Firefighting is a physically demanding occupation that includes strenuous duties performed over long shifts (10–12 h), often across consecutive days [1
]. Annually, Australian firefighters are routinely deployed to undertake planned burn operations [2
]. Planned burns are an important preventative strategy whereby a fire is purposely lit to reduce the size, number, severity, and intensity of future wildfires [3
]. In 2015, 324 planned burns (covering 1964 hectares and 701 km) were conducted throughout Australia [5
]. Due to the ever-increasing threat of wildfire, it is predicted that the number and scale of planned burns will continue to rise [6
]. However, despite being a regular operational duty, little is currently known about firefighters’ physical activity levels during planned burn operations.
The majority of research examining physical activity levels of firefighters on-shift largely focuses on emergency scenarios such as wildfires [7
], with some studies also examining experimentally lit burns [9
]. These studies have typically quantified physical activity levels either within-shift (i.e., 2-h time periods) or for the whole duration of the shift, describing the total volume of activity that firefighters engage in or comparing differences in activity levels between 2-h periods or shifts [7
]. Regardless of the approach, mixed findings have been reported in the literature to date. For example, several studies have reported no differences in activity levels between shifts or between 2-h periods, suggesting that firefighters pace themselves to ensure operations are completed [7
]. In contrast, others have reported that physical activity levels are higher during the first wildfire shift (or 2-h period within-shift) and decrease over time [13
]. Whilst these studies provide insights into how physical activity levels may change within- or between-shifts as a result of situational contexts (e.g., intensity of the fire), the between-person or between-group (e.g., different hydration status groups) nature of the analyses do not account for within-person effects across a shift or between shifts. That is, does the physical activity that a firefighter engages in during one shift (or 2-h period) subsequently affect their physical activity levels in the subsequent shift (or 2-h period)? It has been hypothesised that individuals have an internal ‘set-point’ (activitystat) that controls their physical activity over time, which is similar to other homeostatic processes within the body [15
]. This hypothesis suggests that increases in activity during a given time period result in subsequent decreases in another time point (i.e., activity compensation) to maintain this overall activity set-point [15
]. Given the typical nature of planned burn operations (i.e., long shifts over consecutive days), this may have significant implications for firefighters undertaking physical work. As such, there is a need to examine whether high levels of activity during one time period results in decreases in physical activity in the next time period. Understanding the temporal nature of firefighters’ physical activity will help to identify, for example, whether operational duties may be compromised and if there is a need for strategies to protect the safety of firefighters during planned burn operations (e.g., regular rest breaks, more firefighters in rotation, etc.).
Consequently, the aims of the study were twofold. Firstly, this study quantified firefighters’ physical activity levels and sedentary time within (2-h periods) and across shifts during planned burn operations. Secondly, this study examined whether firefighters’ physical activity and sedentary time during one shift or 2-h period was associated with their activity levels in the following shift or 2-h period.
This study examined firefighters’ SED and physical activity levels during planned burn operations. Firefighters spent 69% of a planned burn shift engaged in LPA. No significant associations were observed between physical activity or SED during one shift or 2-h period with the following shift or 2-h period, respectively, suggesting that the physical activity that a firefighter engages in during one shift (or 2-h period) does not subsequently affect their physical activity levels in the subsequent shift (or 2-h period).
This is the first study to examine firefighters’ physical activity and SED during planned burn operations, finding that ~6%, 69%, and 24% of a whole planned burn shift was spent in SED, LPA, and MPA, respectively. A negligible 0.19 min (<0.01%) was spent in VPA. Similar patterns of physical activity engagement were observed within-shifts. This indicates that, across an average 10.4-h shift, firefighters engage in physical activity of at least a light intensity for 94% of this time (i.e., 9.7 h). This highlights the need for firefighters to sustain their engagement in physical activity over long time periods. Whilst these findings are similar to the physical activity levels reported in wildfire settings by Vincent and colleagues [8
], they largely contrast other published wildfire studies. For example, Raines and colleagues [11
] found that firefighters spent only 3% of a 2-h period engaged in MPA, which is considerably lower than the within-shift findings from the present study. Across whole wildfire shifts, previous research has reported that the proportion of time spent in MPA ranged from 5% to 23% [8
]. Taken together, these findings suggest that firefighters may engage in more physical activity during planned burns compared with wildfires, which is somewhat surprising given the contrasting contexts (i.e., routine operations vs. emergency situations). Differences in monitoring approaches may explain these contrasting findings, which include the lack of non-wear criteria in previous studies (which can result in an overestimation of SED [29
]), wear location (chest, jacket pocket, wrist [11
]), and the definition of MPA [17
]. However, it is also possible that higher activity levels observed during planned burns reflect a different task emphasis across a shift. For instance, during a planned burn, there may be more walking during both the ignition, patrolling, and suppression phases. This can be seen in Figure 1
and Table 1
, where there was a large range between the average time spent in different physical activity intensities. This may have also resulted from a range of fire suppression tasks [30
], differing roles (i.e., monitoring the area or suppressing a spot fire [9
]) or differences in the terrain [31
]. Furthermore, it appears that several firefighters engaged in a higher percentage of MPA when the monitors were worn for longer (data not presented), though wear time was included in the models to adjust for the impact of wear time on activity levels. It is possible that this reflects the differences in the requirements of the shift or the location (i.e., longer shifts require greater engagement in physical activity). Quantifying the MPA required across different roles during planned burn work will directly inform workforce health and safety programs for firefighters. In contrast, the increased focus on suppression duties during emergency fires may require less ambulation and, therefore, return lower physical activity counts. Exploring the patterns of physical activity and the tasks that contribute to these patterns should be a focus of future research.
