Oxygen consumption during fire suppression: error of heart rate estimation

Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption (VO2) relationship. These men then performed a simulated fire suppression protocol during which HR and VO2 were measured simultaneously by a portable physiological monitoring system. Average VO2 in the simulated setting was 31.0 +/- 7.0 ml.kg-1.min-1 at a HR of 176 +/- 9 bpm. This VO2 was significantly (p less than or equal to 0.05) less than the VO2 that would have been predicted by treadmill testing (38.9 +/- 5.0 ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73 +/- 10% VO2 max with a range of 54% to 88%. There was a significant (-0.82; p less than or equal to 0.05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of VO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour.