What does rigor mortis refer to?

Rigor mortis refers specifically to the stiffening of muscles and joints that occurs after death. This phenomenon is a result of biochemical changes in the muscle tissue, where the levels of adenosine triphosphate (ATP) decrease, causing muscles to contract and become rigid. Rigor mortis typically begins a few hours after death, first affecting smaller muscles, such as those in the face and hands, before it spreads to larger muscles. Over time, this rigidity gradually dissipates as decomposition progresses, making it an important consideration in post-mortem examinations and determining the time of death.

The other choices, while related to post-mortem changes, address different phenomena. The accumulation of deoxygenated blood pertains to livor mortis, the settling of blood in the lower parts of the body. Internal body temperature refers to algor mortis, which involves the cooling of the body after death. Evidence of sexual activity after death might indicate forensic considerations but does not relate to the physical changes expressed in rigor mortis.