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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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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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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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Eric D.B. Goulet and Lindsay B. Baker

The B-722 Laqua Twin is a low cost, portable, and battery operated sodium analyzer, which can be used for the assessment of sweat sodium concentration. The Laqua Twin is reliable and provides a degree of accuracy similar to more expensive analyzers; however, its interunit measurement error remains unknown. The purpose of this study was to compare the sodium concentration values of 70 sweat samples measured using three different Laqua Twin units. Mean absolute errors, random errors and constant errors among the different Laqua Twins ranged respectively between 1.7 mmol/L to 3.5 mmol/L, 2.5 mmol/L to 3.7 mmol/L and –0.6 mmol/L to 3.9 mmol/L. Proportional errors among Laqua Twins were all < 2%. Based on a within-subject biological variability in sweat sodium concentration of ± 12%, the maximal allowable imprecision among instruments was considered to be £ 6%. In that respect, the within (2.9%), between (4.5%), and total (5.4%) measurement error coefficient of variations were all < 6%. For a given sweat sodium concentration value, the largest observed difference in mean and lower and upper bound error of measurements among instruments were, respectively, 4.7 mmol/L, 2.3 mmol/L, and 7.0 mmol/L. In conclusion, our findings show that the interunit measurement error of the B-722 Laqua Twin is low and methodologically acceptable.

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Anne Delextrat, Sinead Mackessy, Luis Arceo-Rendon, Aaron Scanlan, Roger Ramsbottom and Julio Calleja-Gonzalez

Sodium bicarbonate (NaHCO 3 ) supplementation has been widely studied as a strategy to delay metabolic acidosis in the muscles during high-intensity short-duration (<10 min) exercise ( McNaughton et al., 2016 ). Ingestion of NaHCO 3 results in a greater concentration of bicarbonate (HCO 3 − ) in

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Luana Farias de Oliveira, Bryan Saunders and Guilherme Giannini Artioli

Sodium bicarbonate (SB) is an ergogenic supplement used to increase blood bicarbonate concentration, buffering capacity and, subsequently, high-intensity exercise capacity and performance ( McNaughton et al., 2016 ). There is a body of evidence indicating that SB is an effective ergogenic

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Siobhan T. Moran, Christine E. Dziedzic and Gregory R. Cox

The aim of this case study was to describe the race nutrition practices of a female runner who completed her first 100-km off-road ultraendurance running event in 12 hr 48 min 55 s. Food and fluid intake during the race provided 10,890 kJ (736 kJ/hr) and 6,150 ml (415 ml/hr) of fluid. Hourly reported carbohydrate intake was 44 g, with 34% provided by sports drink. Hourly carbohydrate intake increased in the second half (53 g/hr) compared with the first half (34 g/h) of the race, as the athlete did not have access to individualized food and fluid choices at the early checkpoints and felt satiated in the early stages of the race after consuming a prerace breakfast. Mean sodium intake was 500 mg/hr (52 mmol/L), with a homemade savory broth and sports drink (Gatorade Endurance) being the major contributors. The athlete consumed a variety of foods of varying textures and tastes with no complaints of gastrointestinal discomfort. Despite thinking she would consume sweet foods exclusively, as she had done in training, the athlete preferred savory foods and fluids at checkpoints during the latter stages of the race. This case study highlights the importance of the sports nutrition team in educating athletes about race-day nutrition strategies and devising a simple yet effective system to allow them to manipulate their race-day food and fluid intake to meet their nutritional goals.