Rigor mortis
Forensic Medicine · Physiology · Pathology
Say it: RIG-ur MOR-tis
Rigor mortis is the temporary stiffening of muscles after death, caused by loss of ATP, which leaves myosin locked onto actin until muscle proteins break down.
Also: postmortem rigidity, cadaveric rigidity
Definition
What is rigor mortis?
Rigor mortis is the stiffness that develops in a body in the hours after death. In living muscle, ATP is needed not only to power contraction but also to end it: when ATP binds a myosin head, the head lets go of the actin filament. After death, cells stop making ATP, so the myosin heads stay attached to actin in fixed cross-bridges and the muscles become rigid.
The stiffening usually shows first in small muscles such as the eyelids and jaw and then spreads to the limbs. In temperate conditions it typically becomes noticeable within a few hours, is fully developed by about 6 to 12 hours, and fades over roughly the next day or two as enzymes and decomposition break down the muscle proteins, leaving the body limp again. Heat, fever and intense muscle activity just before death speed it up, while cold slows it down.
Forensic pathologists use rigor mortis together with body cooling, called algor mortis, and the settling of blood, called livor mortis, to estimate the time since death and to judge whether a body was moved. Because so many factors change its timing, it gives only a rough interval.
Word parts
Where does the term “rigor mortis” come from?
- rigor
- stiffnessLatin rigor
- mortis
- of deathLatin mors, mortis
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Terms that go with it
- Postmortem intervalThe postmortem interval is the time since a person died, estimated by forensic experts from body changes, temperature, insects and other evidence.
- AutopsyAn autopsy is a medical examination of a body after death, inside and out, to find the cause of death and study the effects of disease or injury.
- Skeletal muscleSkeletal muscle is the striated, voluntary muscle tissue attached to bones by tendons that moves the body, holds posture and produces heat.
- SarcomereA sarcomere is the repeating contractile unit of striated muscle, the section of a myofibril between two Z-discs where actin and myosin interact.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 10.3 Muscle Fiber Contraction and Relaxation
- NCBI MeSH: Rigor Mortis
- EBSCO Research Starters: Rigor mortis
- Strete et al. (2025), Estimating the Postmortem Interval: A Systematic Review, Diagnostics
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