Lab Week 7 - Electromyography Flashcards
What is electromyography (EMG)?
Measuring electrical signals from muscles.
What is electromyography (EMG) used for? (4)
- Studying the effects of fatigue and work stress on muscle function
- Analyzing how muscle activation changes with different movement parameters, disease or treatments
- Diagnosing muscle dysfunction or neuromuscular disorders
- Understanding CNS organization in coordinated movement
Describe muscle physiology.
- voltage gradient
- ions distribution
Voltage gradient across the muscle fiber membrane (-90mv)
Due to the distribution of sodium, potassium, and chloride
Name the steps of muscle action potential. (4)
- Action potential generated when muscle fiber depolarized by ~10 mV
- Action potential begins at neuromuscular junction
- Proceeds along muscle fiber in both directions
- Due to exchange of sodium and potassium ions
What is a motor unit?
Motor unit= single motor neuron + all the muscle fibers
it innervates.
See NDC p.7 for illustration
Describe EMG measurements relative to motor units.
EMG consist of the sum of electrical activity from numerous motor units within the detection region.
Motor neurons closer to skin surface has a stronger signal.
–> ex: 5 is deeper than 1, so 5 has a weaker signal
See NDC p.7 for illustration
Name the basic system components of the EMG?
- Differential electrodes
- Ground electrode
- Amplifier & analog to digital converter
- Storage/Display unit
Name the 2 types of electrodes.
- Surface electrodes
- Indwelling electrodes
Describe surface electrodes.
- placement
- invasive?
- muscle isolation?
- deep muscles?
- Placed on the skin
- Noninvasive, easy to apply
- Harder to isolate individual muscles
- Cannot measure deep muscles
See NDC p.9 for illustration
Describe indwelling electrodes.
- placement
- invasive?
- muscle isolation?
- deep muscles?
- Inserted thru skin into muscle
- Invasive (sterile), requires more skill
- Can isolate individual muscles/motor units- small recording area
- Can record deep muscles
See NDC p.9 for illustration
How do the electrodes take measurements?
Differential electrodes look at the difference between 2 signals at a point in time.
See NDC p.10 for illustration
What can we determine with electromyography? (4)
- When a muscle is active
- timing of activation
- duration - Compare muscle activation during different tasks
- When muscles are (or aren’t) working together
- How hard (relative to a maximal contraction) a muscle is working
–> How: By normalizing the EMG traces to a maximum voluntary isometric contractions (MVIC
See NDC p.11-14 for illustration
Describe how to measure when a muscle is active with EMG.
Equipment registers a change in voltage.
See NDC p.11 for illustration
Describe how to compare muscle activation during different tasks with EMG.
Compare amplitude between recordings.
** Doesn’t measure muscle force
See NDC p.12 for illustration
Describe how to measure when muscles are (or aren’t) working together with EMG.
By comparing the EMG traces of multiple muscles
See NDC p.13 for illustration
Describe how to measure how hard (relative to a maximal contraction) a muscle is working.
By normalizing the EMG traces to a maximum voluntary isometric contractions (MVIC)
See NDC p.14 for illustration
What is MVIC?
Maximum voluntary isometric contraction (MVIC)
–> “The maximum force a subject can deliberately generate during a static (isometric) contraction”
Not moving, forcing as much as possible
What is amplitude normalization? AAAAAAAAAAAAa
Activity given / MVIC
Describe MVIC.
- functions (2)
- assumes
- Common and popular method of amplitude normalizing EMG data
- Compare relative voltage of MVIC and some other
movement
MVIC assumed equatable to maximum innervation
Concept of Amplitude Normalization
Why do we normalize amplitude? (3)
- to format in a standardized manner
- to make consistent
- to place in a comparable context
What are the benefits of amplitude normalization?
- Eliminate influence of detection condition (impedance to signal, electrode location)
- Provide a scale for data
What CAN’T be determined by EMG?
- Which muscle (of two) is working harder
- Amount of force a muscle produces
- Number of active motor units
Why can’t we measure the amount of force a muscle
produces with EMG?
Muscles vary in size and function.
Why can’t we measure which muscle (of two) is working
harder with EMG?
Too many unknown variables:
1. No way of knowing # of activated fibers
2. How much force a fiber contributes
3. Not necessarily measuring all active fibers
