Beliefs about hydration and physiology drive drinking behaviours in runners.

BACKGROUND: Exercise-associated hyponatraemia (EAH) is a dilutional hyponatraemia that is caused primarily by the intake of hypotonic fluid beyond the dictates of thirst and exacerbated by the syndrome of inappropriate antidiuretic hormone secretion as well as an inability to mobilise osmotically inactive sodium stores. Runners who drink more than to their thirst do so for a reason, and understanding and curtailing this behaviour will probably decrease the incidence of this highly preventable condition. OBJECTIVE: To determine the beliefs about fluid replacement held by runners and whether these beliefs are reflected in hydration behaviours. METHODS: An online survey was filled out by 197 runners solicited by personal solicitation, e-mail and flyers distributed at three local races in autumn 2009. RESULTS: Most runners (58%) drink only when thirsty. Runners drinking to a set schedule are significantly older, more experienced and faster than those drinking when thirsty. Gastrointestinal distress is the most frequently cited (71.5%) reason to avoid overhydration. Runners have a poor understanding of the physiological consequences of hydration behaviours that frequently reflect messages of advertising. CONCLUSIONS: Runners at highest risk of EAH exhibit behaviour that is shaped by their beliefs about the benefits and risks of hydration. These beliefs are frequently based on misconceptions about basic exercise physiology.

The effect of physiology and hydration beliefs on race behavior and postrace sodium in 161-km ultramarathon finishers.

PURPOSE: To determine if beliefs about physiology and rehydration affect ultramarathon runners' hydration behaviors or if these beliefs increase the risk for exercise-associated hyponatremia (EAH). METHODS: Participants of the 2011 161-km Western States Endurance Run completed a prerace questionnaire, prerace and postrace body-mass measurements, and postrace assessment of serum sodium ([Na⁺]). RESULTS: Of 310 finishers, 309 (99.7%) completed the prerace questionnaire and 207 (67%) underwent postrace blood studies. Twelve (5.8%) finishers had asymptomatic EAH ([Na⁺] range 131-134 mmol/L). The most common hydration plan (43.1%) was drinking according to schedule, and these runners did so to replace fluid lost when sweating (100%) and to avoid dehydration (81.2%). Prerace drinking plan was not associated with postrace [Na⁺] or the development of postrace hyponatremia. There also were no group differences between those with and those without EAH for any other variables including planned energy intake or knowledge of fluid balance. Runners not planning to drink to thirst trended toward more influence from advertisements (P = .056) and were significantly more influenced by scientific organizations (P = .043) than runners with other drinking plans. Finally, runners who believe that EAH is caused by excessive drinking adopted a lower-volume drinking plan (P = .005), while runners who believe that EAH is caused by sodium loss via sweating reported more common use of sodium supplementation during the race (P = .017). CONCLUSIONS: Beliefs regarding the causes of EAH alter race behaviors including drinking plan and sodium supplementation but do not appear to affect the likelihood of developing EAH during a 161-km ultramarathon.