SICE Annual Conference 2013
September 14-17, 2013, Nagoya University, Nagoya, Japan

Wearable Dummy to Simulate Equinovarus
for Training of Physical Therapists
Hiroshi Okumura1, Shogo Okamoto1, Shun Ishikawa1, Yasuhiro Akiyama1 , Kaoru Isogai2 ,Yuji Hirano 3 , and Yoji Yamada1
1

Department of Mechanical Engineering and Science, Nagoya University, Nagoya, Japan2
Department of Physical Therapy, Tokoha University, Hamamatsu, Japan3
Department of Rehabilitation, Yokkaichi Municipal Hospital, Yokkaichi, Japan

Abstract: It is indispensable for physical therapists in training to experience various symptoms during their period of
education; however, such chances are limited in educational institutions. We developed a prototype of a wearable dummyrobot system to simulate equinovarus, which is a typical disorder of the foot caused by stroke, to enhance the trainingof physical therapists (PTs). This wearable dummy system makes it possible to simulate joint disorders, while allowing
the trainees to learn about the complex joint movements of humans, such as those observed in human feet. The dummysystem deforms the foot of a healthy wearer using a wire mechanism so that the resultant foot posture and resistanceforce required for therapeutic operations resemble those of typical equinovarus patients. The resistance forces felt by thetrainees can be tuned by changing the endpoint of the wire. From sensory evaluations involving PTs, it was concluded thatwith potential future improvements, the dummy simulator will become an effective training tool to aid physical therapy
students.
Keywords: Wearable dummy, Equinovarus, Physical therapy.

1. INTRODUCTION

One of the major topics in the development of suchrobot systems is how to make them resemble humanlimbs. Ishikawa et al. proposed a framework fora wearable dummy robot to simulate joint disabilities [6]. Within this framework, a healthy person wears
an exoskeleton-type robot, which simulates the behaviors of joint impairment. As described in section 3.1, thestrength of this approach is that it simulates symptoms as
it allows the students to experience the complex trajectory of human joint motion and the characteristics of theskin and bone.

Physical therapists (PT) play an important role in treating patients whose motor functions are impaired as a result of disorders such as stroke and arthritis. Because
patients’ symptoms substantially depend on individuals
and their types of impairments, physical therapy students
need to experience various symptoms to master therapy
techniques. However, students rarely have the chance toexperience such a variety of symptoms in training institutions. Even during internship training, it is considered
ethically problematic for unqualified trainees to treat patients. Therefore, some research groups have started todevelop dummy robots that simulate patients’ symptoms
to support the education of PTs.

In this study, we simulated foot equinovarus using adummy robot. Equinovarus is common and typical symptom of patients suffering from hemiplegia or spasticity asa result of stroke, and PTs often face this in the field.
At most 40% of stroke patients develop spasticity [7, 8].
If the equinovarus progresses, the patient suffers from a
gait disorder and a severe decline in his/her quality oflife. Therefore, PTs give importance to improving in thesymptoms of equinovarus. Thus far, in earlier studies, thedummy robots have simulated symptoms such as contracture, rigidity, a limited range of joint motion, and clonus.
Despite its importance, there has been a hesitancy in previous studies to use dummy robots to simulate equinovarus. This may be because the behaviors of the humanfoot joint are overly complex and difficult to simulate using a robot, as described in section 2.1.

Masutani et al. developed a robotic leg that simulates
impaired knee joints [1]. The simulated impairments
included a motion-limited joint, jackknife phenomenon,
and articular rigidity. They also focused on its appearance
by forming bone features and covering the robot withskin-like materials. Kikuchi et al. simulated the spastic
movements of a foot joint using a leg and foot robot [2].
Grow et al. compared and validated two representative
spasticity models using a robotic joint [3]. In these studies, they simply modeled human joints as uniaxial joints.
However, human joint movement involves multiple degrees of freedom. Takahashi et al. simulated the stretch
and contraction of a forearm accompanied by the extension and flexion of an upper limb using an oval cam ina robotic joint [4]. Oki Electric Industry Co, Ltd, proposed a robot with six degrees of freedom for the trainings of PTs [5]. Physical therapy students can learn about
the typical dynamic resistances and motions of impaired
joints using these dummy robots.

