Biofeedback Flashcards
What is electromyographic feedback?
A training technique that enables an individual to gain some element of voluntary control over muscular or autonomic nervous system functions using a device that produces an auditory or visual stimuli
what is the functional unit of a muscle
motor unit
what is a motor unit comprised of
a single alpha motor neuron and all of the fibers it innervates
when do muscle fibers contract
when the action potential of the motor nerve which supplies them reaches a depolarization threshold
what does depolarization generate?
an electromagnetic field and the potential can be measured as microvolts
How does all of that tell the measuring device what is happening?
- The depolarization, which spreads along the membrane of the muscle, is the muscle action potential (AP).
- The MUAP is the summation of the individual muscle APs for all of the fibers of a single MU
- Therefore, the EMG signal is the algebraic summation of the MUAPs within the “pick-up” area of the electrode being used. These signals are picked up, amplified, and translated into audible-visible-or both readings
Which units are picked up first
smaller units first, larger units if we need them
can you read more with a larger or smaller contraction?
larger because we can only read what is directly under the electrode field
Does EMG measure force output?
no no no
- just because you are getting higher feedback it does not mean that you are stronger
what might reconditioned individuals display?
- higher levels of EMG activity to exert the same amount of force as exerted by non- deconditioned individuals
- people who are trained are more efficient in using the MUs
What can affect an EMG signal?
fatigue
muscle comprised of predominately one fiber type may have….
- more of a linear relationship under isometric non-fatiguing condition
- Mixed fiber types are more curvilinear
EMG amplitudes are greater for which type of contractions?
- concentric amplitudes are greater than eccentric contractions when lifting or letting down the same load (length- tension issues and force velocity issues)
is EMG/Biofeedback a monitor or a measure?
monitor
* Most devices use some type of analog meter to demonstrate activity. Some meters have objective numbers and others do not
Why is EMG information difficult to compare session to session?
- Electrode placement
- Skin impedance
- Extraneous noise
how can you “normalize” EMG activity to compare performance between sessions?
- by looking at the % of change within each session
- Some elite devices will do this for you
Indications for use of biofeedback
- Decrease unwanted muscle contraction
- Promote muscle contractions
what should biofeedback be?
TASK SPECIFIC
Goals of intervention
- Improve muscle performance
- Reduce pain
- Increase ability to perform functional tasks
- Improve joint integrity and mobility
- Reduce complications of injury
Active Electrode
has built in amplifiers
what are passive electrodes made of
- silver silver chloride
- gold based
what do passive electrodes utilize
bipolar electrode placement where there is a pair of recording electrodes and a reference (or ground) electrode
Since there is no built in amplifier with passive electrodes, what do you gotta do
reduce skin resistance as much as possible before recording
ground electrode
Helps the EMG unit discriminate the muscle activity under the recording electrodes from the noise or extraneous activity
Electrode size
Choose size based on desired recording area
Too large = unwanted noise from adjacent muscles
Too small = not enough sampling –> decreased feedback
Electrode placement
Ground electrode should be on a bony prominence if available (some differing information on this)
Recording electrodes need to run parallel to the muscle fibers
Inter- electrode distance: closer together
more specific information, but limits the recording area (good to start muscle relaxation programs here and then widen them as the patient progresses)
Inter-electrode distance: further apart
gather more data, but may have increased noise from adjacent muscles (good to begin muscle recruitment program here and then narrow them as the patient progresses)
Purpose of amplifier
- Increase the amplitude of the signal
- Units have “gain” (sensitivity) adjustments that range from 0-10 to 0-100 microvolts
Differential Amplifiers
- Determine what is noise by looking
at what is common between the two recording electrodes - It discounts the noise and enhances the signals that are different
Greater amplification =
greater sensitivity
higher sensitivity (high gain) runs in what range?
1-10 microvolts and convey information about small changes in EMG activity
Low sensitivity (low gain) run in what rage?
0-100 microvolts and conveys larger changes in EMG activity
What does filtering aid in
elimination of unwanted electrical signals (noise)
what frequency do movement artifacts occur?
range of < 100 Hz
Most electrical noise is found at what frequencies?
- high
> 100 Hz
What frequency do most EMG signals fall in the range of?
100-1000 Hz
- A filter can be used to narrow this range and only read frequencies occurring at 100- 500Hz
What is a disadvantage of filtering
loss of some EMG activity
Rectification
is taking the positive and negative values of a signal and making them all positive (full-wave rectification) or just eliminating all of the negative values (half-wave rectification)
Integration
- An averaging of the signal
- Rather than displaying every point of a rectified signal an average of every 6 data points of sEMG
activity is plotted - This gives you a “smoother” line
What types of feedback are there?
visual and auditory
what should you consider when choosing the type of feedback
Patient’s age
Preference
Type of desired muscle activity
Stage of training
Time Constraints
- pick up how much integration you are doing
- the time the resistor compact circuit takes to discharge stored signal
- the shorter the time constant the more info you pick up
what is the time constant recommendation for muscle recruitment
0.3 seconds
Threshold
Set threshold level based on desired activity
When the EMG signal reaches this threshold, a threshold detector will either turn on or turn off the feedback
Also consider the intensity of the feedback (how loud, etc.)
Skin Impedance
Essential to reduce impedance as much as possible
Muscle Recruitment
Patient must have some (minimal) ability to perform a voluntary contraction.
Electrode size to suit the size of the muscle
Begin with a wider placement progressing to a narrower placement if needed
Begin with a high sensitivity level and progress to a lower sensitivity level
Preferable time constant around 0.3 seconds
Set threshold just above level of resting activity (baseline) and progress up
Decide on nature and frequency of feedback
deciding on nature and frequency of feedback
Concurrent feedback vs. knowledge of results
May progress from frequent to intermittent feedback
Too much feedback may lead to dependence and limit learning
Muscle Inhibition
Select electrode size appropriate for size of muscle being targeted
Inter-electrode distance should begin small and widen with progress
Initiate sensitivity appropriate to level of activity
Longer time constant initially
Set threshold just below baseline level of activity and progress by lowering it
Documentation should include:
Nature of Rx (muscle recruitment vs. inhibition) Activities performed (remember to make it functional)
Muscle(s) targeted
Electrode type and size
Electrode placement including inter-electrode distance
Unit settings (sensitivity, threshold)
Feedback type
Duration or number of repetitions
