Intrinsic Factors Influencing the Post-Mortem Excitability of Human Muscle

Duijst WLJM, Yuan Q, Jin B and Yan M

Published on: 2025-02-20

Abstract

Background: Post-mortem, supravital muscle reaction (SMR) of skeletal muscle is, like rigor mortis, dependent on energy supply. Intrinsic variables, like peri-mortem body temperature and underlying diseases, influence the rate of cell metabolism in skeletal muscle cells post-mortem, and thus the available energy for SMR.

Objectives: A field study was conducted, comprising deceased found under differing conditions. We investigated the influence of the body temperature of the deceased on the outcome of SMR in the first hour’s post-mortem. In addition, we investigated the influence of sex, age, state of rigor mortis and the length of the period of sickness prior to death on the outcome of SMR. Furthermore, we hypothesized that the outcome of SMR could differ between musculus biceps brachii (MBB) and the musculus brachioradialis (MBR) on the same body examined at the same time, due to a higher in cooling velocity of more peripheral located skeletal muscles (MBR).

Methods: In the period of January 2017 to August 2023 four forensic physicians from two different regions in the Netherlands performed mechanical stimulation of both upper and forearms of deceased with a known or an estimated PMI of < 14 hours, by using a reflex hammer. The research population concerned in-hospital-deaths, out-of-hospital deaths that were transferred to the morgue of a hospital, and out-of-hospital deaths that were examined at the place where the body was found. The sex and age of the deceased, body temperature and state of rigor mortis were registered in the Dutch national register of forensic medicine (Formatus), which was used as a data resource. The length of the period of sickness prior to death was registered separately using a Microsoft Excel. The Welch Two Sample t-test, chi-squared test, logistic regression and multiple logistic regression were performed to investigate the influence of the PMI, body temperature, sex, age, state of rigor mortis and the length of the period of sickness prior to death on the outcome of SMR. Statistical analyses were performed by using SPSS 27.0 and R 4.4.1. Significance was accepted at P<0.05.

Results: In total, 142 cases were included, in which musculus biceps brachii (MBB) and the musculus brachioradialis (MBR) on both arms were mechanically stimulated with a reflex hammer. The population consisted out of 65 males (mean age: 73.4 ± 16.8 years) and 77 females (mean age: 82.1 ± 13.0 years). SMR was present in 74 out of 142 cases (52.1%). The mean PMI did not differ significantly between cases with a positive SMR (157.3 minutes) and cases showing no SMR (168.4 minutes). The number of male cases that showed SMR (63.1%) was significantly higher than the number of female cases (42.9%) that showed SMR. No relationship was observed between age, body temperature, rigor mortis and the period of sickness prior to death, and the outcome of SMR. In 28 out of 142 cases (19.7%) a discrepancy in the outcome of SMR was observed between the MBB and the MBR on the same body. The percentage of observable SMR decreases during successive stages of rigor mortis. No SMR could be observed in case of bodies with fully developed rigor mortis.

Conclusion: The current study shows a significant difference in outcome of SMR in the early hours after death, between male and female deceased. Body temperature, age, rigor mortis and the period of sickness prior to death did not significantly influence the outcome of SMR in the early hour’s post-mortem. In 19.7% of cases a discrepancy in the outcome of SMR was observed between MBB and MBR on the same body.