Training on Muscle Palpation Using
Artiﬁcial Muscle Nodule Models
Kaoru Isogai, Shogo Okamoto, Asuka Noda, Ayumi Matsuzawa
and Yoji Yamada

Abstract We developed a palpation simulator for training on muscle palpation
techniques for myofascial pain syndrome. This simulator consisted of two layersthat resemble the hardness of actual human skin-fat and muscle tissues. Furthermore, a muscle nodule model made of urethane rubber was laid in the simulator.
Five participants were trained on the palpation technique for localizing the muscle
nodule models, using our simulators. After the training session, they localized themuscle nodule models more deﬁnitely than before. The proposed muscle nodule
palpation simulator may improve manual palpation techniques used for examining
myofascial pain syndrome.
Keywords Palpation
syndrome⋅ Simulator ⋅ Muscle nodule ⋅ Myofascial pain

1 Introduction
Many musculoskeletal pains such as neck or back pains are associated withmyofascial pain syndrome, which is caused by myofascial trigger points.
Myofascial trigger points are hyperirritable spots located at the muscle nodules
along the taut bands in the muscle belly [1]. In a clinical setting, myofascial trigger
points are localized by palpation. Therefore, the difference in hardness between amuscle nodule and muscle belly is an important objective for the diagnosis of
myofascial pain syndrome. However, it is demanding for clinicians to ﬁnd theslightly hard spots in the muscles, and previous studies have reported that thelocalization of trigger points by palpation is not reliable [2, 3]. To solve this issue,

K. Isogai (✉) ⋅ A. Noda ⋅ A. Matsuzawa
Department of Physical Therapy, Tokoha University, Hamamatsu, Japane-mail: kisogai@hm.tokoha-u.ac.jp
K. Isogai ⋅ S. Okamoto ⋅ Y. Yamada
Department of Mechanical Science & Engineering, Nagoya University, Nagoya, Japan© Springer Nature Singapore Pte Ltd. 2018
S. Hasegawa et al. (eds.), Haptic Interaction, Lecture Notes
in Electrical Engineering 432, DOI 10.1007/978-981-10-4157-0_57

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we developed an artiﬁcial fat and muscle model for training on palpation for
myofascial pain syndrome.
Because the muscles are palpated through the skin and fat tissues, the muscle
nodule palpation simulator should also consist of subcutaneous and muscular layers. The hardness of the two layers should resemble that of the actual humanskin-fat tissue and muscle tissue, respectively. However, the mechanical characteristics of the human subcutaneous and muscle tissues are nonlinear [4, 5], and thesolid model, which is made up of a unique material, cannot represent themechanical characteristics of human body tissues. Fortunately, a layered rubber
structure is known to realize the mechanical characteristics similar to those ofhuman tissues [5, 6]. Therefore, we also adjusted the mechanical characteristics ofurethane models by adopting a layered structure with fabric sheets between layers.
In this study, we demonstrated that our simulator could improve the palpation
technique used for localizing the muscle nodules by physical therapy trainees.

2 Muscle Nodule Palpation Simulator
We developed a urethane rubber model of human gluteal tissue basis on themethods of our previous study [5]. As shown in Fig. 1, the model was cylindrical inshape, with the height and diameter being 70 mm and 120 mm, respectively. The
upper layer of the model corresponds to the subcutaneous layer, and its thickness
was 12 mm. The lower layer of the model corresponds to the muscle layer, and its
thickness was 58 mm. The thickness of skin-fat and muscle layers were comparable
to the depth of the human gluteal subcutaneous tissues and muscle tissues. A cotton
sheet was laid between the two layers of the skin-fat model and between the skin-fat
and muscle layers. Furthermore, the top surface was covered by a stretchable knit
sheet. These layered structures achieved nonlinear stress-strain characteristics
similar to that of human tissues [5].

Fig. 1 Urethane—made skin-fat and muscle model for muscle nodule palpation

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We embedded a muscle nodule model, which was 31 mm in length, 16 mm inwidth, and 9 mm in thickness, at 24 mm depth from the surface of the muscle
model. The form and burying depth of muscle nodule model were determined basedon opinions from clinicians. The nodule model was made of urethane rubber of405.5 kPa and colored with red ink.

