electromyography

Question 1

What is the purpose of EMG?

Answer 1

Measures electrical signals from muscles

Used for studying muscle function, diagnosing disorders, and understanding CNS organization.

Question 2

For what is EMG used?

Answer 2

• Study of fatigue and work stress on muscle function
• Analysis of muscle activation changes with different parameters: disease/treatment
• Diagnosing muscle dysfunction or neuromuscular disorders
• Understanding CNS organization in coordinated movement

Question 3

What is the voltage gradient across a muscle fiber membrane?

Answer 3

-90mV

This is due to the distribution of Na, K, and Cl ions.

Question 4

Where does an action potential start and how does it propagate?

Answer 4

At the neuromuscular junction and proceeds along muscle fibers in both directions

This occurs due to the exchange of Na and K ions.

Question 5

What is a motor unit?

Answer 5

All the muscle fibers innervated by a single motor neuron

Question 6

What is the link between EMG and motor units?

Answer 6

EMG is the sum of electrical activity from multiple motor units within the detection region

Question 7

What is the relationship between EMG signal strength and the distance of neurons from the surface?

Answer 7

Motor neurons closer to the skin have a stronger signal

Question 8

What are the components of EMG instrumentation?

Answer 8

• Differential electrodes
• Ground electrode
• Amplifier and analog-to-digital converter
• Storage and display unit

Question 9

What are characteristics of surface electrodes?

Answer 9

• Placed on skin
• Noninvasive, easy to apply
• Harder to isolate individual muscles
• Cannot measure deep muscles

Question 10

What are characteristics of indwelling electrodes?

Answer 10

• Inserted through skin into muscle
• Invasive (needles), require more skill to place
• Can isolate individual muscle/motor units, small recording area
• Can record deep muscles

Question 11

What can be determined from EMG?

Answer 11

• When a muscle is active: timing of activation, duration
• Compare muscle activation during different tasks
• When muscles are or are not working together
• How hard a muscle is working relative to maximal contraction (MVIC)

Question 12

What is MVIC normalization?

Answer 12

Maximum voluntary isometric contraction is the maximum force a subject can generate during isometric contraction

Question 13

What is %MVIC?

Answer 13

The recorded activity of a muscle divided by its MVIC

Question 14

Why do amplitude normalization?

Answer 14

• To format a standard manner
• To make consistent
• To place in comparable context

Question 15

What are the pros of amplitude normalization?

Answer 15

• Eliminate influence of detection condition
• Provide a scale for data

Question 16

What are the cons of amplitude normalization?

Answer 16

• Hard to actually contract at 100% especially under injury
• Explosive exercises affect MVIC

Question 17

What can EMG not determine?

Answer 17

• Which muscle applies more force
• Amount of force a muscle produces
• Number of active motor units

Question 18

What are EMG limitations?

Answer 18

• Signal amplitude is inversely proportional to distance
• Crosstalk from adjacent muscles

Question 19

How should electrodes be placed?

Answer 19

• Parallel to muscle fibers
• Place on longitudinal midline
• Not at muscle edge
• Not near tendon