2020 IEEE 9th Global Conference on Consumer Electronics (GCCE)

Effect of Static Stretching Using Foot Stretching
Device in the Elderly: An Interim Report
Senri Hashimoto1, Naomi Yamada1,2, Shogo Okamoto2, Yuma Shiraishi2, Yasuhiro Akiyama2, and Yoji Yamada2
1. Aichi Medical College for Physical and Occupational Therapy, Kiyosu, Japan.
2. Department of Mechanical Systems Engineering, Nagoya University, Nagoya, Japan.
Abstract—The exerciser “Relegs,” a home-use rehabilitation
device, was modified such that static stretching could beperformed. In this study, the effect of static stretching for footusing the modified device was evaluated in twelve healthyelderly people. After stretching, the passive dorsiflexion angle ofthe foot increased significantly and the stretched length of themedial head of the gastrocnemius muscle which was evaluatedusing an ultrasound imaging device shortened significantly. This
indicated that the flexibility of the soft tissues other than muscles
might have been improved by static stretching using an
automated foot stretching machine in the elderly.
Keywords—rehabilitation device, static stretching, ankle joint,
stiffness, muscle tendon junction

I. INTRODUCTION
Static stretching is frequently used as a treatment for
decreased range of motion and increased muscle tone of thefoot. In clinical practice, stretching is performed manually [1,2]; however, thus far, several pieces of equipment have beenstudied to automate foot stretching [3–8], although there areno commercially available ones. Some of them simulate thethree-dimensional manual stretching [7, 8] whereas themajority of them have one degree-of-freedom motion of
dorsi/planter flexion. Most of these are large and unsuitablefor home use. In addition, most studies have targeted healthy
young people and stroke survivors, so their effect on theelderly is not clear.
The exerciser, “Relegs” (LAP, Co., Ltd., Japan), is acommercial device for home rehabilitation. Risk reduction ofRelegs for single failures is achieved relatively easily because
its driving mechanism is based on a pneumatic actuator. The
bellows connected to the part on which the foot is placed
expands due to the inflow of air, and the foot is dorsiflexed(Fig. 1). If the flow of air is stopped, the foot can return to theinitial position slowly. This device was developed to exercise
lower limb muscles continuously at home, but it only performs
repeated plantarflexion and dorsiflexion. Therefore, we
modified the exerciser such that static stretching could beperformed [9, 10]. The effectiveness of foot stretching using
the modified device in young healthy people has already beenshown [10, 11]. However, it has not been clarified which
tissue was stretched. So, in the present study, we focused onchanges in the stiffness of the stretched muscles. Someprevious studies investigated the effect of stretching on
muscle stiffness by measuring the muscle tendon of the foot[12, 13]. Therefore, whether the stiffness of muscles changes
before or after foot stretching using a modified stretching
device was investigated using ultrasound imaging.

II. METHOD
A. Participants
Twelve healthy elderly people (five men and seven
women, 73.2 ± 3.8 years old) (mean ± standard deviation)
participated. They had no foot disorders or pain. All
participants provided informed consent before the experiment.
This study was approved by the Ethics Committee of Aichi
Medical College for Physical and Occupational Therapy.
B. Protocols
An experiment was conducted on the right foot withdorsiflexion stretching using the modified device. The target
muscles for stretching were the gastrocnemius and soleus
muscles. The stretching outcomes were measured before andafter stretching.
Static stretching was performed in the sitting position withthe knee extended and the right leg on the stretching device(Fig. 2). For safety, this device has a mechanism that is driven
only while the user is pressing the switch. Therefore, alloperations were performed with the subject pressing theswitch. Before performing stretching, the subject held theswitch while the foot was dorsiflexed by the stretching device
to an angle at which he or she felt stretched. This angle wasset as the maximum dorsiflexion angle during stretching forThis work was supported by JSPS KAKENHI Grant Number 17K13108 and20K19403 and Grants-in-Aid for individual research in Aichi Medical
College. We also acknowledge technical supports from LAP Co, Ltd.

651

Initial position

Stretch position

Center of rotation

BellowsExtension
Dorsiflexion

Fig. 1. Operation principle of stretching device.

SwitchBellows
Center of rotation
Fig. 2. Situation of static stretching using the device.

978-1-7281-9802-6/20/$31.00 ©2020 IEEE

2020 IEEE 9th Global Conference on Consumer Electronics (GCCE)

MarkerSkin

FatMTJ

MGMAchilles tendon
Distance between
the MTJ and marker
Fig. 3. Left; Image of ultrasonography. Right; Method to measure of the distance between the MTJ and marker in order to identify the stretched lengthof the MGM.

TABLE I.

