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Rigor Mortis - Causes and Stages

Published on Sep 08, 2022 and last reviewed on Dec 26, 2022   -  4 min read


Rigor mortis is the physiologic rigidity of the body occurring after death. This article explains this process in detail.


Rigor mortis, also known as postmortem rigidity, clinically indicates the stiffness of the muscles and joints of the body occurring after the death of an individual. This usually occurs between one to four days and denotes the third stage of death. It is an observable indication of death due to the chemical changes in the muscles leading to a stiffening of the muscles of the hands and legs.

How Is It Caused?

The muscle fibers require the conversion of ATP to ADP for their regular activities and are supported by the sliding filament theory. After death, lactic and pyruvic acid is produced when the respiration halts, and this causes a drop in the intracellular pH. Anaerobic metabolism of glycogen occurring in the muscles leads to glycogen depletion, and thus, ATP concentrations are lowered in the body. Calcium also leaks into the sarcomere and contains actin and myosin protein filaments of muscles arranged in an alternating pattern. In rigor mortis, calcium leaks into the sarcomere. Hence, calcium binds to the filaments creating cross-linking between the filaments. Thus, a pulling motion is developed along the length of the muscle. All this leads to shorter and stiffer muscles.

Some of the major causes of rigor mortis have been explained below:

1. Chemical Changes

Chemical changes in the muscles occurring after the death of a person cause rigor mortis. The process of respiration stops in the person, and the chemical processes dependent on respiration do not occur. The muscles are unable to generate ATP. Ultimately, the actin and myosin filaments remain contracted, and the muscles remain tense.

2. Temperature

The chemical changes tend to occur faster in a person who died at a hot temperature than in a person at a cold temperature. The bodies which are placed in freezing water or ice boxes do not experience the phases of rigor mortis for a few days. The process starts once the defrosting begins in the body.

3. Physical Changes

All the muscles of the body undergo this process. Rigor mortis starts from the eyelids neck, proceeds to the jaw, and lasts for about two to six hours post-death. The mentioned sequence could be correlated to the differing levels of lactic acid amongst muscles, which can be linked to the levels of glycogen and the types of muscle fibers.

The rigor mortis involves various other muscles in the next four to six hours, including the internal organs. Various factors influence the onset of rigor mortis, like the age, physical condition, gender, muscle build of a person, etc. Rigor mortis usually peak after 12 hours and lower after 48 hours. As newborns and children have less muscle mass, rigor mortis becomes undetectable in them.

How Does Rigor Mortis Occur?

All the mechanisms associated with rigor mortis have been summarized below:

  • The sliding fiber hypothesis occurring in the strands of muscles depends on the conversion of ATP to ADP.

  • The absence of respiratory action in the body after death causes a huge reduction in the pH level of the cells in the body as a result of the fusion of pyruvic and lactic acids.

  • When glycolysis occurs in the muscles without oxygen, glycogen exhaustion prompts a lower ATP concentration, and rigidity of muscles is observed.

  • The rigidity of muscles is first observed in smaller muscle bunches that reach from a range of four hours and later move toward bigger muscles. It depends on the minimized amount of ATP at the hour of death.

  • Rigor Mortis plays a major role in reconstructing the postmortem time frame. It keeps the specific position of the body and shows the changes that have occurred, which depends on the rigidity of the body at the time it is revealed.

  • After 36 to 40 hours from death, the body turns into a floppy state.

  • Required flabbiness occurs after death which causes stiffening of the muscles of the jaws, neck, and eyelids.

What Are the Stages of Rigor Mortis?

The rigor mortis can be divided into four main stages: autolysis, bloat, active decay, and skeletonization.

All these stages have been mentioned below in detail:

Stage I: Autolysis

This stage is also called self-digestion and begins after death. The blood circulation and respiration stop soon after death. Hence, the body does not receive oxygen and is also unable to excrete waste. This creates an acidic environment in the body due to the bursting of the cells. The skin and interior of the organs begin to show some rankles. Relaxation of the top layer of the skin is observed. The cell membranes start to produce certain enzymes that eat the cells. Thus autolysis happens.

Stage II: Bloat

The enzymes produced by the cell membranes generate various gasses. The skin shade starts blurring because of the sulfur-containing mixes discharged by the bacteria in the body. As a result, a foul odor is produced by the microorganism during the process of putrefaction, which is the formation of pus.

Stage III: Active Decay

All the body parts experience liquefaction in this stage. All the tissues of the body undergo decay. The leakage of fluids indicates active degradation through the orifices. The soft tissues, like organs, skin, and muscles, undergo liquefaction. During the decay process, the hard tissues or keratinized tissues like hair, cartilage, bones, and other byproducts remain. The body loses most of its weight during this stage.

Stage IV: Skeletonization

Skeletonization has no specific time frame. The final stage of decomposition is when the body's soft tissues deteriorate, and the skeleton can be visualized.


Rigor mortis is the physiologic process occurring in the body after death. This has been used mainly to determine the period since death for a long time. You can consult a specialist online using online medical platforms to know more about this condition.

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Last reviewed at:
26 Dec 2022  -  4 min read




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