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EMG Biofeedback, physiotherapy
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Sreeraj S R
EMG BIOFEEDBACK
Sreeraj S R
Feedback
• Feedback is a response to a particular process
or activity
• According to Weiner, 1948, ‘feedback is a
method of controlling a system by reinserting
into it the results of its past performance’
• Physiological feedback is a self-regulatory
biological system in which the output or
response affects the input either positively or
negatively
Sreeraj S R
Positive Feedback
• Change in one
direction
causes further
change in the
same direction
Uterine
contraction
Pressure on
cervix
Oxytocin
release
Sreeraj S R
Negative Feedback
• Change in one
direction
causes further
change in the
opposite
direction
Body
Temperature
Rises
Body Sweats
more
Body
Temperature
drops
Sreeraj S R
Feedback
• Feedback includes information related to the
sensations associated with some action as well
as information related to the result of the action
relative to some goal or objective.
• Physiological feedback refers to intrinsic
information inherent to movement including
kinesthetic, visual, cutaneous, vestibular, and
auditory signals collectively termed as response
produced feedback
Sreeraj S R
Feedback
• Feedback from some measuring
instrument which provides information
about a biologic function is referred to as
biofeedback
• Also refers to extrinsic information or some
knowledge of results presented verbally,
mechanically, or electronically to indicate
the outcome of some movement
performance
Sreeraj S R
Definition of Biofeedback
• Three professional biofeedback organizations, the Association for
Applied Psychophysiology and Biofeedback (AAPB), Biofeedback
Certification International Alliance (BCIA), and the International
Society for Neurofeedback and Research (ISNR), arrived at a
consensus definition of biofeedback in 2008:
• “is a process that enables an individual to learn how to change
physiological activity for the purposes of improving health and
performance. Precise instruments measure physiological activity
such as brainwaves, heart function, breathing, muscle activity, and
skin temperature. These instruments rapidly and accurately 'feed
back' information to the user. The presentation of this information —
often in conjunction with changes in thinking, emotions, and
behavior — supports desired physiological changes. Over time,
these changes can endure without continued use of an instrument.
http://en.wikipedia.org/wiki/Biofeedback
Sreeraj S R
In Biofeedback>
1. The information is detected,
2. provided in an understandable way to the
patient
who can then, at their own initiation,
3. use the information to achieve a measure of
control over the same process.
i.e. engaging the patient in a ”closed loop”
learning, using feedback until sufficient
development of his motor skills occurs, so that
an “open loop“ movements can be achieved.
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Physiologic
signal
Response by
patient
Physiologic
signal
Response by
patient
Detection
and
feedback
Open Loop
Closed Loop
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every day forms of
biofeedback
Sreeraj S R
you have to have
accurate feedback, of course
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Requirements
• To be realistic and successful, three main
elements are needed in order to enhance
motor learning:
1.Relevant
2.Accurate
3.Speed of information
Most EMG biofeedback devices nowadays
introduce 50 to 100 m sec - delays before the
signal can reach the ears or eyes of the patient
Sreeraj S R
Sreeraj S R
EMG Biofeedback
• Nerve fiber conducts an
impulse to the neuromuscular
junction
• acetylcholine binds to receptor
sites on the sarcolemma
• inducing a depolarization of
the muscle fiber
• creates movement of ions and
thus an electrochemical
gradient around the muscle
fiber
• Changes in potential difference
or voltage associated with
depolarization can be detected
by an electrode placed in close
proximity
Sreeraj S R
EMG Biofeedback
• EMG does not measure muscle
contraction directly
• EMG measures electrical activity
associated with muscle contraction
• Electrical activity of muscle measured in
micro volts (1 volt = 1,000,000 µV)
Sreeraj S R
EMG Biofeedback
Sreeraj S R
EMG Biofeedback
Advantages:
• Can be integrated with other therapeutic
interventions
• an enhancer of the therapy
• reduce patient’s reliance on the therapist
• gain control without reliance on the
therapist,
and once gained,
• to maintain control without either the
therapist or the machine.
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Working
A biofeedback loop. Here the forearm muscles are monitored
to provide a visual readout to the user. The feedback loop is
completed when the user alters her muscle tension to adjust
the readout.
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Working
2 active electrodes and
1 reference electrode
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Working - CMRR
• Two signals are fed to a differential amplifier which
subtracts the signal from one active electrode from the
other active electrode
• Differential amplifier uses reference electrode to
compare the signals of the two active electrodes
• This in effect cancels out or rejects any components that
the two signals coming from the active electrodes have
in common thus amplifying the difference between the
signals
• Ability of the differential amplifier to eliminate the
common noise between active electrodes is called the
common mode rejection ratio (CMRR)
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Working - filtering
• EMG signals are in the range of 0 – 500
Hz
• Frequencies above 500 Hz is filtered out
• The dominant energy of the EMG signal is
in the range of 50 – 150 Hz
• Motion artifacts in the range of 0 – 20 Hz
• Frequencies below 20 Hz are filtered by
using a high pass filter
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Working – Rectification & Integration
Raw EMG activity in muscle is an alternating voltage
- direction or polarity is constantly reversing
Rectification is the summation of electrical activity.
