Proceedings of the 2021 IEEE International
Conference on Intelligence and Safety for Robotics
Nagoya, Japan, March 4-6, 2021

Effect of 4 Weeks of Foot Stretching with an AutomaticStretching Machine: A Case Report*
Naomi Yamada1,2 , Shogo Okamoto2 , Yukiko Fuwa1 , Yasuhiro Akiyama2 , and Yoji Yamada2
B’Abstract— We developed a stretching machine that automatically performed dorsiﬂexion foot stretching, and subsequently
veriﬁed its long-term effect. One participant, with a history ofcervical spine injury, underwent stretching of her left foot for
10 mins, twice a week, for 4 weeks. Before and after the experimental period, the ankle dorsiﬂexion range of motion (ROM),
passive resistive torque during passive dorsiﬂexion, maximum
voluntary contraction (MVC) of the ankle plantarﬂexors, 5-m
walking parameters (time, steps, and cadence), and time upand-go (TUG) test time were evaluated. We found that after
4 weeks of stretching, the ankle ROM was increased, andthe passive torque at 10◦ dorsiﬂexion and MVC had slightly
decreased. Although the 5-m walking time did not change
signiﬁcantly, the TUG test time was 1.2 sec faster. These results
indicate that the rigidity of the foot decreased slightly and thestability during the turning motion increased owing to footstretching using the stretching machine.

ABC’C(Right foot)A: plantarflexion / A’: dorsiflexion
B: inversion / B’ : eversion
C: adduction / C’: abduction
Fig. 1.

I. INTRODUCTION

The three degrees of freedom of the foot movement.

pneumatically driven was modiﬁed with a function to allow
static stretching over a long period [8]. Foot stretching using
this machine in young healthy subjects increased the ankle
joint range of motion and reduced the resistive torque duringpassive dorsiﬂexion. Furthermore, in healthy elderly people,
10 mins of foot stretching using this stretching machineincreased the ankle joint range of motion, and potentiallydecreased the stiffness of the Achilles tendon [9]. These results veriﬁed the immediate effect of our stretching machine;
however, the effect of long-term use remains unclear.
Although several previous studies have investigated theimmediate effects of foot stretching devices, the effectsof long-term interventions have not yet been fully demonstrated. Zhou et al. reported the effect of using an automatic
stretching device three times a week for three months instroke patients [10]. In their study, stretching was performed using the proprioceptive neuromuscular facilitation(PNF) method, in which 15-sec stretching was repeatedly
performed, followed non-static stretching, which involves
continuous stretches over a long period. A systematic review
of a study of chronic foot stretching, including several typesof stretching (i.e., static, dynamic, and PNF), suggested that
more than 8-12 weeks of long-term intervention or morevolume and intensity of each stretching was needed to change
the structure of the muscles and tendons [11]. The stretchingmachine we developed is capable of static stretching for along period, and long-term use of the device is expected
to improve foot function. Therefore, using our stretchingmachine, we examined the effect of stretching when longterm intervention was performed in elderly people with asmaller foot ROM. In this paper, we present the data of one
participant.

Static stretching has the effect of improving range of motion and reducing muscle tone. In clinical practice, stretchingis often performed to treat impairments of the foot. Severalstretching equipment have been studied with the aim of automating foot stretching. One research group at Northwestern
University previously developed a stretching machine foruse in bed-side care, and suggested its effects for stroke
patients [1], [2]. The foot has the three degrees of freedom
as shown in Fig. 1, so that Yoo, et al. developed the threedimensional foot stretching device for use while standing.
They reported that stretching using this device improved
the locomotion ability in stroke survivors [3]. In addition,
Toda, et al. produced a stretching machine which simulated
the therapists’ manual stretching technique, which involves
pulling the heel towards the bottom side during stretching [4].
However, the clinical effect of this machine has neverbeen examined. Furthermore, Yamada, et al. had developeda three-dimensional foot stretching machine for use withsitting [5], [6]. This machine can automatically stretch thefoot, facilitating eversion, abduction, and dorsiﬂexion and isunder improvement to achieve a sufﬁcient effect.
The dorsiﬂex movement is major procedure in clinicalmanual foot stretching [7]. Therefore, in the present study,
we developed a dorsiﬂex stretching machine that can be usedat home. A commercialized automatic foot exerciser that is*This work was supported by JSPS KAKENHI Grant Nos. 17K13108
and 20K19403 and Grants-in-Aid for individual research in Aichi Medical
College. We also acknowledge technical support from LAP Co., Ltd.
1 Faculty of Physical Therapy, Aichi Medical College for Physical andOccupational Therapy, Kiyosu, Japan
2 Department of Mechanical Systems Engineering, Nagoya University,Nagoya, Japan.

978-0-7381-4674-4/21/$31.00 ©2021 IEEEA’74

Center of rotation
Dorsiflexion
Extension

Bellows(a) Initial position(b) Stretching position

Fig. 2. The mechanism of the stretching machine. First, the foot is placedat the initial position (a). By air inﬂow, the bellows are extended and thefoot is dorsiﬂexed (b).

II. M ETHODS
Fig. 3. Stretching situation. The participant sat in a chair and the foot wasplaced on the machine.

A. Participant
The subject is a 68-year-old woman who attended an adultday care center. She had a history of cervical spine injury
caused by an accident 3 years prior. Although she could
walk independently, she presented with a mildly increased
muscle tone in both lower limbs and mild restriction of therange of motion of the ankle joint on both sides. She usually
visited the day care center 5 days a week for individual
rehabilitation. She had no cognitive function problems. We
explained to the patient the purpose and procedure of thisstudy, both verbally and in writing, in advance and obtained
informed consent before the experiment. This study wasconducted with the approval of the ethics committee of Aichi
Medical College (#19204).

