Rigor Mortis - Causes and Stages

Introduction:

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 that occur in the muscles leading to the stiffening of the muscles of the hands and legs. The term livor mortis or post-mortem lividity refers to the collection of blood in the lower part of the body or dependent parts after death which is characterized by a dark purple discoloration of the skin. Similarly, algor mortis (cold death) refers to the change in temperature after the death of a person.

How Is It Caused?

The muscle fibers require the conversion of ATP (adenosine triphosphate) to ADP (adenosine diphosphate) 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. Rigor mortis is a change that occurs after the death of a person usually two hours after death.

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

1. Chemical Changes: Chemical changes in the muscles that happen after the death of a person causes 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 who died 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 defrosting begins in the body.

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

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, and so on. Rigor mortis usually peaks after 12 hours and lowers after 48 hours. As newborns and children have less muscle mass, rigor mortis becomes undetectable in them.

How Does Rigor Mortis Occur?

The term rigor mortis is derived from the Latin language which means ‘stiffness (rigor) of death (mortis)’. 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 maintains 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 that occurs after death causes stiffening of the muscles of the jaws, neck, and eyelids.

What Are the Stages of Rigor Mortis?

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. 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 producing certain enzymes that eat the cells. Thus, autolysis (knockdown of the cells or tissues by their own enzymes) happens.

Stage II (Bloat): The enzymes produced by the cell membranes generate various gases. 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 microorganisms during the process of putrefaction, which is the formation of pus.

Stage III (Active Decay): All the body parts experience liquefaction at 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.

Conclusion:

Rigor mortis is the physiologic process that occurs in the body after death. This has been used mainly to determine the period after death for a long time. Rigor mortis sets in around three hours after death and reaches maximum stiffness after 12 hours and gradually disappears approximately 72 hours after death. Rigor mortis is at its peak at about 12 hours. The applications of rigor mortis are in the field of criminological science and the meat industry as its onset and resolution act as central variables for the meat to get tender.