Transcript Electromyography: Processing

Electromyography:
Relationships & Applications
D. Gordon E. Robertson, PhD, FCSB
Biomechanics Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, Canada
Biomechanics Laboratory, University of Ottawa
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Isometric EMG
• linear relationship for submaximal contractions
• exponential relationship over full range
• can be used as a control signal to regulate
myoelectrically controlled devices
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Isometric EMG
• exponential over full range
especially when normalized
to maximum force
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Force-velocity
• Hill’s equation
illustrates that as
speed of muscle
shortening
increases, force
decreases
• but for eccentric
contractions force
increases with speed
of lengthening
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Force-velocity-length
• force varies
with both
length and
velocity of
contraction
• also prehistory, i.e.,
prestreched,
fatigued, or
relaxed
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Maximum EMG
• experiment by
Komi
• measured EMG of
three muscles
• measured
maximum force at
different speeds of
contraction
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Maximum EMG
• results of force
similar to Hill’s
equation and
Gordon &
Huxley
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Maximum EMG
• EMGs did not
vary across
velocity of
contraction
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EMG during Dynamic
Contractions
• strong correlation between level of
concentric contraction and EMG
• weak correlation between level of eccentric
contraction and EMG
• EMG level is often greater during a brief
rapid MVC then during a sustained MVC
• following figures show biceps and triceps
brachii during a horizontal rapid flexion
extension movement, an electrogoniometer
was used to monitor elbow angle
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Biceps
Triceps
Concentric flexion
by biceps
Concentric extension
by triceps
Angle
Velocity
Accel.
Flexion
Extension
Flexing
Extending
Concentric extensionConcentric flexion
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Low EMG to
stop extension
Biceps
Triceps
Angle
Flexion
Extension
Velocity
Accel.
Stopping extension
with biceps
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Stopping flexion
with triceps
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Biceps
In this trial flexion
was stopped by
ligaments and bones
Triceps
Angle
Flexion
Extension
Flexing
Velocity
Extending
Accel.
Biomechanics Laboratory, University of Ottawa
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