Abstract
Violation of the National Institute of Occupational Safety and Health (NIOSH) heat stress recommendations by exceeding the allowable wet bulb globe temperature (WBGT) for a given work intensity and work-rest ratio augments acute kidney injury (AKI) risk. Here, we tested the hypothesis that exceeding the allowable work intensity at a given WBGT and work-rest ratio would also worsen AKI risk. Twelve healthy adults completed two NIOSH recommendation compliant trials and one noncompliant trial consisting of a 4 h (half workday) exposure. Work-rest ratio was fixed at 30 min of walking and 30 min of rest each hour. Work intensity (metabolic heat production) was prescribed as a function of WBGT-412 ± 51 W [27.3 ± 0.3°C; high-intensity compliant (C(high))], 290 ± 75 W [31.6 ± 0.2°C; low-intensity compliant (C(low))], and 410 ± 61 W [31.7 ± 0.2°C; high-intensity noncompliant (NC(high))]. AKI risk was quantified by the product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase 2 normalized to urine specific gravity ([IGFBP7·TIMP-2](USG)). Peak core temperature was higher in NC(high) trial (38.3 ± 0.4°C) compared with the compliant trials (C(high): 38.0 ± 0.3°C; C(low): 37.8 ± 0.4°C; P ≤ 0.0095). [IGFBP7·TIMP-2](USG) increased from pre- to immediately postexposure in all trials (time effect: P = 0.0454) but the peak increase was not different between trials [C(high): 0.89 ± 1.7 (ng/mL)(2)/1,000; C(low): 0.78 ± 1.7 (ng/mL)(2)/1,000; NC(high): 1.0 ± 1.4 (ng/mL)(2)/1,000; P = 0.7811]. Violating the NIOSH recommendations by exceeding either the allowable work intensity (i.e., NC(high) vs. C(low)) or WBGT (i.e., NC(high) vs. C(high)) resulted in a modest elevation in peak core temperature but did not modify AKI risk.NEW & NOTEWORTHY We demonstrate that violation of the National Institute for Occupational Safety and Health heat stress recommendations by exceeding allowable work intensity by ∼120 W or environmental limits by ∼4°C wet bulb globe temperature (WBGT) at 30-min work-rest per hour results in a modest elevation in peak core temperature but does not augment acute kidney injury risk compared with scenarios that adhered to the NIOSH recommendations during simulated occupational heat stress.