Specifications

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Lt
The length of the tendon. This appears to be constant, but the
tendon length actually changes slightly over the movement with
the changes of muscle force as described above.
LmtDot
The contraction velocity of the muscle-tendon unit. The value is
positive because the muscle is getting longer.
LmDot
The contraction velocity of the contractile element of the muscle.
The value is positive because the muscle is getting longer.
Activity
This is the muscle activity before correction for the change in
muscle length caused by the elastic elongation of the muscle.
The complicated variation is caused by the interplay between
change of moment arm of the applied force, the passive force in
the muscle and the change of muscle strength with the
contraction.
Corrected-
Activity
This is the muscle activity after correction for the tendon
elongation. The difference between this graph and the one above
is that the activity toward the end is higher after correction. This
can be difficult to understand and illustrates the complexity of
muscle modeling. The reason is the following: The force in the
muscle reduces towards the end of the movement. When the
force is reduced, the tendon contracts, and this means that the
muscle must elongate even more. Since the muscle length is
already in the interval where further elongation will cause
decreased strength, the tendon contraction has the effect of
increasing the muscle activity.