Heavy-intensity Work In Uncompensable Heat Stress Conditions On Intestinal Strain In Young And Older Females

During uncompensable occupational heat stress, heat-mitigation controls are required to prevent rises in core temperature (Tco) above recommended limits (≥1 °C above rest) in non-heat acclimated workers. We recently introduced guidance on initial stay times (IST), which define the duration of continuous work that can be performed before controls should be implemented. While we showed that ISTs were similar between young and older females across a range of ambient conditions (wet-bulb globe temperature (WBGT) of 26, 29, and 32 °C), older individuals may experience excess intestinal-associated elevations in inflammation for the same elevation in Tco (i.e., ≥1 °C) which may exacerbate the risk of heat injury. PURPOSE: To assess biomarkers of intestinal strain and inflammatory responses during heavy-intensity work in ambient conditions exceeding recommended elevations in Tco of ≥1 °C for young and older females. METHODS: On separate days, 12 young (mean[SD]: 22[2] years) and older (62[5] years) females performed heavy-intensity treadmill walking (metabolic heat production of ~260 W/m2) in WBGT of 26, 29, and 32 °C until an increase in Tco (rectal) of 1 °C. Thereafter, participants rested in a thermoneutral room (22 °C) for 2 hours. Plasma intestinal fatty acidy binding protein (iFABP) and c-reactive protein (CRP) were assessed at baseline, end-exercise (i.e., at IST), and after 2 hours of seated recovery via enzyme-linked immunosorbent assays (ELISAs). Data were analyzed via a two-way repeated measures ANOVA, with Fisher’s LSD post hoc comparisons (P < 0.05). RESULTS: While a condition main effect was observed for iFABP in young women (p = 0.033), no changes occurred in the older group. However, iFABP was elevated in the older compared to young group at all time points (+441.5 pg/mL [SD 175]; p ≤ 0.036). No differences in CRP were observed in either group (all p ≥ 0.373). CONCLUSION: Our findings indicate that increasing iFABP concentrations across conditions in young females may reflect elevations in intestinal strain during heavy-intensity work to a 1 °C increase in Tco in warm-hot ambient conditions. Despite this, older females exhibited higher iFABP concentrations relative to young across all conditions. It remains to be determined if downstream inflammatory signaling was altered by heavy-intensity work in the heat. Supported by: Workplace Safety and Insurance Board (Ontario)