Cardiorespiratory and thermoregulatory response of working in fire-fighterprotective clothing in a temperate environment

The cardiorespiratory and thermal responses of two intensities of treadmill exercise were compared for brief periods (12 min) in fire ensemble (FE) bu t without self contained breathing apparatus, and sports ensemble (SE), in a temperature environment. A further experiment explored the responses of s ubjects exercising in FE over a prolonged period (60 min). Eighteen male fi re-fighters wearing either FE or SE walked on a level treadmill for 6 min a t 5 km.h(-1) increasing to 7 km.h(-1) for 6 min. Following a recovery inter val of 1 h, the exercise protocol was repeated in the second ensemble; the order of ensemble was balanced. Heart rate (HR), rectal temperature (T-re), (V) over dot O-2 max and rating of perceived exertion (RPE) were monitored continuously under both ensembles. At 7 km.h(-1), (V) over dot O-2 was sig nificantly higher (p < 0.05) in FE (36.1 and 39.9 ml.kg(-1).min(-1)) than i n SE and represented 74% (V) over dot O-2 max. There were no changes T-re. In experiment 2, following a rest interval of at least 36 h, eight subjects in FE walked on the treadmill at 6 km.h(-1) (gradient 10%) for 60-min also in temperate conditions, where HR, T-re and RPE were recorded at 10-min in tervals. During the 60-min exercise in FE, HR reached 161 beats.min(-1) and T-re increased to 38.3 degrees C. Despite considerable subject discomfort, T-re remained below dangerous levels (38.4 degrees C). When RPE were compa red with a physiological strain index (PSI) calculated from T-re and HR dat a over 60 min, there was no significant difference (p < 0.05) with a correl ation coefficient (r) of 0.98. The results suggest that RPE and PSI are clo sely related when exercise is sufficiently prolonged or intense to elevate T-re and HR in fire-fighters wearing FE in temperate conditions. If further investigation confirms this relationship for hot humid conditions in which fire-fighters operate, then with training, it may provide individuals with a valid measure of dangerous levels of perceived heat strain.