Proper Hydration – A Delicate Balance

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Now that the summer racing season is well upon us, we are inundated with admonitions to drink copious amounts of fluids. But is it possible to drink too much? Or drink the wrong thing? The answer to both is sometimes. The key is to maintain a proper fluid balance, which I’ll explain shortly.

Here in the Pacific Northwest, we do not have the heat and humidity that much of the rest of the country endures each summer. We all know that the summers here are the nicest of anywhere – but don’t tell anybody. But it pays to be prepared if one of your local competitions falls during a heat wave, or if you are racing somewhere with more extreme temperatures and humidity.

Endurance athletes need to be mindful of several heat-related illnesses. Dehydration is the most common, and is caused by fluid output exceeding fluid intake. The primary loss of fluid while exercising is through sweat. When we exercise, heat is produced, and sweating is one of the body’s mechanisms for cooling itself. The amount of sweat produced varies widely between individuals. In very hot and humid conditions, sweating becomes less effective and the body’s core temperature rises, increasing strain on the cardiovascular system, which hurts performance. The athlete may be irritable, and experience headache, dizziness, fatigue and cramps. Treatment is re-hydration. Prevention is simple – hydrate before, during, and after exercise, especially during warm weather (see sidebar).

Athletes can suffer a serious illness called exertional heat stroke if the body’s core temperature rises above 104 degrees during exercise. The athlete may become confused and disoriented, accompanied by nausea, vomiting, headache, and dizziness. It may be fatal if untreated, so immediate medical attention is imperative. Treatment is to cool the body down, preferably by immersion in cold water. Exertional heat stroke is more prevalent in the sprint and Olympic distance triathlons than in the longer Ironman distance, primarily because the shorter runs are done at a much higher effort (90% VO2 max vs. 60-65% VO2 max), which generates more body heat.

When sweating, you lose not only water but also electrolytes, the most important of which is sodium. When the concentration of sodium in the blood falls to an abnormally low level, you can develop a very serious condition called exertional hyponatremia. It occurs when more water is consumed than lost through sweat (and urine), and the sodium lost is not adequately replaced. Athletes who drink too much water before, during or after prolonged exercise (lasting longer than 4 hours) in warm, humid climates appear to be most at risk. Other factors are fitness level and heat acclimatization. Athletes who are less fit or haven’t trained in warm weather produce more sodium in their sweat. Some people are “salty sweaters” who naturally lose more sodium. Female and beginning marathoners, and triathletes appear to be more at risk; they are out on the course for many hours, tend to be hyper-vigilant about staying hydrated before and during the race, but often drink only water. Those on a low salt diet or taking diuretics for hypertension may be sodium depleted, and therefore more susceptible.

Signs of hyponatremia include confusion, swelling of the hands and feet, increasing headache, nausea and vomiting. If not recognized and treated, the brain can swell, leading to seizure, coma and sometimes death. It may appear similar to heat stroke, except there is no elevation of temperature with hyponatremia. Exertional hyponatremia develops over several hours, usually late in the race or even in the first hours afterward. Treatment requires immediate medical attention, often with intravenous saline. No one suspected of having hyponatremia should be given any fluids that do not contain electrolytes.

It’s unclear how frequently this condition occurs, but almost 30% of the competitors in the 1984 Hawaii Ironman Triathlon were found to be hyponatremic. A woman running the 1998 LaSalle Banks Chicago Marathon collapsed at mile 24 and later died of hyponatremia. Patti Finke MS, exercise physiologist and marathon coach, points out that the number of slower and less prepared participants in marathons has increased substantially. “Lack of training, along with overhydration with water before and during the race, seem to be the primary causes.” She also says that “it’s important to remember that dehydration is a much more common problem than hyponatremia.”

Prevention is actually very simple: in endurance events lasting longer than 4 hours, do not drink just water – drink a sports drink that contains electrolytes. Most of these drinks also contain carbohydrates (a 6-8 % concentration is best) to replace the energy lost during exercise. Finke recommends that ultra runners eat salty foods like pretzels every five miles during races. Practice drinking and eating while cycling and running so that your digestive system gets used to it. Figure out what food and drink agree with you prior to race day.

It’s also helpful to put salt on food and to eat salty foods (pretzels, tomato juice and pickles, for example) during periods of warm weather training. Melinda Manore PhD, RD, a professor in nutrition and food management at Oregon State University, does not recommend taking salt tablets. “It’s too easy to take too much, and they can irritate the stomach and cause cramping.”

“It’s not unusual for people to experience fluids sloshing around in their stomach during a race or training run, but it seems to be more common during an event,” remarks Dr. Manore. “Most people don’t have access to aid stations during long training runs and simply carry one or two bottles with them. But when it comes to a race situation some people may actually drink more than they are accustom to simply because it is available.”

Dr. Manor also explains some of the physiological reasons of why it is important to replace sweat with fluids containing sodium. “Sodium helps to actively transport glucose (broken down form of sugar molecules that contain water and nutrients) into the cells, which in turn, gets into the bloodstream. The goal is to pass the fluids through the stomach quickly and into the small intestine, which is where most of the fluids are absorbed, thus transporting the glucose into the bloodstream where it is needed. If you overload the stomach on race day with more fluids that you typically consume during training, then it is more likely that the sloshing will occur.”

Thirst is not a good indicator of fluid loss, because if you’re thirsty, you are already dehydrated. In her book Endurance Sports Nutrition, Suzanne Girard Eberle MS, RD, recommends weighing yourself before and after exercising in the heat to get an idea of how much you sweat. “Replace every pound lost during daily exercise with at least two cups (16 ounces) of fluid as soon as possible, or better yet, try to consume that amount of fluid while you exercise.” For example, if you ran for half an hour and lost one pound, you should drink 32 ounces during every hour of warm weather running.

To cope successfully with warm weather while training and racing, the key is balancing fluid intake and loss. Use common sense and drink appropriately.

National Athletic Training Association guidelines for hydration:

  • 17-20 oz 2-3 hours prior to event
  • 7-10 oz 10-20 min prior to event
  • 7-10 oz every 10-20 min during event

Post-event:

  • Correction of any accumulated fluid loss, preferably within two hours, with a sports drink containing water, carbohydrates, and electrolytes
  • Ingestion of a carbohydrate-containing drink if exercise session lasts more than 45 to 50 minutes or if it is intense
  • Inclusion of sodium chloride in fluids if exercise session is to last longer than four hours

DeeAnn Dougherty, PT, OCS practices orthopedic manual physical therapy in the Portland area. She is one of the Portland Marathon Training Clinic coaches and is USATF Level 2 and RRCA certified

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