3 Experiment: Training on Muscle Nodule Palpation
by Using Artiﬁcial Urethane Simulators
Our muscle nodule palpation simulator was intended to aid training on palpation.
To conﬁrm the availability, we investigated the effect of the training on localizationof the muscle nodule model by using the simulator. This study was conducted withthe approval of the internal review board of Tokoha University (Registration no.
2014-015H).

3.1

Stimuli: Artiﬁcial Muscle Nodules

As shown in Fig. 2, we developed four types of simulators that differed in terms of
the position and direction of muscle nodule models, and one that did not contain amuscle nodule model. Simulator CS contained the muscle nodule model at theposition of the circular center. Simulators DRS, DCS, and DSS contained themuscle nodule model at the position 15 mm deviated from the circular center, andthe models oriented radial, circumferential, and slant directions, respectively. The
participants were blinded to the conditions of the muscle nodule model because all
simulators were covered with an opaque knit cloth.

Fig. 2 Positions of muscle nodule models in the urethane models

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3.2

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Participants

Five physical therapy trainees participated in this experiment. None of them had
used the simulators for muscle palpation and they were unaware of the objectives ofthe present study.

3.3

Procedures

3.3.1

Localization of Nodule Prior to the Training Session

After all the participants were presented a muscle nodule model, they received
explanations that some simulators would contain the muscle nodule model within aradius of 30 mm from the circular center at the half depth of the simulator. They
were instructed not to lift the simulator and not to peep from the side. Furthermore,they were told not to push the simulator with excessive force, which might cause
pain if applied on the actual human body. The participants were allowed to examine
each of the four types of simulators—DRS, DCS, DSS, and NS—within 1 min.
Simulator CS was not used in the localization task. The simulators were presented
in a random order and direction. During each trial, they judged whether the muscle
nodule model existed in the simulator. If they judged that the muscle nodule model
existed, they placed a paper leaf, which imitated the outer shape of muscle nodulemodel, on the top surface of the simulator, judging both position and direction. All
the participants repeated the procedures mentioned above 20 times, i.e., ﬁve repetition for each type of simulator.

3.3.2

Training Session by Using Palpation Simulator

All the participants were trained on palpation using simulator CS to know thesensation experienced by palpating the muscle nodule model for 5 min. They wereallowed to lift the simulator and to check the position of the muscle nodule modelby looking through the transparent bottom of the simulator. After the training, they
were required to freely describe their impressions about the training.

3.3.3

Localization of the Nodule After the Training Session

All participants repeated the same task described in Sect. 3.3.1. Thereafter, they
freely described their impressions about the effect of the training session on theirjudgment.

Training on Muscle Palpation …

3.4339Analysis

For the trials in which the simulator was perceived to contain the muscle nodule
model, we measured the gaps of distance and rotational angle between the silhouettes of the muscle nodule model that was projected to the top surface of thesimulator and the paper leaf placed by each participant. We regarded the participants’ answers as correct when the distance and angle gaps were smaller than
16 mm and 30°, respectively. We applied Wilcoxon signed rank test on the correct
answer ratios for simulators DRS, DCS, and DSS. Note that we excluded theanswer for simulator NS, for which the participants mostly responded correctly,
from the analysis because they would increase the apparent correct answer ratios.

3.5Results

Figure 3 shows the mean correct answer ratios for each session and the results ofthe statistical analysis. The correct answer ratios for the position signiﬁcantlyimproved after training. According to the introspective reports provided by theparticipants after the training session, they could acquire exploratory motion tosense the muscle nodule model deep in the simulator, and they understood theappropriate strength of pressure required to identify the muscle nodule model.
Furthermore, in their introspective reports after the post-training session, the effectsof the training session were positively recognized. They reported that they could
utilize the experiences acquired through the training session.

Fig. 3 Correct answer ratios
for a localization task before
and after the training session

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4 Conclusions
In this study, we demonstrated that the localization techniques for the slightly hard
spot in the muscle model had improved after a training session using our palpation
simulator. The localization experiments and introspective reports from the trainees
suggested the beneﬁcial influences of the knowledge of haptic sensations felt
because of nodules in the muscle and exploratory hand motions for effective palpation. The models used in the present study exhibited stress-strain characteristics
similar to those of the human gluteal tissues. In addition, these models are believed
to be similar to actual human tissues [5]. Clinicians’ examination ability for themyofascial pain syndrome may improve by a training program using oursimulators.

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