In locations where temperatures and environments are moderate, rigor mortis begins to set in one to two hours after death. The stiffening affects the small, involuntary (i.e., autonomic) muscles of the body first, including those in the eyelids, around the internal organs, and heart. Next, rigor mortis is evidenced in small voluntary muscles, such as the jaw and neck. It eventually spreads throughout the entire body, from the neck down. It usually reaches its peak at approximately 12 hours after death. A body generally remains in full rigor for 12 or so more hours before the stiffening subsides and completely dissipates by the 36-hour mark.