To determine the overall increase and decrease in
electrical activity, deflection toward the negative pole
must be flipped upward toward the positive pole
EMG signal is then smoothed to eliminate the
peaks and valleys or high frequency
fluctuations
The signal may then be integrated by measuring
the area under the curve for a specified period
of time. Integration forms the basis for
quantification of EMG activity.
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Visual cues
1. Meter read outs
2. Flashing lights
3. Oscilloscope
4. Computer screens
Auditory cues
1. Changing tones
2. Clicks
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Features of the BF Devices
• Gain settings, low & high
• Sound
• Threshold
• Peak Hold facility
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Gain settings
• On low gain settings the machine will
require a greater signal before the output
changes - in other words, it is less
sensitive.
• On higher gain settings, a small amount of
EMG activity will be easily seen by the
patient.
Sreeraj S R
Sound
• Most EMG biofeedback devices offer an
audible feedback in addition to the visual
information
• the change in sound is such that the
frequency of the ‘beeps’ increases with
increased EMG activity.
Sreeraj S R
Threshold
• Incorporation of a threshold system
enables the patient targets to be set.
• The audible signal can be adjusted so that
it will only be heard if the patient achieves
a preset activity level.
• to achieve an increase in muscle activity,
the threshold can be set so that the
audible feedback only comes on when
50% of the scale has been achieved.
Sreeraj S R
Peak Hold facility
• Some devices offer a peak hold facility which enables
either the signal to be fed back on a continuous basis i.e.
Peak Hold OFF.
• With the Peak Hold ON, the display does not change
instantly, but reports the peak activity in the previous 3
second recording period.
• This facility can be useful especially in later stage
recovery or rehabilitation, when sustained activity is
more important than instantaneous EMG spikes.
• In early rehabilitation, it is preferable to use the
instantaneous feedback as it is far less confusing i.e.
Peak Hold OFF.
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Equipment
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Electrode Placement
• Silver/Silver Chloride
construction
• judicious electrode
placement
• electrode spacing
• Noise/ movement artefact
• active electrodes should be
placed in parallel with the
dominant muscle fibres
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Uses
• Facilitate muscle contractions
• Promote increased motor recruitment
• Regain neuromuscular control
• Decrease muscle spasm
• Promote relaxation
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Indications• Stroke
• Spinal cord injury
• Recovering and improving muscle action
• Chronic musculoskeletal injury
• Pain
• Posture control
• Balance and mobility
• Trunk muscle re education
• Respiratory muscle control
• Incontinence
• Stress related conditions
• Hypertension
• Idiopathic Raynaud’s disease
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Contraindications
• If the patient is prohibited from moving the joint or isometric contractions, then BF should NOT be used
• Unhealed tendon grafts
• Avulsed tendons
• Third degree tears of muscle fibers
• Unstable fracture
• Injury to joint structure, ligaments, capsule, or articulating surface
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Technique for Motor Recruitment
• Position pt., Explain to pt., Work in quiet area.
• Apply sensors to an area to demonstrate the desired A-V
signal and activity.
• Adjust to the most sensitive level that picks up any
MUAP that pt. can produce
• Instruct pt. to try to produce an A-V signal
• As voluntary muscle activity improves, the A-V signal will
increase. Adjust the gain to decrease the sensitivity, so
pt. has to work harder to recruit more muscle units.
• As pt. masters in one position, change positions
• Document all parameters. Tx duration 30-60 min
• Clean up
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Inhibition of Spasticity
• Goal: decrease undesirable muscle activity that may be
interfering with functional movement.
• Eval. spasticity, Explain to pt., Apply sensors and
demonstrate desired activity.
• Find the least sensitive setting that produces minimal A-
V feedback
• Have pt relax, use techniques and have pt. lower the A-V
signal.
• As the signal decreases, lower the shaping controls
(gain), to a more sensitive level. As pt. relaxes better,
continue to increase sensitivity
• Change positions
Sreeraj S R
• A simple device to
provide feedback to
ensure quality, and
precision in exercise
performance and testing.
• Monitors position of the
low back and provides
feedback when the
abdominal muscles are
not actively or effectively
protecting the spine.
Sreeraj S R
References
1. http://en.wikipedia.org/wiki/Biofeedback
2. http://bme2.aut.ac.ir/~towhidkhah/MotorControl/Resources/EMG.pdf
3. http://www.electrotherapy.org/modalities/biofeed.htm
4. Low & Reed, Electrotherapy Explained, principle and Practice, 4th edition,
2009, Elsevier,
5. Jagmohan Singh, Textbook of Electrotherapy,1st Edition, 2005, Jaypee
Publications.