Effect Of Beverage Temperature On The Relation Between Perceptual And Physiological Strain During Exercise-heat Stress

To safeguard individuals who work in the heat, it is recommended to monitor core temperature and heart rate (HR), albeit these measurements can be logistically challenging in real-life scenarios. The perceptual strain index (PeSI, derived from measures of rating of perceived exertion (RPE) and thermal sensation (Ts)) requires no direct monitoring, and is thought to reflect the physiological strain index (PSI). Regular water ingestion is recommended during work in the heat to maintain hydration status and mitigate increases in core temperature. However, it remains unclear if beverage temperature influences a worker’s perception of heat strain. While the ingestion of cold fluid is commonly advised, workers may consume beverages that have been heated by the warm environment. PURPOSE: To assess the effect of beverage temperature on the relation between PeSI and PSI during intermittent work in the heat. METHODS: Twenty adults (10 females, mean [SD], age: 23 [3] years, VO2peak: 39.9 [6.0] mL/kg/min) performed four 15-min bouts of moderate-intensity (fixed metabolic heat production: 200 W/m2) cycling in the heat (400C, 15% RH), each separated by a 15-min rest. On separate days, participants consumed 5.2 g/kg of either cold (ice-slurry, 00C) or warm fluid (37.50C) before the first and third exercise bout. At the end of each exercise bout, rectal temperature (Trec) and HR were recorded to calculate PSI (0-10 scale), and RPE and Ts were recorded to calculate PeSI (0-10 scale). Trec, HR, Ts and RPE were compared via two-way ANOVA. Relations between PSI, PeSI and beverage temperature were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. RESULTS: Trec, HR, Ts and RPE increased over time (all P<0.001) but were not influenced by beverage temperature (all P≥0.09). While PeSI increased with PSI (P<0.001), no differences were observed between cold and warm fluid ingestion (P=0.26). However, mean bias [95% LoA] between PSI and PeSI were large in both the cold (-2.1 [-5.7 - 1.5]) and warm fluid condition (-1.8 [-4.8 - 1.2]). CONCLUSIONS: While beverage temperature did not influence the association between PeSI and PSI, we showed that PeSI does not accurately reflect the level of physiological strain experienced by workers performing their duties in the heat. Natural Sciences and Engineering Research Council of Canada and Mitacs