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 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 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.