In articulo mortis Health Dictionary

The stiffening of muscles that starts 3–4 hours after death.

It is usually complete after about 12 hours; the stiffness then disappears over the next 48–60 hours.

Physical exertion before death makes rigor mortis begin sooner.

The sooner rigor mortis begins, the quicker it passes.

These facts are used to help assess the time of death.... rigor mortis