Key result
Cold fluid worsens agreement between physiological and perceptual strain versus warm fluid during simulated heat work.
Why the study?
Monitoring the physiological strain index in the heat is logistically challenging, and it remains unclear whether cold fluid ingestion influences an individual's perception of heat strain.
Does cold fluid ingestion influence the relation and agreement between perceptual and physiological strain during simulated work in a hot environment in young adults?
Does cold fluid ingestion influence the relation and agreement between perceptual and physiological strain during simulated work in a hot environment in young adults?
Absolute Event Rate: -2.1% vs -1.8%
p-value: p=0.008
Cold fluid ingestion worsens the agreement between physiological and perceptual strain during work in a hot environment without reducing core temperature or heart rate.
May warrant caution relying on perceptual strain with cold fluids; leaves open effects on heat safety monitoring.
Cold fluid ingestion is recommended during work to maintain hydration status and physiological function. While monitoring the physiological strain index (PSI) during work in the heat is recommended, it is logistically challenging. Subjective estimates, i.e., perceptual strain index (PeSI), are thought to reflect PSI. However, it remains unclear if cold fluid influences an individual's perception of heat strain. Twenty young adults (10 females) performed four 15-min bouts of moderate-intensity (200 W/m 2 ) cycling in the heat (40°C, 13% RH), each separated by 15-min rest. On separate days, participants consumed 2 boluses consisting of 5.2 g/kg of cold (0°C) or warm fluid (37.5°C) before the first and third work bout. Rectal temperature (Tc) and heart rate (HR) were recorded to calculate PSI (0–10 scale). Rating of perceived exertion (RPE) and thermal sensation (TS) were recorded to calculate PeSI (0–10 scale). Tc, HR, TS, and RPE were compared between experimental trials and across work bouts via two-way ANOVAs. Relation between PSI, PeSI and fluid temperature were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. Tc, HR, TS and RPE were not influenced by fluid temperature (P ≥ 0.09), nor was the relation between PeSI and PSI (P = 0.11). Mean bias [95% LoA] between PSI and PeSI was greater in cold (−2.1 [-5.7 – 1.5]) compared to the warm fluid condition (−1.8 [-4.8 – 1.2], P = 0.008). While the relation between PeSI and PSI was not influenced by beverage temperature the agreement between measures was worsened following cold fluid ingestion. • Cold fluids (10.4 g/kg) do not reduce core temperature or heart rate during simulated work. • Similarly, cold fluids did not influence perceived strain • Agreement between physiological and perceptual strain was worse after fluid ingestion • Cold fluids worsen the agreement between physiological and perceptual strain.
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O’Connor et al. (2025) studied Simulated work in a hot environment (n=20). Cold fluid ingestion (0°C) vs. Warm fluid (37.5°C) was evaluated on Mean bias between physiological strain index (PSI) and perceptual strain index (PeSI) (p=0.008). Cold fluid ingestion worsened the agreement between physiological and perceptual strain compared to warm fluid (mean bias -2.1 vs -1.8; P=0.008) during simulated work in the heat.
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