lab 7: EMG Flashcards
what does EMG stand for
electromyography
what does EMG
measure
measuring elecrtical signals from muscles
what are the 4 reasons EMG is used
1) studying the effects of faitgue and work stress on muscle function
2) analyzing how muscle activation changes with different movement parametes, disease or treatments
3) diagnosing muscle dysfunction or neuromuscular disorders
4) understanding CNS organization in coordinated movement
true or false: the voltage gradient across the muscle fiber membrane is about what mV
90 mV
why is there a voltage gradient across the muscle fiber gradient
due to distrubition of sodium, potassium and chloride
the voltage graidne tis due to a distribution of what 3 ions
sodium
potassium
chloride
when is action potential generated for muscle physiology
when muscle fiber depolarized by 10 mv
action potentioal is generated when muscle fiber depolarized by BLANK
10 mv
WHERE does action potential begin
at neuromuscular junction
action potential is due to exchange of what
sodium and potassium ions
true or false: action potential proceeds along the muscle fiber in only 1 directino
false, in both directions
what is a motor unit
single motor neuron and all the muscle fibers it innervates
EMG consists of the sum of electrical activity from what
numerous motor units within the detection region
do EMG constic of the sum of electrical activtiy from numerous or a single motor unit within the detection region
numerous
true or false: motor neurons closer to skin surface hve a stronger signal
true
motor neurons closer or further to skin surface hve a stronger signal
closer
what are the basic system components of instrumentation of EMG
differential electrodes
ground electrode
amplifier and analogy to digital converted
strorage/display unit
SURFACE or indwelling: placed on the skin
surface
SURFACE or indwelling: inserted thru skin into muscle
indwelling
SURFACE or indwelling: non invasive, easy to apply
surface
SURFACE or indwelling: invasive (sterile) requires more skill
indwelling
SURFACE or indwelling: harder to isolate individual muscles
surface
SURFACE or indwelling: can isolate individual muscles/motor units -small recording area
indwelling
SURFACE or indwelling: cannot measure deep muscles
surface
SURFACE or indwelling: cannot measure deep muscles
surface
SURFACE or indwelling: can record deep muscles
indwelling
explain the placement, invasion, isolation and measurement of the surface electrode method
1) placed on the skin
2) non invasive and easy to apply
3) harder to isolate individial muscles
4) cannot measure deep muscles
explain the placement, invasion, isolation and measurement of the indwelling electrode method
1) inserted thorugh skin into muscle
2) invasive, requires more skinn
3) can isolate indivudal muscles/motor units (small recording area)
4) can record deep muscles
which has a. smaller recording area, surface or indwelling
indwelling
true or false: the emg record potential difference between electrodes
true
what are the 4 things you can determine from EMG
1) when a muscle is active
2) compare muscle activation during different tasks
3) when muscles are (or arent) working together
4) how hard (relative to a maximal contaction) a muscle is working
how can we measure when a muscle is active during an emg
equipment registers a change in voltage
what spefically can we determine about when a muscle is active
timing of activation
duration
how can we compare muscle activation during differen tasks using EMG
compare the amplitudes between recordings
how can we determine when muscles are /arent working together
by comparing the EMG traces of multiple muscles
how can we determine how hard (relative to a maximal contraction) a muscle is working
by normalizing the EMG traces to a maximum voluntary isometric contraction
what does MVIC stand for
maximum voluntary isometric contraction
what is maximum voluntary isometric contraction
the maximum force a subject can deliberatly generate during a static (isometric) cotnraction
what is a common and population method of amplitude normalizing EMG data
maximum voluntary isometric contraction (MVIC)
MVIC is assumed equatable to what
maximum innervation
how do youcalculate percent MVIC
get MVIC (from isometric contraction in mV)
get max mV during activity
%MVIC =Max activty/MVIC
* 100
what are the 3 functions of amplitude normalization
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 (impedence to signal, electrode location)
provide a scale for data
what are the critisism of amplitude normalization
can the patient actially contact to 100%
what type of exercise (is it relevant to activity)
what are the 3 things EMG cannot determine
1) which muscle (of two) is working harder
2) amount of force a muscle produces
3) number of active motor units
CAN or cannot determine: number of active motor units
cannot
CAN or cannot determine: amount of force a muscle produces
cannot
CAN or cannot determine: which muscle (of two) is working harder
cannot
CAN or cannot determine: when is muscle is active
can
CAN or cannot determine: compare muscle activation during different tasks
can
CAN or cannot determine: when muscles are (or arent) working together
can
CAN or cannot determine: how hard (relative to a maximum contraction) a muscle is working
can
why can we not determine which muscle (of two) is working harder
because muscles vary in size and function
(greater activtiy does not necerailly mean greater force)
true or false: (greater activtiy does not necerailly mean greater force)
true
explain why we cannot determine the amount of force a muscle produced from EMG
too many unknown variables
1) no way of knowing # of activated fibers
2) how much force a fiber contributes
3) not necesarily measuring all active fibers
does Emg measure force?
no it measures level of activity, not force
what are the too many unknown variables that make it so that you cannot measure the force a muscle produces
1) no way of knowing # of activated fibers
2) how much force a fiber contributes
3) not necesarily measuring all active fibers
why can we not determine the number of active motor units
some active fibers are not accessible to equipment (too deep)
what are the 2 EMG limitations
signal amplitude is inversly proportional to distance
crosstalk
explain crosstalk
electrodes over an adjacent muscle pick-up a signal via skin conduction
what reduces amplitude that is not distance,
incrased body fat
true or false and explain: difficult to record deep fibers/muscles
true because signal amplitude is inversely proportional to distance
what are the 4 guidelines for skin preperation
1) mark the location of the electrode
2) shave the area over the muscle
3) clean the area with rubbing alcohol
4) apply the electrode only after the alcohol evaporates
true or false: the electrodue is positioned parallel or perpendicular to muscle fibers
parallel
the electrode should be placed along what midline
longitudinal midline
true or false and why: the electrode can be placed at midline or muscle edge
false, do not place at muscle edge because it may pick up adjacent muscle signal
why can you not place the electrode near the tendon
thinner and fewer fibers
