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EMG SITE LOCATION USING AN ELECTRODE ARRAY
Farrell T.R.1, Hanson W.J. 1, Johannson J.L. 1, Klodd E.J. 1, Edell D.J.2, Sexton S.V. 2, Yuhan, J.A. 2
1
2
Liberating Technologies, Inc., Holliston, MA InnerSea Technology, Inc., Bedford, MA
INTRODUCTION
Our group is developing a microprocessor-based
knee controller that will use myoelectric inputs from
the user to assist in the control of the knee joint.
While muscle locations are relatively fixed in ablebodied subjects, amputation surgery often causes
residual muscles to be located in atypical positions.
One challenge is accurately identifying the locations
of the residual muscles for electrode placement.
the maximum EMG signal was rarely more than 2 cm
from the palpated location.
METHODS
The locations of the residual surface muscles were
first palpated and then marked on the surface of the
residual thigh. An electrode array consisting of 32
channels of bipolar EMG recordings (bipolar
recordings with 4 cm spacing) arranged in roughly a
12 cm diameter circle was placed on the residual limb
over the palpated muscle site (Fig. 1) and held in
place using an elastic bandage. The user was then
asked to perform a movement associated with the
targeted muscle. For example, the subject was asked
to flex the hip when rectus femoris was targeted.
The EMG signals were recorded in real time and used
to create a heat map in which larger EMG signals
corresponded to ‘hotter’ colors (Fig. 2). The heat map
was used to determine the location of the maximum
EMG signal. This location was then compared to the
palpated location.
Figure 2. Heat map created as subject performs hip
flexion to activate the rectus femoris. The non-centered
red area indicates that largest EMG activity was located
near, but not exactly under, the palpated site.
DISCUSSION
The standard methods of locating EMG sites by
iteratively moving an electrode around the surface of
a limb assumes that the user is producing the same
contraction every time. Our results indicate that being
able to view many potential EMG locations
simultaneously allows for quick and accurate
determination of the locations that produce the
maximum EMG amplitudes. While it provided a good
estimate, we found that the mechanical displacements created during palpation are not completely
indicative of the location of the maximum EMG signal.
While this system was developed for finding lower
limb muscle sites, we believe a smaller version could
also be used to find optimal upper limb sites as well.
CONCLUSION
The electrode array has proven useful in locating the
residual limb sites that create the largest EMG signal.
REFERENCE AND CKNOWLEDGEMENTS
Figure 1. Muscle sites were palpated and the 32 channel
electrode array was centered on the palpated site.
RESULTS
Results from the first three subjects reveal the largest
EMG amplitude was rarely located directly under the
palpated site. However, the location that produced
U.S. Patent # 5,341,813 “Prosthetic electrode array
diagnostic system.”
This research and development project was conducted by
the QinetiQ North America Technology Solutions Group
team and made possible by a contract awarded and
administered by the U.S. Army Medical Research & Materiel
Command (USAMRMC) and the Telemedicine & Advanced
Technology Research Center (TATRC) under contract
W81XWH08C0729.
American Academy of Orthotists & Prosthetists
37th Academy Annual Meeting and
Scientific Symposium
March 16-19, 2011