PROJECT-AQUARIUS .2. LIMITATIONS OF MAXIMUM OXYGEN-UPTAKE FOR PREDICTING THE STRAINS OF BUILDING FIRELINE WITH A RAKEHOE

In three-stage graded work tests we compared men's responses to labora tory step tests with their responses to building fireline with a rakeh oe (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) over dot(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 uni ts RPE respectively. At higher work rates the average difference in th e response to raking and stepping decreased for HR (the opposite respo nse to that found in laboratory studies of arm work), increased for (V ) over dot(E), and did not change for RPE. Contrary to the usual findi ng for arm work, the firefighters' average maximal oxygen uptake ((V) over dotO(2max)) was the same for raking and stepping, although the ob servers' raking (V) over dotO(2max) was 10 % (P<0.01) less than their stepping (V) over dotO(2max). These findings imply that firefighters r ake mainly with their arms and upper body at normal work rates, but re cruit additional trunk and leg muscles at higher work rates to achieve a 'whole-body' (V) over dotO(2max) - which is greater than could be a chieved with the arm work of normal raking and would thus lead to unde restimates of strain and fatigue. Seventeen (50%) of the firefighters, but only one (8%) of the observers, had greater (V) over dotO(2max) f or raking than for stepping, suggesting that regular practice with han d tools had enhanced the firefighters' raking performance through loca l muscle training and improved technique.