The objective of this study was to verify the feasibility of using a wearable dummy system to simulate
equinovarus for the training of PTs. Because the complex foot joint movements are accompanied by equinovarus, it is difficult to simulate these using robotic joints.
On the other hand, the wearable dummy system is potentially able to realize such complex joint motions. The
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2.2 Pathology of equinovarus
Equinovarus is a foot deformity that affects hemiplegia patients. Fig. 2 shows both of the feet of patient suffering from equinovarus. The disordered foot takes adduction, supination, and plantar flexion positions primarily as a result of shortening or hypertonia of the triceps
surae muscle, tibialis posterior muscle, flexor digitorum
longus muscle, and flexor hallucis longus muscle. In theacute phase, the intensity of the foot deformity is mild,and equinovarus is accompanied by spasticity. However,in the chronic phase, the intensity of the deformity increases, and equinovarus is accompanied by contracture,
where contracture means a condition where the range ofjoint motion is restricted. Therefore, it is difficult to restore a foot to the standard position, which is the positionof the foot joint when a human assumes a standing position. Whereas PTs typically treat equinovarus by manually stretching the disordered feet, robotic rehabilitation
or treatment devices for equinovarus have been studied
with bright prospects [10, 11].

X
Z

Y

Fig. 1 Three principle axes of joint complex.

3. WEARABLE DUMMY TO SIMULATEEQUINOVARUS

Fig. 2 Equinovarus. Left: disordered. Right: normal.

3.1 Advantages of wearable dummy
A patient dummy for training PTs requires the following functions. First, the joint resistance force and reaction force patterns that PTs feel when they move the affected body parts of patients should be accurate. Second, it should have human-like characteristics, such as
the skin, bone, and weight of a human body, to imitate a real human. Finally, it is necessary to simulate
complex joint movements which have multiple degrees
of freedom. Any dummy used for training should balance these functions. The foot of a patient suffering withequinovarus takes an adduction, supination, and plantar
flexion position. Therefore, we anticipated that complex devices would be needed to simulate equinovarus in
joint movements with multiple degrees of freedom. Thus,
we proposed the development of a wearable dummy.
This wearable dummy is an exoskeleton robot worn bya healthy person. It imitates the resistance forces of disabled joints or joint behaviors caused by various symptoms. The wearable dummy allows complex joint movements, such as a supination movement and slight plantar flexion movement, accompanied by adduction movement. Moreover, it has human-like characteristics, suchas the feel of skin, bone, weight, and the shape of a human body. Therefore, it can produce the resistance force
symptoms of equinovarus and spasticity using actuators,
while maintaining human characteristics.

dummy system for equinovarus has some design parameters. We validated the effects of these parameters on thebasis of physical models and experiments. Furthermore,
we sought ways to improve the wearable dummy basedon the introspective reports of PTs.

2. EQUINOVARUS TARGETED FOR
SIMULATION
2.1 Foot joint regarded as joint complex
The complex foot joint movements are accompanied
by equinovarus because many joints exist in the foot joint.
However, if we regard them as a joint complex, we cantreat the foot joint as one joint having three degrees offlexibility [9]. Fig. 1 shows how the three principle axesof this joint complex cross each other in a medial positionof both malleoli. The X-axis passes through both malleoli, and corresponds to an axis of the talocrural joint. Thisaxis conditions the plantar or dorsal flexion movement in
the sagittal plane. The Y axis is along the lower leg, andconditions the adduction or abduction movement in thehorizontal plane. The Z axis passes from the malleoli tothe tips of the toes in the sagittal plane. This axis conditions the supination or pronation movement by directing
the sole toward the inside or outside. The movements
around these three principle axes are not independent ofeach other. Therefore, movements around two principle axes are accompanied by movement around the otherprinciple axis. For example, a supination movement andslight plantar flexion movement are is accompanied by an
adduction movement.

