Ask Dr. H: From ancient parts to mystery of death
Q: With Halloween approaching, I'd like to ask a creepy question: Why does a body stiffen up from rigor mortis after death?
A: Halloween approaches, and little ghouls and goblins will soon be scurrying door to door. The mystery of death and what lies beyond has long fascinated man. From a biological viewpoint, death is a much simpler concept. It's not an event, but a process. This is because the various tissues and organs in the living body die at different rates.
Rigor mortis is due to a complex chemical reaction. During life, our muscles require energy (fuel). They need lots of oxygen. However, during strenuous work or exercise, this is in short supply. Heavy muscle use causes a buildup of lactic acid. It contributes to the feeling of muscle fatigue and "burn." Haven't we all felt that "burn" in our legs with climbing stairs?
During life, the lactic acid quickly dissipates once we rest our muscles. In death, this cannot happen. The breakdown of muscle fuel (glycogen) in death leads to irreversibly high levels of lactic acid. This leads to a complex reaction in which the components of muscle fibers fuse together to form a gel. This gel is what makes the body feel stiff in death. Once the muscle is moved, the stiffness is broken, and the gel will not re-form.
The stiffness begins at once and becomes complete in two to three hours, developing faster in the head, neck, and arms than in the legs. High metabolic activity in the time just before death, such as running or playing tennis, leads to higher levels of lactic acid and a shorter time for rigor mortis to develop. For those who are muscular, the rigor comes on more slowly and lasts longer. Rigor mortis lasts for 12 to 24 hours, after which decomposition begins.
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