Just a random question, would a sharp object pierce your muscle more(stabbed with the same amount of force) when the muscle is flexed or when relaxed?

  • $\begingroup$ I would say that it would depend largely on the muscle. $\endgroup$ – Rory M Feb 28 '12 at 19:41
  • $\begingroup$ lets say any large muscle, abdominals, hamstrings, shoulder, etc @RoryM Edit: or are you talking about the muscle density? $\endgroup$ – stackErr Feb 28 '12 at 19:44
  • $\begingroup$ Depends on the stabbing force and how sharp the object is. $\endgroup$ – kmm Feb 28 '12 at 21:11
  • $\begingroup$ I suppose in theory the density of the tissue has increased during contraction if you stab in the middle so (preparing for a possible physics disaster) that would mean less penetration for constant force from an identical object $\endgroup$ – Rory M Feb 28 '12 at 22:36

Well, if we look in very basic detail at how muscle contraction works within a myofibril of the sarcomere:

Animation of muscle contractions

N.b. this isn't on a loop and only plays through seven times

The red lines represent actin filaments whilst the blue lines represent myosin filaments. During muscle contraction the filaments move over each other:

Relaxed myofibril

Partially Contracted myofibril

(Over)Contracted myofibril

As shown in the above diagrams the "more contracted" a muscle is then the smaller the size of the H zone (the area where there are just myosin filaments).

So if we consider a penetrating impact that went through a plethora of identically aligned sarcomeres (obviously this is not the case in nature) then we could presume that (et ceteris paribus) the object would not penetrate as deeply into a contracted muscle as it will hit more tissue on its route than in a relaxed muscle.

  • 3
    $\begingroup$ Thanks for a very detailed and clearly explained answer! Pity i didnt take Bio during high school...interesting stuff $\endgroup$ – stackErr Mar 25 '12 at 12:16

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