EMG Flashcards
within any motor units are all the muscle fibers the same type?
yes
signal propagates through voltage gated channels in ?of the muscle
neurolemma and sarcolemma
EMG measures?
the AP’s that travel along the muscle fibers
2 common methods of EMG
- in dwelling electrodes
2. surface electrodes
what are the advantages/disadvantages of in dwelling electrodes?
A: record from a single MU, deep musculature, little cross talk
D: can be painful, single MU may not represent entire muscle, hard to measure dynamic activity
what are the advantages and disadvantages of surface electrodes?
A: easy to record, global muscle activity, minimal discomfort
D: cross talk, can only be used for superficial muscles, can affect the movement pattern
surface electrodes measure what?
amp reads the change in voltage at the sensor that accompanies the AP
what is the problem with unipolar recordings?
picks up other signals because the sensors are very sensitive to electrical charge of everything around in the room or any movement
why bipolar recording better?
- signal and noise is sampled from 2 different poles so when you subtract them you’ll just be left with the EMG
what is the new signal called that is gained form bi polar recording and why is it called this?
it is called MOTOR UNIT AP because it is the electrical activity associated with all the muscle fibers in a motor unit contracting
each motor unit has its own characteristic?
motor unit AP
EMG electrodes record many motor units at different times and the resultant recording is the?
sum of many motor units (gives us a gross estimation of activity of whole muscle)
what is the henneman size principle
orderly recruitment form small MU to large
– fine movements, conserve energy
3 considerations when measuring EMG
- placement (neuromuscular junction and motor end plate)
- EMG signal processing
- electromechanical delay (EMD)
with placement you want the electrode to be on the muscle? and the MAUPs to pass parallel to the ? distance b/w electrodes
- belly, midway between the tendon and the nearest innervation zone
- shortest
don’t set electrodes up at?
motor end plate or lateral edges or both electrodes at a innervation zone because they will cancel each other out
how we process EMG can tell us about? (3)
and the raw signal can tell us about?
- timing of muscle activity
- force
- muscle fatigue
-timing (onset/ offset)
what are the 2 steps of processing and what does this produce?
- take the absolute value of the signal, called full wave rectification
- take an average value over a specific time period (rot mean square)
besides root mean square, what is another way take averages?
– the resulting tracing is called?
use filters to take an instantaneous average of the signal
–> linear envelope
what is the EMG force relationship?
- the magnitude of the processed EMG can be used in the muscle mechanics to predict the muscle contributing force
what is the electromechanical delay? how long?
- the delay between the neural activation of the muscle and the development of the muscle tension
- -> 30-50ms depending on muscle and joint
a single MAUP does what during fatigue? and a surface EMG does what with increasing fatigue?
- MAUP: decreased amplitude with fatigue
- EMG: increased amplitude with fatigue b/c more MU are recruited to produce the same force
the frequency of MUAP relates to?
- with fatigue what happens to frequency?
- the type of muscle fibers active
- frequency spectrum of EMG decreases muscle force and decrease dispersion (thin) (changes in frequency component)
EMG must be what? to allow for comparisons
normalized
norm EMG = EMG/max EMG
