I question their explanation.
As you move the ankle the muscle fibers may lengthen and shorten.
However, I wonder what the fiber orientation would look like when you stand on your tip toes.
In this position, the fibers would be quite short and would have a lot of tension.
This would be different than passively moving the ankle into plantar flexion with the subject relaxed.
On tip toes there was active contraction of the muscle.
With pasive motion, there may not have been any sliding of the sarcomeres.
You may get wavy muscles with the passive motion, but it is not shorter than short.
Back in undergrad, I did a physiology lab where we took the muscle of the frog out of the frog and stimulated.
When it was attached to the bone it was a certain length.
When detached, it shortened to less than that legngth, but could be stretched passively to its physiologic range of lengths.
It could be stimulated to contract and various lengths.
The force that it produced varied with length.
Proving a fact that should have been in the textbooks that those researchers should have read and thought about.
This is the factor that we use in Structural Relief Therapy.
Chronically hypertonic muscles, often with motor points that have become trigger points, held in a shortened position passively for 90 seconds release the feed back loop that is holding them hypertonic.
Slowly bringing the muscle to its resting length restore a proper resting tone.
Hans Albert Quistorff, LMP
Antalgic Posture Pain Specialist
What is a chronically hypertonic muscle?
What causes a muscle to be chronically hypertonic?
If the muscle is hypertonic, isn't it already in its shortened position.
If this is true how do you hold it there?