Heat Loss Is Impaired in Older Men on the Day after Prolonged Work in the Heat

Med Sci Sports Exerc. 2018 Sep;50(9):1859-1867. doi: 10.1249/MSS.0000000000001643.


Purpose: Prolonged work in the heat may exacerbate the rise in core temperature on the next work day, especially in older workers who display impairments in whole-body heat loss that increase body heat storage and core temperature relative to young adults during heat stress. We therefore evaluated whether whole-body heat loss in older adults was impaired on the day after prolonged work in the heat.

Methods: Whole-body heat exchange and heat storage were assessed in nine older (53-64 yr) men during three 30-min bouts of semirecumbent cycling at fixed rates of metabolic heat production (150 [Ex1], 200 [Ex2], 250 W·m [Ex3]), each separated by 15-min recovery, in hot-dry conditions (40°C, 20% relative humidity), immediately before (day 1), and on the day after (day 2) a prolonged, work simulation (~7.5 h) involving moderate-intensity intermittent exercise in 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 (mean ± SD) during Ex1 did not differ between days 1 and 2 (151 ± 15 and 147 ± 14 W·m, respectively; P = 0.27), but was attenuated on day 2 during Ex2 (181 ± 15 W·m) and Ex3 (218 ± 16 W·m) relative to day 1 (192 ± 14 and 230 ± 19 W·m, respectively; both P < 0.01). Consequently, body heat storage throughout the protocol on day 2 (276 ± 114 kJ) was 31% greater than on day 1 (191 ± 87 kJ; P < 0.01).

Conclusions: Prolonged work in the heat causes next-day impairments in whole-body heat loss, which exacerbate heat storage and may elevate the risk of heat injury on the following day in older workers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Body Temperature Regulation*
  • Calorimetry, Indirect
  • Exercise*
  • Fatigue
  • Heart Rate
  • Hot Temperature*
  • Humans
  • Male
  • Middle Aged
  • Organism Hydration Status
  • Thermogenesis
  • Time Factors