electromyography Flashcards
What is the purpose of EMG?
Measures electrical signals from muscles
Used for studying muscle function, diagnosing disorders, and understanding CNS organization.
For what is EMG used?
- 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
What is the voltage gradient across a muscle fiber membrane?
-90mV
This is due to the distribution of Na, K, and Cl ions.
Where does an action potential start and how does it propagate?
At the neuromuscular junction and proceeds along muscle fibers in both directions
This occurs due to the exchange of Na and K ions.
What is a motor unit?
All the muscle fibers innervated by a single motor neuron
What is the link between EMG and motor units?
EMG is the sum of electrical activity from multiple motor units within the detection region
What is the relationship between EMG signal strength and the distance of neurons from the surface?
Motor neurons closer to the skin have a stronger signal
What are the components of EMG instrumentation?
- Differential electrodes
- Ground electrode
- Amplifier and analog-to-digital converter
- Storage and display unit
What are characteristics of surface electrodes?
- Placed on skin
- Noninvasive, easy to apply
- Harder to isolate individual muscles
- Cannot measure deep muscles
What are characteristics of indwelling electrodes?
- 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
What can be determined from EMG?
- 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)
What is MVIC normalization?
Maximum voluntary isometric contraction is the maximum force a subject can generate during isometric contraction
What is %MVIC?
The recorded activity of a muscle divided by its MVIC
Why do amplitude normalization?
- To format a standard manner
- To make consistent
- To place in comparable context
What are the pros of amplitude normalization?
- Eliminate influence of detection condition
- Provide a scale for data
What are the cons of amplitude normalization?
- Hard to actually contract at 100% especially under injury
- Explosive exercises affect MVIC
What can EMG not determine?
- Which muscle applies more force
- Amount of force a muscle produces
- Number of active motor units
What are EMG limitations?
- Signal amplitude is inversely proportional to distance
- Crosstalk from adjacent muscles
How should electrodes be placed?
- Parallel to muscle fibers
- Place on longitudinal midline
- Not at muscle edge
- Not near tendon
