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EMG BIOFEEDBACK

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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

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Positive Feedback

• Change in one

direction

causes further

change in the

same direction

Uterine

contraction

Pressure on

cervix

Oxytocin

release

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Negative Feedback

• Change in one

direction

causes further

change in the

opposite

direction

Body

Temperature

Rises

Body Sweats

more

Body

Temperature

drops

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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

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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

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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

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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

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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

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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

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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)

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EMG Biofeedback

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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.

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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.

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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.

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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

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• 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.

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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.