Biomedical Engineering Reference
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( a )
( b )
Figure 10.18 EMG and muscle tension recorded on a storage oscilloscope during
varying isometric contractions of the biceps muscles. Note the delay between the EMG
and the initial build-up of tension, time to reach maximum tension, and drop of tension
after the EMG has ceased. ( a ) During a gradual build-up and rapid relaxation. ( b )
During a short 400-ms contraction.
2. How do other agonist muscles share the load at that joint, especially
if some of the muscles have more than one function (Vredengregt and
Rau, 1973)?
3. In many movements, there is antagonist activity. How much does this
alter the force being predicted by creating an extra unknown force?
With the present state of knowledge, it appears that a suitably calibrated
linear envelope EMG can be used as a coarse predictor of muscle tension for
muscles whose length is not changing rapidly.
10.4.2 Electromyogram during Muscle Shortening and Lengthening
In order for a muscle to do positive or negative work, it must also undergo
length changes while it is creating tension. Thus, it is important to see how
well the EMG can predict tension under these more realistic conditions. A
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