3.2 Description of wearable dummy to simulate
equinovarus
The wearable dummy deforms the foot of a wearer inan equinovarus position. Moreover, it presents the reaction force pattern of equinovarus to a trainee performing
an manual examination. Fig. 3 shows a manual examination of an equinovarus patient. When a PT performs a
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Fig. 3 Manual examination of equinovarus patient.
Fig. 6 Change in distance between rotation center of human ankle and idler.

Fig. 4 Wearable dummy system for simulating equinovarus.
(a) Range of endpoint(b) Endpoints

Fig. 7 Sole of wearable device. The end point of the wire
can be adjusted within the red rectangle.
in the current control mode as the driver for the DC motor.
A wire extended from the sole went through the idler, andwas wound by a DC motor. We made a wire run along thetibialis posterior muscle in order to simulate equinovarus
accompanied by the contracture and hypertonia of the tibialis posterior muscle. Fig. 5 shows a foot transformed
into the equinovarus position by the wearable dummy.

Fig. 5 Simulated equinovarus: Foot transformed by
wearable dummy from different view points.

3.3.2 Mechanism for adjusting equinovarus
The degree of deformity and resistance forces felt by
PTs are diverse and correspond to the acuteness of theequinovarus symptoms. Therefore, the wearable dummy
was equipped with a mechanism for adjusting the degreeof deformity and resistance force felt by trainees in order
to simulate equinovarus more faithfully. There are three
types of parameters that could be adjusted. These parameters were the tension by the motor, positions of the idler,and endpoints of the wire. The torque applied to the footwas changed by changing the tension of the motor, whichcaused a change in the magnitude of the resistance force
felt by trainees in the standard position.
Fig. 6 shows the change in the moment arm between
the rotation center of the plantar flexion and tension applied to a foot by changing the position of an idler. This
produced a change in the magnitude of the resistanceforce felt by the trainees in the direction of the plantar
flexion in the standard position. When the idler position was high, due to the short moment arm, the plantar
flexion torque applied to the foot was small. In contrast,
when the idler position was low, the long moment arm
produced the large flexion torque.

manual examination against the foot of a patient sufferingfrom equinovarus, they apply force to it in the abduction,
pronation, and dorsal flexion directions. The hands of thePT perceive resistance forces in the adduction, supination, and plantar flexion directions from the foot of thepatient. The wearable dummy produces these resistanceforces for the trainee performing the examination.
3.3 Mechanism of wearable dummy to simulate
equinovarus
3.3.1 Mechanism forcing foot into posture of equinovarus
positionFig. 4 shows a prototype of the wearable dummy wedeveloped. This wearable dummy was composed of ashoe, and a cuff attached to the lower part of the knee
joint. A DC motor (Maxon motor, RE35, maximum continuous torque 97.2 mNm, torque constant 38.8 mNm/A)
with a gear head (Maxon motor, GP 32 HP, gear ratio
23:1) was attached to the cuff that was designed carefullysuch that it would not cause any pain to the wearer. We
used a servo amplifier (Maxon motor, 4-Q-DC ADS 50/5)
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Table 1 Physical parameters for each endpoint. Angles,
link lengths, forces, and torques at basic foot position.

Endpoint

IIIIIθ1 [rad]θ2 [rad]θ3 [rad]l1 [mm]l2 [mm]l3 [mm]f1 [N]
τ1 [Nm]τ2 [Nm]τ3 [Nm]

Idler

f1

Wire

I

Fig. 8 Tension applied to sole (endpoints of wire).

