Project Aquarius .11. Effects of fitness, fatness, body size, and age on the energy expenditure, strain, and productivity of men suppressing wildland fires

Multiple-regression analyses were done to evaluate the effects of aerobic fitness (maximum oxygen uptake per kg fat-free mass), fatness (body fat content, %), body size (as reflected in fat-free mass), and age on the strain (i.e. the physiological and subjective responses) and fireline productivity of four crews of firefighters (N=21) while (1) they undertook 'line rakes', in which they attempted to suppress well-developed experimental bushfires of intensities commonly faced by hand-tool crews, and also built fireline in the same way without fire, during three summers in Australian eucalypt forests; and (2) they underwent the Shvartz heat-tolerance test, which requires 15 minutes of step-climbing at a fixed pace in a room temperature of 23 degrees C. The results showed that the expected effects of fitness and fatness, established through laboratory studies and confirmed in the Shvartz test, were attenuated or absent during the line rakes, apparently because of self pacing and the absence of rapid climbing. In the line rakes fitter men did not work harder than the less fit but were more productive and efficient and had somewhat lower heart rates; fatter men tended to be more productive than leaner men but did not experience greater strain; bigger men (as measured by fat-free mass) were more productive than smaller men; age had no effect on strain or productivity; and associations observed during work in both the line rakes and the Shvartz test were already present before the work commenced, apparently because of emotional arousal. Responses in the Shvartz test (including the heat-tolerance score) were uncorrelated with their counterparts in the line rakes, emphasising the limited application of laboratory findings to normal fire-suppression duties. Productivity and efficiency in timed trials of firefighters' line-building performance were uncorrelated with their counterparts during the line rakes. We conclude that the adverse effects of fatness or low aerobic fitness are minimized by work practices that allow firefighters to adjust their own pace, but will become apparent whenever the pace is fixed, the terrain is steep, or some emergency calls for sustained maximal effort.