AUTHOR=Chlíbková Daniela , Nikolaidis Pantelis T. , Rosemann Thomas , Knechtle Beat , Bednář Josef 

TITLE=Maintained Hydration Status After a 24-h Winter Mountain Running Race Under Extremely Cold Conditions

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.01959

DOI=10.3389/fphys.2018.01959

ISSN=1664-042X

ABSTRACT=<p><bold>Background:</bold> To date, no study has examined the hydration status of runners competing in a 24-h winter race under extremely cold environmental conditions. Therefore, the aim was to examine the effect of a 24-h race under an average temperature of -14.3°C on hydration status.</p><p><bold>Methods:</bold> Blood and urine parameters and body mass (BM) were assessed in 20 finishers (women, <italic>n</italic> = 6; men, <italic>n</italic> = 14) pre- and post-race.</p><p><bold>Results:</bold> Five (25%) ultra-runners had lower pre-race plasma sodium [Na<sup>+</sup>] and 11 (52%) had higher pre-race plasma potassium [K<sup>+</sup>] values than the reference ranges. Post-race plasma [Na<sup>+</sup>], plasma osmolality, urine osmolality and urine specific gravity remained stable (<italic>p</italic> &gt; 0.05). The estimated fluid intake did not differ (<italic>p</italic> &gt; 0.05) between women (0.30 ± 0.06 L/h) and men (0.46 ± 0.21 L/h). Runners with a higher number of completed ultra-marathons (<italic>r</italic> = -0.50, <italic>p</italic> = 0.024) and higher number of training kilometers (<italic>r</italic> = -0.68, <italic>p</italic> = 0.001) drank less than those with lower running experience. Pre-race and post-race plasma [Na<sup>+</sup>] were related to plasma osmolality (<italic>r</italic> = 0.65, <italic>p</italic> = 0.002, <italic>r</italic> = 0.69, <italic>p</italic> &lt; 0.001, respectively) post-race, but not to fluid intake (<italic>p</italic> &gt; 0.05). BM significantly decreased post-race (<italic>p</italic> = 0.002) and was not related to plasma [Na<sup>+</sup>] or fluid intake (<italic>p</italic> &gt; 0.05). Post-race hematocrit and plasma [K<sup>+</sup>] decreased (<italic>p</italic> &lt; 0.001) and transtubular potassium gradient increased (<italic>p</italic> = 0.008). Higher pre-race plasma [K<sup>+</sup>] was related to higher plasma [K<sup>+</sup>] loss post-race (<italic>p</italic> = -0.85, <italic>p</italic> &lt; 0.001).</p><p><bold>Conclusion:</bold> Hydration status remained stable despite the extremely cold winter weather conditions. Overall fluid intake was probably sufficient to replenish the hydration needs of 24-h runners. Current recommendations may be too high for athletes competing in extremely cold conditions.</p>