how long before rigor mortis sets in?
At the moment of death, the muscles relax completelyâa condition called primary flaccidity.. The muscles then stiffen, perhaps due to coagulation of muscle proteins or a shift in the muscle's energy containers (ATP-ADP), into a condition known as rigor mortis. All of the body's muscles are affected. Rigor mortis begins within two to six hours of death, starting with the eyelids, neck, and jaw. This sequence may be due to the difference in lactic acid levels among different muscles, which corresponds to the difference in glycogen levels and to the different types of muscle fibers.