The six stages of rigor mortis in humans include absent, minimal, moderate, advanced, complete and passed, according to the Medicolegal Death Investigators' training manual on Education Portal. When rigor mortis occurs, the body's muscles harden after death in a gradual process.
On average, during rigor mortis, within zero to eight hours, the body starts to stiffen, but is still able to be moved, according to Education Portal. Eight to 12 hours after death, muscles become stiff and stay stiff for up to 24 hours from the time of death. Between 24 and 36 hours after death, the stiffness of muscles begins to decrease, and the muscles are more flexible.