RESULTS OF THE DORSIFLEXION ANGLE AND THE STRETCHED LENGTH OF THE MGM

Dorsiflexion angle (°)
Pre
Post

18.3 ± 5.0
24.1 ± 6.1*

Stretched length of MGM (standardized data)
0°
5°
10°
15°
0.1 ± 14.6
1.0 ± 17.0
−2.8 ± 5.6−1.6 ± 9.6−6.1 ± 11.5
−2.9 ± 6.2−1.4 ± 5.0−1.0 ± 9.7+#

average ± standard deviation*: p < 0.01 for pre vs post in t-test+: p < 0.01 for pre vs post in two-way analysis of variance#: p < 0.01 for measurement angle in two-way analysis of varianceeach subject. Two minutes of static stretching was performed
using the device at this dorsiflexion angle. This was repeated
for five sets, with the maximum dorsiflexion angle set eachtime. In total, static stretching was performed for ten min in
one experiment. It took ~30 s to set the angle between sets.
C.

Outcome measure
To investigate the stretching effect, the passive
dorsiflexion angle of the foot and the stretched length of themedial head of the gastrocnemius muscle (MGM) wasmeasured. Each measurement was performed in the supine
position with the knee at 30° flexion. The dorsiflexion angle
was measured manually using a goniometer. The stretchedlength of the MGM was evaluated using an ultrasonicdiagnostic imaging device (ARIETTA Prologue, Hitachi, Co.,
Ltd, Japan). With reference to the method of Morse et al. [12],in order to define the stretched length of the MGM, themuscle tendon junction (MTJ) of the MGM was identified
using the ultrasound imaging device before measurement. An
acoustic reflection marker was attached to the skin near theMTJ of the subject, and the probe of the ultrasound imaging
device was placed so that the marker and MTJ could beviewed at the same time. The marker was attached to theexact same place in the evaluation before and after stretching.
The images were taken using an ultrasound imaging system
while the subject's foot was passively dorsiflexed from 0° to15° in 5° increments. Image processing software (Image J,National Institute of Health, USA) was used to calculate thelength from the acoustic reflection marker to the MTJ at eachangle. The change in the distance between the MTJ andmarker for each angle was defined as the stretched length ofthe MGM (Fig. 3).

D. Data analysis
The dorsiflexion angles before and after stretching werecompared using a paired t-test. The length of the extended
MGM was standardized to eliminate individual differencesamong subjects, and the average value of each subject was set
to 0 by subtracting each data value from the average value ofall data before and after stretching within each subject.
Subsequently, two-way analysis of variance was performed
using two factors, “pre- and post-stretching” and“measurement angle.” The significance level was set at p <0.05.
III. RESULTS
The results are shown in Table I. The dorsiflexion angle
significantly increased from 18.3 ± 5.0° before to 24.1 ± 6.1°
after stretching (t(11) = 2.20, p < 0.001). The stretched lengthof the MGM was analyzed in seven people, excluding
subjects whose passive dorsiflexion angle did not reach 15°
during measurement. The two-way analysis of variance
identified that the stretched length of the MGM significantly
decreased after stretching (F(1,5) = 3.90, p < 0.001). There
was also a significant difference between the measurement
angle (F(3,5) = 2.66, p < 0.001), while there was nosignificant interaction (p = 0.45).
IV. CONCLUSION AND DISCUSSION
In this study, the effects of the foot stretching device forhealthy elderly people were investigated. As a result, thedorsiflexion ROM significantly increased and the stretchedlength of the MGM significantly decreased after stretching.
In our previous study of healthy young people [10],stretching with the device reduced the resistance torque of theankle joint during passive dorsiflexion. This indicated that the652

978-1-7281-9802-6/20/$31.00 ©2020 IEEE

2020 IEEE 9th Global Conference on Consumer Electronics (GCCE)

ankle stiffness had decreased. Some previous studies
investigating the effect of stretching by measuring the MTJ
reported that the displacement of the MTJ increased; that is,
the muscle stiffness of the foot decreased [12, 13]. In thisstudy, while we focused on the length of the MGM andevaluated the change in the displacement of the MTJ before
and after stretching using an ultrasonic imaging system, thelength decreased after stretching. In other words, by static
stretching using the device, tissues other than thegastrocnemius muscle was stretched so that the dorsiflexionangle increased. Kubo et al. [14] and Kato et al. [15] reported
that static stretching for 10 to 20 min decreased tendon
stiffness over muscle stiffness. The present study performed
10-min stretching totally for each subject. Therefore, thetendon stiffness might have decreased due to continued
proper stretching by the device. That is, the foot stretching
device might have improved the flexibility of the soft tissues,
such as the Achilles tendon and joint capsule.

muscle tendon unit in vivo,” J. Orthop. Res., vol. 29, pp. 1759–1763,
November 2011.
[14] K. Kubo, H. Kanehisa, and T. Fukunaga, “Effect of stretching training
on the viscoelastic properties of human tendon structures in vivo, ” J.
Appl. Physiol., vol. 92, pp. 595–601, 2002.
[15] E. Kato, H. Kanehisa, T. Fukunaga, and Y. Kawakami, “Changes inankle joint stiffness due to stretching : The role of tendon elongation ofthe gastrocnemius muscle,” Eur. J. Sport Sci., vol. 10(2), pp. 111–119,
March 2010.

