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

Abstract

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.

Cumulative effects of successive workdays in the heat on thermoregulatory function in the aging worker

“…Consistent with our recent work [4], we observed impaired WB-NHL (Figure 1(c)) primarily due to reduced evaporative heat loss on day 2 relative to day 1 (Figure 1(a)). Reductions in WB-NHL were also observed across days 2-5 (Figure 1(c)).…”

“…In our recent work [4], we tested the hypothesis that those next-day rises in core temperature in middle-aged workers may be partly ascribed to reduced whole-body net heat loss (evaporative heat lossdry heat gain; WB-NHL). Using direct calorimetry, we assessed time-dependent changes in WB-NHL in men aged 53-64 years during heat stress tests involving exercise at increasing, fixed rates of metabolic heat production (150, 200 and 250 W m −2 ) in hot, dry conditions.…”

“…This experimental trial (~100 hours) comprised five identical heat stress tests (0700-1000 hours, days 1-5), four work simulations (1000-1800 hours, days 1-4) and four recovery and sleep periods (1800-0700 hours, days 1-4). As in our previous experiment [4], WB-NHL was evaluated during exercise at increasing, fixed rates of metabolic heat production (150, 200 and 250 W m −2 ) in hot, dry conditions during each heat stress test (2.5 hours), while each work simulation (7.5 hours) involved moderate intensity, intermittent work in similarly hot, dry conditions to replicate an arduous workday [1].…”

“…increasing heat loads equivalent to 35, 46 and 58% of the participant's peak aerobic power), each followed by 15-min recovery in hot, dry conditions (40°C and~10% relative humidity) during each heat stress test (days 1-5). Full details of the experimental procedures each day are provided elsewhere [4].…”

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity

“…Importantly, in young adults, previous research reported no impairment of heat loss and no additional heat storage on the day after performing 7.5 h of fixed-paced physical work in hot dry conditions (Notley et al 2018b). However, impairments in heat loss on day two vs day one were found in older adults completing a similar protocol (Notley et al 2018a). These observations are of particular relevance as they indicate that our current findings may reasonably translate to settings in which extended work is performed on multiple successive days (i.e.…”