Biofeedback

Electromyography

analysis of muscle electrical activity (physiologic signal)

electrical signals of interest are?

motor unit action potentials

providing insight regarding control of voluntary/ reflexive movement

EMG typically used BLANK electrodes

surface electrodes

Fine-wire or needle electrodes can also be used (mainly for research or diagnostic testing)

larger and more superficial muscles produce more BLANK signals

more prominent

2 primary mechanisms to regulate muscle force

rate coding

recruitment

of additional motor units

EMG activity BLANK muscle force

DOES NOT EQUAL**

rate coding

rate at which the motor units are fired

EMG signals reflects BLANK activity under electrodes

summed

theres BLANK among muscles that are close to one another

crosstalk

ex: gastrocs and soleus

BLANK electrode arrangement typically used for surface EMG

bipolar

2 electrodes

common signal is attenuated*

PLACE electrodes over area with BLANK, avoiding BLANK

muscle fibers

avoiding motor point (ex: tendon)

align electrodes BLANK to muscle fibers

parallel -@ muscle belly

harder with pennate muscles

EMG signal: Low frequency

movement artifact

movement of skin on overlying muscle

EMG signal: High frequency

signal noise

rectify EMG signal ?

'smooth' it; oscillating between positive and negative, from a noisy raw signal to a clean one

Analysis: what are we looking at when looking at EMG signal ?

EMG amplitude and/pr muscle onset-offset timing

OR

signal frequency

BLANK often used to analyze muscle activity levels

mean or peak EMG amplitude

Rectify signal so all values are BLANK

positive

full wave rectified

Biofeedback is usually trying to one of 3 things

facilitate a muscle contraction or inhibit muscle activity, or retrain muscle recruitment pattern