Health and performance can be affected by body composition (BC) [1
]. In light of this, studying BC has received considerable research attention when examining physical performance [2
]. Body fat percentage (BF%) and lean body mass are of interest to coaches and athletes because of their importance in athletic performance [1
]. The relationship between nutrition and performance is well established in the literature and optimal nutrition is thus widely accepted as a means to enhance performance and recovery [8
]. The intensity and duration of certain sports, impacts the number of calories burned and research shows that sports with higher physical activity influence BC [7
Wildland firefighters (WLFFs) are considered tactical athletes [12
], a term used to describe those in service professions that require significant physical fitness and performance [13
]. While wildland firefighting may not be considered a sport, the physical and nutritional demands of the occupational activities [14
] can be comparable to or exceed those of athletes [16
]. In the Western United States, WLFF duties often require fighting fires in steep terrain, in high temperatures, and with smoke-degraded air quality.
Wildland firefighting includes a wide range of line-based positions including hand crews, fuels crews, engine crews, hotshot crews, and aviation crews such as Helitack and smoke jumpers. All agency line-based WLFFs are required to pass a Work Capacity Test at the light, moderate, or arduous level [18
]. These requirements vary depending on the position of the WLFF. The light walk test requires a 1.6 km walk test in a 16 min period with no pack. The moderate field test requires a 3.2 km hike with a 11.3 kg pack in 30 min. The arduous past test requires a 4.8 km hike with a 20.4 kg pack in 45 min [18
Smokejumpers, the focus of this research, must pass the arduous pack test and in addition must be able to do, at the minimum, seven pull-ups, 45 sit-ups, 25 push-ups, and a 2.4 km run in less than 11 min. They must be able to perform a gear pack-out with a 50 kg pack over 4.8 km in 90 min or less [19
Smokejumpers are WLFF who parachute from planes, often in remote areas, to combat wildfires [20
]. They are typically dispatched at the national level, including Alaska and Canada [21
]. They must be in excellent physical condition and possess a high degree of emotional well-being and mental alertness [21
]. Employment for a typical fire season can be May to October [22
], however, research shows that the fire season has grown by 30 days in the last 20+ years with wildfires starting earlier in the spring and continuing later in the fall [23
]. This may increase a WLFFs commitment of continuous physical job demands in duration and might ultimately test the physical and nutritional components that are essential for optimal health and performance.
Many factors such as body size and composition contribute to performance [24
]. BF% that is either too high or too low may have negative impacts on health and fitness [25
]. Having a higher BF% lowers the endurance of individuals, which allows fatigue to set in quicker than those with lower BF% [1
]. Therefore, many athletes and athletic teams have their BC assessed on a regular basis [26
]. Monitoring and evaluation of WLFF BC throughout the fire season may be of interest for both the individual and members of a team. For example, mean BC levels for a crew might be integrated into a general overall health assessment throughout the fire season, in order to inform individuals when nutritional requirements are insufficient and/or where deficiencies may be occurring.
Monitoring BC may also provide firefighting agencies with beneficial feedback in regard to conditioning programs and nutritional guidelines to achieve and maintain optimal BC for WLFFs. Additionally, with cardiac events being the leading cause of WLFF deaths [28
], BC could also be a useful tool to predict underlying health issues before a WLFF is placed in less than ideal situations. To evaluate WLFF BC changes associated with work over the course of a fire season, a pilot study with a United States smokejumper crew was initiated in 2017. One aim of this study was to evaluate changes in body fat percentage and body weight immediately before and after the fire season. Due to the reported physical job demands, long work days, lack of reported sleep and recovery between shifts, and the reported nutritional habits that were documented from an earlier survey [29
], it was hypothesized that smokejumpers would undergo BC changes over the course of the season.
Research on changes in body composition of smokejumpers throughout the fire season is limited. Understanding BC changes can provide firefighting agencies with beneficial feedback in regard to conditioning and nutritional guidelines given BC can determine performance [24
]. It was anticipated that smokejumpers would undergo BC changes during the season due to the arduous and physical demands of the job. The data indicates 78% of participants underwent what could be construed as an unfavorable BC change—meaning body weight remained constant or increased while body fat increased—indicating a loss of lean mass.
