| Summary: | Abstract This study investigated the effects of weight increase of firefighters’ boots on physiological and psychological strain. Seven young males (70.9 ± 4.8 kg in body mass, BM) participated in the following four boot conditions while wearing standard firefighting personal protective equipment: 3.2, 3.9, 4.6, and 5.3 kg (4.5, 5.5, 6.5, and 7.5%BM). The results showed that the four boot conditions resulted in no differences in rectal temperature, mean skin temperature, energy expenditure and overall thermal comfort during walking, while increments in heart rate were greater for 5.3 kg than for other three conditions (P < 0.05). Subjects felt less warm and had less uncomfortable feet during exercise for the 3.2 kg condition compared to the three other heavier conditions (P < 0.05). These results indicate that psychological strain due to the load carried on the feet appeared earlier (between 4.5 to 5.5%BM) than physiological strain in terms of heart rate (between 6.5 to 7.5%BM). We finally suggest a 5% body mass upper limit for boot weight because subjective strain of the feet may be a valuable preliminary alarm for the physiological strain of firefighters wearing heavy boots.
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