Physiological and perceptual strain of firefighters during graded exercise to exhaustion at 40 and 10 °C

Abstract

Purpose. To study whether perceptual identification should be included as a measure to evaluate physiological stress. Methods. Physiological variables oxygen uptake (V_O2), ventilation, heart rate, blood lactate concentration, rectal temperature (T_rec) and mean skin temperature, and perceptual variables rate of perceived exertion, thermal sensation and time to exhaustion, were measured at submaximal and maximal intensities during graded exercise on a treadmill to exhaustion in 12 firefighters wearing protective clothing and extra mass at 40 and 10 °C. Physiological strain index (PhSI) and perceptual strain index (PeSI) were calculated. Results. Apart from T_rec, all physiological and perceptual variables were higher at submaximal intensities of 40 °C. Time to exhaustion was 16% shorter and the corresponding V_O2 was reduced by 7% in the heat. A high correlation (r = 89) between PhSI and PeSI was found at both temperatures. PeSI scores were equal to PhSI at both ambient temperatures, except at the two highest intensities in the heat, where PeSI was higher. Conclusions. These findings support use of perceptual identification to evaluate physiological stress. However, at very high intensities under hot conditions the perceptual strain was estimated higher than the physiological strain. More precise indexes are needed to include perceptual measures in safety standard.

Keywords:

• firefighters
• physiological strain index
• perceptual strain index
• ambient conditions
• body temperature

Acknowledgements

The authors are grateful to the members of the Trondheim Fire Brigade who volunteered as participants for this study. They also thank Fire Engineer L. Smistad for his support in performing the experiments. The authors are also indebted to researcher J. I. Medbø, National Institute of Occupational Health, for advice and constructive criticism of the manuscript, and to E. Hjeltereie for technical assistance during the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Erna von Heimburg http://orcid.org/0000-0002-1319-1710

Mariann Sandsund http://orcid.org/0000-0003-2221-2242

Tone Pedersen Rangul http://orcid.org/0000-0002-6633-6725

Randi Eidsmo Reinertsen http://orcid.org/0000-0002-0297-7232