View source for Rigor mortis

{{Short description|Postmortem stiffening of the limbs of a corpse}}
{{About|the sign of death}}
{{Use dmy dates|date=July 2021}}
{{Wiktionary}}
{{Signs of death}}

'''Rigor mortis'''{{efn|Although [[British English]] uses the spelling ''[[rigour]]'', this is not used in ''rigor mortis'' because the phrase is in Latin.}} ({{ety|la|rigor|stiffness||mortis|of death}}), or '''postmortem rigidity''', is the fourth [[stages of death|stage of death]]. It is one of the recognizable [[Death#Signs|signs of death]], characterized by stiffening of the limbs of the [[cadaver|corpse]] caused by chemical changes in the [[Skeletal muscle|muscles]] postmortem (mainly calcium).<ref name="saladin">Saladin, K. S. 2010. ''Anatomy & Physiology'': 6th edition. McGraw-Hill.</ref> In humans, rigor mortis can occur as soon as four hours after death. Contrary to folklore and common belief, rigor mortis is not permanent and begins to pass within hours of onset. Typically, it lasts no longer than eight hours at room temperature.{{citation needed|date=April 2024}}

== Physiology ==
[[File:People Dead 1991 in Sandwip.jpg|thumb|220px|right|Corpses of victims of the [[1991 Bangladesh cyclone]] in [[Sandwip]] displaying signs of rigor mortis]]
After death, aerobic respiration in an organism ceases, depleting the source of oxygen used in the making of [[adenosine triphosphate]] (ATP). ATP is required to cause separation of the [[Myofibril|actin-myosin]] [[Sliding filament theory|cross-bridges]] during relaxation of muscle.<ref name="auto">Hall, John E., and Arthur C. Guyton. Guyton and Hall Textbook of Medical Physiology. Philadelphia, PA: Saunders/Elsevier, 2011. MD Consult. Web. 26 January 2015.</ref> When oxygen is no longer present, the body may continue to produce ATP via anaerobic [[glycolysis]]. When the body's [[glycogen]] is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges.<ref>{{cite journal|last1=Fremery|first1=Donald|date=3 February 1959|title=Biochemistry of Chicken Muscle as Related to rigor mortis and Tenderization|journal=Journal of Food Science|volume=25|issue=1|pages=73–87|doi=10.1111/j.1365-2621.1960.tb17938.x}}</ref><ref name="Ask a Scientist">{{cite web|url=http://www.newton.dep.anl.gov/askasci/zoo00/zoo00248.htm|title=Classroom Resources - Argonne National Laboratory}}</ref>

Calcium enters the [[cytosol]] after death. Calcium is released into the cytosol due to the deterioration of the [[sarcoplasmic reticulum]]. Also, the breakdown of the [[sarcolemma]] causes additional calcium to enter the cytosol. The calcium activates the formation of actin-myosin cross-bridging. Once calcium is introduced into the cytosol, it binds to the troponin of thin filaments, which causes the troponin-tropomyosin complex to change shape and allow the myosin heads to bind to the active sites of actin proteins. In rigor mortis, [[myosin]] heads continue binding with the active sites of actin proteins via [[adenosine diphosphate]] (ADP), and the muscle is unable to relax until further enzyme activity degrades the complex. Normal relaxation would occur by replacing ADP with ATP, which would destabilize the myosin-actin bond and break the cross-bridge. However, as ATP is absent, there must be a breakdown of muscle [[Tissue (biology)|tissue]] by [[enzyme]]s (endogenous or bacterial) during [[decomposition]]. As part of the process of decomposition, the myosin heads are degraded by the enzymes, allowing the muscle contraction to release and the body to relax.<ref>{{Cite web|url=http://chemistry.about.com/cs/biochemistry/a/aa0|title=About.com (archived)}}{{dead link|date=June 2020|bot=medic}}{{cbignore|bot=medic}}</ref>

Decomposition of the myofilaments occurs between 48 and 60 hours after the peak of rigor mortis, which occurs approximately 13 hours after death.<ref name="saladin" />
<!-- Placeholder for diagram of Sarcomere including Actin and Myosin -->

== Applications in meat industry ==
Rigor mortis is very important in the [[meat industry]]. The onset of rigor mortis and its resolution partially determines the tenderness of [[meat]]. If the post-slaughter meat is immediately chilled to 15&nbsp;°C (59&nbsp;°F), a phenomenon known as cold shortening occurs, whereby the muscle sarcomeres shrink to a third of their original length. <!-- the muscles don't actually shrink, just change shape This will lead to the loss of water from the meat along with many of the [[vitamins]], [[minerals]], and [[water-soluble]] proteins. The loss of water makes the meat hard and interferes with the manufacturing of several meat products like [[cutlet]] and [[sausage]].{{Citation needed|date=January 2010}}-->

Cold shortening is caused by the release of stored [[calcium]] ions from the [[sarcoplasmic reticulum]] of muscle fibers, in response to the cold stimulus. The calcium ions trigger powerful muscle contraction aided by ATP molecules. To prevent cold shortening, a process known as electrical stimulation is carried out, especially in beef carcasses, immediately after [[Animal slaughter|slaughter]] and [[skinning]]. In this process, the [[Cadaver|carcass]] is stimulated with [[alternating current]], causing it to contract and relax, which depletes the ATP reserve from the carcass and prevents cold shortening.<ref>{{cite book|url=https://books.google.com/books?id=M3wmO3ynTUwC&pg=PA13|title=New Zealand Journal of Agricultural Research|publisher=The Royal Society of New Zealand|author=The Royal Society of New Zealand|page=13|year=1976}}</ref>

== Application in forensic pathology ==
[[File:Postmortem interval changes (stages of death).png|thumb|500px|Timeline of postmortem changes (stages of death).]]
The degree of rigor mortis may be used in [[forensic pathology]] to determine the approximate time of death. A dead body holds its position as rigor mortis sets in. If the body is moved after death, but before rigor mortis begins, forensic techniques such as [[livor mortis]] can be applied. Rigor mortis is known as [[transient evidence]], as the degree to which it affects a body degrades over time.

== See also ==
* [[Cadaveric spasm]]

== Notes ==
{{Notelist}}

== References ==
{{Reflist}}

== Bibliography ==
* Bear, Mark F; Connors, Barry W.; Paradiso, Michael A., [https://books.google.com/books?id=75NgwLzueikC ''Neuroscience, Exploring the Brain''], Philadelphia : Lippincott Williams & Wilkins; Third Edition (1 February 2006). {{ISBN|0-7817-6003-8}}
* Robert G. Mayer, "Embalming: history, theory, and practice", McGraw-Hill Professional, 2005, {{ISBN|0-07-143950-1}}
* "Rigor Mortis and Other Postmortem Changes - Burial, Body, Life, Cause, Time, Person, Human, Putrefaction." Encyclopedia of Death and Dying. 2011. Web. 4 December 2011. <[http://www.deathreference.com/Py-Se/Rigor-Mortis-and-Other-Postmortem-Changes.html Rigor Mortis and Other Postmortem Changes - burial, body, life, cause, time, person, human, Putrefaction].
* Saladin, Kenneth. Anatomy and Physiology: The Unity of Form and Function, 6th ed. McGraw-Hill. New York, 2012.

{{Death}}

[[Category:Signs of death]]
[[Category:Latin medical words and phrases]]
[[Category:Forensic pathology]]