{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,3]],"date-time":"2026-05-03T01:27:25Z","timestamp":1777771645647,"version":"3.51.4"},"reference-count":27,"publisher":"American Physiological Society","issue":"1","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Applied Physiology"],"published-print":{"date-parts":[[2008,7]]},"abstract":"<jats:p>This study compared measured serum [Na<jats:sup>+<\/jats:sup>] (S<jats:sub>[Na+]<\/jats:sub>; brackets denote concentration) with that predicted by the Nguyen-Kurtz equation after manipulating ingested [Na<jats:sup>+<\/jats:sup>] and changes in body mass (\u0394BM) during prolonged running in the heat. Athletes (4 men, 4 women; 22\u201336 yr) ran for 2 h, followed by a run to exhaustion and 1-h recovery. During exercise and recovery, subjects drank a 6% carbohydrate solution without Na<jats:sup>+<\/jats:sup>(Na<jats:sup>+<\/jats:sup>0), 6% carbohydrate solution with 18 mmol\/l Na<jats:sup>+<\/jats:sup>(Na<jats:sup>+<\/jats:sup>18), or 6% carbohydrate solution with 30 mmol\/l Na<jats:sup>+<\/jats:sup>(Na<jats:sup>+<\/jats:sup>30) to maintain BM (0%\u0394BM), increase BM by 2%, or decrease BM by 2% or 4% in 12 separate trials. Net fluid, Na<jats:sup>+<\/jats:sup>, and K<jats:sup>+<\/jats:sup>balance were measured to calculate the Nguyen-Kurtz predicted S<jats:sub>[Na+]<\/jats:sub>for each trial. For all beverages, predicted and measured S<jats:sub>[Na+]<\/jats:sub>were not significantly different during the 0%, \u22122%, and \u22124%\u0394BM trials (\u22120.2 \u00b1 0.2 mmol\/l) but were significantly different during the +2%\u0394BM trials (\u22122.6 \u00b1 0.5 mmol\/l). Overall, Na<jats:sup>+<\/jats:sup>consumption attenuated the decline in S<jats:sub>[Na+]<\/jats:sub>(\u22122.0 \u00b1 0.5, \u22120.9 \u00b1 0.5, \u22120.5 \u00b1 0.5 mmol\/l from pre- to postexperiment of the 0%\u0394BM trials for Na<jats:sup>+<\/jats:sup>30, Na<jats:sup>+<\/jats:sup>18, and Na<jats:sup>+<\/jats:sup>0, respectively) but the differences among beverages were not statistically significant. Beverage [Na<jats:sup>+<\/jats:sup>] did not affect performance; however, time to exhaustion was significantly shorter during the \u22124% (8 \u00b1 3 min) and \u22122% (14 \u00b1 3 min) vs. 0% (22 \u00b1 5 min) and +2% (26 \u00b1 6 min) \u0394BM trials. In conclusion, when athletes maintain or lose BM, changes in S<jats:sub>[Na+]<\/jats:sub>can be accurately predicted by changes in the mass balance of fluid, Na<jats:sup>+<\/jats:sup>, and K<jats:sup>+<\/jats:sup>during prolonged running in the heat.<\/jats:p>","DOI":"10.1152\/japplphysiol.00130.2008","type":"journal-article","created":{"date-parts":[[2008,5,4]],"date-time":"2008-05-04T01:49:02Z","timestamp":1209865742000},"page":"91-99","source":"Crossref","is-referenced-by-count":29,"title":["Quantitative analysis of serum sodium concentration after prolonged running in the heat"],"prefix":"10.1152","volume":"105","author":[{"given":"Lindsay B.","family":"Baker","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"James A.","family":"Lang","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"W. 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