EMG

Question 0

Two ways to increase force

Answer 0

1)recruitment-increase motor units
Recruit small then larger, non fatiguable to fatigueable
2)rate coding-increasing firing frequency
Higher AP frequency-unfused tetanus then tetanus

Question 1

EMG

Answer 1

Records wave of depolarization from MUAP (sum)

MUAP faster and larger in fast twitch

Question 2

Recruitment

Answer 2

➡️smaller MU, lower activation thresholds…walking low threshold MU used over gait cycle
➡️high threshold , fast twitch with more forceful action…stumble
➡️MU recruitment by intensity: slow twitch fibers to 40%, then fast twitch at 80%

Question 3

Rate coding

Answer 3

➡️frequency of AP depends upon 1)type of contraction/velocity 2)fiber type
➡️small muscles -all MU usually recruited within 30-50% MVC

Question 4

EMG linear envelop

Answer 4

Full wave rectification

Low pass filter -high frequency in EMG signal removed

Question 5

Factors affecting surface EMG signal

Answer 5

• muscle fiber diameter
• number of muscle fibers
• skin resistance
• signal conditioning
• number of active motor units
• distance from skin surface to muscle fiber
• muscle fiber conduction velocity
• fiber type and location
• inter electrode spacing
• orientation of electrodes

Question 6

Signal properties

Answer 6

1⃣frequency
2⃣amplitude
3⃣offset (vertical)
4⃣phase shift (horizontal)

Question 7

Filters

Answer 7

Low pass filter: removes frequency above filter
High pass filter: removes frequencies below cut off
Bandpass filter: removes frequencies above and below cutoff

Question 8

Fatigue EMG amplitude mechanisms

Answer 8

➡️EMG magnitude increases recruitment of more MU to retain force and they will be larger
➡️synchronized recruitment: simultaneous firing of MU yields larger EMG amplitude signal (normally fire a synchronously)

Question 9

Fatigue-EMG frequency domains

Answer 9

MUAP conduction velocity decreases
➡️longer for MUAP to complete
➡️MUAP refraction period increases
Fast twitch motor units drop out (slow twitch remains)