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Eric D.B. Goulet, Adrien De La Flore, Félix A. Savoie and Jonathan Gosselin

Hyperhydration has been demonstrated to improve work capacity and cardiovascular and thermoregulatory functions, enhance orthostatic tolerance, slow or neutralize bone demineralization, and decrease postdive bubble formation. Adding sodium or glycerol to a hyperhydration solution optimizes fluid retention. Sodium and glycerol produce their effect through different physiological mechanisms. If combined into a hyperhydration solution, their impact on fluid retention could potentially be greater than their singular effect. We compared the effect of salt-induced hyperhydration (SIH), glycerol-induced hyperhydration (GIH), and salt + glycerol-induced hyperhydration (SGIH) on fluid balance responses during a 3-hr passive experiment. Using a randomized, crossover, and counterbalanced experiment, 15 young men (22 ± 4 years) underwent three, 3-hr hyperhydration experiments during which they ingested 30 ml/kg fat-free mass (FFM) of water with an artificial sweetener plus either (a) 7.5 g of table salt/L (SIH), (b) 1.4 g glycerol/kg FFM (GIH), or (c) 7.5 g of table salt/L + 1.4 g glycerol/kg FFM (SGIH). After 3 hr, there were no significant differences in plasma volume changes among experiments (SIH: 11.3% ± 9.9%; GIH: 7.6% ± 12.7%; SGIH: 11.3% ± 13.7%). Total urine production was significantly lower (SIH: 775 ± 329 ml; GIH: 1,248 ± 270 ml; SGIH: 551 ± 208 ml) and fluid retention higher (SIH: 1,127 ± 212 ml; GIH: 729 ± 115 ml; SGIH: 1,435 ± 140 ml) with SGIH than either GIH or SIH. Abdominal discomfort was low and not significantly different among experiments. In conclusion, results show that SGIH reduces urine production and provides more fluid retention than either SIH or GIH.

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Eric D.B. Goulet

Glycerol-induced hyperhydration (GIH) has been shown to improve fluid retention and endurance performance compared with water-induced hyperhydration. The goal of this article is to report on what is known and unknown about how glycerol-containing hyperhydration solutions (GCHSs) are processed at the stomach and intestine level, propose strategies to improve the efficacy of GIH, and provide research questions for future studies. Through statistical analyses, it is demonstrated that the effectiveness of GCHSs in increasing fluid retention is maximized when fluid ingestion is in the upper range of what is normally administered by studies (~26 ml/kg body weight) and the duration of the protocol is no longer than the time it takes for the glycerol-fluid load to be totally or nearly completely integrated inside the body. The rate of gastric emptying and intestinal absorption of GCHSs is unknown. However, based on an analysis of indirect evidence obtained from human studies, it is proposed that most glycerol (~80 g) and fluid (~1,700 ml) ingested during a typical GIH protocol can be integrated inside the body within 60–90 min. Whether the stress associated with competition could alter these figures is unknown. Research in rats indicates that combining glycerol with glucose at a 3:1 ratio accelerates intestinal absorption of both glycerol and water, thereby potentially improving the efficacy of GIH. Human studies must be conducted to determine how GCHSs are processed by the gastrointestinal system and whether adding glucose to GCHSs could improve the technique’s efficacy.

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Eric D.B. Goulet, Mylène Aubertin-Leheudre, Gérard E. Plante and Isabelle J. Dionne

The authors determined, through a meta-analytic approach, whether glycerol-induced hyperhydration (GIH) enhances fluid retention and increases endurance performance (EP) significantly more than water-induced hyperhydration (WIH). Collectively, studies administered 23.9 ± 2.7 mL of fuid/kg body weight (BW) with 1.1 ± 0.2 g glycerol/kg BW, and hyperhydration was measured 136 ± 15 min after its onset. Compared with WIH, GIH increased fluid retention by 7.7 ± 2.8 mL/kg BW (P < 0.01; pooled effect size [PES]: 1.64 ± 0.80, P < 0.01, N = 14). The use of GIH was associated with an improvement in EP of 2.62% ± 1.60% (P = 0.047; PES: 0.35 ± 0.13, P = 0.014, N = 4). Unarguably, GIH significantly enhances fluid retention better than WIH. Because of the dearth of data, the effect of GIH on EP must be further investigated before more definitive conclusions can be drawn as to its ergogenic property.

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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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Timothy D. Noakes

The hyponatremia of exercise may exist in symptomatic and asymptomatic forms. Symptomatic hyponatremia is usually characterized by severe alterations in cerebral function including coma and grand ma1 seizures; it develops especially in less competitive athletes who have maintained high rates of fluid intake during endurance events lasting at least 5 hours. The hyponatremia becomes symptomatic when the volume of excess fluid retained exceeds 2 to 3 liters. The etiology of the condition is unknown. Possibly as many as three or more pathologies (abnormal fluid retention possibly due to inappropriate ADH secretion, abnormal regulation of the extracellular fluid volume, translocation of sodium into a "third space") must be present for symptomatic hyponatremia to develop. The avoidance of overhydration would appear to be the only certain way that susceptible individuals can prevent symptomatic hyponatremia. Sodium chloride containing solutions ingested in physiologically significant concentrations would likely prevent a possible "third space" effect.

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

Research, 45 ( 10 ), 697 – 700 . PubMed ID: 23794401 doi:10.1055/s-0033-1347263 10.1055/s-0033-1347263 Hoffman , M.D. , Bross , T.L. , & Hamilton , R.T. ( 2016 ). Are we being drowned by overhydration advice on the Internet? The Physician and Sportsmedicine, 44 ( 4 ), 343 – 348 . PubMed ID

Open access

Alan J. McCubbin, Bethanie A. Allanson, Joanne N. Caldwell Odgers, Michelle M. Cort, Ricardo J.S. Costa, Gregory R. Cox, Siobhan T. Crawshay, Ben Desbrow, Eliza G. Freney, Stephanie K. Gaskell, David Hughes, Chris Irwin, Ollie Jay, Benita J. Lalor, Megan L.R. Ross, Gregory Shaw, Julien D. Périard and Louise M. Burke

for flexibility in fluid and electrolyte intake strategies, ensuring access to sufficient fluid for upper estimates of fluid and electrolyte needs, but adjusting to prevent overhydration if exercise intensity or ambient temperature is lower than expected. In many cases, ad libitum fluid intake will be

Open access

Shona L. Halson, Louise M. Burke and Jeni Pearce

); athletes should have adequate fluid available or request additional supplies from cabin staff to remain well hydrated. Of course, overhydration should be avoided, especially if it leads to interrupted sleep due to the need for toilet breaks. The diuretic effect of caffeine has been overstated in many

Open access

Louise M. Burke, Linda M. Castell, Douglas J. Casa, Graeme L. Close, Ricardo J. S. Costa, Ben Desbrow, Shona L. Halson, Dana M. Lis, Anna K. Melin, Peter Peeling, Philo U. Saunders, Gary J. Slater, Jennifer Sygo, Oliver C. Witard, Stéphane Bermon and Trent Stellingwerff

progresses • Periodization of nutrition to meet specific (i.e., terrain, surface and environmental conditions) training and competition demands • Ad libitum fluid intake for protection against dehydration and overhydration. Assess gastrointestinal tolerance to race food and fluid, and adjust accordingly