EMG

Question 1

what exactly does EMG measure

Answer 1

APs in the sarcolemma

Question 2

what is EMG measured in

Answer 2

voltage time event

Question 3

EMG applications

Answer 3

diagnostic purposes 
-NCV, H-reflex, M-waves, F-waves
Motor Control Studies
-muscle activation level and pattern 
-fiber typing 
-pattern of activity during movement
-pathologies

Question 4

muscle force can be estimated form EMG signal on what time of contraction and what kind of relation ship and why does it work with this contraction type

Answer 4

isometric, linear or curvilinear relationship, works because length stay constant

Question 5

what does muscle length change in EMG and what kind of confounder is it

Answer 5

orientation of electrons with respect to muscle, it is a methodological confounder that needs to be accounted for

Question 6

what is a 3 burst EMG pattern and where it is seen

Answer 6

agonist-antagonist-agonist
associated with rapid, unidirectional mov’t
more evident at faster velocities
impaired 3 burst pattern with pathologies

Question 7

describe intramuscular EMG

Answer 7

thin needle inserted in to muscle
picks up EMG for a single MU
measure voltage change for all muscle fibres in the Unit
give firing rate and recruitment information

Question 8

describe surface EMG

Answer 8

sum of all activity of active MU’s in a muscle
usually two electrodes and a ground are used
distance between electrodes (2cm) determines pick up

Question 9

how must surface EMG electrodes be places

Answer 9

on same side of NMJ and reasonably large distance apart

Question 10

monopolar vs bi polar EMG

Answer 10

bi: common noise (skin, fat, connective tissue, muscles not of interest) are cancelled out
mono: reduced ability to detest what is happening in muscle of interest
easily contaminated by activity in other muscles

Question 11

bipolar recording steps (2)

Answer 11

voltage between signal at each electrode and ground is determined
difference between the voltage (V1-V2) by each electrode is calculated and then amplified

Question 12

equation for finding difference in voltage and multiplying by g for bi polar EMG

Answer 12

Vo = G (EMG1-EMG2)

Question 13

what is raw EMG

Answer 13

unprocessed

Question 14

what is rectified EMG and what is it good for

Answer 14

absolute value of EMG signal is calculated and good for measuring peak amplitude of signal and timing events (cutaneous reflexes)

Question 15

what is integrated EMG and what it is good for

Answer 15

summation of the area of the rectified EMG

takes into account time of activation

Question 16

what causes noise in EMG

Answer 16

movement of electrodes and cables
activity in distant muscles
electromagnetic reactions

Question 17

what does EMG filtering to

Answer 17

takes out noise by modifying frequency content

Question 18

what is the Hz range surface EMG is often filtered to?

Answer 18

30-300 HZ

Question 19

what is a low pass filter

Answer 19

removes all frequency above

Question 20

what is a high pass filter

Answer 20

removes all frequency below

Question 21

what is a band pass filter

Answer 21

everything outside of the band is gone

Question 22

increasing filter order does what

Answer 22

increases strength of attenuation (attenuation= decreasing signals)

Question 23

what is bad about to sharp of attenuation

Answer 23

you get band ripple, which is modification of the signal, which you don’t want

Question 24

what is phase lag

Answer 24

when a filter changes the time scale of a EMG recording

Question 25

how is phase lag fixed

Answer 25

double filter is used - pass forward to filter, then pass back to reverse the phase lag

Question 26

nyquist Shannon sampling frequency is

Answer 26

signals must be digitally sampled at a minimum of 2x the maximum frequency component of the signal in order to accurately reproduce it

Question 27

what is the minimum EMG frequency for sampling we should use

Answer 27

1000 Hz

Question 28

what happens is we sample below the minimum frequency

Answer 28

we lose important information because we will not be having the right sampling frequency to catch all the important signals

Question 29

what is oversampling

Answer 29

sampling above what er actually need to sample (above the nyquist Shannon minimum) so we make Sure we get all the that we need

Question 30

what is wavelet analysis

Answer 30

samples can broken down into frequency components

Question 31

what is a fast Fourier transform

Answer 31

when signals are transformed from the time domain to the frequency domain

Question 32

why do we normalize EMG

Answer 32

absolute value varies person to person and day to day based on subcutaneous tissue, skin impedance, electrode placement, etc.

Question 33

what do we normalize EMG to

Answer 33

MVC, peak to mean level during certain reference condition, maximal muscle activation level by simulation, etc.

Question 34

filtering and normalization procedures depend on

Answer 34

particular behaviour/activity being studied

Question 35

do we normalize EMG if looking at timing (temporal)

Answer 35

no

Question 36

what happenes if we sample at frequency

Answer 36

change scale of teh waveforms

Question 37

what is optimal oversampling amount

Answer 37

5-10x Mac frequency

Question 38

what does truncation mean

Answer 38

to cut off signal, signal gets flatted at the level it is truncated at

Question 39

what is the “ideal” filter

Answer 39

set at a value and everything outside doesn’t exist