Race to Rigor Mortis

After reading through the information provided, you will move on to my game board. On the game board, Race to Rigor Mortis, you will be tested on the information from this paper while trying to be the last player to decompose. Rigor mortis is a natural postmortem physiological phenomenon resulting in the rigidifying of all muscles when metabolic activity terminates and adenosine triphosphate (ATP) is no longer produced (Shedge, 2020). I will explore the Unit 5 objective related to how rigor mortis affects muscle fiber contraction through the topics of temperature, illness, pre-mortem activities, and body mass. I will describe the 6 stages of rigor mortis, when they occur on the post mortem timeline, and  situations that can affect each stage. 

Chemical imbalance is the only reason for muscle contraction postmortem because there are no longer nervous system signals present after death and adenosine triphosphate (ATP) synthesis is stopped (Shedge, 2020). The whole process of rigor mortis can happen over a twenty four to forty eight hour time frame beginning at two hours post death and reaching max rigidity around twelve hours (Presnell, 2020). Rigor mortis happens in six stages, those stages in order are: absent, minimal, moderate, advanced, complete, and passed (Radhakrishnan, 2022). As the body progresses in stages, the stiffness increases until reaching the passed stage where rigor mortis is complete and the body moves into stages of death. Death has 5 stages, in order these are pallor mortis, algor mortis, rigor mortis, livor mortis, and decomposition (Radhakrishnan, 2022). 

The starting point of rigor mortis happens when the adenosine triphosphate levels drop to eighty five percent of its normal level and peak rigidity occurs when the body reaches fifteen percent normal adenosine triphosphate levels (Radhakrishnan, 2022). During the first stage of rigor mortis, absent, the muscles are still soft and movable due to the minimal amounts ATP created by anaerobic glycolysis (Radhakrishnan, 2022). Postmortem changes in muscle rigidity start when muscle fibers are overloaded with calcium affecting the muscle fiber elasticity (Shedge et al., 2023). Postmortem muscles stay contracted because the myosin heads are bound to the actin due to lack of ATP at the cross-bridge detachment (Cooper, 2009). When the body is alive, intracellular calcium levels decrease because ATP is produced. Then calcium is pumped back into the sarcoplasmic reticulum (SR) but after death muscles stay contracted until muscle proteins break down the fibers causing the myosin to release (Cooper, 2009). 

Rigor mortis follows proximal to distal progress and occurs in both voluntary and involuntary muscles. In the second (minimal) stage of rigor mortis, the smaller muscles of the jaw and eyelids are hardened first because exhaustion of ATP is quicker in smaller muscles (Shedge et al., 2023). The third (moderate) stage of rigor mortis affects the larger muscles which take longer to deplete ATP and is when the body is obviously no longer loose or flexible (Radhakrishnan, 2022). In general rigor mortis, starts with the smaller facial muscles, working its way through the upper limbs then down to the lower limbs with the fingers and toes being the last to stiffen (Kori, 2018). The fourth (advanced) stage is where most of the body has stiffened and fifth (complete) stages of rigor mortis where the whole body is hard and inflexible (Radhakrishnan, 2022). 

The first stage of death, pallor mortis, happens within the first fifteen to thirty minutes and is depicted by increased paleness due to the halt of blood circulation (Radhakrishnan, 2022). The second stage of death, algor mortis,  is when the postmortem body cools to match the temperature of the surrounding environment (Radhakrishnan, 2022). As a result the third stage, rigor mortis, can be manipulated by both heat and cold (Dillon, 2023). Exposure to high heats, high voltage electrocution, fever, and scalding liquids have been shown to increase the denaturation of the tissue proteins (Shedge et al., 2023). Postmortem cold exposure of the bodies subjected to subzero temperatures showed signs of biological fluids and subcutaneous fat freezing which leads to body stiffening as well (Shedge et al., 2023). The clothing on the body will also affect the rate of cooling. Obese bodies will cool at a slower rate because, as we learned in unit 3, fat cells have an insulation function and store oxygen in the cells (Pounder, 2000). Higher temperatures increase the breakdown of cells by their own enzymatic action of ATP leading to a more rapid rigidity in muscles (Almulhim & Menezes, 2023). Lower temperatures delay the onset and prolong the duration of rigor mortis (Pounder, 2000).  

In rare cases involving intense physical and/or emotional stress, cadaveric spasm of the muscles that were used abundantly right before death may experience instantaneous rigor (Shedge et al., 2023).  Physical exercise prior to death can cause rigor mortis to set in faster because exertion uses oxygen and ATP (Helmenstine, 2021). Those who have darker skin, are severely anemic, or who have died of severe hemorrhage may not have the dermal manifestation of the fourth stage of death, livor mortis (Almulhim & Menezes, 2023). Postmortem lividity typically happens within six to eight hours after death as the result of blood pooling under the force of gravity (Rijen Shrestha et al., 2019).  Illness such as amyotrophic lateral sclerosis (ALS) which causes muscle paralysis will delay rigor mortis (Kori, 2018). Rigor mortis will be more rapid in those who are unable to produce normal levels of ATP such as those who suffer from malnutrition (Knapp, 2020). Illnesses like hypoxia where oxygen levels in the tissues are decreased can lead to lactic acidosis and increase the rate of rigor (Whitehair, 2012). Bodies with illness like cancer or extremely low muscle mass like those of young children and babies may have reports of lack of stiffness during the hours where rigor mortis is expected (Kori, 2018). 

Ultimately, the chemical breakdown of actin and myosin is unavoidable after death, so absence of rigor mortis is not accepted by the scientific community (Knapp, 2020). The sixth stage of rigor mortis (passed) and the fifth (decomposition) stage of death happens because of autolysis (Knapp, 2020). Autolysis is the breakdown of cells by their own enzymatic action and is mainly a microscopic process, rather than one viewed by the naked eye like the other stages of rigor mortis (Pasca & Ulasan, 2014). The postmortem body returned to a limp state after rigor mortis happens because of the breakdown of the actin and myosin binding sites (Almulhim & Menezes, 2023). 

In conclusion, the time of onset of rigor mortis in general conditions appears in the first one to two hours after death, reaching peak rigidity around twelve hours postmortem. The speed and onset of rigor mortis will be accelerated with higher internal or external temperatures, lower body mass individuals, unclothed bodies, and those with lower ATP levels at time of death (exercise or illness). The onset and rate of rigor mortis is slowed by lower internal and external temperatures, higher body mass individuals, and clothed bodies.  Rigor mortis happens because without ATP separating the actin-myosin cross bridges in the muscle they stay in a contracted state until autolysis begins. The body begins to soften in the same order from face to feet completing the twenty-four-hour cycle because of autolysis. Now that you have finished the reading, proceed to the game board. Good Luck!