Our findings indicate that the TLV® guidelines do not prevent body core temperature from exceeding 38°C in older workers. Furthermore, a stable core temperature was not achieved within safe limits (i.e., ≤38°C) indicating that the TLV® guidelines may not adequately protect all individuals during work in hot conditions.
Performing exercise in the heat can increase the risk of health complications, especially among middle-aged and older adults who have impaired whole-body heat loss (WBHL) relative to young adults. 1 That risk may be higher among patients with type 2 diabetes due to abnormalities in cutaneous vasodilation and sweating, which facilitate WBHL. 2 However, repeated brief exercise for 7 days or more during heat exposure (heat acclimation) may mitigate this risk by enhancing WBHL. 3 We therefore assessed whether type 2 diabetes impairs heat loss in physically active middle-aged and older adults during exercise heat stress and whether heat acclimation could offset any impairment.
Introduction
Increasing age is associated with decrements in sweat rate that compromise whole-body total heat loss (evaporative + dry heat exchange) in both men and women during moderate-to-vigorous exercise in dry heat. Similarly, young women also display reductions in sweating (that lower evaporative heat loss) relative to young men in such conditions. Nevertheless, it remained unclear whether these effects act synergistically to exacerbate the age-related decline in whole-body total heat loss in women relative to men. We therefore assessed the interrelation between age and sex on whole-body total heat loss during light, moderate, and vigorous exercise in dry heat.
Methods
To achieve this, we used direct and indirect calorimetry to assess whole-body total heat loss and metabolic heat production (respectively) in 46 men and 34 women age between 18 and 70 yr. Participants performed three, 30-min bouts of cycling at metabolic heat productions of 150 (light), 200 (moderate), and 250 (vigorous) W·m−2, each separated by 15-min recovery in dry heat (40°C, ~15% relative humidity).
Results
Whole-body total heat loss was ~5% lower in women relative to men during moderate and vigorous exercise (both, P < 0.01), irrespective of age. Total heat loss declined with age during moderate and vigorous exercise in both men and women (all, P < 0.050), although the rate of that decline (~4% per decade) was similar between men and women across all exercise bouts (all, P > 0.050).
Conclusions
We show that, when assessed in dry heat, whole-body total heat loss is lower in women relative to men, irrespective of age. Furthermore, total heat loss declines with increasing age in both men and women during moderate-to-vigorous exercise, albeit the rate of that decline is not appreciably modified by sex.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.