## Timeline of Rigor Mortis Development **Key Point:** Rigor mortis is a post-mortem change caused by depletion of ATP and cross-linking of actin and myosin filaments, resulting in muscle stiffening. ### Temporal Progression | Time Interval | Stage | Characteristics | |---|---|---| | 2–4 hours | Onset | Begins in eyelids, jaw, and neck muscles | | 4–12 hours | Progressive spread | Descends through trunk and limbs | | 12–24 hours | Complete | Entire body becomes rigid | | 24–48 hours | Peak rigidity | Maximum stiffness achieved | | 48–72 hours | Resolution | Begins to disappear due to decomposition | **High-Yield:** The complete involvement of the entire body typically occurs between **12–24 hours** post-mortem. This is a frequently tested timeline in forensic pathology. **Clinical Pearl:** Rigor mortis follows a predictable cephalocaudal (head-to-toe) progression. Early rigor in the eyelids and jaw is often one of the first observable post-mortem changes. **Mnemonic:** **RIGOR** — **R**igidity **I**ncreases **G**radually **O**ver **R**ecognizable hours (12–24 for completion). ### Factors Affecting Rigor Mortis Timing - **Accelerating factors:** High ambient temperature, muscular exertion before death, sepsis, electrocution - **Delaying factors:** Cold environment, cachexia, prolonged illness - **Absent/weak rigor:** Infants, elderly, severely debilitated individuals [cite:Parikh's Textbook of Medical Jurisprudence & Toxicology Ch 3]
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