Study Questions Lab 5 EMG Flashcards

1
Q
  1. Exercise 1:
    Plot the absolute integral of muscle contraction against absolute integral of EMG signals for each muscle clinch. EMG will be X-axis and Muscle Force Y-axis
A

a

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2
Q
  1. Exercise 1:

Is there a linear relationship btwn muscle activity (EMG) and grip strength (force)?

A
  • Yes
  • With an increase in grip strength there is an increase in force and an increase in EMG activity. This shows that there is increased muscle activity with increased demands for force generation.
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3
Q
  1. Exercise 1:

Do muscle fibres have refractory period lie nerve fibres

A
  • No functional refractory period
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4
Q
  1. Exercise 3:

Which muscles, pronator or biceps, had the most EMG activity during winning?

A

Biceps Brachii had more activity during the winning phase of the arm wrestling. The Biceps were being used to push the opponents are towards the table.

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5
Q
  1. Exercise 3:

Which muscles, pronator or biceps, had the most EMG activity during losing?

A

Pronator Teres had greater activity during the losing phase of the exercise.

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6
Q
  1. Exercise 3:

Does flexion or extension affect strength of EMG activity in either muscles?

A

Yes, it would affect the EMG activity. During flexion the anterior muscles are stretched therefore increasing their activity and during extension the posterior muscles are stretched and their activity is increased on the EMG.

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7
Q
  1. Exercise 4:

Which muscles, anterior or posterior, had the most EMG activity during flexion?

A

anterior

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8
Q
  1. Exercise 4:

Which muscles, anterior or posterior, had the most EMG activity during extension?

A

posterior

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9
Q
  1. Exercise 4:

Does flexion or extension of the fingers affect strength of EMG activity in either groups of muscles?

A

The posterior muscle group of the forearm causes extension of the wrist. The anterior muscle group in the forearm causes flexion of the wrist. Both flexion and extension of the fingers will have an effect on the strength of EMG activity. Flexion of fingers will increase the EMG amplitude during wrist flexion, while extension of fingers will decrease it. The opposite is true of wrist extension.

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10
Q
  1. Exercise 5:
    Does the strength of the EMG activity in the muscles of the anterior forearm differ btwn flexion w/a weight and w/out a weight?
A

Flexion with the weight increases EMG activity in the anterior forearm muscles than flexion without weight. The muscles has to work harder in order to extend the hand. The greater force required to contract the anterior muscles is shown with an increase in the EMG activity.

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11
Q
  1. Exercise 5:
    Does the strength of the EMG activity in the muscles of the posterior forearm differ btwn extension w/a weight and w/out a weight?
A

Extension with the weight increases EMG activity in the posterior forearm muscles than extension without weight. The weight makes it more challenging to extend the hand since more muscles fibers need to contract in order to produce the required energy.

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12
Q
  1. Exercise 6:
    Compare the parameters for EMG bursts from the TA during each of the activities. When was TA activity the greatest? The least?
A
  • One leg rocking back
  • Single leg support produced more EMG activity since the muscle was required to generate more force to maintain balance. During the single leg support there is greater contraction of the muscles to keep the individual upright.
  • Rocking backwards produced more EMG activity in the anterior muscles since these muscles were needed to help stabilize the individual. Compared to Dorsiflexion, plantar flexion has greater TA activity since TA was stretched during that motion.
  • The activity is the lowest during standing erect on both legs.
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13
Q
  1. Exercise 6:
    Compare the parameters for EMG bursts from the gastrocnemius during each of the activities. When was gastrocnemius activity the greatest? The least?
A
  • rocking forward one leg
  • standing erect
  • With single leg support the muscle needs to work hard and produce more force to keep the individual stable/balanced which translates into a greater EMG signal. Gastrocs are most active during plantar flexion compared dorsiflexion
  • When standing erect on both feet there was the least activity because during that activity the person is very stable, and the muscles do not need much activity to keep the individual in that position.
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14
Q
  1. General EMG Q’s
    When someone holds a heavier barbell the electromyogram recorded from electrodes over active muscles increases. Explain why.
A

When holding a heavier barbell, electrical activity of the muscles must
increase to provide more contraction. This involves increasing the frequency of
action potentials from motor neurons, leading to more muscle fiber activation and
tension generation. Larger motor units (e.g. innervating a greater number of
muscle fibers) are recruited. Overall result is increased stimulation of muscle
fibers and in # of fibers recruited.

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15
Q
  1. General EMG Q’s

Surface electrodes are prone to “crosstalk.” What does this mean?

A
  • Crosstalk means that there is interference being picked up of the EMG signals from muscles not being investigated
  • So instead of isolating the activity of the muscle of interest, its EMG signal is amplified due to the firing occurring in a nearby muscle e.g. test signal of Biceps brachii but due to poor placement of electrodes you pick up some of electrical activity of thetriceps brachii as well. This will cause distortion of the signal
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16
Q
  1. General EMG Q’s

Define the term “common mode rejection”

A
  • Is the removal of 60 Hz signal thru differential amplifier
  • Involves electronic subtraction of the common signal from the electrical potential obtained at each of the two recording electrodes, in this case 60 Hz hum
17
Q
  1. General EMG Q’s
    Describe 5 factors that can affect relationship btwn amt of force exerted and muscle electrical activity measured by electromyography
A
  • *ASK
    1. Cross-talk occurring from other active muscles nearby.
  • Makes it difficult to pick up the signal of interest without receiving additional signals from the nearby muscles. (esp if using surface electrodes)
  1. Distance between electrode and active area
    - If placed away from muscle
    belly and likely a decrease in amplitude
  2. Properties of overlying tissue such as adipose tissue
  3. The quality of contact between the electrode and the skin
    - Poor preparation of skin, not shaving, not cleaning with alcohol and not using electrode paste, and not using a reference electrode will distort the amplitude of the EMG signal and may not give a true representation of the actual force generated by the muscle.
  4. Synergistic muscles involvement
    - Involvement of synergistic muscles in force generation would lead to a higher net force production which is not representative of the muscle of interest that is being tested
    - Ideally the force measured should only come from the muscle of interest and there should not be any contribution of synergistic muscles