Why does a lifeless body become stiff?

A few minutes after the death of a person, his lifeless body becomes rigid, this is called cadaveric rigidity. What explains this phenomenon?

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The subject is not very pleasing, but the question arises: what explains that the body becomes rigid in the first moments following the death of a person? Cadaveric rigidity is one of the key elements that enables forensic pathology to accurately determine the time at which death occurred.

This rigidity is characterized by a loss of elasticity of the tissues, in particular of the muscles, and it intervenes between thirty minutes and two hours after the death of a person. In the first place, it is the muscles of the face and the neck that are affected by this phenomenon which then progresses down the body. The maximum intensity is reached between six and ten hours after death, is maintained at this stage before disappearing gradually after two or three days. This is the beginning of decomposition.

However, these moments of appearance, evolution and disappearance may change because they depend on several factors such as the proportion of muscle cells, the initial temperature of the body (knowing that a corpse loses about 1 ° C per hour) The ambient temperature, the presence of toxic products or the early handling of the body.

The phenomenon of stiffness is explained with two proteins in the form of filaments, actin and myosin in the heart of the muscle cells. At death, there is a loss of the tightness of the sarcoplasmic reticulum, a kind of pouch located in the muscle cell and containing calcium ions. However, in order to remove this calcium, energy is needed which is no longer available after death, which leads to the accumulation of calcium. Then, the fibers of actin and myosin remain attached, which causes the immobilization of the muscle. On decomposition, the structure of the filaments of actin and myosin as well as the bonds which unite them are destroyed and the stiffening stops.