What is Rigor Mortis?

Malcolm Tatum
Malcolm Tatum

Rigor mortis is a condition that begins to develop in the body after death takes place. Essentially, the action of rigor mortis is to begin a process where the muscles in the body begin to stiffen. In most situations, the corpse will begin to undergo the process of rigor mortis at roughly three hours after death takes place and will continue to experience the muscle stiffening for anywhere from thirty-six to seventy-two hours.

Rigor mortis occurs when the muscles in the body begin to stiffen after death.
Rigor mortis occurs when the muscles in the body begin to stiffen after death.

Rigor mortis takes place due to the fact that once a living entity is dead, there is no longer a steady flow of adenosine triphosphate or ATP flowing into the muscles. ATP is required to help the muscles release from the state of contraction that is caused by the presence of calcium ions that flow into the muscles and act as a bridge or connection between the actin and myosin that is present in the muscle fiber. With no ATP to initiate a release of that connection, the muscles continue to contract, making the dead body go rigid. It is only when the fibers in the muscles begin to decompose that the bond between actin and myosin fibers breaks down, and the muscles in the body begin to lose their rigidity.

The state of rigor mortis can help determine time of death during an autopsy.
The state of rigor mortis can help determine time of death during an autopsy.

The reality of rigor mortis often led to situations where the corpse would be watched on the first night after death took place. Commonly referred to as “sitting with the body”, the purpose of the action was to prevent the stiffening muscles from working the corpse into positions that were not suitable for burial traditions. Often, several people would remain with the corpse throughout the night, and straighten limbs or lower the torso of the body back into a prone position when muscle stiffening would cause a knee or elbow to bend, or the corpse to bend at the waist and appear to sit up.

The state of rigor mortis can also help medical examiners and law enforcement professionals to determine the approximate time of death when the individual did not expire in a care facility, or while loved ones were nearby. Along with other factors, the degree of muscle stiffening that is present during autopsies procedures helps to narrow the range for the time of death, and thus provide valuable clues when foul play is suspected.

Rigor mortis sets in when there is no longer a steady stream of ATP.
Rigor mortis sets in when there is no longer a steady stream of ATP.
Malcolm Tatum
Malcolm Tatum

After many years in the teleconferencing industry, Michael decided to embrace his passion for trivia, research, and writing by becoming a full-time freelance writer. Since then, he has contributed articles to a variety of print and online publications, including wiseGEEK, and his work has also appeared in poetry collections, devotional anthologies, and several newspapers. Malcolm’s other interests include collecting vinyl records, minor league baseball, and cycling.

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Discussion Comments


I just looked up what this was for some homework. And even though this is something that happens to everyone, I would hate having to watch someone's dead body. If they suddenly moved or sat up, I would jump, drop the pen or wherever I'm holding, and run! Forget it! Why stay with a dead person who is randomly sitting up? Creepy. Just creepy.


Apparently there are a few places where people take donated bodies and study how the different rates of decomposition work in different conditions, including rigor mortis.

And it's actually important for more reasons than just determining how long ago the person died. If they have rigor mortis then the body stays stiff even if it is moved, so the police can tell if someone moved the body from where it was originally, perhaps to dump it.


@KoiwiGal - I didn't realize that the effects were that strong either. I knew that there were a lot of traditions surrounding the body where people would stay with it for a few days after the death, but I thought that was more to do with saying goodbye, or maybe conducting particular rituals or whatever.

It must have been horrible back when you were responsible for your parents after they died and you may have had to handle their body and make sure it didn't go into a weird shape.

I guess it's not surprising that so many religions and myths have stories about people being possessed.

Even knowing that what causes rigor mortis is missing ATP I think it would still freak me out if someone I knew was dead started bending their elbow.


I guess this is one of the details that is often conveniently overlooked in police investigation TV shows. They do mention it sometimes when they are talking about how they know how long the body has been lying there, but the bodies are almost always just floppy and definitely not moving around into odd shapes like it says here.

I guess if they showed what might actually happen people would think it was a show about the supernatural, because I would never expect a corpse to suddenly sit up a few hours after death and rigor mortis onset.

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