Severity Of Core Temperature Afterdrop And Recovery Following Cold Water Immersion In Military Personnel

PURPOSE: Cold-water immersion (CWI) can cause rapid body cooling, leading to dangerous physiological consequences. Core temperature (Tc) afterdrop, a continued decline in Tc even after the individual exits the cold water environment, is well-documented with laboratory data reporting ranges from 0.5 - 1.1 °C. However, field conditions often include combined cold air, wind, and colder water, and may lead to more severe Tc afterdrop. Understanding the magnitude of Tc afterdrop and recovery in field settings is essential for preventing cold-related injuries and optimizing post-immersion rewarming. PURPOSE: To investigate the magnitude of Tc afterdrop and recovery following an outdoor CWI. METHODS: Eighty-six military personnel (mean ± SD: age 26 ± 8 yrs, ht 175 ± 15 cm, wt 81 ± 12 kg; BMI 26.1 ± 4.9 kg/m2) participated in a 10-min outdoor CWI (water: 1.5 °C, air: -4 °C). Tc data were analyzed from the minute of water exit through the recovery stage (one hour following water exit). Tc afterdrop was defined as the difference between Tc at water exit and the minimum Tc reached thereafter, with a rate of afterdrop (RoA) calculated by dividing this Tc by the time taken to reach the minimum Tc. Similarly, the rate of recovery (RoR) was defined as the difference between the minimum Tc and the Tc regained by the end of the recovery stage, divided by the time between the two. A Pearson correlation analysis was conducted to examine the relationship between the RoA and RoR. RESULTS: Participants experienced a mean Tc afterdrop of 1.3 °C (SD = ± 0.6, range: 0.3-3.2 °C), occurring ~26 min post-immersion. At the end of recovery, participants’ Tc returned to 36.5 °C, recovering 87% of the heat lost during the afterdrop phase. A moderate negative correlation was found between RoA and RoR, r(84) = -0.33, p = 0.002, indicating that participants who experienced a faster afterdrop rate tended to recover more quickly. CONCLUSIONS: Findings suggest that the magnitude of Tc afterdrop following outdoor CWI is notably higher than previously reported in laboratory settings, likely attributed to greater cold stress encountered in field conditions that are often not replicated in laboratory settings. Such results emphasize the importance of understanding Tc afterdrop dynamics in real-world conditions and should be used to optimize recovery following accidental CWI. Supported by: This work was supported by the Office of Naval Research under work unit no. 62417.