<P> Cold shortening is caused by the release of stored calcium ions from the sarcoplasmic reticulum of muscle fibers, in response to the cold stimulus . The calcium ions trigger powerful muscle contraction aided by ATP molecules . To prevent cold shortening, a process known as electrical stimulation is carried out, especially in beef carcasses, immediately after slaughter and skinning . In this process, the carcass is stimulated with alternating current, causing it to contract and relax, which depletes the ATP reserve from the carcass and prevents cold shortening . </P> <P> The degree of rigor mortis may be used in forensic pathology, to determine the approximate time of death . A dead body holds its position as rigor mortis sets in . If the body is moved after death, but before rigor mortis begins, forensic techniques such as livor mortis can be applied . If the position in which a body is found does not match the location where it is found (for example, if it is flat on its back with one arm sticking straight up), that could mean someone moved it . </P> <P> Several factors also affect the progression of rigor mortis, and investigators take these into account when estimating the time of death . One such factor is the ambient temperature . When conditions are warm, the onset and pace of rigor mortis are sped up by providing a conducive environment for the metabolic processes that cause decay . Low temperatures, however, slow them down . Therefore, for a person who dies outside in frozen conditions rigor mortis may last several days more than normal, so investigators may have to abandon it as a tool for determining time of death . </P>

When does rigor mortis set in and how long does it last