Article
DATSURYOKU Sensor—A Capacitive-Sensor-Based Belt for
Predicting Muscle Tension: Preliminary Results
Akihiko Murai
1,2,
* , Shusuke Kanazawa
1
, Ko Ayusawa
1
, Sohei Washino
1
, Manabu Yoshida
1
and
Masaaki Mochimaru
1
Citation: Murai, A.; Kanazawa, S.;
Ayusawa, K.; Washino, S.; Yoshida,
M.; Mochimaru, M. DATSURYOKU
Sensor—A Capacitive-Sensor-Based
Belt for Predicting Muscle Tension:
Preliminary Results. Sensors 2021, 21,
6669. https://doi.org/10.3390/
s21196669
Academic Editors: Pietro Picerno,
Andrea Mannini and Clive D’Souza
Received: 31 August 2021
Accepted: 3 October 2021
Published: 7 October 2021
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4.0/).
1
Human Augmentation Research Center, National Institute of Advanced Industrial Science and Technology,
Chiba 277-0882, Japan; kanazawa-s@aist.go.jp (S.K.); k.ayusawa@aist.go.jp (K.A.); s.washino@aist.go.jp (S.W.);
yoshida-manabu@aist.go.jp (M.Y.); m-mochimaru@aist.go.jp (M.M.)
2
PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan
* Correspondence: a.murai@aist.go.jp; Tel.: +81-3-3599-8058
Abstract:
Excessive muscle tension is implicitly caused by inactivity or tension in daily activities,
and it results in increased joint stiffness and vibration, and thus, poor performance, failure, and
injury in sports. Therefore, the routine measurement of muscle tension is important. However,
a co-contraction observed in excessive muscle tension cannot be easily detected because it does
not appear in motion owing to the counteracting muscle tension, and it cannot be measured by
conventional motion capture systems. Therefore, we focused on the physiological characteristics of
muscle, that is, the increase in muscle belly cross-sectional area during activity and softening during
relaxation. Furthermore, we measured muscle tension, especially co-contraction and relaxation, using
a DATSURYOKU sensor, which measures the circumference of the applied part. The experiments
showed high interclass correlation between muscle activities and circumference across maximal
voluntary co-contractions of the thigh muscles and squats. Moreover, the circumference sensor
can measure passive muscle deformation that does not appear in muscle activities. Therefore, the
DATSURYOKU sensor showed the potential to routinely measure muscle tension and relaxation,
thus avoiding the risk of failure and injury owing to excessive muscle tension and can contribute to
the realization of preemptive medicine by measuring daily changes.
Keywords:
DATSURYOKU (muscle relaxation); wearable sensing; capacitive sensor; preemptive medicine
1. Introduction
The rapid aging of the population and declined birthrates as well as advanced medical
technology and increased medical requirements have rapidly increased medical costs and
demand for nursing care. In addition, the number of young people in the workforce
is reducing. Therefore, protecting the lives of the elderly and their families as well as
coping with the rising burden of medical costs are becoming major issues. To address these
issues, a new direction of medicine has been proposed as preemptive medicine, which
aims to diagnose and predict diseases with a certain probability, and to provide therapeutic
intervention in the early stage of disease onset, when there are no clinical symptoms and
no abnormalities in the usual examination findings [
1
]. The above proposal focuses on
diseases with genetic predisposition based on biomarkers, such as biochemical findings of
protein, RNA, and imaging findings. However, to avoid an increase in demand for nursing
care and the burden of medical costs, the motor system for diseases caused by the decline
in physical and cognitive functions and daily exercise habits associated with aging (as
typified by the decline in walking ability owing to pain and dullness of knee joints, such as
knee osteoarthritis) should be improved to enable people to live independently for a longer
period and extend their health span. Preemptive medical treatment for diseases related to
such motor functions requires diagnosis and prediction in the early stages of disease onset
Sensors 2021, 21, 6669. https://doi.org/10.3390/s21196669 https://www.mdpi.com/journal/sensors
