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Physiology of the Wildland Firefighter: Managing Extreme Energy Demands in Hostile, Smoky, Mountainous Environments

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Abstract

Wildland firefighters (WLFFs) are inserted as the front‐line defense to minimize loss of natural resources, property, and human life when fires erupt in forested regions of the world. The WLFF occupation is physically demanding as exemplified by total daily energy expenditures that can exceed 25 MJ/day (6000 calories). WLFFs must also cope with complex physical and environmental situations (i.e., heat, altitude, smoke, compromised sleep, elevated stress) which challenge thermoregulatory responses, impair recovery, and increase short‐ and long‐term injury/health risks while presenting logistical obstacles to nutrient and fluid replenishment. The occupation also imposes emotional strain on both the firefighter and their families. The long‐term implications of wildfire management and suppression on the physical and mental health of WLFFs are significant, as the frequency and intensity of wildland fire outbreaks as well as the duration of the fire season is lengthening and expected to continue to expand over the next three decades. This article details the physical demands and emerging health concerns facing WLFFs, in addition to the challenges that the U.S. Forest Service and other international agencies must address to protect the health and performance of WLFFs and their ability to endure the strain of an increasingly dangerous work environment. © 2023 American Physiological Society. Compr Physiol 13:4587‐4615, 2023.

Figure 1. Figure 1. Expected metabolic load variability during wildfire management (simulated and live activities) and training/conditioning. Data collection during simulated fireline observation via indirect calorimetry 14. GPS derived estimated metabolic load during live fireline assignments and training 120. Measures of Tvent prior to and following the season 47. Simulated escape from Ruby et al. 107.
Figure 2. Figure 2. Theoretical model that depicts the implications of shift operations, the energy expenditure of physical activity (EEA), and nutrient intake on expected glycogen depletion and recovery (dotted line). Anticipated values of daily EEA are represented (800–3500 kcal/24 h) in red across the varied phases of an extended assignment. The campfire graphic represents the intensity of the wildfire assignment. Postshift CHO access is represented by lower levels of intake (<<) and higher levels of intake (>). The average expected energy expenditure of activity (EEA) is represented as less than average EED (<) or higher than the average EEA on assignments (>>>). The expected range of EEA values is derived from prior work 40,109. The expected range of muscle glycogen values is derived from prior samples on the fireline 39.
Figure 3. Figure 3. Timeline of a heat‐related injury during arduous wildland fire management with the individual drinking behavior prior to presenting with heat injury and their body core temperature over time. Adapted, with permission, from Cuddy JS and Ruby BC, 2011 37.
Figure 4. Figure 4. Theoretical concepts surrounding the occupational factors of wildland fire management that influence deconditioning, pollutant exposure, and chronic stress triad (DPST) and potential countermeasures that may reduce seasonal health in wildland firefighters. PM2.5, fine particulate matter.
Figure 5. Figure 5. Physical characteristics of male and wildland firefighters on assignment and a comprehensive description of the measured energy demands, fluid budgets, nutrient intake, work shift characteristics (length, equipment, cardiovascular, and thermal loads), and seasonal responses and their relationship to the Standard Fire Orders 4.


Figure 1. Expected metabolic load variability during wildfire management (simulated and live activities) and training/conditioning. Data collection during simulated fireline observation via indirect calorimetry 14. GPS derived estimated metabolic load during live fireline assignments and training 120. Measures of Tvent prior to and following the season 47. Simulated escape from Ruby et al. 107.


Figure 2. Theoretical model that depicts the implications of shift operations, the energy expenditure of physical activity (EEA), and nutrient intake on expected glycogen depletion and recovery (dotted line). Anticipated values of daily EEA are represented (800–3500 kcal/24 h) in red across the varied phases of an extended assignment. The campfire graphic represents the intensity of the wildfire assignment. Postshift CHO access is represented by lower levels of intake (<<) and higher levels of intake (>). The average expected energy expenditure of activity (EEA) is represented as less than average EED (<) or higher than the average EEA on assignments (>>>). The expected range of EEA values is derived from prior work 40,109. The expected range of muscle glycogen values is derived from prior samples on the fireline 39.


Figure 3. Timeline of a heat‐related injury during arduous wildland fire management with the individual drinking behavior prior to presenting with heat injury and their body core temperature over time. Adapted, with permission, from Cuddy JS and Ruby BC, 2011 37.


Figure 4. Theoretical concepts surrounding the occupational factors of wildland fire management that influence deconditioning, pollutant exposure, and chronic stress triad (DPST) and potential countermeasures that may reduce seasonal health in wildland firefighters. PM2.5, fine particulate matter.


Figure 5. Physical characteristics of male and wildland firefighters on assignment and a comprehensive description of the measured energy demands, fluid budgets, nutrient intake, work shift characteristics (length, equipment, cardiovascular, and thermal loads), and seasonal responses and their relationship to the Standard Fire Orders 4.
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Brent C. Ruby, Robert H. Coker, Joe Sol, John Quindry, Scott J. Montain. Physiology of the Wildland Firefighter: Managing Extreme Energy Demands in Hostile, Smoky, Mountainous Environments. Compr Physiol 2023, 13: 4587-4615. doi: 10.1002/cphy.c220016