(S1W3) Electromyography (EMG) part 3

Question 1

What does sEMG stand for?

Answer 1

surface electromyography

Question 2

sEMG

Answer 2

• Commonly active bipolar systems (bipolar = two electrodes)
• Differential amplifiers (amplifying the difference between those two electrodes.
• Also subtracting or removing any common noise.
• EMG electrodes look at the difference in action potentials recorded at two positions along the muscle or muscle fibre
• also trying to subtract any signal that is not related to that action potential
• Measuring surface muscle only - e.g. easier to detect gastrocnemius than soleus
• Global (whole muscle) pick-up because not going into muscle to measure specific motor unit
• Inexpensive
• easy to apply, but difficult to apply well.
• Commonly used for sports movements

Question 3

What are the 4 main things to consider when positions electrodes?

Answer 3

1. electrode seprartion and shape
   * how far apart
   * the further away they are, the more different between the two that we are able to detect
   * however the further away = increasing the other signals we are picking up such as cross talk, noise
2. cross talk between muscles
   * are you detecting signals from other nearby muscles
3. belly of muscle
   * the biggest, thickets part of muscle
   * amplitude of singal you are interested in is biggest at the muscle belly
   * increasing the amount of signal you are detecting relative to other sources of info
4. parallel to muscle fibres
   * want the electrodes to in the direction of the muscle fibres

• also cleand and shave the area of skin so nothing interferes with signal

Question 4

reference electrode

Answer 4

• placed on an area with no muscle e.g. knee cap
• whatever signal the reference electrode is getting is something we are not interested in e.g. electrical noise

Question 5

Most of the things we actually measure or are interested in are ________ signals.

Answer 5

analogue

Question 6

analogue to digital converter (ADC)

Answer 6

• signals we are interested in are actually analogue signals (continuous signals)
• but we are just taking a digital measurement with a finite number of steps e.g. taking a digital measurement every second
• potential for errors within this