 2416–2423.
[7] Mariya I Gonkova, Elena M Ilieva, Giorgio Ferriero, and Ivan Chavdarov. 2013.
Effect of radial shock wave therapy on muscle spasticity in children with cerebral
palsy. International Journal of Rehabilitation Research 36, 3 (2013), 284–290.
[8] Takashi Goto, Swagata Das, Yuichi Kurita, and Kai Kunze. 2018. Artificial Motion
Guidance: an Intuitive Device based on Pneumatic Gel Muscle (PGM). In The
31st Annual ACM Symposium on User Interface Software and Technology AdjunctProceedings. ACM, 182–184.
[9] Taryn A Harvey, Benjamin C Conner, and Zachary F Lerner. 2021. Does Ankle
Exoskeleton Assistance Impair Stability During Walking in Individuals with
Cerebral Palsy? Annals of Biomedical Engineering 49, 9 (2021), 2522–2532.
[10] Steven J Korzeniewski, Jaime Slaughter, Madeleine Lenski, Peterson Haak, andNigel Paneth. 2018. The complex aetiology of cerebral palsy. Nature Reviews
Neurology 14, 9 (2018), 528–543.
[11] Karen W Krigger. 2006. Cerebral palsy: an overview. American family physician
73, 1 (2006), 91–100.
[12] Zachary F Lerner, Diane L Damiano, and Thomas C Bulea. 2017. The effects of
exoskeleton assisted knee extension on lower-extremity gait kinematics, kinetics,
and muscle activity in children with cerebral palsy. Scientific reports 7, 1 (2017),
1–12.
[13] Sophie Levitt and Anne Addison. 2018. Treatment of cerebral palsy and motor
delay. John Wiley & Sons.
[14] Laura Muñoz-Bermejo, Jorge Pérez-Gómez, Fernando Manzano, Daniel ColladoMateo, Santos Villafaina, and José C Adsuar. 2019. Reliability of isokinetic knee
strength measurements in children: A systematic review and meta-analysis. PLoS
One 14, 12 (2019), e0226274.
[15] Karin B Nelson and Jonas H Ellenberg. 1982. Children who ‘outgrew’cerebral
palsy. Pediatrics 69, 5 (1982), 529–536.
[16] Karin B Nelson and Judith K Grether. 1999. Causes of cerebral palsy. Current
opinion in pediatrics 11, 6 (1999), 487–491.
[17] Huu Tho Nguyen, Van Chon Trinh, Thanh Danh Le, et al. 2020. An adaptive fast
terminal sliding mode controller of exercise-assisted robotic arm for elbow joint
rehabilitation featuring pneumatic artificial muscle actuator. In Actuators, Vol. 9.
Multidisciplinary Digital Publishing Institute, 118.
[18] NIH. 2013. Cerebral Palsy: Hope Through Research | National Institute of Neurological Disorders and Stroke.
https://www.ninds.nih.gov/Disorders/PatientCaregiver-Education/Hope-Through-Research/Cerebral-Palsy-HopeThrough-Research[19] Toshiro Noritsugu and Toshihiro Tanaka. 1997. Application of rubber artificial muscle manipulator as a rehabilitation robot. IEEE/ASME Transactions onmechatronics 2, 4 (1997), 259–267.
[20] Pia Ödman, Barbro Krevers, and Birgitta Öberg. 2007. Parents’ perceptions of thequality of two intensive training programmes for children with cerebral palsy.
Developmental Medicine & Child Neurology 49, 2 (2007), 93–100.
[21] Kazunori Ogawa, Chetan Thakur, Tomohiro Ikeda, Toshio Tsuji, and Yuichi Kurita.
2017. Development of a pneumatic artificial muscle driven by low pressure andits application to the unplugged powered suit. Advanced Robotics 31, 21 (Nov
2017), 1135–1143. https://doi.org/10.1080/01691864.2017.1392345[22] Evelyn J Park, Tunc Akbas, Asa Eckert-Erdheim, Lizeth H Sloot, Richard W
Nuckols, Dorothy Orzel, Lexine Schumm, Terry D Ellis, Louis N Awad, andConor J Walsh. 2020. A hinge-free, non-restrictive, lightweight tethered exosuitfor knee extension assistance during walking. IEEE transactions on medical
robotics and bionics 2, 2 (2020), 165–175.
