Saturday, April 14, 2012

Fluid Needs in Endurance Athletes

There is much literature out in the scientific community as well as popular magazines and sports nutrition websites that stress the importance of drinking fluids during long endurance events such as a marathon, adventure race, or any high intensity exercise lasting two hours or more (Hsieh, 2004).  With all the different sports drinks out on the market, it can be overwhelming to know what to drink during this type of exercise and how often.  Because of this confusion, people may just want to consume plain water, especially if it is one of the drinks provided on the course during a race.  Water is always offered during these long endurance events, as well as one type of sports drink that contains ratios of carbohydrates and electrolytes, such as Powerade or Gatorade.  However, if the person is a new to endurance exercise or racing, and gets gastrointestinal issues from the sugar in these sports drinks, they may be more inclined to drink water.  With more and more individuals signing up for marathons and endurance events of greater distance, there is a concern with consuming too much plain water (Hsieh, 2004).  Some of these individuals may not be knowledgable about nutrition and fluid intake during these events.  Also, some of the participants are out on the course for five to six hours during a marathon, and even longer during an ultraendurance event lasting five hours or more.  During the course of these races, these individuals may end up consuming way too much water, causing their blood sodium concentration to be off balance.  A condition, called hyponatremia, occurs if an athlete consumes too much plain water, causing intoxication.
Hyponatremia can occur at times in endurance athletes who experience greater sweat losses and drink too much plain water throughout exercise, which results in the loss of salt during the workout or race (Bean, 2010).  Urine production is decreased during high intensity exercise, which causes the body to have a hard time amending the balance between sodium loss and excessive water intake.  The concentration of salt in the blood becomes diluted as the amount of fluid in the blood rises from drinking too much plain water.  Because of this, issues can arise with the heart, brain, and muscle contractions if sodium blood concentrations are reduced.  Bloating, nausea, dizziness, going in and out of consciousness and seizures from the brain swelling are symptoms of hyponatremia.  Dehydration also causes these symptoms as well, so an athlete must closely monitor their fluid intake to avoid both of these conditions (Bean, 2010).  “If you are sweating heavily for long periods of time, drink dilute electrolyte/carbohydrate drinks rather than plain water.  These will help avoid hyponatremia, maintain better fluid levels in the body, spare muscle glycogen and delay fatigue” (Bean, 2010). 
An article from reported that 13 percent of runners from the Boston Marathon in 2002 may have been affected by hyponatremia.  Furthermore, four female runners have died from this condition over the last 12 years after running a marathon (Burfoot, 2004).  This is interesting because, according to the article, the Boston Marathon attracts the fastest, most fit, and skilled runners in the world; one would think they would know what signs to watch out for regarding fluid intake.  According to Burfoot (2004), Dr. Speedy studied hyponatremia in triathletes at the Ironman Triathlon in Auckland in the mid 1990s.  He found that 18 percent of finishers developed this condition.  Dr. Noakes found in the early 2000s that marathon runners should drink just 400 to 800 milliliters an hour, or 13.5 to 27 ounces of fluid.  This contrasted with many sports medicine associations at the time, such as the American College of Sports Medicine (ACSM), causing much debate because ACSM recommended at least 20 to 40 ounces of fluid an hour.  These were the recommendations up until 2003, when a major study by the New England Journal of Medicine was published, stating that hyponatremia is indeed a very serious condition, and explained why runners might not need to consume so much fluid (Burfoot, 2004). 
This study recorded blood sodium levels and body weight before and after the Boston Marathon in 488 runners, finding that 63 accrued hyponatremia when they finished.  “The researchers also performed a sophisticated ‘multivariate analysis’ to identify what actually caused hyponatremia among the afflicted runners, identifying three primary triggers: 1) weight gain during the marathon from excessive fluid consumption; 2) a finishing time slower than four hours; and 3) very small or very large body size” (Burfoot, 2004).  Out of these three factors, the largest was weight gain during the marathon.  One other interesting result was that a sports drink does not shield an athlete from developing hyponatremia, because there is very little salt in sports drinks, not much different than water.  Other studies have found that females develop hyponatremia more so than males, however, the researcher from this study, Dr. Almond, says that he does not think that just being female predisposes one to hyponatremia.  Yet, many women who are small in body size and run for more than four hours are at risk (Burfoot, 2004).  Dr. Almond wants runners to still drink fluids during a marathon, however, he states that “They should simply aim for a safe middle-ground in their hydration strategies” (Burfoot, 2004). 
According to Bob Murray, who is a Hawaiian Ironman finisher, a director of the Gatorade Sports Science Institute, and has a Ph.D. in exercise physiology, says that sports drinks do not protect a person against hyponatremia if the athlete drinks too much of that sports drink during a race.  He says that any extra sodium in sports drinks than already contained must not be added because hydration will then be hindered.  However, Murray says that consuming Gatorade rather than just plain water may dull decreasing sodium concentrations in the blood, which can help shield a runner from a more serious form of hyponatremia (Burfoot, 2004).  An afflicting question is always asked after Murray’s talks, which is “If dehydration is so damn bad for you, why are the marathon winners often the most dehydrated runners on the course? ‘I can only say that I believe they'd perform even better with more fluids,’ he answers. ‘Our advice remains unchanged: Drink to minimize weight loss, but don't overdrink. And favor a good sports drink over water’” (Burfoot, 2004). 
