17. EMG

Question 1

What is Electromyography

Answer 1

Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them

Motor neurons transmit electrical signals that cause muscles to contract

EMG translates these signals into graphs, sounds, or numerical values that a specialist interprets

Question 2

EMG is the electrical activity from all active motor units close to the electrodes - Graph

Question 3

How is the EMG signal Recorded?

Answer 3

The EMG signal is recorded using an electrode

• Surface Electrodes: Stickers placed on the skin
• Indwelling Electrodes: Needles Inserted into the muscle

Question 4

What are the advantages/disadvantages
of using Surface Electrodes?

Answer 4

Advantages

• Quick, easy to apply
• Minimal discomfort

Disadvantages

• Mainly used only for superficial muscles
• Hard to record dynamic actions
• May affect movement patterns of subject

Question 5

What are the advantages/disadvantages
of using Indwelling Electrodes?

Answer 5

Advantages

• Extremely sensitive
• Record single muscle activity
• Access to deep musculature

Disadvantages

• Extremely sensitive
• Requires trained professionals
• Detection area may not be representative of entire muscle

Question 6

How are Electrodes placed on the body?

Answer 6

2 electrodes placed over the muscle Bipolar arrangement

Reference Electrode
Typically placed on a bony prominence

Question 7

What locations are electrodes placed on the body?

Answer 7

Electrodes should be placed close together

• The actual spacing depends upon the size of the muscle
• The smaller the muscle, the smaller the space should be between electrodes

Electrodes should be placed close to the belly of the muscle

• The quality of the signal will decrease as the electrodes move away from the midline or towards the attachment sites

Question 8

What is an Amplifier?
What is the differential signal?

Answer 8

Wires connected to the electrodes send the signal to an amplifier

The amplifier records the difference between the two signals (differential signal)

Muscle Action Potential is very small (1-10 mV)

Signal is amplified around 1,000-5,000 times creating a signal of at least 1 V