A COMPARISON BETWEEN A PHYSIOLOGICAL AND PERCEPTUAL STRAIN INDEX FOR INDICATING HEAT STRESS OF FIREFIGHTERS

Abstract

Recent findings have shown that a perceptual strain index (PeSI) using measures of thermal comfort (TC) and ratings of perceived exertion (RPE) was similar to the physiological strain index (PhSI) calculated from measures of rectal temperature (Tre) and heart rate (HR) during exercise in the heat (Tikuisis et al. MSSE 34: 1454–1461, 2002). PURPOSE It was the purpose of this study to examine whether PeSI was similar to PhSI for firefighters wearing protective clothing in warm environments. METHODS Thirty-seven Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8 km/h, 5% grade), moderate (M, 4.5 km/h, 2.5% grade), light (L, 4.5 km/h) or very light (VL, 2.5 km/h) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Subjects performed a familiarization trial followed by experimental trials at 25°C, 30°C and 35°C with 50% relative humidity. Measures of TC, RPE, Tre and HR were recorded after 20 min of exercise and every 30 min thereafter until exhaustion. RESULTS After 20 min of exercise PeSI (2.15 ± 0.81) was significantly lower than PhSI (3.05 ± 0.60) regardless of the environmental conditions or metabolic rate. As the duration of exercise increased to 50 min with light exercise the underestimation of PhSI with PeSI was maintained. At exhaustion, PeSI (6.18 ± 1.32) was significantly lower than PhSI (6.89 ± 0.60) but this difference was evident only at 25°C (5.78 ± 1.62 and 6.80 ± 0.77 for PeSI and PhSI, respectively) and 30°C (5.94 ± 1.59 and 6.96 ± 0.72 for PeSI and PhSI, respectively). At 35°C there was no difference between PeSI (6.80 ± 1.52) and PhSI (6.91 ± 0.67). CONCLUSIONS It was concluded that PeSI underestimates PhSI for these firefighters working at various intensities and environmental conditions but the underestimation was less prevalent in the warmest climate. Supported by the Province of Ontario Workplace Safety Insurance Board.