Electromyography: Relationships & Applications

D. Gordon E. Robertson, PhD, FCSB

Biomechanics Laboratory,School of Human Kinetics,University of Ottawa, Ottawa, Canada

1Biomechanics Laboratory, University of Ottawa

Biomechanics Laboratory, University of Ottawa 2

Isometric EMG

• linear relationship for submaximal contractions• exponential relationship over full range• can be used as a control signal to regulate

myoelectrically controlled devices

Biomechanics Laboratory, University of Ottawa 3

Isometric EMG • exponential over full range

especially when normalized to maximum force

Biomechanics Laboratory, University of Ottawa 4

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

Biomechanics Laboratory, University of Ottawa 5

Force-velocity-length

• force varies with both length and velocity of contraction

• also pre-history, i.e., prestreched, fatigued, or relaxed

Biomechanics Laboratory, University of Ottawa 6

Maximum EMG

• experiment by Komi

• measured EMG of three muscles

• measured maximum force at different speeds of contraction

Biomechanics Laboratory, University of Ottawa 7

Maximum EMG

• results of force similar to Hill’s equation and Gordon & Huxley

Biomechanics Laboratory, University of Ottawa 8

Maximum EMG

• EMGs did not vary across velocity of contraction

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

Biomechanics Laboratory, University of Ottawa 9

Biceps

Triceps

Angle

Velocity

Accel.

Biomechanics Laboratory, University of Ottawa 10

Flexion Extension

FlexingExtending

Concentric flexionConcentric extension

Concentric flexion by biceps

Concentric extension

by triceps

Biceps

Triceps

Angle

Velocity

Accel.

Biomechanics Laboratory, University of Ottawa 11

Flexion Extension

Low EMG to stop extension

Stopping flexion with triceps

Stopping extension

with biceps

Biceps

Triceps

Angle

Velocity

Accel.

Biomechanics Laboratory, University of Ottawa 12

Flexing

Extending

Flexion Extension

In this trial flexion was stopped by

ligaments and bones