Week 9

Question 1

You can measure muscle force with EMG

Answer 1

False

You measure electrical muscle activity

Question 2

In general, what does muscle force scale with

Answer 2

Electrical activity

Question 3

What is electrical activity measured in

Answer 3

mV or V

Question 4

What are the two types of electrical myography

Answer 4

sEMG - surface

Fine wire/needle

Question 5

What are the pros of sEMG

Answer 5

Non invasive

Re usable

Better for dynamic tasks

Better for measuring more muscle at a time

Better for measuring larger muscles

Question 6

What are the pros of fine wire electrodes

Answer 6

Higher accuracy

Can measure a specific portion of muscle

Less noise / cross talk

Better for simple tasks

Better for measuring smaller muscles

Question 7

What type of tasks or activities would be better for surface

Answer 7

Dynamic tasks

Larger muscles

More muscles

Question 8

What type of tasks or activities would be better for fine wire

Answer 8

Simple tasks

Smaller muscles

Question 9

sEMG electrodes are either

Answer 9

Disposable

or

Re usable (wired or wireless)

Question 10

What are the pros and cons of disposable electrodes

Answer 10

Pros:
Cheap
Easily applied
Can change the distant apart

Cons:
Less accurate
Less quality

Question 11

Re usable electrodes are either

Answer 11

Wired or wireless

Question 12

What should you look out for when placement of the electrode

Answer 12

Generally best to place in the muscle belly

Place electrodes parallel to muscle fiber

Refer to published guidelines for specific muscle locations

Question 13

The recommended placement of 2 active electrodes is

Answer 13

Around 2 cm

Question 14

What factors are influenced by the placement of 2 active electrodes

Answer 14

Bigger distance = bigger detection area

Bigger distance = less selectivity and greater chance of cross talk

Question 15

What is a ground electrode

Answer 15

Helps reduce noise and grounds the electric signal

Place on body landmark
Dont place on a muscle

Question 16

What factors affect sEMG Data Quality

Answer 16

Cutaneous fat

Muscle depth

Skin impedance

Muscle cross talk

Movement artifact

Question 17

More cutaneous fat does what to the signal

Answer 17

Dampens and weakens

Question 18

How does the skin impede the signal

Answer 18

Oily skin

Hair on the skin

Question 19

Muscle cross talk is

Answer 19

When you pick up electrical activity from muscles that are near by

Question 20

Movement artifact is basically

Answer 20

When you are moving at high velocity you can add to the electrical signal

Question 21

How would you prepare a participant for data collection

Answer 21

Shave hairs in area

Clean skin with alcohol pad - dead skin cells and dirt

Apply conductive electrode gel

Question 22

What is filtering

Answer 22

Filter out certain frequencies to eliminate some noise:

Below 20 Hz and above 500 Hz

Question 23

What kind of frequencies are filtered out

Answer 23

Non physiologic signals can enter the sEMG data:

Electrical noise (DC offset) from wall outlet
Movement artifact

Question 24

What is smoothing

Answer 24

Short transient spikes in your EMG data are common

Therefore smoothing will help eliminate or attenuate these huge spikes

Makes data more representative of the overall muscle contraction and easier to analyze

Most common option is RMS - root mean square

Question 25

What is the most common way to smooth data

Answer 25

RMS - root mean square

Question 26

Can you determine the type of muscle contraction with EMG (concentric, eccentric, isometric)

Answer 26

False

Question 27

What do you actually measure in sEMG

Answer 27

Muscle activity amplitude (peak) Muscle activity amplitude (average) Muscle activity timing (onset, offset, duration)

Question 28

What is normalisation

Answer 28

People are going to have different levels of factors (e.g hairs etc) Normalise it to a Maximum voluntary contraction (MVC or MVIC) This is done by performing a max contraction before testing Contracting during the test are normalised to this value e.g. MVC 100mv Testing = 10 mv Muscle activation = 10% of MVC

Question 29

MVIC stands for

Answer 29

Maximum voluntary isometric contraction

Question 30

What are the limitations of using MVC to normalise

Answer 30

Participant does not perform a true maximum contraction Position of MVC test may not be the same position the muscle will be recorded in during the trial Participant can exceed 100% MVC if the trial consists of eccentric muscle activity

Question 31

How do you negate them not giving a maximal contraction

Answer 31

Have them warm up Give them encouragement during the test Multiple trials to get to max Show them their max and them ask them to beat it - competitiveness

Question 32

MVC during motion is difficult due to

Answer 32

Maintaining speed electrodes can move etc

Question 33

How do we measure/quantify timing (onset/offset/duration) of the muscle and when it turns on and off

Answer 33

Calculations Visual inspection

Question 34

The method of calculations to determine onset/offset involves

Answer 34

A numerical threshold for when the muscle turns on or off is determined by complex formulas or calculations Types of threshold are: Number of standard deviations above resting baseline % of peak EMG

Question 35

The method of visual inspection to determine onset/offset involves

Answer 35

Onset/offset is estimated by the researcher visually Has been proven to be valid and reliable

Question 36

Timing relationship between key events during gait/cutting/jumping

Answer 36

Muscle activation onset/offset is generally calculated relative to initial contact (onset) or toe-off (offset) Example: Gluteus medius onset occurred 30 ms prior to initial contact

Question 37

Timing relationship between key events in relation to other muscles

Answer 37

Muscle onset/offset can be quantified in relation to other muscle onset/offset Example: Lateral gastroc activated 20 ms prior to medial gastroc

Question 38

You can measure muscle force with EMG

Answer 38

False

Question 39

Surface EMG is better for dynamic tasks compared to fine wire or needle EMG

Answer 39

True

Question 40

Electrodes should generally be placed where on the muscle

Answer 40

On the muscle belly, parallel with the muscle fibers, with a 2 cm distance between active electrodes

Question 41

Which of the following would not affect sEMG data quality

Answer 41

Number of muscles being studied

Question 42

Which of the following is recommended before EMG data collection

Answer 42

Clean skin with alcohol pad

Question 43

The purpose of filtering and smoothing your data, respectively, is to reduce or eliminate signal noise, and to make your data easier to analyze

Answer 43

True

Question 44

It is acceptable to compare EMG amplitude data between participants without normalizing the data to a maximum voluntary contraction (MVC)

Answer 44

False

Question 45

If a participant's peak EMG during MVC is 250 mV, and during data collection their data EMG is 375 mV, their EMG relative to MVC would be what percent?

Answer 45

150%

Question 46

Why might trial EMG exceed MVC EMG

Answer 46

The participant was lazy and did not provide a true MVC The contraction is eccentric, and eccentric contractions can lead to more EMG than isometric contractions The testing position was not adequate for producing a true MVC

Question 47

Assuming you use the same criteria for each trial and muscle, it is reliable and valid to use visual inspection to determine EMG onset and offset

Answer 47

True