A 52-year-old man is found dead in his home 18 hours after being last seen alive. On examination, the body shows complete rigor mortis affecting all muscle groups. Which factor is the COMMONEST cause of accelerated onset and intensity of rigor mortis in this case?

Explanation

## Factors Affecting Rigor Mortis Onset and Intensity **Key Point:** Rigor mortis develops faster and is more intense in conditions that **accelerate ATP depletion** and increase **muscle metabolism before death**. ### Factors Accelerating Rigor Mortis | Factor | Mechanism | Effect on Rigor | |---|---|---| | **High temperature** | ↑ Metabolic rate, faster ATP depletion | **ACCELERATES onset** | | **Physical exertion before death** | Muscle glycogen depletion, lactate buildup | **ACCELERATES onset** | | **Fever/hyperthermia** | ↑ Enzyme activity, faster rigor development | **ACCELERATES onset** | | **Seizures/convulsions** | Intense muscle contraction, ATP exhaustion | **ACCELERATES onset** | | **Electrocution/poisoning** | Muscle hyperactivity | **ACCELERATES onset** | ### Factors Delaying Rigor Mortis | Factor | Mechanism | Effect on Rigor | |---|---|---| | **Low temperature** | ↓ Metabolic rate, slower ATP depletion | **DELAYS onset** | | **Starvation** | Low muscle glycogen reserves | **ACCELERATES onset** (paradoxically) | | **Muscular dystrophy** | Abnormal muscle metabolism | **Variable** | | **Infant/newborn** | Lower muscle mass, different metabolism | **Delayed/absent** | **High-Yield:** The **commonest cause of accelerated rigor mortis is high ambient temperature combined with physical exertion before death**. Both increase metabolic demand and ATP consumption. ### Mechanism: Why Temperature + Exertion Accelerates Rigor 1. **Physical exertion before death** → muscle glycogen depleted → lactate accumulates → acidosis 2. **High ambient temperature** → ↑ enzyme kinetics → faster ATP hydrolysis → faster rigor onset 3. **Combined effect** → rigor can appear within 2–4 hours instead of the typical 6–12 hours **Clinical Pearl:** In cases of death during physical activity (exercise, struggle, heat exposure), rigor mortis may be **"cadaveric spasm"** — a form of instant rigor due to extreme muscle contraction. This is different from true rigor mortis but appears similar. **Mnemonic:** **"HEAT"** — **H**igh temperature, **E**xertion, **A**ccelerates, **T**ime (rigor onset). ### Why Other Options Are Wrong **Low temperature + immobilization:** This combination actually **DELAYS** rigor mortis because low temperature slows metabolism and enzyme activity. Immobilization alone does not accelerate rigor. **Age and sex:** While some sources suggest slight variations, **age and sex are NOT the commonest factors** affecting rigor mortis intensity. Temperature and exertion are far more significant.