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Rigor Mortis: Definition, Timeline & Stages

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  • 0:00 What is Rigor Mortis?
  • 0:20 Timeline of Rigor Mortis
  • 0:50 Timeline Factors
  • 1:30 The Stages of Rigor Mortis
  • 2:30 Lesson Summary
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Lesson Transcript
Instructor: Earl Crowe

Earl has over 20 years of lecturing experience and has a master's degree in criminal justice.

What was the time of death? This is often asked by family members of the deceased after a death investigator completes the initial investigation. One of the most important processes after death is rigor mortis. Learn more about this term, the timeline and its various stages.

What is Rigor Mortis?

Rigor mortis is the medical term that is used to describe the hardening of body muscles after death. It's the result of the body's loss of adenosine triphosphate (or ATP), which is a substance that gives energy to the muscles. Rigor mortis is a valuable tool to any death investigation since it can narrow down the timeframe of death. Another term for rigor mortis is postmortem rigidity.

Timeline of Rigor Mortis

There are many factors to consider when examining rigor mortis in order to come to any conclusions or findings about a person's death. This is the general timeline that rigor mortis will follow under regular conditions:

0 to 8 Hours: The body starts to stiffen, but is still movable
8 to 12 Hours: Muscles become completely stiff
12 to 24 Hours: Muscles stay stiff
24 to 36 Hours: Stiffness dissipates and muscles become flexible

Timeline Factors

In the earlier timeline, the times listed were a general rule under normal conditions. Many factors can alter the timeline for rigor mortis. The following lists indicate factors that will potentially slow down or speed up the rigor mortis process:

First, here are examples of what accelerates rigor mortis:

  • Exercise prior to death
  • Hot environmental temperatures
  • Convulsions
  • Electrocution
  • High body temperature and fever
  • Drugs that increase body temperature

Now, here are some examples of what decreases the rate of rigor mortis:

  • Hypothermia
  • Cold environmental temperatures
  • Pneumonia
  • Hemorrhages
  • Nervous diseases

The Stages of Rigor Mortis

According to the Medicolegal Death Investigators Training Manual, there are six stages of rigor mortis in humans. Their stages are:

  1. Absent
  2. Minimal
  3. Moderate
  4. Advanced
  5. Complete
  6. Passed

If you're working as a medicolegal death investigator, these stages would be combined when completing examinations. The four combined stages used in the field are:

  1. Absent
  2. Present (a combination of minimal and moderate)
  3. Complete (a combination of advanced and complete)
  4. Passed

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