Pronounced dilation may be observed post-mortem, especially in children. As already mentioned, the muscles of the whole body lose their tone when death occurs and before the rigor mortis begins. In children, rigor mortis may fix an enlarged opening, and this finding may persist after rigor mortis has faded. Dilation is therefore not a sufficient marker of penetrative abuse. Another complication for the veterinarian is the still largely undocumented variation in the timing of the appearance and disappearance of stiffness that may exist between species and age groups of the wide range of animals examined. Because of these variables, it is advisable to consider rigor mortis only as an approximate indication of the post-mortem interval. Rigor mortis can make it difficult to examine the palms and internal aspects of the fingers, so current marks or defensive injuries that are found here may be missed. Rigor mortis is probably one of the most well-known taphonomic changes and is the process that causes the muscles of the body to stiffen, resulting in stiffness due to a series of chemical changes in muscle structure. The muscle fibers that move through life due to the slippery filament theory rely on the conversion of ATP to ADP. After death, when breathing stops, intracellular pH decreases due to the production of lactic and pyruvic acid. Anaerobic glycolysis of glycogen in the muscles causes a breakdown of glycogen and therefore a decrease in the concentration of ATP. Calcium also escapes into the sarcomere, where the protein filaments actin and myosin are present in an alternate arrangement, where calcium then binds so that cross-linking between the filaments can take place.
This causes a pulling movement along the muscle, making it shorter and stiffer. In a living individual, ATP would be used to dissociate cross-linking in fibers and, therefore, the stiffness associated with the change would be reversed while being fixed post-mortem (Powers, 2005). The occurrence and duration of rigor mortis is determined by several factors. Indian conditions are different from temperate countries, when the time elapsed since death has to be estimated. Indian textbooks report that rigor mortis begins in 2-3 hours, takes about 12 hours to develop, lasts another 12 hours, and takes about 12 hours to pass. [3,4] Rigor mortis can recover after the rupture of gravity, and significant stiffness can recur if the rupture occurs before the end of the process. [8] Many factors such as exercise, cause of death, temperature, and diet influence the onset or progression of full-body rigor mortis. [6] In this case, where rigor mortis is well established over the entire body, the body must have reached the place of disposal after weighing the usual possibilities, i.e. 2 to 6 hours after death (place of occurrence). Livor mortis is a technique used to decide whether the body was removed after death before the onset of rigor mortis.
The causes of rigor mortis are explained in detail below: The usual position after death is that of the supine position. The unusual posture of the deceased after death, although in some cases was observed; could contribute to several discoveries such as unusual post-mortem colorations. [2] Rigor mortis develops in the body after death, a position in which the body is present at its appearance. In the early 19th century, Nysten (1811) conducted experiments on criminals in France immediately after their beheading on the guillotine, observing that rigor mortis began in the jaw muscles and then progressed distally to the feet and toes. This sequence was challenged by Shapiro (1950, 1954), who suggested that it began at the same time in all muscles, but the variation in the size of different joints and muscles meant that larger muscles took longer to develop rigor mortis, giving the impression that it progressed through the body from proximal to distal. Krompecher designed an experiment to measure the intensity of rigor mortis in the forelimbs of rats compared to the hind legs of rats, which used different forces at different times of rigor mortis (Krompecher and Fryc, 1978a). The hind legs had a muscle mass 2.89 times greater than that of the forelimbs. The results showed that, although there was no difference between the forelimbs and hind limbs in terms of the time it took to achieve full development of rigor mortis, the onset and relaxation of rigor mortis in the forelimbs, which had the smallest muscle mass, was faster. In contrast, Kobayashi and colleagues (2001), who experimented in vitro with the spinae muscles of rat erector, found that although the volume of muscle samples varied, there was no difference in the development and resolution of rigor mortis.