ᶅ stand up

ᶆ walkᶇ turnchairᶉ sit down

ᶈwalk3m

Fig. 4. Outline of time up and go test. The time taken from standing up,
walking to a target placed 3-m away, turning around it, walking to the return
point, and sitting in the chair is measured.

C. Biomechanical and functional measurements
Biomechanical and functional measurements were performed before and after the 4 week experiment. For biomechanical measurements, passive foot dorsiﬂexion angle, passive resistance torque during passive dorsiﬂexion, and maximum voluntary contraction (MVC) of active plantarﬂexion
were evaluated. The dorsiﬂexion angle was manually measured using a goniometer. The passive resistive torque wasevaluated using a handheld dynamometer by measuring thereaction force from the bottom of the foot when passively
dorsiﬂexed to 0◦ , 5◦ , and 10◦ . MVC was measured as theparticipant was pushing the handheld dynamometer ﬁxed tothe frame with the bottom of the foot in the plantar ﬂexion
direction. Passive torque and MVC were measured threetimes each, and the average was used as the representativevalue.
As functional measurements, the time, number of steps,and cadence during normal 5-m walking and time up and go
test (TUG) results were evaluated. Cadence was calculated
as the number of steps per second. In the TUG, the time
taken from standing up, walking to a target placed 3 m away,turning around it, walking to the starting point, and sittingin the chair (Fig. 4) is measured. The result of the TUG test
is usually used to evaluate balance ability. For 5-m walking
and TUG, each measurement was taken twice, and the fastertimes were used as the representative values for each test.

B. Stretching method
The stretching machine we developed is pneumaticallydriven, and the mechanism is shown in Fig. 2. When air
ﬂows into the bellows, the foot is dorsiﬂexed. As the machineis driven with the hold-to-run method, air continues to ﬂow
while the user holds the switch.
To stretch the foot, a certain dorsiﬂexion angle must
be maintained. Before stretching, the foot was passively
dorsiﬂexed by the stretching machine, and the air pressure
when the user experienced stretching in the lower limbs
was recorded. The stretching intensity was thus determinedby setting this value as the upper limit of the air inﬂow
during stretching,. After this, to perform foot stretching, theuser held the switch to allow upward air inﬂow until theydecided that the stretching intensity had been reached, andthe foot was kept in the dorsiﬂexion position. The machine
was programmed to automatically block the inﬂow of air
when the speciﬁed stretching time was reached.
The patient’s left foot was stretched in the experimentbecause it had more movement restrictions than the rightfoot. The left foot was placed on the stretching machine
while the patient sat in a chair. Her knee joint was extended,and she operated the switch with her dominant right hand(Fig. 3). Static dorsiﬂexion stretching using the stretchingmachine was performed twice a week for 4 weeks. Eachsession was performed for 10 min by repeating 5 sets of 2min static stretching. The stretching intensity was set eachtime before the 2 min of stretching.

III. R ESULTS
The results are shown in Table I．As a result of stretchingwith the device for 4 weeks, the range of motion of the ankle75

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R ESULTS OF BIOMECHANICAL AND FUNCTIONAL MEASUREMENTS PRE
AND POST 4 WEEKS STRETCHING

ROM (°)
Passive torque (Nm)MVC (Nm)
5m walk

at 0°
at 5°
at 10°
time (sec)steps (step)cadence (step/sec)

TUG (sec)Pre10
5.0±0.9
4.7±0.4
6.0±0.6
4.5±0.9
4.4
11
2.5
8.9

Post
15
4.3±0.6
5.1±1.1
5.6±0.4
3.5±0.2
4.5
112.4
7.7

mean±standard deviation
ROM: range of motion in passive dorsiﬂexion
MVC: maximum voluntary contraction in planterﬂexion
TUG: time up and go test
0°, 5°, 10°: passive foot dorsiﬂexion angle during measurement

dorsiﬂexion increased by 5◦ . The passive torque decreasedslightly at 0◦ and 10◦ dorsiﬂexed and increased at 5◦ dorsiﬂexed. The MVC in plantarﬂexion decreased by 1.0 Nm. In
the 5m walk, the number of steps did not change, and thetime and cadence showed minimal changes. The TUG timewas 1.2 sec faster after 4 weeks.
IV. DISCUSSIONIn this study, we investigated the effect of long-term
use of the stretching machine we developed, in addition
to normal rehabilitation. The participant performed 10-min
foot dorsiﬂexion stretching using the machine twice a week
for 4 weeks. After the experimental period, the dorsiﬂexion
range of motion of the ankle increased by 5◦ and the passive
torque at 10◦ dorsiﬂexed foot decreased, indicating decreasedfoot rigidity. We hypothesized that foot stretching using
the machine mitigated the muscle tone, thereby increasing
the ankle range of motion for a participant who had slight
hypertonia of the lower limb because of the cervical spine
injury. Moreover, it is possible that the ankle plantar ﬂexion
muscle strength also decreased due to the reduction in lower
limb muscle tone. Additionally, although the results of 5m walking did not change signiﬁcantly, the TUG time wasshortened. TUG measures both straight walking and turning;
accordingly, the time could be reduced because the turning
became smoother. Thus, it was predicted that the subject sbalance ability had improved.
The limitation of this study is that the experimental period
was only 4 weeks. Previous studies have suggested that continuous foot stretching for 8-12 weeks or longer is desirable
to assess long-term effects [11], and veriﬁcation over a longer
period is required. In addition, this study reports the effectsof machine use in only one participant; further studies withhealthy participants and a larger sample size are required toverify our results.
R EFERENCES[1] 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
and active movement training of ankle and mobility impairments instroke,” NeuroRehabilitation, vol. 32, no. 3, pp. 625–634, 2013.

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