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Med Sci Sports Exerc. 2018 Feb;50(2):318-326. doi: 10.1249/MSS.0000000000001444.

Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men?

Author information

1
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA.

Abstract

PURPOSE:

Heat strain is known to be exacerbated on the second of consecutive work days. We therefore evaluated whether prolonged work in the heat would impair whole-body heat loss capacity on the next day.

METHODS:

To evaluate this possibility, we assessed changes in whole-body heat exchange and heat storage in eight young (26 ± 4 yr) men during heat stress tests performed on the same day before (day 1) and on the day after (day 2) a prolonged work simulation. Each heat stress test involved three, 30-min bouts of semirecumbent cycling at fixed rates of metabolic heat production (200 W·m (Ex1), 250 W·m (Ex2), and 300 W·m (Ex3)), each separated by 15-min recovery, under hot, dry conditions (40°C, 20% relative humidity). The work simulation (7.5 h) involved three moderate-intensity intermittent work bouts (2 h), each separated by 30-min rest breaks, under similarly hot, dry conditions (38°C, 34% relative humidity). Total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was quantified as the temporal summation of heat production and loss.

RESULTS:

Total heat loss did not differ between days 1 and 2 (P = 0.66) and averaged (mean ± 95% confidence interval) 185 ± 7 W (Ex1), 233 ± 7 W (Ex2), and 261 ± 5 W (Ex3) across test days. Consequently, the change in body heat storage was also similar between days 1 and 2 (P = 0.32), averaging 133 ± 15 kJ (Ex1), 99 ± 16 kJ (Ex2), and 184 ± 15 kJ (Ex3) across test days.

CONCLUSIONS:

When assessed under controlled laboratory conditions in young men, prolonged work in the heat does not seem to impair whole-body heat loss or exacerbate heat storage on the following day.

PMID:
28991046
DOI:
10.1249/MSS.0000000000001444
[Indexed for MEDLINE]

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