Although objective or subjective nutritional data were not collected in this initial phase of the study, one possible explanation could be that the nutritional requirements of these participants were not being met. For example, observations in the data that participants maintained body weight, increased fat mass, and lost lean mass from the beginning of the season to the end of the season may suggest that inadequate protein and carbohydrate consumption is occurring during the fire season. However, a follow-up study that includes monitoring detailed dietary intake would be needed to evaluate this hypothesis.
One explanation for the changes in BC may be that pre-season BF% was measured immediately after a two week refresher course when the smokejumpers were all training together on a daily basis. This two week period includes extensive physical training and jumping and individuals are expected to be in peak condition prior to the refresher course. Many WLFFs may also conduct pre-fire season conditioning, especially cardiovascular training. Once fire season begins, periods of inactivity during in between fires coupled with dietary habits can potentially lead to accumulation of body fat which can also affect performance and fitness levels [34
]. This possible occurrence could be useful to study in future research. Additionally, objective data on diet on and off the fireline, including quantifying time spent in different levels of exertion along with a larger sample size will help further explain underlying trends.
Other studies examining BC of tactical athletes provides contrasting results. Sell and Livingston [35
] found BF% of interagency hotshots (n = 20) to be 12.9% ± 2.3% at mid-season but did not elaborate further. Their research is incomplete as a baseline of BF% was not measured prior to the fire season and further BF% data was not collected. Cuddy et al. [36
] measured WLFF (n = 16) body weight before and after a single day shift but this information was only measured for water turnover and there was no bodyweight difference among the groups studied. Ruby et al. [15
] found that total body mass of 14 WLFFs over a five day period decreased but attributed the results to total body water loss.
The relationship between simulated job performance tasks, body fat percent, and lean body mass on firefighters has also been reported [4
]. Williford et al. [4
] examined 100 individuals to determine their body fat percent and ability to perform a simulated job task. Results showed a statistically significant relationship between BF% and the time to perform the simulated fire line job tasks. As BF% increased, time to perform the simulated job tasks increased. They also found a negative relationship between lean mass and job-related performance. As the amount of muscle mass increased, the time to perform the job tasks decreased. The study concluded that percent of body fat and lean body mass were important predictors of job performance. Firefighters with greater fat-free weight and less fat mass tended to perform the simulated job tasks in less time [4
]. With a lengthening fire season [23
], what remains to be seen is if BC changes are significant enough to decrease job performance in the WLFF population.
Possible limitations of this study are the participant group and limited sample size (n = 9) which limits our ability to generalize results. Additionally, participants were from the same base, all male, and with an occupational weight limit of 90.7 kg, both of which may have had an impact on possible weight changes throughout the study. Having all-male study participants limits further implications/suggestions for female WLFFs. Future research will include assessing hydration while monitoring BC during the fire season and during the off-season (January) to track longitudinal changes in a larger population in order to address limitations.
Another limitation of our research may be the use of skinfold calipers, which have a ±3.5% error associated with BF% readings [32
]. While skinfold calipers are widely recognized and used for field testing [1
], discrepancies exist between skinfold caliper results and the reference laboratory method of DXA, which may provide a more accurate measure of BC [37
]. Therefore, to ensure consistency throughout the study, body fat caliper testing was performed by a single observer who is a trained ACE certified trainer with prior experience. The measurements were conducted at the same time of day and the participants were instructed to follow the same guidelines each time to ensure adequate hydration. Although hydration status was not assessed, this may be another possible limitation in the study and should be included in future research.
In conclusion, these results indicate that WLFFs underwent BC changes across the 2017 fire season. It should be mentioned that changes in fat mass may be associated with other physiological changes as the body adapts. The depth of physiological changes that WLFFs undergo longitudinally over the course of the year is an area that merits further research due to the high number of cardiovascular related deaths [25
] that have occurred in a seemingly “physically fit” and “healthy” population. Monitoring variables such as sleep, training, nutrition, hydration, and recovery, both on and off fire assignments, is needed in order to determine which variable(s) are contributing factors affecting BC changes. Such information will allow for creation of interventions for WLFFs to better maintain BC during the fire season.