This is the first study to examine associations between time spent in different physical activity intensities or SED during any given planned burn shift or 2-h period and the time spent in these activities in the following day or 2-h period. No significant associations were observed between- or within-shifts, which suggests that the amount of physical activity or SED a firefighter engages in during one shift (or 2-h period) does not result in decreased (or increased) physical activity or SED levels in the following time period (i.e., not consistent with the activitystat hypothesis [15
]). This largely supports the findings of Vincent and colleagues [8
], who used this analytical approach to examine the activity levels of firefighters during wildfire suppression. Whilst they found that firefighters were able to maintain their activity levels between shifts, they also found that the amount of LPA engaged in one shift was associated with increased LPA and MPA in the following shift [8
]. This contrasts the current study where no such observations were noted. Interestingly, despite the differences in analytical approaches, the within-shift findings are consistent with the previous wildfire literature [11
]. Overall, these findings suggest that firefighters will adopt self-pacing strategies that allow them to sustain their physical activity and SED across the shift [32
]. This is further supported by the data in Figure 2
, which shows firefighters spend the vast majority of their shift performing LPA. Arguably, engagement in LPA would be more sustainable across a shift compared with higher activity intensities. These findings may also be attributable to, in part, the experience of the firefighters. In this study, the sample had eight years of firefighting experience. It is possible that such pacing strategies may develop with experience, as has been previously found in athletes [33
]. Therefore, future research is needed to look into the possible moderating effects of different variables, such as firefighter experience, on the within-shift physical activity patterns.
It should be noted that it is difficult to compare the current findings to previous research that has used between-person or between-group designs to examine firefighters’ physical activity levels during wildfire suppression, which have shown mixed findings to date. Such designs may be affected by day-to-day variations in ambient temperature [7
], hydration [11
], nutrition [34
], or suppression duties that could explain the more commonly observed decreases in physical activity or SED between shifts or 2-h periods. Using a within-person design (i.e., time points clustered within individuals), the results from the current study suggest activity levels are maintained within- and between-shifts despite day-to-day changes in the working environment, including different tasks, duties, weather conditions, and working locations [9
]. Importantly, as these findings suggest that physical activity levels during one shift (or one period of a shift) do not affect activity levels in the following shift (or shift period), it appears that operational modifications such as more regular breaks and additional personnel may not be needed to ensure planned burn operations are effectively completed.
Overall, the lack of associations between physical activity or SED across consecutive planned burn shifts and within planned burn shifts (2-h periods) is interesting given the finding that firefighters spent ~153 min engaged in MPA across an average shift. With Australian physical activity guidelines recommending that adults aged 18–64 year accumulate at least 150 min of MPA a week [35
], these results highlight that one planned burn shift is equivalent to the minimal amount of physical activity that should be accumulated a week to benefit health. Indeed, firefighters accumulated up to four times the volume of physical activity in one shift compared with daily population estimates [36
]. If this high amount of physical activity is performed regularly, there is the possibility that there may be a benefit to aerobic conditioning [38
]. The activity levels also lend support to previous observations that aerobic capacity is one of the important fitness components (along with strength endurance [39
]) for land management firefighters [40
]. In order to identify how firefighters maintain high volumes of physical activity during long planned burn shifts, future research should examine how physical activity is accumulated (i.e., frequency and duration of activity bouts). This will provide crucial insights into potential pacing strategies and may help to identify optimal activity patterns that could inform workforce training programs to optimise the conditioning and minimise the fatiguing impacts of fireground work.
The strengths of the current study include using a multilevel modelling approach to explore physical activity associations, which accounts for within-person factors of non-independent data [24
]. Furthermore, this is the first study to explore physical activity and SED associations within a firefighting shift, providing some context to previous pacing suggestions. However, this study used a convenience sample drawn from multiple Australian fire and land management agencies. Although this method has been used previously to collect data for a firefighting population [8
], a small sample resulted; therefore, it is possible that the current study may be underpowered. This may contribute, at least in part, to the lack of significant associations observed. Another potential limitation is that data were collected in 1-min epoch lengths, which may have underestimated the reported VPA, as firefighters typically engage in high-intensity suppression tasks for short durations (e.g., <1-min [30
]). Future research should investigate utilising shorter epoch lengths to allow a more detailed assessment of VPA. Furthermore, the Actical accelerometer was worn on the wrist, which has been found to more accurately capture upper body movements [19
] that are involved in the majority of firefighting suppression tasks [30
]. However, the wrist location may also record motions that are not related to the suppression task, such as fidgeting [19
]. In addition, the current analyses were adjusted for several covariates identified a priori (age, sex, BMI, wear time, experience, and sleep duration). However, the study was not powered to examine the moderating effects of these covariates on firefighters’ physical activity and SED levels. It is recommended that future researchers examine the physical activity patterns (including associations) across different samples (e.g., older and younger firefighters and those with a larger or smaller BMI) of firefighters to identify whether there are specific cohorts who may need more targeted safety controls to sustain their physical activity and SED across one shift or multiple shifts.