<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Rigor mortis (Latin: rigor "stiffness", mortis "of death"), the third stage of death, is one of the recognizable signs of death, caused by chemical changes in the muscles post mortem, which cause the limbs of the corpse to stiffen . In humans, rigor mortis can occur as soon as 4 hours post mortem . </P> <P> After death, respiration in an organism ceases, depleting the source of oxygen used in the making of adenosine triphosphate (ATP). ATP is required to cause separation of the actin - myosin cross-bridges during relaxation of muscle . When oxygen is no longer present, the body may continue to produce ATP via anaerobic glycolysis . When the body's glycogen is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges . </P>

When does rigor mortis set in in humans