Rigor mortis typically begins within which time frame after death?

• A. 2-4 hours
• B. Immediately
• C. 12-24 hours
• D. 3-5 days

Answer: (A)

Rigor mortis is the muscle stiffening that happens after death due to biochemical changes in muscle fibers when ATP is no longer available to relax the muscles. As cells run out of energy, calcium leaches into the muscle fibers and actin–myosin cross-bridges form, locking the muscles in place. This process doesn’t happen instantly; it typically begins within a few hours, commonly around two to four hours after death.

From there, stiffness progresses to a peak over roughly the next several hours and is usually fully developed by about 12 hours, remaining for another day or so before dissipating as decomposition progresses. Temperature and other factors can shift this timing a bit— hotter conditions accelerate onset, cooler conditions slow it—but the usual window to expect the start of rigor is about two to four hours postmortem.