Which description defines rigor mortis?

• A. The postmortem cooling
• B. The color change in the skin
• C. The settling of blood due to gravity
• D. The stiffening of the body muscles after death

Answer: (D)

Rigor mortis is the stiffening of the body’s muscles after death caused by chemical changes in the muscle tissue when ATP is no longer available. Once circulation stops, cells run out of oxygen and ATP, calcium leaks into muscle fibers, and the myosin heads form cross-bridges with actin without a means to break them. That locks the muscles in place, producing rigidity. It typically starts in small muscles of the face a few hours after death, spreads to larger muscle groups, peaks around about 12 hours, and then gradually dissipates over the next day or two as decomposition progresses. This is distinct from algor mortis, the cooling of the body, and livor mortis, the settling of blood that causes skin discoloration. Recognizing rigor mortis helps in estimating a time frame since death when used alongside other indicators.