Muscular relaxation immediately after death is followed by the onset of gradual rigidity without shortening of the muscle. Since muscle continues to metabolize for a short time after somatic death, or from products built up during the death event, glycogen is converted into lactic acid. As the pH falls, there is a physical change in the muscle protoplasm. Since there is no regeneration of ATP in dead muscle, this process proceeds in one direction only. The sol is converted into a gel as the actin of the muscle is physically changed. Since this is a chemical process, heat accelerates and cold decelerates the process. Acidosis, uremia or other medical conditions promoting a lowered pH accelerate the process. Although the process begins essentially immediately, rigor is recognizable in 1-6 hours, is maximum in 6-24 hours, and disappears in 12-36 or more hours.
Once the physical change of the muscle is forced, that degree of change will not reoccur, so that if someone has broken the rigor, it will not reform. If only partial, some rigor will continue to form. This is an unreliable method of indicating the time of death. It is affected by illness, temperature, activity before death, and the physical conditions where the body is placed or found. It may be poorly formed in the young or the old. It is an aid in the general determination of death at best and should not be relied on as a single indicator of the time of death.
Once the physical change of the muscle is forced, that degree of change will not reoccur, so that if someone has broken the rigor, it will not reform. If only partial, some rigor will continue to form. This is an unreliable method of indicating the time of death. It is affected by illness, temperature, activity before death, and the physical conditions where the body is placed or found. It may be poorly formed in the young or the old. It is an aid in the general determination of death at best and should not be relied on as a single indicator of the time of death.
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