Connor Graham1, Nathan B Morris1, Amy E Harwood1, Ollie Jay2. 1. Thermal Ergonomics Laboratory, Exercise and Sports Science, Faculty of Health Sciences, University of Sydney, Sydney, NSW, 2141, Australia. 2. Thermal Ergonomics Laboratory, Exercise and Sports Science, Faculty of Health Sciences, University of Sydney, Sydney, NSW, 2141, Australia. ollie.jay@sydney.edu.au.
Abstract
PURPOSE: To assess whether ad libitum water ingestion of different temperatures is sufficient to prevent dehydration-related exacerbations of thermal and cardiovascular strain, during exposure to conditions representative of a heatwave. METHODS: Twelve participants (mean ± SD; 25 ± 4 years) exercised for 180 min at 3 METs in 40.1 ± 0.6 °C, 40.4 ± 2.1%RH four times: (i) consuming 20 °C water ad libitum (AL20); (ii) consuming 4 °C water ad libitum (AL4); (iii) replacing no fluids (NOFR); (iv) replacing sweat losses (FULLFR). Fluid consumption (FC), dehydration (%DEH), rectal temperature (Tre), rate-pressure product (RPP), forearm blood flow (FBF), mean skin temperature (Tsk), and local sweat rate (LSR) were measured/determined. RESULTS: FC was greater in AL20 (1.30 ± 0.41 L) than AL4 (1.03 ± 0.32 L; P = 0.003). %DEH was lower (P < 0.001) in AL20 (0.11 ± 0.76%), AL4 (0.43 ± 0.64%), and FULLFR (0.01 ± 0.12%) compared to NOFR (1.93 ± 0.28%). %DEH was lower in AL20 than AL4 (P = 0.003). In NOFR, end-trial changes in Tre were greater (P < 0.001) (1.05 ± 0.27 °C) compared to all other trials, but similar among AL20 (0.72 ± 0.30 °C), AL4 (0.76 ± 0.25 °C) and FULLFR (0.74 ± 0.35 °C). End-trial RPP was higher (P < 0.001) in NOFR (12,389 ± 1578 mmHg·bpm) compared to all other trials, but similar among FULLFR (11,067 ± 1292 mmHg·bpm), AL20 (11,214 ± 2078 mmHg·bpm) and AL4 (11,089 ± 1795 mmHg·bpm). No differences in Tsk or LSR were observed among trials, but FBF was lower in NOFR compared to FULLFR (2.84 ± 0.69 vs. 3.52 ± 0.96 ml/100 ml/min; P = 0.029). CONCLUSION: 4 °C or 20 °C ad libitum water ingestion prevented dehydration levels that exacerbate thermal/cardiovascular strain, despite blunted fluid intake with 4 °C water. Higher core temperatures with NOFR are attributed to impaired internal heat distribution secondary to a lower FBF.
PURPOSE: To assess whether ad libitum water ingestion of different temperatures is sufficient to prevent dehydration-related exacerbations of thermal and cardiovascular strain, during exposure to conditions representative of a heatwave. METHODS: Twelve participants (mean ± SD; 25 ± 4 years) exercised for 180 min at 3 METs in 40.1 ± 0.6 °C, 40.4 ± 2.1%RH four times: (i) consuming 20 °C water ad libitum (AL20); (ii) consuming 4 °C water ad libitum (AL4); (iii) replacing no fluids (NOFR); (iv) replacing sweat losses (FULLFR). Fluid consumption (FC), dehydration (%DEH), rectal temperature (Tre), rate-pressure product (RPP), forearm blood flow (FBF), mean skin temperature (Tsk), and local sweat rate (LSR) were measured/determined. RESULTS: FC was greater in AL20 (1.30 ± 0.41 L) than AL4 (1.03 ± 0.32 L; P = 0.003). %DEH was lower (P < 0.001) in AL20 (0.11 ± 0.76%), AL4 (0.43 ± 0.64%), and FULLFR (0.01 ± 0.12%) compared to NOFR (1.93 ± 0.28%). %DEH was lower in AL20 than AL4 (P = 0.003). In NOFR, end-trial changes in Tre were greater (P < 0.001) (1.05 ± 0.27 °C) compared to all other trials, but similar among AL20 (0.72 ± 0.30 °C), AL4 (0.76 ± 0.25 °C) and FULLFR (0.74 ± 0.35 °C). End-trial RPP was higher (P < 0.001) in NOFR (12,389 ± 1578 mmHg·bpm) compared to all other trials, but similar among FULLFR (11,067 ± 1292 mmHg·bpm), AL20 (11,214 ± 2078 mmHg·bpm) and AL4 (11,089 ± 1795 mmHg·bpm). No differences in Tsk or LSR were observed among trials, but FBF was lower in NOFR compared to FULLFR (2.84 ± 0.69 vs. 3.52 ± 0.96 ml/100 ml/min; P = 0.029). CONCLUSION: 4 °C or 20 °C ad libitum water ingestion prevented dehydration levels that exacerbate thermal/cardiovascular strain, despite blunted fluid intake with 4 °C water. Higher core temperatures with NOFR are attributed to impaired internal heat distribution secondary to a lower FBF.
Authors: Gabrielle E W Giersch; Margaret C Morrissey; Cody R Butler; Abigail T Colburn; Zachariah S Demarais; Stavros A Kavouras; Ollie Jay; Nisha Charkoudian; Douglas J Casa Journal: Physiol Rep Date: 2021-07