What Are the 6 Stages of Rigor Mortis?

Stages of rigor mortis.

After death, the body undergoes a series of changes that occur in stages. Rigor mortis is the third stage after death, in which the muscles harden and become stiff, caused by the lack of adenosine triphosphate (ATP), which gives energy to the muscles. Rigor mortis is a significant tool for any death examination because it can narrow down the time frame of death.

Learn more about what causes rigor mortis, as well as its stages and how long it lasts.

Muscles need energy to function, in the form of adenosine triphosphate. Our muscle fibers are made of two protein bands called myosin and actin, which move toward one another, contracting the muscle. Energy is then needed to let the bands separate from one another, relaxing the muscles.

Following death, the muscles become weak because the brain cannot tell the muscles to contract or relax. The muscles still have energy reserves that can be used, so the muscles stay relaxed. After a few hours, this energy reserve starts to drain until it is completely depleted. Without any respiration activity or food consumption, no ATP is produced. Hence, the muscles freeze in the position they are in. Although this begins to affect the entire body simultaneously, the smaller muscles such as those in the eyelids, face, and fingers turn visibly stiff first.

The six stages of rigor mortis include:

1. Absent: The body can still get a small amount of energy anaerobically. The muscles are still soft and movable.
2. Minimal: The body's muscles will start to stiffen in this stage. The facial muscles are the first to show signs of stiffness.
3. Moderate: More body muscles begin to harden, and it becomes obvious that the body is no longer loose or flexible.
4. Advanced: Most of the muscles in the body are now stiff and do not bend.
5. Complete: All muscles in the body become hard and inflexible.
6. Passed: Rigor mortis is complete, and the body now moves into the phases of livor mortis and finally decomposition.

The stages of death include:

1. Pallor mortis: The main change that occurs is increased paleness because of the suspension of blood circulation. This is the first sign and occurs quickly, within 15-30 minutes of death.
2. Algor mortis: Humans are warm-blooded creatures, which means that we keep a consistent body temperature, regardless of the external environment. The brain is our temperature regulator, and the circulatory framework is the principal heat dissipator. After death, the brain cells stop signaling, and the heart stops pumping blood, which means the body begins to match the external temperature. Our normal body temperature level is 98.6°F (37°C). Assuming the surrounding temperature around the dead body is not the same, it normally takes somewhere in the range of 18-20 hours for the body's temperature to match the external temperature.
3. Rigor mortis: Following death, the body will turn stiff over a few hours. The muscles become loose and limp with death, yet the entire body will stiffen after a couple of hours because the muscle fibers contract and freeze and cannot disengage and relax.
4. Livor mortis: This is the last phase of death. When the heart stops pumping, the blood is pulled by gravity and begins to collect in certain areas depending on the position of the body. Lividity begins with the skin where the blood has settled, giving it a bright red tone. After a few hours, the color changes from red to blue or purple. This can take about 6-8 hours.
5. Decomposition: This stage includes two distinct cycles: autolysis and putrefaction. Autolysis starts when the cells start to release enzymes and go on for about 2 hours after cells starved of oxygen die and lose their structure. After autolysis comes putrefaction where the dead body becomes bloated and decays, and dry phases of decomposition begin. Bacteria inside the body produce gases that the non-breathing corpse can't diffuse. The eyes and tongue might protrude and begin to smell of death. Bloating normally starts around the second day after death and proceeds to last for 5-6 days.

When does rigor mortis set in?

The 6 stages of rigor mortis begin within 2 hours of death and peak at about 12 hours.

Why does rigor mortis occur?

Rigor mortis occurs because of chemical changes in the muscles after death. Rigor mortis occurs in all the muscles, including the voluntary skeletal muscles, the smooth muscles around blood vessels, respiratory passages, the gastrointestinal tract, the bladder, and the uterus. and the heart muscles. Muscle contraction and relaxation require calcium, ATP, and many chemical reactions. To understand why and how rigor mortis occurs, we first need to understand how muscle works.

To make muscles contract, the brain sends electrical nerve signals leading to the release of a chemical known as acetylcholine at the region where nerve ends are connected to the muscles (neuromuscular junction). This opens channels on the muscle fiber membranes, and sodium ions flow through, and depolarize the membranes. This allows calcium ions to flow in and cause the muscle proteins myosin and actin to bind, resulting in muscle contraction.