REFERENCES[1]N. Yamada, S. Okamoto, Y. Akiyama, and Y. Yamada, “Principalmotion analysis of manual stretching techniques for the ankle joints,”
J. Phys. Ther. Sci., vol. 32, 2020, in press.
[2] N. Yamada, S. Okamoto, H. Okumura, Y. Yamada, K. Isogai, and K.
Kawakami, “Similarities and differencies in manual stretching ofphysical therapists for equinovarus,” Proceedings of IEEE/SICE
international symposium on system integration, pp. 490–495, 2014.
[3] G. Waldman, C. Y. Yang, Y. Ren, L. Liu, X. Guo, R. L. Harvey, E. J.
Roth, and L.Q. Zhang, “Effects of robot-guided passive stretching andactive movement training of ankle and mobility impairments in stroke”,
NeuroRehabilitation, vol. 32(3), pp. 625–634, 2013.
[4] Y. Ren, Y. N. Wu, C. Y. Yang, T. Xu, R. L. Harvey, and L. Q. Zhang,“Developing a Wearable Ankle Rehabilitation Robotic Device for inBed Acute Stroke Rehabilitation,” IEEE Trans. Neural Syst.
Rehabilitation Eng., vol. 25(6), pp. 589–596, 2017.
[5] K. Chen, B. Xiong, Y. Ren, A. Dvorkin, D. Gaebler-Spira, C. Sisung,and L. Zhang, “Ankle passive and active movement training in children
with acute brain injury using a wearable robot,” J. Rehab Med, vol.
50(1), pp. 30–36, 2018.
[6] T. Hideki, T. Matsumoto, and S. Sugihara, “Simple geometricalanalysis for mechanizing the ankle joint stretching treatment procedureof a PT using a numerical calculation”, J. Adv. Mech. Des. Syst.
Manuf., vol. 13(2), JAMDSM0034, 2019.
[7] N. Yamada, S. Okamoto, Y. Akiyama, K. Isogai, and Y. Yamada,“Ankle stretching rehabilitation machine for equinovarus: Design andevaluation from clinical aspects,” Proceedings of IEEE international
conference on systems, man, and cybernetics, pp. 1687–1692, 2017.
[8] T. Kimura, S. Okamoto, N. Yamada, Y. Akiyama, K. Isogai, and Y.
Yamada, “Ankle stretching rehabilitation machine for equinovarus:
Automation of eversion and flexion control,” Proceedings of IEEE
International Conference on Systems, Man, and Cybernetics, pp. 2696–2700, 2017.
[9] Y. Shiraishi, S. Okamoto, N. Yamada, K. Inoue, Y. Akiyama, and Y.
Yamada, “Pneumatic-driven ankle stretching machine,” Proceedings ofIEEE Global Conference on Life Sciences and Technologies, pp. 10–
11, Osaka, Mar 2019.
[10] Y. Shiraishi, S. Okamoto, N. Yamada, K. Inoue, Y. Akiyama, and Y.
Yamada, “Pneumatically-driven stretching machine for ankle
dorsiﬂexion: Safety concepts and eﬀectiveness test involving healthy
young subjects,” Robomech J., vol. 7, article 10, 2020.
[11] Y. Shiraishi, S. Okamoto, N. Yamada, K. Inoue, Y. Akiyama, and Y.
Yamada, “Effective position of the rotation axis of an ankle stretchingmachine and the effect of misalignment,” Journal of BiomechanicalScience and Engineering, vol. 15, p. 20-00202, 2020.
[12] C. I. Morse, H. Degens, O. R. Seynnes, C. N. Maganaris, and D. A.
Jones, “The acute effect of stretching on the passive stiffness of thehuman gastrocnemius muscle tendon unit,” J. Physiol., vol. 586.1, pp.
97–106, 2008.
[13] M. Nakamura, T. Ikezoe, and N. Ichihashi, “Actue and prolonged effectof static stretching on the passive stiffness of the human gastrocnemius653

978-1-7281-9802-6/20/$31.00 ©2020 IEEE