Thermal-work strain during Marine rifle squad operations in Afghanistan

• Published in: Military medicine 2013-10, Vol.178 (10), p.1141-1148
• Main Authors: Welles, Alexander P, Buller, Mark J, Margolis, Lee, Economos, Demetri, Hoyt, Reed W, Richter, Mark W
• Format: Article
• Language: English
• Subjects: Adult; Afghan Campaign 2001; Anthropometry; Body Temperature; Exercise; Heart Rate; Heat; Heat Stress Disorders - physiopathology; Humans; Maximum oxygen consumption; Metabolism; Military exercises; Military Personnel; Military training; Models, Biological; Naval Medicine; Physical Exertion - physiology; Physiology; Seasons; Skin; United States; Weather; Young Adult
• ISSN: 0026-4075; 1930-613X
• DOI: 10.7205/MILMED-D-12-00538

The physiological burden created by heat strain and physical exercise, also called thermal-work strain, was quantified for 10 male Marines (age 21.9 ± 2.3 years, height 180.3 ± 5.2 cm, and weight 85.2 ± 10.8 kg) during three dismounted missions in Helmand Province, Afghanistan. Heart rate (HR) and core body temperature (T core) were recorded every 15 seconds (Equivital EQ-01; Hidalgo, Cambridge, United Kingdom) during periods of light, moderate, and heavy work and used to estimate metabolic rate. Meteorological measures, clothing characteristics, anthropometrics, and estimated metabolic rates were used to predict T core for the same missions during March (spring) and July (summer) conditions. Thermal-work strain was quantified from HR and T core values using the Physiological Strain Index (PSI) developed by Moran et al. July PSI and T core values were predicted and not observed due to lack of access to in-theater warfighters at that time. Our methods quantify and compare the predicted and observed thermal-work strain resulting from environment and worn or carried equipment and illustrate that a small increase in ambient temperature and solar load might result in increased thermal-work strain.