MC 2 (electromyography - lectures and labs)

Question 1

What is electromyography?

Answer 1

the registration and interpretation of the electrical activity associated with the contraction of skeletal muscle

Question 2

How do an electromyograph and electromyogram differ?

Answer 2

electromyograph: instrument used to record EMG
electromyogram: the recording of the electrical signal generated by neuromuscular activity

Question 3

Motor unit = ?

Answer 3

MU = motor neuron + muscle fibres it innervates

Question 4

What is an innervation ratio?

Answer 4

the number of muscle fibres per motor neuron

larger muscles have greater innervation ratios

Question 5

Describe a muscle fibre action potential (MAP)

Answer 5

>alpha motor neuron activated 
  by CNS
>action potential propagates 
  down to motor plates
>neuromuscular transmission 
  elicits action potential in muscle 
  fibre.
>MAP propagates along fibre

Question 6

How does action potential vary with fibre type?

Answer 6

• fast twitch = higher amplitude
• fast twitch = quicker
  conduction

Question 7

How does action potential vary with measurement site?

Answer 7

• further away = reduced
  amplitude
• further away = time delay

Question 8

What is MUAP?

Answer 8

Motor Unit Action Potential:

the summation of electrical signals generated by all the muscle fibres of a motor unit

Question 9

What is MUAPT

Answer 9

Motor Unit Action Potential Time:

the sequence of MUAPs from repeated neural stimulation

Question 10

What is Henneman’s size principle?

Answer 10

Motor units are recruited in order of increasing size

Question 11

What are the two configurations of electrodes when recording EMG signals?

Answer 11

Monopolar: one electrode

Bipolar: two electrodes, improves signal:noise by attenuating common noise across the two inputs

Question 12

What is noise?

Answer 12

unwanted signal detected by the electrodes

e.g. other biological signals (ECG) or external sources (mains electricity)

Question 13

Two electrode locations?

Answer 13

surface: for studies of surface muscle
indwelling: for studies of deep muscles and small or adjacent muscles where cross-talk may occur

Question 14

What is cross-talk?

Answer 14

the signal from other muscles than what electrodes were intended for

Question 15

What is the proper surface electrode location?

Answer 15

SENIAM guidelines
- middle of the muscle 
  between the origin and 
  insertion
- away from tendinous area 
  and motor point
- parallel to the underlying 
  fibres

Question 16

How would you prepare the skin for an EMG reading

Answer 16

Delsys adhesive interface and skin preparation techniques
> shave
> alchohol wipe
> abrade (sandpaper)

Question 17

Why is the correct EMG prep procedure necessary?

Answer 17

better electrode contact with skin reduces noise

increases signal

greater signal:noise

reduced cross talk

Question 18

How can you reduce cross talk?

Answer 18

• smaller electrode
• less adipose tissue
• careful prep

Question 19

What are the 5 influences on an EMG signal?

Answer 19

1. skin electrode interface: dead skin etc. provides
   resistance to the signal
2. sub-cutaneous fat: less fat = greater signal:noise
3. distance from electrode
4. muscle length
5. blood flow fatigue

Question 20

What are we able to gather from raw EMG data?

Answer 20

1. timing of activation

2. evidence of muscle activity

Question 21

What does EMG NOT measure?

Answer 21

FORCE

Question 22

What does a rectified EMG graph show?

Answer 22

absolute values (-2mV —– 2mV)

Question 23

What does an integrated EMG (iEMG) graph show

Answer 23

the trend in muscular activity by the area under sections of a rectified EMG curve

Question 24

What is the formula for average rectified EMG (arEMG)?

Answer 24

arEMG = iEMG / t

Question 25

How do you achieve a smoother signal output line on a arEMG graph?

Answer 25

longer time windows

Question 26

Can EMG be used as a form of biofeedback?

Answer 26

Yas.
Petrofsky (2001) showed EMG biofeedback to be effective in reducing the disturbance of walking patterns during stance phase (trendelenburg gait)