Project Aquarius .3. Effects of work rate on the productivity, energy expenditure, and physiological responses of men building fireline with a rakehoe in dry eucalypt forest

Four crews of firefighters built fireline for 7 min periods (with intervening rests), without fire, at self-chosen 'slow', 'normal', and 'fast' rates in Australian eucalypt forests. Individuals differed twofold for energy expenditure (EE, measured as oxygen uptake by the Douglas bag technique) and relative work load (RWL, i.e % of maximum oxygen uptake), and threefold for productivity and efficiency (productivity per unit EE). They maintained their differences in all stages of the test and also while suppressing free-running wildland fires, showing that the work rate adopted was a stable characteristic of the individuals' work behaviour. The technique of raking fireline did not constrain EE but instead allowed firefighters to call upon their maximum work capacity for urgent tasks with no reduction in efficiency. EE, RWL, and heart rate increased linearly with productivity whereas perceived exertion and pulmonary ventilation increased curvilinearly, rising steeply at 'fast' work rates. We suggest that perceived exertion and the ventilatory threshold (the upper limit of comfortable breathing) provide the cues by which firefighters pace themselves at sustainable work rates that balance their fireline productivity against its physiological cost. The findings were highly consistent over four crews, three summers, and two regions and are thus generally applicable to bushfire suppression in southern Australia.