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Martin D. Hoffman and Thomas M. Myers

Symptomatic exercise-associated hyponatremia (EAH) is known to be a potential complication from overhydration during exercise, but there remains a general belief that sodium supplementation will prevent EAH. We present a case in which a runner with a prior history of EAH consulted a sports nutritionist who advised him to consume considerable supplemental sodium, which did not prevent him from developing symptomatic EAH during a subsequent long run. Emergency medical services were requested for this runner shortly after he finished a 17-hr, 72-km run and hike in Grand Canyon National Park during which he reported having consumed 9.2–10.6 L of water and >6,500 mg of sodium. First responders determined his serum sodium concentration with point-of-care testing was 122 mEq/L. His hyponatremia was documented to have improved from field treatment with an oral hypertonic solution of 800 mg of sodium in 200 ml of water, and it improved further after significant aquaresis despite in-hospital treatment with isotonic fluids (lactated Ringer’s). He was discharged about 5 hr after admission in good condition. This case demonstrates that while oral sodium supplementation does not necessarily prevent symptomatic EAH associated with overhydration, early recognition and field management with oral hypertonic saline in combination with fluid restriction can be effective treatment for mild EAH. There continues to be a lack of universal understanding of the underlying pathophysiology and appropriate hospital management of EAH.

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J. Luke Pryor, Evan C. Johnson, Jeffery Del Favero, Andrew Monteleone, Lawrence E. Armstrong, and Nancy R. Rodriguez

Postexercise protein and sodium supplementation may aid recovery and rehydration. Preserved beef provides protein and contains high quantities of sodium that may alter performance related variables in runners. The purpose of this study was to determine the effects of consuming a commercial beef product postexercise on sodium and water balance. A secondary objective was to characterize effects of the supplementation protocols on hydration, blood pressure, body mass, and running economy. Eight trained males (age = 22 ± 3 y, V̇O2max = 66.4 ± 4.2 ml·kg-1·min-1) completed three identical weeks of run training (6 run·wk-1, 45 ± 6 min·run-1, 74 ± 5% HRR). After exercise, subjects consumed either, a beef nutritional supplement (beef jerky; [B]), a standard recovery drink (SRD), or SRD+B in a randomized counterbalanced design. Hydration status was assessed via urinary biomarkers and body mass. No main effects of treatment were observed for 24 hr urine volume (SRD, 1.7 ± 0.5; B, 1.8 ± 0.6; SRD+B, 1.4 ± 0.4 L·d-1), urine specific gravity (1.016 ± 0.005, 1.018 ± 0.006, 1.017 ± 0.006) or body mass (68.4 ± 8.2, 68.3 ± 7.7, 68.2 ± 8.1 kg). No main effect of treatment existed for sodium intake—loss (-713 ± 1486; -973 ± 1123; -980 ± 1220 mg·d-1). Mean arterial pressure (81.0 ± 4.6, 81.1 ± 7.3, 83.8 ± 5.4 mm Hg) and average exercise running economy (V̇O2: SRD, 47.9 ± 3.2; B, 47.2 ± 2.6; SRD+B, 46.2 ± 3.4 ml·kg-1·min-1) was not affected. Urinary sodium excretion accounted for the daily sodium intake due to the beef nutritional supplement. Findings suggest the commercial beef snack is a viable recovery supplement following endurance exercise without concern for hydration status, performance decrements, or cardiovascular consequences.

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Alan J. McCubbin, Gregory R. Cox, and Ricardo J.S. Costa

During endurance exercise, muscular contractions produce heat, resulting in sweating to support thermoregulation ( Sawka et al., 2007 ). Considering sodium is the most abundant electrolyte present in sweat, prolonged heavy sweating can cause significant sodium losses ( Baker, 2017 ). While this is

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Kevin C. Miller, Brendon P. McDermott, and Susan W. Yeargin

). Many studies associate EAMCs with fluid, sodium (Na + ), potassium (K + ), or chloride (Cl − ) losses because of their importance in fluid balance, muscle contraction, and nerve conduction. Sweat losses, whether matched or unmatched by fluid or dietary intake, may result in hypohydration, acute or

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Nathan Philip Hilton, Nicholas Keith Leach, Melissa May Craig, S. Andy Sparks, and Lars Robert McNaughton

Gastrointestinal (GI) disturbances are widely reported following sodium bicarbonate (NaHCO 3 ) supplementation ( Burke & Pyne, 2007 ; Cameron et al., 2010 ; Kahle et al., 2013 ), and although the etiology of GI disturbances involves multiple mechanisms, the neutralization of gastric acid is

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Ronald J. Maughan, Phillip Watson, Philip A.A. Cordery, Neil P. Walsh, Samuel J. Oliver, Alberto Dolci, Nidia Rodriguez-Sanchez, and Stuart D.R. Galloway

) promote longer term retention of the ingested volume ( Maughan et al., 2016 ). These differences in fluid retention are likely due to mechanisms involving both fluid delivery to the circulation ( Calbet & Holst, 2004 ; Mahe et al., 1992 ) and the effect of electrolytes (particularly sodium) on expansion

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Charles S. Urwin, Rodney J. Snow, Dominique Condo, Rhiannon Snipe, Glenn D. Wadley, and Amelia J. Carr

Performance of high-intensity (> 90% VO 2 max) and/or short-duration (< 420 s) exercise may be partially limited by blood acidosis (decreased blood pH and blood bicarbonate concentration ([HCO 3 − ]); Carr et al., 2011 ). Sodium citrate and sodium bicarbonate are frequently used buffering agents

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Michael F. Bergeron

A 17-year-old, nationally ranked, male tennis player (AH) had been experiencing heat cramps during tennis match play. His medical history and previous physical exams were unremarkable, and his in-office blood chemistry profiles were normal. On-court evaluation and an analysis of a 3-day dietary record revealed that AH's sweat rate was extensive (2.5 L · hr−1) and that his potential daily on-court sweat sodium losses (89.8 mmol · hr of play') could readily exceed his average daily intake of sodium (87.0-174.0 mmol · day−1). The combined effects of excessive and repeated fluid and sodium losses likely predisposed AH to heat cramps during play. AH was ultimately able to eliminate heat cramps during competition and training by increasing his daily dietary intake of sodium.

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William H. Gurton, Steve H. Faulkner, and Ruth M. James

agents exist that elicit a metabolic alkalosis which improves the capacity to buffer H + during high-intensity exercise. Perhaps the most well-established and extensively researched is sodium bicarbonate (NaHCO 3 ). 4 This nutritional supplement enhances the extracellular buffering response by

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Rodrigo dos Santos Guimarães, Alcides Correa de Morais Junior, Raquel Machado Schincaglia, Bryan Saunders, Gustavo Duarte Pimentel, and João Felipe Mota

, studies have sought to reduce the impact of metabolic acidosis ( Bishop et al., 2004 ; Jones et al., 2016 ), increasing extracellular H + buffering and increasing muscles’ potential hydrogen (pH) through sodium bicarbonate (NaHCO 3 ) supplementation ( Krustrup et al., 2015 ). An increased repeated