(S1W3) Electromyography (EMG) part 6

Question 1

using percentage of maximum voluntary contraction

Answer 1

• rather than expressing data in mV or V, expressing as a % of your maximum voluntary contraction (EMG signal when muscle is maximally active)
• means we can compare different muscles to each other that might have different amounts of fat or connective tissue on top
• and if you do tests on different days, even if the electrode is placed somewhere with a slightly weaker signal, you will also get a weaker signal for maximum voluntary contraction, so you can express results as a % and compare to the % you got last time you tested

Question 2

How do we identify exactly where there is a change on an EMG?

Answer 2

• zoom in
• take the average (mean) point where nothing is happening
• assuming it is normally distributed noise around the mean, we know that 99.7% of data points are within 3 standard deviations of the mean
• so 99.7% of the data points are within a certain range
• the moment the signal goes outside of that range something has changes

Question 3

applications of EMG

Answer 3

• clinical - e.g. testing nerve function as a sign of neurological conditions
• resistance training - which muscles involved in a movement and to what degree
• research - how are the muscles controlled
• simulation - can use EMG to evaluate models
• biofeedback - give a person information about how active different muscles are so they can train to use certain muscles more or less

Question 4

What is closed loop control?

Answer 4

a control system that uses feedback

Question 5

What is Dewhurst’s experiment?

Answer 5

• hold elbow at 90° with eyes closed
• extra weight will be added (you don’t know when it’s coming)
• arm will fall but you will return it to 90°
• then look at EMG signal and see M1, M2, and M3

Question 6

What are the 3 response types?

Answer 6

• M1 - reflex (monosynaptic) - no conscious control
• M2 - triggered / pre-programmed / long loop - no conscious control
• M3 - voluntary - conscious control

Question 7

3 response types applied to Dewhurst’s experiment

Answer 7

• M1 - reflex - arm falls and biceps lengthen so muscle spindle stimulates that same muscle to contract and brings it back to 90°
  M2 - pre-programmed (you’re thinking as soon as my arm starts to fall I will bring it back to 90°) which is triggered by the stimulus of feedback
  M3 - actively thinking my arm is falling, I’ll lift it back up