Dear Biomch-L list,

I have some questions in relation to the mechanical properties of skeletal muscle tissue:

1. Has the resting stiffness induced in passive living muscle due to muscle tone been quantified in the literature (e.g. compared to freshly dead tissue)?
2. Does muscle tone (and therefore its induced stiffness component) instantly disappear after death?
3. Is a mild state of rigor mortis mechanically similar to stiffness induced by muscle tone?
4. Mechanoreceptors in muscle e.g. muscle spindles are capable of measuring stretch/stretch rate. Muscle spindles are known to increase muscle stiffness as a certain stretch threshold/stretch rate threshold is exceeded. Is there any data known on threshold deformation/deformation rates that result in enhanced stiffness of muscle?
5. Is this stretch reflex only present in extension or is there any data known on stiffness increase/decrease due to a certain compression/compression rate (e.g. perpendicular to the muscle fibre direction)?
6. In the biomechanical literature the words 'passive muscle' are sometimes used for freshly dead tissue (without muscle tone induced resting stiffness), however in literature on living tissue the words 'passive muscle' are also used to describe relaxed, un-stimulated muscle at rest (with muscle tone). Since living and freshly dead tissue are mechanically different (e.g. due to the lack of muscle tone) what is the correct use of the word 'passive'? To me passive is the opposite of active which implies the tissue is alive and therefore it seems like the word should be used solely as a property of living tissue in vivo (even though it may be physically possible to activate freshly excised tissue).

Kind regards,

Kevin Moerman, PhD student Trinity College Dublin, Ireland
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