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Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men?
Med Sci Sports Exerc 2018; 50(2):318-326MS

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.

Authors+Show Affiliations

Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, CANADA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

28991046

Citation

Notley, Sean R., et al. "Does a Prolonged Work Day in the Heat Impair Heat Loss On the Next Day in Young Men?" Medicine and Science in Sports and Exercise, vol. 50, no. 2, 2018, pp. 318-326.
Notley SR, Meade RD, Friesen BJ, et al. Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men? Med Sci Sports Exerc. 2018;50(2):318-326.
Notley, S. R., Meade, R. D., Friesen, B. J., D'Souza, A. W., & Kenny, G. P. (2018). Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men? Medicine and Science in Sports and Exercise, 50(2), pp. 318-326. doi:10.1249/MSS.0000000000001444.
Notley SR, et al. Does a Prolonged Work Day in the Heat Impair Heat Loss On the Next Day in Young Men. Med Sci Sports Exerc. 2018;50(2):318-326. PubMed PMID: 28991046.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men? AU - Notley,Sean R, AU - Meade,Robert D, AU - Friesen,Brian J, AU - D'Souza,Andrew W, AU - Kenny,Glen P, PY - 2017/10/11/pubmed PY - 2018/11/16/medline PY - 2017/10/10/entrez SP - 318 EP - 326 JF - Medicine and science in sports and exercise JO - Med Sci Sports Exerc VL - 50 IS - 2 N2 - 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. SN - 1530-0315 UR - https://www.unboundmedicine.com/medline/citation/28991046/Does_a_Prolonged_Work_Day_in_the_Heat_Impair_Heat_Loss_on_the_Next_Day_in_Young_Men L2 - http://Insights.ovid.com/pubmed?pmid=28991046 DB - PRIME DP - Unbound Medicine ER -