AUTHOR=Chapin Andrea C. , Arrington Laura J. , Bernards Jake R. , Kelly Karen R. 

TITLE=Thermoregulatory and Metabolic Demands of Naval Special Warfare Divers During a 6-h Cold-Water Training Dive

JOURNAL=Frontiers in Physiology

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.674323

DOI=10.3389/fphys.2021.674323

ISSN=1664-042X

ABSTRACT=Introduction: Extreme environments induce changes in metabolic rate and substrate use. Cold-water full-body submersion for extended periods of time is inevitable for training and missions carried out by Naval Special Warfare divers. Anthropometric, physiologic, and metabolic data have been reported from partial immersion in cold water in non-thermally protected men; however, data is limited in thermally protected divers in extremely cold water. 
Objective: Assess thermoregulatory and metabolic demands of Naval Special Warfare divers during a prolonged cold-water submersion. 
Materials and Methods: Sixteen active-duty U.S. Navy Sea Air and Land (SEAL) operators tasked with cold-water dive training participated. Divers donned standard military diving equipment and fully submerged to a depth of ~ 6 meters in a pool chilled to 5°C for a 6-hour training exercise. Metabolic measurements were obtained via indirect calorimetry for 10-minutes pre-dive and 5-minutes post dive. Heart rate, skin temperature, and core temperature were measured throughout the dive.
Results: Core temperature was maintained  (36.8 ± 0.4°C) and was not correlated to body composition (body fat percentage, lean body mass) or metabolic rate. SEALs were not at risk for non-freezing cold injuries as mean skin temperature was 28.5 ± 1.6°C at end of the 6-hour dive. Metabolic rate (kcal/min) was different pre- to post-dive, increasing from 1.9 ± 0.2 kcal/min to 2.8 ± 0.2 kcal/min, p < 0.001, 95% CI [0.8, 1.3], Cohen’s d effect size 2.3. Post-dive substrate utilization was 57.5% carbohydrate, 0.40 ± 0.16 g/min, and 42.5% fat, 0.13 ± 0.04 g/min. 
Conclusion: Wetsuits supported effective thermoprotection in conjunction with increase in thermogenesis during a 6-hour full submersion dive in 5°C. Core temperature was preserved with an expected decrease in skin temperature. Sustained cold-water diving resulted in a 53% increase in energy expenditure. While all participants increased thermogenesis, there was high inter-individual variability in metabolic rate and substrate utilization. Variability in metabolic demands may be attributable to individual physiologic adjustments due to prior cold exposure patterns of divers. This suggests that variations in metabolic adjustments and habituation to the cold were likely. More work is needed to fully understand inter-individual metabolic variability to prolonged cold-water submersion.