Under Nysten's Law, which region is affected last by rigor mortis?

• A. Legs and feet
• B. Head
• C. Chest
• D. Arms

Answer: (A)

Rigor mortis follows a defined progression after death. After death, muscle stiffening begins in the small muscles of the face and neck, then moves to the upper limbs, then the chest/trunk, and finally the lower limbs. The legs and feet end up being the last region affected because they contain the largest muscle groups, and it takes more time for the biochemical changes that lock the muscles (loss of ATP and calcium-driven actin-mosin cross-bridge formation) to reach and change all those fibers. Temperature and body conditions can speed or slow the overall timing, but the order remains head-to-toe. So, the legs and feet are the region affected last.