April182012
Rigor Mortis
1) What is rigor mortis?
After death, the muscles of the body are initially flacid and the joints are relaxed
1-3 hours after death, rigor mortis sets in, causing the muscles to stiffen
Once the muscles have stiffened, the body remains in the position until rigor passes or is broken
2) Time scale for rigor mortis

Immediately after death (rare) - cadaveric spasm can occur (rigor mortis sets in within minutes of death)
1-2 hours after death (normally) - rigor mortis sets in
~3-4 hours after death - rigor mortis becomes noticeable
10-12 hours after death - body is in full rigor and remains stiff for another 24-36 hours

3) Cellular changes during rigor mortis

Rigor mortis affects both skeletal and smooth muscle
There is a rise in intracellular concentration of calcium ions in muscle cells after death which causes the troponin and tropomyosin of the muscles to move aside
Actin and myosin can then bind together to form cross bridges which results in the stiffening of the body until the proteins begin to degrade

 4) Rigor mortis and muscle contraction

The cellular changes that take place during rigor mortis are similar but not identical to physiologic muscle contraction
Both processes involve calcium ions and ATP/ADP but rigor mortis does not involve muscular shortening (rigor mortis involves disappearance of ATP and creatine phosphate from the muscles)
Muscular shortening is also easily reversed, whereas the stiffening in rigor mortis stays in place until it is broken or until it passes
5) Development of rigor mortis
Rigor mortis develops in all the muscles at the same time but is visible in smaller muscle groups first
If rigor is physically broken in one area, it does not redevelop due to the chemical cross linking of the actin and myosin being irreversible
If rigor is overcome before it is fully developed (e.g by freezing the body) te process will subsequently continue to completion when conditions are returned to normal, although the area will be less stiff than it otherwise would have been
6) Factors affecting time of onset

The time of onset of rigor can vary a certain amount according to two main factors: the pH of the muscle at the moment of death (determined by activity prior to death) and the amount of glycogen present in the muscle (linked to pH of the muscle)
The internal and environmental temperatures also play a part - a higher temperature increases the rate of glycolysis, which results in a shorter interval between death and onset of rigor and in an increase in muscle shortening
7) Other factors
Rigor mortis develops quicker at higher temperatures and is affected by the decedent’s activity prior to death. A higher internal body temperature causes more lactic acid to be produced, which accelerates the development of rigor
Accelerated rigor can also be found in some drug-related deaths as certain substances (for example cocaine, PCP and methamphetamine) can cause higher internal body temperatures even if the environmental temperature is not raised
Physical activity before death also causes accelerated rigor due to a higher internal body temperature and increased lactic acid production
References
Bate-Smith, E. C., Bendall, J. (1949) Factors Determining the Time Course of Rigor Mortis. J. Physiol. 110, pp 47-65.
Bendall, J. R. (1951) The Shortening of Rabbit Muscles During Rigor Mortis: IT’s Relation to the Breakdown of Adenosine Triphosphate and Creatine Phosphate and to Muscular Contraction. J. Physiol. 114, pp 71-88.
Dix, J., Graham, M. (2000) Time of Death, Decomposition and Identification: An Atlas. Florida: CRC Press.
Gunn, A. (2009) Essential Forensic Biology. West Sussex: Wiley Blackwell.

Rigor Mortis

1) What is rigor mortis?

  • After death, the muscles of the body are initially flacid and the joints are relaxed
  • 1-3 hours after death, rigor mortis sets in, causing the muscles to stiffen
  • Once the muscles have stiffened, the body remains in the position until rigor passes or is broken
2) Time scale for rigor mortis
  • Immediately after death (rare) - cadaveric spasm can occur (rigor mortis sets in within minutes of death)
  • 1-2 hours after death (normally) - rigor mortis sets in
  • ~3-4 hours after death - rigor mortis becomes noticeable
  • 10-12 hours after death - body is in full rigor and remains stiff for another 24-36 hours
3) Cellular changes during rigor mortis
  • Rigor mortis affects both skeletal and smooth muscle
  • There is a rise in intracellular concentration of calcium ions in muscle cells after death which causes the troponin and tropomyosin of the muscles to move aside
  • Actin and myosin can then bind together to form cross bridges which results in the stiffening of the body until the proteins begin to degrade
 4) Rigor mortis and muscle contraction
  • The cellular changes that take place during rigor mortis are similar but not identical to physiologic muscle contraction
  • Both processes involve calcium ions and ATP/ADP but rigor mortis does not involve muscular shortening (rigor mortis involves disappearance of ATP and creatine phosphate from the muscles)
  • Muscular shortening is also easily reversed, whereas the stiffening in rigor mortis stays in place until it is broken or until it passes

5) Development of rigor mortis

  • Rigor mortis develops in all the muscles at the same time but is visible in smaller muscle groups first
  • If rigor is physically broken in one area, it does not redevelop due to the chemical cross linking of the actin and myosin being irreversible
  • If rigor is overcome before it is fully developed (e.g by freezing the body) te process will subsequently continue to completion when conditions are returned to normal, although the area will be less stiff than it otherwise would have been
6) Factors affecting time of onset
  • The time of onset of rigor can vary a certain amount according to two main factors: the pH of the muscle at the moment of death (determined by activity prior to death) and the amount of glycogen present in the muscle (linked to pH of the muscle)
  • The internal and environmental temperatures also play a part - a higher temperature increases the rate of glycolysis, which results in a shorter interval between death and onset of rigor and in an increase in muscle shortening

7) Other factors

  • Rigor mortis develops quicker at higher temperatures and is affected by the decedent’s activity prior to death. A higher internal body temperature causes more lactic acid to be produced, which accelerates the development of rigor
  • Accelerated rigor can also be found in some drug-related deaths as certain substances (for example cocaine, PCP and methamphetamine) can cause higher internal body temperatures even if the environmental temperature is not raised
  • Physical activity before death also causes accelerated rigor due to a higher internal body temperature and increased lactic acid production

References

Bate-Smith, E. C., Bendall, J. (1949) Factors Determining the Time Course of Rigor Mortis. J. Physiol. 110, pp 47-65.

Bendall, J. R. (1951) The Shortening of Rabbit Muscles During Rigor Mortis: IT’s Relation to the Breakdown of Adenosine Triphosphate and Creatine Phosphate and to Muscular Contraction. J. Physiol. 114, pp 71-88.

Dix, J., Graham, M. (2000) Time of Death, Decomposition and Identification: An Atlas. Florida: CRC Press.

Gunn, A. (2009) Essential Forensic Biology. West Sussex: Wiley Blackwell.

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