The calcium ions are stored in a structure called sarcoplasmic reticulum in the muscle fiber, and a fraction of a second after the influx, calcium is pumped back into its storage space. ATP, which is produced from oxygen, breaks the bond between actin and myosin, allowing the muscle to relax and be ready for the next contraction.

With death, the muscles first totally relax because the brain can no longer send signals, and this is known as primary muscular flaccidity. There is a residual store of ATP in the cell and muscles stay relaxed for a while. Chemical changes start occurring. Without oxygen, a small amount of ATP production continues with the anaerobic breakdown of glucose, which produces lactic acid and pyruvic acid. The intracellular environment becomes acidic and corrosive. Calcium leaks into the intracellular space making actin and myosin bind, which stay bound because there is no ATP to release them. The muscles gradually become stiff and inflexible.

Overall, the process of rigor mortis goes on for 24-48 hours. Factors such as surrounding temperature, cause of death, temperature of the body, previous levels of fitness and muscle mass, drug abuse, infection, and availability of nutrients and adenosine triphosphate immediately before the death may shorten or lengthen these times. Rigor mortis comes to an end because of the decomposition of the muscles and the body, a cycle called secondary flaccidity.

The overall timeline of rigor mortis under ordinary conditions is as follows:

• 0-8 hours: Body begins to harden but is still movable
• 8-12 hours: Muscles become fully stiff
• 12-24 hours: Muscles stay solid and stiff
• 24-36 hours: Stiffness disperses, and muscles become flexible

The natural sequence of appearance and disappearance of rigor mortis is muscles of the face and head, neck, chest, upper appendage, abdomen, and lower appendage.

If the body is embalmed immediately after death, rigor mortis does not occur. The embalmer can also massage the muscles, and move and bend the joints to the extent possible, to remove rigor mortis. Once rigor mortis is broken in such a fashion, it will not return.

What is stage 3 of rigor mortis?

In general, rigor mortis is described in 6 stages, starting with the first stage immediately after death when it is completely absent, and the final 6th stage when it has resolved. In both these stages, the body is completely flaccid. The third stage in this process would be described as moderate, with many of the muscles stiff and immobile. However, rigor mortis may also be described in four stages, excluding the absent stages, which means that the third stage is when it is advanced, has set in most of the muscles, and the body is inflexible.

How long does it take rigor mortis to set in?

Rigor mortis begins to set in approximately 2 hours after death and is completed in about 8 to 12 hours and may last up to 24 hours or more. However, these timelines are highly variable depending on many factors. The process is speeded up in higher ambient temperatures and is slowed down in colder climates. In hot conditions, rigor mortis passes also quickly and decomposition can start within 24 hours.

Strenuous activity just before death can quicken the process of rigor mortis, because ATP stores would already have been low, along with lactic acid buildup. Other conditions that can deplete ATP and accelerate rigor mortis are electrocution, high temperature, convulsions, muscle disorders that cause muscle stiffening, infection, cerebral hemorrhage, severe illness, use of substances such as cocaine or amphetamine, and strychnine poisoning. Rigor mortis sets in very fast in newborns. In people with extremely low muscle mass, rigor mortis may be minimal or not form at all.

Cold temperatures can slow down the cooling of the body to match atmospheric temperature, as well as the process of rigor mortis. The stiffness that comes from extreme cold or heat is different from rigor mortis, which is a chemical process. If a body is frozen before rigor mortis sets in, it can set in after the body thaws.

Why do bodies stiffen after death?

Bodies stiffen after death because of rigor mortis, a series of chemical reactions in the muscles that make them contract and stay contracted. Bodies once again become flaccid after a period when proteins break down, and enzymes and bacteria cause cellular destruction and decomposition.

Another rare cause of stiffness after death is known as cadaveric spasm. This occurs immediately after death, without the initial flaccidity that happens with rigor mortis. Cadaveric spasm usually occurs only in a small group of muscles, for instance, a clenched hand, due to extreme physical or emotional stress just before death. This is generally seen only in situations such as war, fighting, plane crashes, and falling from a height.

Can a live person get rigor mortis?

A live person cannot get rigor mortis. The word, by definition, means “stiffness after death,” and refers to the chemical processes that occur within muscle cells due to ATP depletion, which starts after death. Rigor mortis can set in rapidly after death in certain conditions, but a live person can never have rigor mortis. Some illnesses can cause involuntary muscle contraction that persists, including tetanus infection which causes lockjaw (trismus), but these cannot be termed rigor mortis. Tissue death can happen in a live person due to lack of blood supply, but this causes gangrene or necrosis, and nor rigor mortis.