(S1W3) Electromyography (EMG) part 5

Question 1

summing action potentials

Answer 1

• We have lots of motor units innervated by lots of motor neurons.
• We are measuring the total of multiple action potentials
• The deeper the muscle fibre, the lower the amplitude of the signal we are going to detect.

Question 2

signal to noise ratio

Answer 2

• The signal we get is the sum of the true signal + noise
• The true signal is the true muscle excitation.
• We have also got some noise around that
• when you put those two things together, you have got a signal with some high frequency noise on top of it.
• we want to reduce the amount of noise and maximise the true signal.

Question 3

Why is it difficult to get good EMG data?

Answer 3

• it is a very small electrical signal
• signal is insulated by:
• connective tissue
• fat
• skin
• other muscles (depending on which muscle you are measuring)
• (some of these are active materials (e.g. other muscles) so the properties change with time, e.g. the amount of fat over that signal is going to be constantly changing so it’s not like there is a constant number we can add or subtract from the signal)

Question 4

full wave recification

Answer 4

• raw sEMG data will be positive and negative
• so we need to recitfy it so it is all positive

Question 5

low pass filter

Answer 5

• removing high frequency signals and keeping low frequency signals
• we are interested in the low frequency muscle excitation signal not the high frequency noise

Question 6

steps from raw EMG to the signal we look at

Answer 6

• full wave rectification to make all data positive
• low pass filter to filter out noise