Rotation center ofhuman ankle
l1

f 11

Force sensor

Idler

τ2

l2

I

θ1

Idler

τ1

Foot

(a) Bottom view

X

f 12
θ2

Rotation center of human ankle

Z(b) Front view

f 13

=
τ3

τ2

=

Idler

Fig. 10 Measurement of adduction torque or force.

θ3

=
=

sin θ1
f 1 l2
1 − cos2 θ1 sin2 θ2
f13 l3sin θ1√f 1 l3 ,1 − cos2 θ1 cos2 θ3

(2)

(3)

respectively. We measured θ1 –θ3 and l1 –l3 when theendpoints of the wire were at I–III, and calculated τ1 –
τ3 by (1) to (3). These values are summarized in Table 1.
The torques were calculated with f1 being 8.3 N. τ1 becomes larger as the endpoint shifts from III to I. In otherwords, the adduction torque applied to the foot increases
as the endpoint shifts from III to I. By contrast, τ2 becomes smaller as the endpoint shifts from III to I. Hence,the supination torque is highest when the endpoint is at
III, and exhibits smaller values for II and I. Planter flexion torque τ3 is small under each condition because l3 issmall. To increase τ3 , the position of the idler is lowered.
3.4 Measurement of adduction torque using force sensor
We measured the adduction torques or forces causedby the dummy system using different endpoints. Measuring the torques applied to the foot on each principle axis isdifficult, partly because the three axial motions of the footare not independent of each other. As a beginning point,
we focused on the adduction force under the basic ankle

f11 l1cos θ2
f 1 l1
1 − cos2 θ1 sin2 θ2
f12 l2II

Y

Rotation center of human ankle

The position of the endpoint of the wire could be varied within the range shown as a red rectangle in Fig. 7(a).
The angle between the shoe and the wire changed withthe endpoint. Accordingly, the direction of tension f1
represented in Fig. 8 changed, and the resistance force
felt by the trainees in the adduction and supination direction changed.
Fig. 9 shows a physical model of the wearable dummythat explains the principle behind the changes in the resistance forces in the adduction, supination, and planter
flexion directions. Fig. 9 shows the projection of f1 fromthe bottom, front, and side views, where f11 , f12 , and f13
represent f1 on these planes. l1 , l2 , and l3 are the momentarms between the rotation center of the human ankle andf11 , f12 , and f13 , respectively. θ1 , θ2 , and θ3 are the angles between the shoe and f11 , f12 , and f13 , respectively.
τ1 , τ2 , and τ3 are the adduction, supination, and plantar
flexion torques and are expressed as

=

f

τ1

(c) Side viewFig. 9 Trihedral figures of wearable dummy system

=

Wall

III

Rotation center of human ankle
l3
τ3
Idler

τ1

Endpoint of wireI
II
III
0.25 0.55 1.13
1.11 1.05 1.03
0.47 0.81 1.30
9368
23
89.4 87.8 87.5
16
8.3
0.69 0.42 0.11
0.37 0.56 0.71
0.065 0.09 0.12

(1)

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4. FREE DESCRIPTION BY PHYSICAL
THERAPISTS

