Week 9 Flashcards
You can measure muscle force with EMG
False
You measure electrical muscle activity
In general, what does muscle force scale with
Electrical activity
What is electrical activity measured in
mV or V
What are the two types of electrical myography
sEMG - surface
Fine wire/needle
What are the pros of sEMG
Non invasive
Re usable
Better for dynamic tasks
Better for measuring more muscle at a time
Better for measuring larger muscles
What are the pros of fine wire electrodes
Higher accuracy
Can measure a specific portion of muscle
Less noise / cross talk
Better for simple tasks
Better for measuring smaller muscles
What type of tasks or activities would be better for surface
Dynamic tasks
Larger muscles
More muscles
What type of tasks or activities would be better for fine wire
Simple tasks
Smaller muscles
sEMG electrodes are either
Disposable
or
Re usable (wired or wireless)
What are the pros and cons of disposable electrodes
Pros:
Cheap
Easily applied
Can change the distant apart
Cons:
Less accurate
Less quality
Re usable electrodes are either
Wired or wireless
What should you look out for when placement of the electrode
Generally best to place in the muscle belly
Place electrodes parallel to muscle fiber
Refer to published guidelines for specific muscle locations
The recommended placement of 2 active electrodes is
Around 2 cm
What factors are influenced by the placement of 2 active electrodes
Bigger distance = bigger detection area
Bigger distance = less selectivity and greater chance of cross talk
What is a ground electrode
Helps reduce noise and grounds the electric signal
Place on body landmark
Dont place on a muscle
What factors affect sEMG Data Quality
Cutaneous fat
Muscle depth
Skin impedance
Muscle cross talk
Movement artifact
More cutaneous fat does what to the signal
Dampens and weakens
How does the skin impede the signal
Oily skin
Hair on the skin
Muscle cross talk is
When you pick up electrical activity from muscles that are near by
Movement artifact is basically
When you are moving at high velocity you can add to the electrical signal
How would you prepare a participant for data collection
Shave hairs in area
Clean skin with alcohol pad - dead skin cells and dirt
Apply conductive electrode gel
What is filtering
Filter out certain frequencies to eliminate some noise:
Below 20 Hz and above 500 Hz
What kind of frequencies are filtered out
Non physiologic signals can enter the sEMG data:
Electrical noise (DC offset) from wall outlet Movement artifact
What is smoothing
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
What is the most common way to smooth data
RMS - root mean square
Can you determine the type of muscle contraction with EMG (concentric, eccentric, isometric)
False
What do you actually measure in sEMG
Muscle activity amplitude (peak)
Muscle activity amplitude (average)
Muscle activity timing (onset, offset, duration)
What is normalisation
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
MVIC stands for
Maximum voluntary isometric contraction
What are the limitations of using MVC to normalise
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
How do you negate them not giving a maximal contraction
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
MVC during motion is difficult due to
Maintaining speed
electrodes can move
etc
How do we measure/quantify timing (onset/offset/duration) of the muscle and when it turns on and off
Calculations
Visual inspection
The method of calculations to determine onset/offset involves
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
The method of visual inspection to determine onset/offset involves
Onset/offset is estimated by the researcher visually
Has been proven to be valid and reliable
Timing relationship between key events during gait/cutting/jumping
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
Timing relationship between key events in relation to other muscles
Muscle onset/offset can be quantified in relation to other muscle onset/offset
Example:
Lateral gastroc activated 20 ms prior to medial gastroc
You can measure muscle force with EMG
False
Surface EMG is better for dynamic tasks compared to fine wire or needle EMG
True
Electrodes should generally be placed where on the muscle
On the muscle belly, parallel with the muscle fibers, with a 2 cm distance between active electrodes
Which of the following would not affect sEMG data quality
Number of muscles being studied
Which of the following is recommended before EMG data collection
Clean skin with alcohol pad
The purpose of filtering and smoothing your data, respectively, is to reduce or eliminate signal noise, and to make your data easier to analyze
True
It is acceptable to compare EMG amplitude data between participants without normalizing the data to a maximum voluntary contraction (MVC)
False
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?
150%
Why might trial EMG exceed MVC EMG
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
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
True
