A body is found 18 hours after death in a temperate environment. Rigor mortis is well established throughout. When rigor begins to pass off in a sequential manner, which body region loses rigor LAST, and why?

• A Neck, because it contains the largest muscle groups
• B Lower limbs (legs), because they are most distant from the site of ATP depletion initiation
• C Hands and feet, because glycolysis is fastest in distal extremities
• D Lower limbs and trunk, because rigor disappears in the reverse order of its appearance (lower limbs last, face first) ✓

Explanation

Rigor mortis appears in the order: jaw → neck → face → upper limbs → trunk → lower limbs (following the Nysten's law pattern of descending progression). It disappears in the reverse order: face and jaw first, lower limbs last. This is because the larger lower limb muscles have greater glycogen stores, sustaining ATP production longer before irreversible actomyosin cross-linking occurs. By 24–36 hours it has usually passed off completely in temperate conditions.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.