week 8

Question 1

what is EMG a representation of

Answer 1

the sum of all motor unit action potentials within the detecting range of electrodes

Question 2

does EMG tell us muscle force

Answer 2

no it tells us about muscle effort but if we know the effort and the length we can estimate force

Question 3

how is force increased in 2 ways

Answer 3

recruit more motor units
rate coding

Question 4

how does motor unit recruitment increase force

Answer 4

size principle (small to large) and correlates with the fatigue resistance of the MUs
more metabolically efficient this way

Question 5

how does rate coding increase force

Answer 5

how often a motor unit will fire eventually resulting in force teatnus

Question 6

how does recruitment relate to the EMG signal

Answer 6

as more MUs fire or are active there is a greater chance multiple MUAPs will summate causing a greater signal

Question 7

how does rate coding relate to EMG signal

Answer 7

as more motor units fire often a greater chance of MUAPs summating

Question 8

what are the 6 EMG analysis techniques

Answer 8

• raw amplitude
• rectification
• linear envelope
• integrated EMG
• root mean square
• normalization

Question 9

what is the EMG linear envelope (two steps)

Answer 9

1. full-wave rectification (only positive values)
2. low pass filter (2-10Hz)

Question 10

4 parts to recording EMG signal

Answer 10

• via electrodes
• monopolar or bipolar arrangement
• placement
• skin resistance

Question 11

what factors affecting surface EMG signal can we control

Answer 11

• electrode-skin interface
• signal conditioning
• inter-electrode spacing
• orientation of electrodes

Question 12

4 basic features of signal analysis (signal properties)

Answer 12

frequency = how many waves over a time
amplitude = how big it is
vertical offset = bias removal
phase shift = horizontal starting at 0 or max

Question 13

what is a time domain

Answer 13

amplitude of a signal at each point in time

Question 14

what is a frequency domain

Answer 14

amplitude of signal at each frequency

Question 15

how do we go from time domain to frequency domain

Answer 15

use Fourier transform

Question 16

what does a fourier analysis allow us to do

Answer 16

breakdown a signal into sine waves and the sine waves tell us frequency, amplitude, and phase

Question 17

frequency analysis (0-0.1)

Answer 17

bias

Question 18

frequency analysis (0-1)

Answer 18

drift (bias will change overtime slowly)

Question 19

frequency analysis (0-1000Hz)

Answer 19

white noise (contains all possible frequencies)

Question 20

frequency analysis (0-10Hz)

Answer 20

human movement (tremor)

Question 21

frequency analysis (10-500Hz)

Answer 21

surface EMG sin waves buried in the frequency that can be super rapid oscillations

Question 22

frequency analysis (10-1000Hz)

Answer 22

indwelling EMG (needle in muscle)

Question 23

frequency analysis (10-60Hz)

Answer 23

ECG

Question 24

when converting an analog signal to digital how often do you need to take a measure?

Answer 24

must sample at least 2x + 1 the highest frequency present in the signal

ex. highest approximate frequency is 500Hz so 1001

Question 25

what does power =

Answer 25

amplitude ^2

Question 26

why aren't filters perfect

Answer 26

remove some of what we want, and keep some of what we don't want since we cant get rid of all the noise and we just want to reduce it. to preserve the signal we are interested in

Question 27

what does a LPF of 2-10Hz do in the linear envelope

Answer 27

causes a delay (shifting the signal forward in time) to mimic the real electromechanical delay between AP and force

Question 28

what is EMG amplitude influenced by

Answer 28

demand, muscle length, muscle velocity, rate coding, recruitment, joint position

Question 29

slow twitch vs fast twitch in terms of EMG amplitude

Answer 29

in general, FT have larger diameter thus faster conduction velocity when something moves fast = fast frequency contents = increased Conduction velocity

Question 30

depth of fibre with respect to electrode and EMG amplitude

Answer 30

larger MUs are more superficial within the muscle. causing an influence on the electrical activity recorded since they are closer to where they are being recorded. so they appear they are moving faster

Question 31

what is fatigue

Answer 31

decreased ability of a muscle to produce force. but is recoverable

Question 32

what does EMG look like to maintain MAX force

Answer 32

force will decrease over time and so will EMG amplitude

Question 33

what does the effort to maintain subMAX force look like in terms of EMG

Answer 33

EMG amplitude will increase as recruitment of more MUs to maintain force and larger superficial MUs will begin to be recruited. also can get synchronous firing of MUs to yield a larger amplitude EMG signal

Question 34

why/how does MUAP conduction velocity decrease with fatigue

Answer 34

due to alterations in metabolite concertation (pH) within muscle. Electrodes see MUAPs for longer giving the appearance the shape change and lower frequency conduction velocity of the electrodes decreased as it moves sower in acidic environments and frequency content will be lower due to lower conduction velocity

Question 35

how does MUAP duration increase and amplitude decrease

Answer 35

due to changes in Na+ and k+ gradients causing MUAP shape to change

Question 36

what is mean power frequency

Answer 36

weighted average (higher frequencies are weighted heavier)

Question 37

what is median power frequency

Answer 37

frequency that divides power spectrum in half