EMG

Question 1

Why do we measure muscle activity?

Answer 1

To get a full understanding of muscle activity

Question 2

What is studying muscle activity useful?

Answer 2

Devising strength and mobility programmes
– Explaining and preventing injuries
– Estimating and calculating internal forces

Question 3

Define kinesiological analysis

Answer 3

Way in which we analyse human movement is through

analysis

Question 4

What important factors must be taken into account when using kinesiological analysis?

Answer 4

Muscle tend to pull at both attachments

Many muscles cross more than one joint

Question 5

What are the four types of muscle actions?

Answer 5

Sustained force movement
Passive movements
Guided movement
Ballistic movement

Question 6

What are sustained force movements? what do they do?

Answer 6

Force is applied by contracting agonist muscles
– concentric, eccentric, or isometric

• Antagonists are relaxed.
• The sustained force can be
fast or slow, strong or weak

Question 7

What are passive movements and what do they do?

Answer 7

Without continuing muscle contraction.

– Manipulation - by another force or person.
– Inertial Movement - a continuation of preestablished movements

Question 8

What are ballistic movements and what do they do?

Answer 8

Compound movement
• 1st phase concentric
• 2nd phase inertial
• 3rd phase eccentric

– deceleration of the joint

Question 9

What is EMG?

Answer 9

Electromyography (EMG) is a technique for evaluating and
recording the electrical activity produced by skeletal muscles.

It detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated.

Question 10

What is EMG measured in?

Answer 10

Volts (V) or microvolts (µV)

Question 11

What is the peripheral nervous system for?

Answer 11

Branching nerves outside of spinal cord

Question 12

What is the motor unit for?

Answer 12

Connection between the nervous system an muscle

Question 13

What happens with depolarisation of the muscle membrance?

Answer 13

Action Potential (AP) travels down the nerve

This creates a voltage difference (neg on outside)

Reaches the muscle and stimulates a muscle AP
that can be recorded

Question 14

What are the clinical uses of EMG?

Answer 14

Diagnostic

Ergonomics

Decision making before/after
surgery

Neuromuscular or orthopedic impairment

Product design

Question 15

What are the six sport uses for EMG?

Answer 15

To detect if a muscle is active
When is a muscle active
If a muscle more or less active
To detect if when a muscle fatigue
To detect if there is a coactivation
Physical activity

Question 16

What does surface EMG do?

Answer 16

Allows examination of surface muscles

Question 17

What does in-dwelling EMG do and is it common or uncommon and why?

Answer 17

Allows examination of deep muscles

Not commonly used in sport science as
– Very invasive
– Limited in dynamic contractions

Question 18

What do you do in the preparation phase on EMG?

Answer 18

Decide on a ‘navigation’ technique to identify electrode location and landmark regions.
Use a pen to mark landmarks and orientation lines. Use a flexible scale band to measure
distances. Follow the SENIAM guidelines.

Question 19

What happens in the skin preparation phase?

Answer 19

Remove the hair – improves the adhesion of the electrodes especially for sweaty skin types
3. Clean the skin (abrasive vs. sand paper vs. alcohol wipes)

Question 20

What happens in the sensor location phase?

Answer 20

Attach electrodes parallel to muscle fibres. If possible avoid motor end plates and select
muscle belly portions.

Question 21

Where should the electrodes not be placed in the sensor location phase?

Answer 21

• NOT on outside edges – crosstalk
• NOT on motor point
• NOT on tendon –
• Between motor point (innervation zone) and tendon – point where muscle begins to twitch with the lowest amount of current
• Muscle belly Orientation of electrodes
• Parallel with muscle fibre

Question 22

What should you avoid with EMG?

Answer 22

Crosstalk = when the detected signal contains noise from another muscle

• Common in small, close muscles e.g. the forearm

Question 23

What are the intermediate factors affecting EMG signal?

Answer 23

Detection volume of electrodes
• Filtering effect of electrodes
• Cross-talk from neighboring muscles

Question 24

What are the three deterministic factors affecting EMG signal?

Answer 24

• Amplitude
• Duration
• Shape

Question 25

How do you normalise EMG signals?

Answer 25

Processed EMG signals can only be compared with those recorded from the same muscle without removal of the electrodes
.
Can over come this by:
Expressing each data point on of processed EMG as a proportion of a peak EMG from a max isometric contraction of the same muscle processed in the same way

Can tell us how active the muscle is as a % of MVC