Rigor mortis starts when muscle ATP is reduced below: (LQ)
Rigor mortis is stiffening of muscle after death due to decrease of ATP up to 15 % (or 85% of normal), increase in lactic acid and fall of H+.
a. Order of AppearanceQ: First appears in involuntary muscles (heart) →voluntary muscles → upper eyelids → neck →jaw → face →chest → upper limbs →abdomen → lower limbs, begins 1-2 hrs after death and takes further 2 hrs to develop- lasts 18 – 36 hrs in summer and 24 – 48 hrs or even more in winter.
b. No rigor mortis- Foetus < 7 mths, Heat stiffening, Embalming.
c. Rigor is tested by- trying to lift eyelids, depressing the jaw, bending neck and thighs, and noting if it is absent, partial, complete, passing-phase or passed-off.