Project Aquarius 2. Limitations of Maximum Oxygen Uptake for Predicting the Strains of Building Fireline With a Rakehoe

Abstract

In three-stage graded work tests we compared men's responses to laboratory step tests with their responses to building fireline with a rakehoe (McLeod tool) in dry eucalypt forest. The subjects were experienced firefighters and the scientific observers (novices at raking fireline) who carried out the investigation. At the average energy expenditure of raking fireline in bushfire suppression (655 W, oxygen uptake 1.9 1 min^-1) the firefighters' heart rate (HR), pulmonary ventilation ((V)_E), and rating of perceived exertion (RPE) were higher in raking than in stepping by 18 beats min^-1, 13 1 min^-1 and 0.5 units RPE respectively. At higher work rates the average difference in the response to raking and stepping decreased for HR (the opposite response to that found in laboratory studies of arm work), increased for (V) _E, and did not change for RPE. Contrary to the usual finding for arm work, the firefighters' average maximal oxygen uptake (VO_2max) was the same for raking and stepping, although the observers' raking (VO_2max) was 10 % (P<0.01) less than their stepping (VO_2max). These findings imply that firefighters rake mainly with their arms and upper body at normal work rates, but recruit additional trunk and leg muscles at higher work rates to achieve a 'whole-body' (VO_2max) — which is greater than could be achieved with the arm work of normal raking and would thus lead to underestimates of strain and fatigue. Seventeen (50%) of the firefighters, but only one (8%) of the observers, had greater (VO_2max) for raking than for stepping, suggesting that regular practice with hand tools had enhanced the firefighters' raking performance through local muscle training and improved technique.