[23] Dilip R Patel, Mekala Neelakantan, Karan Pandher, and Joav Merrick. 2020. Cerebral palsy in children: a clinical overview. Translational pediatrics 9, Suppl 1(2020), S125.
[24] Peter Rosenbaum, Nigel Paneth, Alan Leviton, Murray Goldstein, Martin Bax,
Diane Damiano, Bernard Dan, Bo Jacobsson, et al. 2007. A report: the definitionand classification of cerebral palsy April 2006. Dev Med Child Neurol Suppl 109,
suppl 109 (2007), 8–14.
[25] Lizzette J Salmeron, Gladys V Juca, Satesh M Mahadeo, Jiechao Ma, Shuangyue Yu,
and Hao Su. 2020. An Untethered Electro-Pneumatic Exosuit for Gait Assistanceof People With Foot Drop. In Frontiers in Biomedical Devices, Vol. 83549. American
Society of Mechanical Engineers, V001T09A009.
[26] Marlene Sandlund, Katarina Dock, Charlotte K Häger, and Eva Lindh Waterworth.
2012. Motion interactive video games in home training for children with cerebral
palsy: parents’ perceptions. Disability and rehabilitation 34, 11 (2012), 925–933.
[27] Manon Maitland Schladen, Yiannis Koumpouros, and Peter Lum. 2021. Factors Mediating Use of Advanced Rehabilitation Technologies in the Home. In
International Conference on Applied Human Factors and Ergonomics. Springer,
141–147.
[28] N Smania, M Gandolfi, V Marconi, A Calanca, C Geroin, S Piazza, P Bonetti,
P Fiorini, A Consentino, C Capelli, et al. 2011. Applicability of a new robotic
walking aid in a patient with cerebral palsy. Eur J Phys Rehabil Med 147, 2 (2011),
135–40.

340[29] Goto Takashi, Das Swagata, Wolf Katrin, Lopes Pedro, Kurita Yuichi, and Kunze
Kai. 2020. Accelerating Skill Acquisition of Two-Handed Drumming using Pneumatic Artificial Muscles | Proceedings of the Augmented Humans International
Conference. AHs ’20: Proceedings of the Augmented Humans International Conference (Mar 2020), 1–9. https://doi.org/10.1145/3384657.3384780[30] Osman Ulkir, Gazi Akgun, and Erkan Kaplanoglu. 2018. Mechanical design andanalysis of a pneumatic ankle foot orthosis. In 2018 Electric Electronics, Computer
Science, Biomedical Engineerings’ Meeting (EBBT). IEEE, 1–4.
[31] Pedro Valadão, Harri Piitulainen, Eero A Haapala, Tiina Parviainen, Janne Avela,
and Taija Finni. 2021. Exercise intervention protocol in children and young
adults with cerebral palsy: the effects of strength, flexibility and gait training
on physical performance, neuromuscular mechanisms and cardiometabolic risk
factors (EXECP). BMC Sports Science, Medicine and Rehabilitation 13, 1 (2021),
1–19.
[32] Yulin Wang and Benny Lo. 2021. A Soft Inflatable Elbow-Assistive Robot forChildren with Cerebral Palsy. In 2021 IEEE 17th International Conference on
Wearable and Implantable Body Sensor Networks (BSN)(IEEE BSN 2021). Athens,
Greece.
[33] Masataka Yamamoto, Yusuke Kishishita, Koji Shimatani, and Yuichi Kurita. 2019.
Development of new soft wearable balance exercise device using pneumatic gel
muscles. Applied Sciences 9, 15 (2019), 3108.
[34] Maria Zuurmond, David O’Banion, Melissa Gladstone, Sandra Carsamar, Marko
Kerac, Marjolein Baltussen, Cally J Tann, Gifty Gyamah Nyante, and Sarah Polack.
2018. Evaluating the impact of a community-based parent training programme
for children with cerebral palsy in Ghana. PloS one 13, 9 (2018), e0202096.