What physiological change does rigor mortis represent?

Rigor mortis represents muscle stiffening that occurs after death due to several biochemical processes. After the heart stops pumping and blood circulation ceases, oxygen levels in the body decline, affecting muscle cells. The muscles initially relax, but then as energy sources in the cells (specifically ATP) deplete, the myosin heads in the muscle fibers become stuck to the actin filaments, causing the muscles to stiffen. This process typically begins within a few hours of death and can last for several days, depending on various factors including temperature and the individual's condition prior to death.

Other physiological changes like loss of body heat, lack of oxygen, and fluid accumulation may occur in the body after death, but they do not directly define the condition of rigor mortis. Rigor mortis specifically indicates the stiffening of muscles, making this the most accurate choice in understanding this post-mortem phenomenon.