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Racing in the Heat
Endurance Sports and Heat
As endurance athletes we face many obstacles in our effort to meet our goals. Training, nutrition, stretching and rest are the main concerns of our preparation. What about race day problems that we cannot always be prepared for, though? What about heat, wind and rain? All of these environmental factors can negate months of focused training and sacrifice.
For years customary thought has been that dehydration was the major culprit of poor
endurance performance in excessively hot conditions. Athletes were told to drink
as much water as possible. The truth is that it’s not only dehydration that is a
problem but hyperhydration. Hyperhydration, otherwise known as hyponatremia, is the
state of an abnormally low concentration of sodium in the blood serum. Sodium (salt)
and chloride (an electrolyte) act to distribute water evenly throughout the body
and into muscle tissue and skin. Dehydration is still a major cause of exercise-
The human body is made up of approximately 65% water. The brain, skin, muscles and central nervous system all rely on water balance to function properly. During exercise, people lose between 16 ounces and 3 quarts of water an hour. This is a wide range and the trick is finding out how much you lose in certain conditions. Don’t be fooled into believing that this is a problem that only happens in heat — excessive cold can cause a water imbalance as can excessive wind that taxes the body and cools the sweat on the skin much quicker than normal.
What happens during hyponatremia. Your blood serum is a delicate balance of sodium
and other electrolytes that adjust your blood’s osmolarity to carefully deliver it
throughout your body. If you drink too much water, thereby diluting your blood serum,
then you change your blood’s osmolarity and ability to transport itself. A recent
study by the New England Journal of Medicine reported that 13% (62) of the runners
studied at the Boston Marathon (488) showed excessive fluid consumption coupled with
weight gain and severe electrolyte depletion. Two other studies showed similar results.
A study at the 1997 Ironman New Zealand showed that of the 330 finishers 18% were
hyponatremic. A study at the Hawaii Ironman World Championships showed that 29% of
the all the athletes at that race were hyponatremic. Furthermore, two of the studies
showed that females were more susceptible to this disorder. It was postulated that
this is due to women being more “vigilant” with water consumption. It appears that
what happens is that athletes focus on water consumption and forget how important
electrolytes are to their performance. In fact, sweat contains between 2.225 and
3.4 grams of salt per liter and in a long race, an athlete can easily lose 1 liter
or more per hour. In a 12-
What can you do? First, you need to determine how much water you lose in a certain
temperature over a certain time. So, if you can determine that you lose 1 pound of
water in 1 hour of running in 85 degrees, you will know that you need exactly 16
ounces of water per hour at that pace and in those conditions. From there, you need
to determine how much sodium is lost and how you can replace it. This can be done
through solid foods (pretzels, crackers) or you can take electrolyte supplements
like e-
Another concern is medicating on race day with aspirin, NSAIDS or ibuprofen. These can interfere with kidney function and disrupt water distribution.
In conclusion it’s clear that the concept of hyponatremia can be as much of a problem as dehydration. As an athlete, it’s imperative that you know your body’s needs and reactions to certain conditions. Furthermore, it isn’t enough to practice with what you have — find out what your endurance event has on the course and experiment with that product to evaluate if it works for you. All the proper training in the world and the best taper can be ruined with a lack of preparation in the areas I have discussed.
Following are some symptoms to look for if you are concerned with hyponatremia following extended workouts or races: weight gain, bloating, nausea, headache, cramps, disorientation, slurred speech, confusion, convulsions.
By Greg Mueller, USAT certified triathlon coach
Resources:
Almond CS Shin AY , Fortescue EB, et al, Hyponatremia among runners in the Boston
Marathon, N England Journ Med 2005, 352:1550-
Triathlete Magazine, July 2005, The truth about Hyponatremia, Dr. Krishna R. Polu
Speedy et al, 1999, Ironaman New Zealand Study
Davis et al, 2001
Runnersweb.com/running/news/rw-
Spinalhealth.net/hyponatremia.html