title: Quantitative analysis of serum sodium concentration after prolonged running in the heat.
abstract: This study compared measured serum [Na(+)] (S([Na+]); brackets denote concentration) with that predicted by the Nguyen-Kurtz equation after manipulating ingested [Na(+)] and changes in body mass (DeltaBM) during prolonged running in the heat. Athletes (4 men, 4 women; 22-36 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(+) (Na(+)0), 6% carbohydrate solution with 18 mmol/l Na(+) (Na(+)18), or 6% carbohydrate solution with 30 mmol/l Na(+) (Na(+)30) to maintain BM (0%DeltaBM), increase BM by 2%, or decrease BM by 2% or 4% in 12 separate trials. Net fluid, Na(+), and K(+) balance were measured to calculate the Nguyen-Kurtz predicted S([Na+]) for each trial. For all beverages, predicted and measured S([Na+]) were not significantly different during the 0%, -2%, and -4%DeltaBM trials (-0.2 +/- 0.2 mmol/l) but were significantly different during the +2%DeltaBM trials (-2.6 +/- 0.5 mmol/l). Overall, Na(+) consumption attenuated the decline in S([Na+]) (-2.0 +/- 0.5, -0.9 +/- 0.5, -0.5 +/- 0.5 mmol/l from pre- to postexperiment of the 0%DeltaBM trials for Na(+)30, Na(+)18, and Na(+)0, respectively) but the differences among beverages were not statistically significant. Beverage [Na(+)] did not affect performance; however, time to exhaustion was significantly shorter during the -4% (8 +/- 3 min) and -2% (14 +/- 3 min) vs. 0% (22 +/- 5 min) and +2% (26 +/- 6 min) DeltaBM trials. In conclusion, when athletes maintain or lose BM, changes in S([Na+]) can be accurately predicted by changes in the mass balance of fluid, Na(+), and K(+) during prolonged running in the heat.
authors.affiliation: Noll Laboratory, Kinesiology Department, Pennsylvania State University, University Park, Pennsylvania , USA.
authors.forename: Lindsay B
authors.initials: LB
authors.lastname: Baker
authors.forename: James A
authors.initials: JA
authors.lastname: Lang
authors.forename: W Larry
authors.initials: WL
authors.lastname: Kenney
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D054874:Athletic Performance / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D004040:Dietary Carbohydrates / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009929:Organ Size / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D011188:Potassium / Q000097:blood / Q000378:metabolism / Q000652:urine; D015532:Rehydration Solutions / Q000494:pharmacology; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000097:blood* / Q000378:metabolism / Q000652:urine; D013542:Sweat / Q000737:chemistry; D013546:Sweating / Q000187:drug effects
chemical_list: D004040:Dietary Carbohydrates; D015532:Rehydration Solutions; D012964:Sodium; D011188:Potassium