It's 4:30 AM as the laces of the thick soled fire boots are tightened. The only light comes from a headlamp and the inside of the tent is covered in dew. As the tent is unzipped, the stars above the Los Padres National Forest light the clear sky: it is freaking cold. A 2-member researcher team flew in by helicopter the day before to link up with a Hotshot crew they are studying. It’s not every day urine sample collection is prefaced with a helicopter ride into the wilderness.
Wildland firefighters
For the last 25+ years, Brent Ruby from the University of Montana has been chasing down samples through the mountains of the western United States from a unique team. These are the men and women hired on for wildfire season. These are the men and women in the yellow and green known as Hotshots. And Ruby’s research group is not your average lab coat team of scientists. Ruby and his team subscribe to a unique brand of data collection well outside of the confines of the standard clinic and exercise science laboratory.
Hotshots are a unique breed of adventure seeker, outdoor enthusiast, and athlete rolled into package of grit, determination, and earth/dirt/sweat scented nomex (the flame-resistant yellow jersey and green cargo work pants). These crews make up an elite workforce of the forest and serve as the first line of defense in the protection of life, property, and natural resources. Hotshots work long hours (averaging 12–16-hour days) over 14-day assignment periods. The work shifts are physically demanding with each crewmember managing a rucksack of gear, food, water, and hand tools weighing as much as 30 kg (65 lbs) (1). In a typical 5-month fire season, Hotshots can easily work 1000 hours of overtime.
The demands of wildland firefighters
The best way to describe the physical work requirements of the job boil down to basic tactics: hike, dig, saw, repeat. The ground is rocky and uneven and the terrain is vast. Hollow, burned-out trees are fragile and potentially deadly spires that rise up from the ash covered forest floor. The main goal of fire management through the lens of a Hotshot is to dig a fire break in front of and eventually around the perimeter of the active flame front.
Ruby and his research teams started using doubly labeled water to document the energy demands of Hotshots back in the mid 1990’s. This technique uses stable isotopes of hydrogen and oxygen to calculate total daily energy expenditure (TDEE) and is considered the gold standard approach for measures in “free-range-humans.” Hotshots regulate their work pace strategically so as to not overheat, reeling in the intensity with heart rates averaging below 140 bpm most of the time. However, because of the long hours of each work shift, TDEE ranges from 3,000-6,200 kcals/day (2-4x BMR) (2).
Hotshots self-support during much of the daily work shift consuming a wide range of snacks, food items, military rations and fluids. The diet is boring and predictable without a lot of variety. However, when crews have access to meals in fire camp before and after the long work shift, they average about 5.5 g/kg/day for carbohydrates and 1.8 g/kg/day for protein (3). Total daily sodium intake is around 6,500 mg/day. The total water budgets are enormous because of the dry environment, persistent work and sweat rates (averaging 7-10 L/day) (4). Amazingly and despite the lack of high quality catered and painstakingly quantified training table dietary strategies, crews manage. It is only when crews are limited to military rations (MRE) that their daily intake is compromised, leading to an inability to restore resting muscle glycogen (5).
A special breed of athletes
Because the work is unpredictable and anything but steady state, it is impractical to superimpose hourly carbohydrate suggestions. Instead, crews are recommended to self-regulate based on a perceived work intensity, considering a continuum of fuel needs. More frequent eating episodes are recommended during harder segments of the work shift to sustain performance (24-45 g/episode every 90 minutes or so) (6). On the fireline, the benefits of supplemental carbohydrate extend well beyond hiking and digging better. Poor decisions out here can have fatal consequences.
Far from the stadiums, and pitches of professional/premier leagues, Hotshots hike and dig in a unique forest arena without the crowds and fanfare. Theirs are not the salaries of professional athletes and the intent of this research is not to develop strategies to run faster or score more goals. These research efforts seek to inform policy and safety and to offer an evidence-based approach to educate and inform the federal agencies that hire, train and support wildland firefighters (7). This research is done for and with the men and women in the yellow and green.
Reference
Metabolic Demand of Hiking in Wildland Firefighting. Sol JA, Ruby BC, Gaskill SE, Dumke CL, Domitrovich JW. Wilderness Environ Med. 2018.
Total energy expenditure during arduous wildfire suppression. B.C. Ruby, T.C. Shriver, T.W. Zderic, B.J. Sharkey, C. Burks, and S. Tysk. Medicine and Science in Sports and Exercise, 34(6): 1048-1054, 2002.
Total Energy Intake and Self-Selected Macronutrient Distribution During Wildland Fire Suppression. Marks AN, Sol JA, Domitrovich JW, West MR, Ruby BC. Wilderness Environ Med. 2020 Jun;31(2):188-196.
Work Patterns Dictate Energy Demands and Thermal Strain During Wildland Firefighting. Cuddy JS, Sol JA, Hailes WS, Ruby BC. Wilderness Environ Med. 2015 Mar 12. pii: S1080-6032(14)00429-3. doi: 10.1016/j.wem.2014.12.010.
Work Patterns Dictate Energy Demands and Thermal Strain During Wildland Firefighting. Cuddy JS, Sol JA, Hailes WS, Ruby BC. Wilderness Environ Med. 2015 Mar 12. pii: S1080-6032(14)00429-3. doi: 10.1016/j.wem.2014.12.010.
Supplemental feedings increase self-selected work output during wildfire suppression, Cuddy JS, Gaskill SE, Sharkey BJ, Harger SG, Ruby BC. Med Sci Sports Exerc. 39(6):1004-12, 2007.
Physiology of the Wildland Firefighter: Managing Extreme Energy Demands in Hostile, Smoky, Mountainous Environments. Ruby BC, Coker RH, Sol J, Quindry J, Montain S. J Compr Physiol. 2023 Mar 30;13(2):4587-4615. doi:10.1002/cphy.c220016. PMID: 36994767