Resistance in directionof adduction fy [N]65Five PTs experienced the resistance forces presented
by the wearable dummy and freely gave comments. Here,
we aimed to acquire subjective and descriptive opinions, which tend to be missed in objective evaluation
tasks. They performed manual examinations, as shown in
Fig. 3, against a healthy person wearing the dummy. The
wearer sat in a chair. The endpoint and motor’s torquewere varied among I–III and 3.4–11 N, respectively. The
following opinions were highlighted.
Two PTs appreciated that the resistance forces simulated by the current dummy system were similar to thoseof a typical equinovarus patient. The other PTs pointed
out that larger resistance forces were required to simulate equinovarus in the chronic phase with muscle contracture. Such large forces can be simply realized byusing a motor with larger outputs. Furthermore, two of
the five PTs stated that the individual differences between
equinovarus patients were well represented by changing
the endpoints of the wire.
The resistance forces felt by the PTs were approximately constant regardless of the foot joint angle because
the DC motor installed on the wearable dummy generated constant torques. However, the resistance forces that
the PTs feel from the patients are naturally proportional
to the degree of dorsal flexion in the foot. They suggested
that the implementation of these proportional changes in
the resistance forces would lead to a more realistic simulation. It should be noted that such control of the motor
torque according to the joint angle should be introducedin the future. Furthermore, the effects of spasticity will
be realized. When spasticity is combined with equinovarus, the resistance forces perceived by PTs depend on
the joint velocity [12]. Three PTs commented that thesimulation of spasticity would be beneficial for the education of trainees.
In the acute and recovery phases of equinovarus, as a
PT treats the foot of a patient with equinovarus, its range
of joint motion is extended. Such changes in equinovarus
over time were called for by two PTs.

4
3
2
1
0

Endpoint
Ⅰ End
Endpoint
Endpoint
End pointⅠ
point Ⅱ
Ⅱ End
point Ⅲ
Fig. 11 Averages and standard deviations of resistanceforces in direction of adduction. Adduction forces
can be varied by adjusting the wire endpoint.
Table 2 Comparison of τ1 (adduction torque) values
between physical model and measurements.

Model [Nm]Measurement [Nm]

I
0.69
0.63

Endpoint
IIIII
0.42 0.11
0.48 0.35

posture. The adduction force is mainly produced by τ1 .
As shown in Fig. 10, a force sensor (MINI, BL-Autotech
Inc., Kobe, Japan) was fixed to the inner side of the footand used to measure the Y -axial forces (fy ) caused by
the wire tension. The force was measured twenty times,
with each measurement period being approximately 1 s.
The final values were computed as the averages of all thetrials. During the measurement, the DC motor generated
a tension of 8.3 N, and the wearer of the dummy systemstayed relaxed.
The average forces were 4.68 ± 0.96, 3.58 ± 0.72,
and 2.58 ± 0.42 N for the endpoints of I, II, and III, respectively. The average adduction forces were then transformed into the torques around the rotation center of theankle for comparison with the values computed from themodel in the previous section. As shown in Fig. 11, theaverage adduction torques were 0.62, 0.48, and 0.35 Nm
for the endpoints of I, II, and III, respectively. Table 2
shows a comparison of these torques between the measurements and physical model. These values did not exactly match, possibly because of the differences in theconditions. In particular, the positional relationships between the rotation center of the human ankle and the idler
might be the major source of the error. In the physicalmodel, their X and Z coordinates were supposed to beequal; however, they were not equal during the measurement. Nonetheless, the ordinal relationships among thethree conditions matched between the model and measurements. The measured forces decreased as the endpoint moved from the toe (I) to the heel (III).

5. CONCLUSION
In this article, we reported a prototype wearable
dummy system that simulates equinovarus. Earlier studies hesitated to use a dummy robot to simulate such
symptoms, mainly because of the complex behaviors of
the human foot joint. A wearable-type dummy allowed
us to simulate equinovarus in feet while maintaining the
intrinsic movements of human foot joints. The simulator
worn by a healthy person used a DC-motor driven string
attached to his/her foot to transform it. Consequently, thefoot was constrained in an equinovarus position. A few
of the parameters of the dummy system were adjustable,
which allowed the simulated foot to represent various levels of severity or individual differences between equinovarus patients. For example, the adduction torque could
be varied as much as two fold by changing the wire’s end2276

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point in the sole. For the assessment of the system, physical therapists experienced and evaluated the simulated
equinovarus using several combinations for the endpointof the wire and its tension. They felt that the dynamic
control of the string tension would provide a better simulation. We expect that such an improvement will realizea more effective dummy system in the future.

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ACKNOWLEDGEMENT
This work was supported in part by the Naito Foundation.

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