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.
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CG: approved final manuscript. NBM: provided analysis supervision. Approved final manuscript. AEH: contributed to construction and editing of manuscript. Approved final manuscript. OJ: manuscript editing. Supported study discretionary funding of consumables etc. Provided overall supervision of project. Approved final manuscript.
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Graham, C., Morris, N.B., Harwood, A.E. et al. Ad libitum water consumption off-sets the thermal and cardiovascular strain exacerbated by dehydration during a 3-h simulated heatwave. Eur J Appl Physiol 120, 391–399 (2020). https://doi.org/10.1007/s00421-019-04283-7
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DOI: https://doi.org/10.1007/s00421-019-04283-7