After death, the body undergoes a series of changes that occur in stages. Rigor mortis is the third stage 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 to any death examination because it can narrow down the timeframe of death.
There are 6 stages of rigor mortis, which begin within 2 hours of death and peak at about 12 hours. Overall, the process of rigor mortis goes on for 24-48 hours.
6 stages of rigor mortis
- Absent: The body is still able to get a small amount of oxygen anaerobically. The muscles are still soft and movable.
- Minimal: The body's muscles will start to turn stiff in this stage. The face muscles are the first to be affected.
- Moderate: More body muscles begin to harden, and it becomes obvious that the body is no longer loose or flexible.
- Advanced: Most of the muscles in the body are now stiff and do not bend.
- Complete: All muscles in the body become hard and inflexible.
- Passed: Rigor mortis is complete, and the body now moves into the phases of livor mortis and finally decomposition.
Understanding the process of rigor mortis
Muscles need energy to function, in the form of adenosine triphosphate. Our muscles 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 muscle.
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 stiff first.
What are the stages of death?
- 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.
- 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 exactly the same, it normally takes somewhere in the range of 18-20 hours for the body’s temperature to match the external temperature.
- Rigor mortis: Following death, the body will turn stiff. The muscles become loose and limp, yet the entire body will stiffen after a couple of hours.
- 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.
- Decomposition: This stage includes two distinct cycles: autolysis and putrefaction. Autolysis starts when the cells start to release enzymes and goes 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 of postmortem and proceeds to last for 5-6 days.
How long does rigor mortis last?
The course of rigor mortis begins in 2 hours of death and peaks at about 12 hours. 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 sequence of appearance and disappearance of rigor mortis is muscles of the face and head, neck, chest, upper appendage, abdomen, and lower appendage.
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