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When I press my finger, even with relatively little force, into beef or chicken (say, at a grocery store), the indentation remains.

When I poke a cow with my finger, the indentation does not remain. When I squeeze my own arm, even with the same (or greater) amount of force used to alter the shape of meat with my finger, my arm remains the same shape afterwards.

What is the difference between dead and living muscle tissue, with respect to mechanisms that allow it to maintain its shape? Does living muscle tissue somehow actively maintain its shape while dead tissue cannot? Is it something more passive, such as a breakdown of something in dead muscle tissue that makes it more malleable (and if so, what)?

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  • $\begingroup$ If you pounded your forearm with a baseball bat with time and force equivalent per ounce of muscle as using a tenderizing mallet, I guarantee you it would not spring back into shape at any time. Likely it would need to be amputated. Likewise, punching a large cow as hard as you can doesn't mean you've done no permanent damage to any muscle fibers simply because it doesn't change shape perceptibly. You need to compare apples to apples. Active transport (of fluids, etc) doesn't occur in dead tissue. Your question needs to be reframed in different terms. $\endgroup$
    – anongoodnurse
    Mar 28, 2015 at 20:53
  • $\begingroup$ @anongoodnurse That's why I also gave the example of "poking". I can permanently alter the shape of meat with very little force (finger marks in meat at the grocery store from casual handling by customers are not uncommon), and applying that same force to my arm does not have the same effect. Does that cover the concern? $\endgroup$
    – Jason C
    Mar 28, 2015 at 20:55
  • $\begingroup$ When you poke meat to indent it, a lot of what is being displaced by your finger is fluid (and it takes more that "just a very little force" or it would be unrecognizable after handling by several people) . There is no ability of dead tissue to redistribute that displaced fluid and remove the dent. It doesn't much matter the tissue - muscle or subcutaneous soft tissue in peripheral edema, for example. No active energy expenditure = no reactive movement. $\endgroup$
    – anongoodnurse
    Mar 28, 2015 at 20:59
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    $\begingroup$ @anongoodnurse It sounds like this active redistribution of fluid in living tissue that you mention is a possible answer to my question. Can you elaborate in an answer? $\endgroup$
    – Jason C
    Mar 28, 2015 at 21:00
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    $\begingroup$ @anongoodnurse you should summarize that into an answer. Thanks. $\endgroup$
    – cagliari2005
    Mar 29, 2015 at 5:46

2 Answers 2

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Capillary refill time is defined as the time taken for the capillaries to refill after the blood in them has been squeezed out by pressure. It is widely used as a quick way to determine the effectiveness of the circulatory system in humans by doctors.

In a normal living organism, the capillaries will take time to refill after they have been emptied. Muscle volume consists of the cell volume (which is fixed in the absence of lysis), the blood, as well as lymph and other intracellular fluids (which will be displaced elsewhere when it is deformed by pressure).

When the organism is dead, there is no more circulation in both the blood and lymphatic systems, and therefore any fluids squeezed out by pressure will remain elsewhere, and the deformation is permanent without any regulatory effect by the circulatory system.

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One difference between living and dead tissue, but specific to muscles is tonus. In living skeletal muscle, random nerve impulses fire to keep muscles in a partially contracted, ready-to-use state. Without this low-level tension sarcomeres, the basic units of skeletal muscle, would not recover from being poked and could more easily be pulled out of optimal position and damaged.

sarcomere

And yes, there are also structural changes unique to dead meat. Rigor mortis happens when the sarcomeres exhaust all ATP after death and become trapped in a bound state. Eventually putrefaction sets in and enzymes break off the mechanism and the muscle becomes permanently flaccid.

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