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
