What best describes rigor mortis?

• A. It is stiffness or rigidity in the muscular mass that freezes the joints.
• B. It is a cooling of the body temperature to ambient conditions.
• C. It is the settling of blood in dependent parts of the body causing a blue-purple color.
• D. It is the dehydration of tissues due to environmental humidity.

Answer: (A)

Rigor mortis describes the temporary stiffening of the body's muscles after death due to the loss of cellular energy. When life ends, ATP runs out in muscle cells, calcium leaks into the fibers, and the myosin heads remain bound to actin. That locking of the cross-bridges causes the muscles to become rigid, effectively freezing the joints in their positions. This stiffness isn’t about the body cooling or about blood pooling; those processes are algor mortis and livor mortis, respectively. Rigor mortis follows a time course—it starts in small muscles, then spreads, peaks, and eventually dissipates as decomposition progresses. This distinction helps forensic investigators estimate a postmortem timeline and differentiate the stages of postmortem change.