Hyponatremia can occur in any endurance athlete, not just the marathon runner.  A study titled, “Prevalence of exercise-associated hyponatremia in male ultraendurance athletes,” decided to examine the occurrence of hyponatremia in other endurance athletes, rather than the commonly studied marathon runner and Ironman triathlete (Knechtle et al., 2011).  They investigated ultraswimmers, ultracyclists, as well as ultramarathon runners.  The chosen events to investigate these athletes were the “Marathon Swim” in Lake Zurich, Switzerland, (26.4K or 16.4 mi), the “Swiss Cycling Marathon” (720K or 447.4 mi), the “Swiss Bike Masters,” the “100-km Lauf Biel,” an ultramarathon, and the “Swiss Jura Marathon,” which is a 350K (217.5 mi) run through the mountains (Knechtle et al., 2011).  Fifteen ultraswimmers, 37 ultra-mountain bikers, 28 road cyclists, 95 ultramarathon runners, and 25 mountain ultramarathon runners took part in this study.  Alterations were assessed in blood sodium levels, body mass, hematocrit, and chemicals in the urine.  Fluid intake was documented by the participants.  One might suspect that the prevalence of hyponatremia may be more pronounced in these ultraendurance athletes since they are exercising for a long period of time.  However, only 12 competitors, or 6%, developed hyponatremia, meaning that hyponatremia is still a serious problem in endurance athletes of any type, not just marathon runners and triathletes (Knechtle et al., 2011). 
According to Hsieh (2004), athletes are more likely to develop hyponatremia if they have a slower finishing time, are female, the race is in the heat, or they have taken anti-inflammatory medications.  During the 2000 Pittsburgh Marathon, where the temperature reached 32.2 degrees Celsius, and the humidity was at 50%, 5.6% of the finishers had accrued hyponatremia (Hsieh, Roth, & Davis et al., 2002).  On the other hand, another study that was conducted 13 years before on the same race, where the temperature was a lot cooler, did not find one runner with hyopnatremia (Nelson, et al., 1989).  Many other studies did not find this serious condition during races in cooler weather (Whiting, Maughan, & Miller, 1984; Occhi, Gemma, & Buselli et al., 1987; Refsum, Tveit, & Meen et al., 1973).  Hsieh (2004) also reports that females and athletes with slower finishing times are more prone to developing hyponatremia.  Because of their smaller body mass, females might not need as much fluid intake as the current recommendations.  Also, those participating in races that finish with slower times do not need as much fluid intake either because they are exercising at a lower intensity.  It is also possible that athletes can develop hyponatremia from using anti-inflammatory drugs, which cause a reduction in the glomerular filtration rate activated by a decrease in the formation of prostaglandin, however more studies are needed to confirm this belief (Hsieh, 2004).   
Hyponatremia can often look like other issues commonly experienced by endurance athletes, such as heat stroke, hypoglycaemia, gastroenteritis, exercise exhaustion, and exercise-associated collapse (Hsieh, 2004).  Those with blood sodium saturations over 125-130 mmol/L might have a less serious form of hyponatremia, consisting of cramps, light-headedness, vomiting, lethargy, nausea, and oedema.  With this lesser form of hyponatremia, some individuals may not even show any symptoms.  However, more serious cases of hyponatremia have dangerous symptoms, which can lead to death.  “More severe symptoms include mental status changes, encephalopathy, seizure, pulmonary oedema and death.  The subtlety and similarity of these signs and symptoms to those of other exercise-related illnesses may delay diagnosis and, at times, result in iatrogenic worsening of a patient’s condition through vigorous intravenous hydration” (Garigan & Ristedt, 1999).  It is very important, therefore, to take necessary precautions in order to prevent this condition from getting more serious, or developing at all.
It is recommended to comsume 500 mL/h or less, especially for those individuals who take longer to finish races (Hsieh, 2004).  Many sports drinks that contain carbohydrate-electrolyte (CE) blends are aimed at replacing carbohydrate and electrolyte loss through sweat, help increase race performance, improve the absorption of fluids in the intestine, increase the physiological drive to drink, as well as help increase recovery (Hsieh, 2004).  These drinks are preferable to water in order to avoid hyponatremia because they contain some sodium which helps retain water in the body, lessening some of the need to drink (Hsieh, 2004).  “The exact composition of the CE solution does not appear to make a significant difference on performance or physiological parameters.  High sodium (>25-30 mEq/L) and glucose content (>12%) may be poorly tolerated.  Gastric emptying may be decreased by high carbohydrate or calorie content.  Most commercial sports drinks are sufficiently dilute to avoid these problems” (Hsieh, 2004).  These solutions are even more dilute than what the World Health Organization suggests for fluid intake, and should not be the only drink used when  loss of electrolytes and fluids is large, agreeing with Burfoot (2004).  Since these sports drinks are weak in their electrolyte concentrations, in order to prevent hyponatremia, some athletes will swallow salt pills over the course of their race.  However, studies have shown that there is not a significant difference between athletes who use these salt pills during their race and those who do not (Vrijens & Rehrer, 1999; Sanders, Noakes, & Dennis, 2001; Speedy, Thompson, & Rodgers, et al., 2002; Sanders, Noakes, & Dennis, 1999).
It is very important that the athlete pays particular attention to how much fluid they are drinking before and during an intense bout of exercise, especially one lasting two hours or more in hot and humid conditions.  There is a very fine line between too much and too little fluid intake.  The athlete must drink enough to avoid dehydration, but not so much (especially plain water) that their blood sodium concentration because diluted, causing the dangerous condition of hyponatremia.  I think that adhering to these guidelines, as well as practicing and training with different sports drinks to find out which drink, and how much intake is needed before and during the event or exercise bout, will help the athlete become more aware of the condition and able to prevent it. 

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