Hyponatremia is a state of low sodium ions in the circulating blood, often referred to as serum sodium concentration levels. (1)
In long endurance events lasting more than four hours such as marathons, triathlons, cycling or long hikes, sodium is lost as we perspire. However, salt loss from sweat seems to have little effect on hyponatremia.(2) By just drinking plain water instead of a salt-enhanced water (0.06% sodium chloride) in conjunction with a salt restricted diet could cause hyponatremia. Most endurance athletes are frequently on low calorie diets which lower the amount of salt ingested. Chronic salt deprivation may lead to decreased body sodium and may predispose athletes to hyponatremia when they over hydrate with pure water.
Symptoms of this condition can sometimes be confused for other exertional heat illness such as heat exhaustion or heat stoke. Although the symptoms are similar, Hyponatremia is distinguishable by the serum sodium level.(3) Unfortunately, as Personal Trainers we dont have the ability to draw blood, so there would be no way for us to know what the serum sodium levels would be.
Four factors contribute to hyponatremia
-over consumption and retention of fluids
-loss of sodium in the sweat
-decreased sodium intake
-spacing salt into unabsorbed water in the gut.
Drinking (water) to Death
There are now at least 21 publications describing the life-threatening consequence of fluid overload in runners, triatheletes, army personnel and even recreational hikers. Compared with this irresistible proof, the evidence of any health consequences during exercise of modest levels of dehydration (body masses of 2-8%) is nonexistent. In fact, up to 1969, endurance athletes were encouraged not to drink during exercise.(4) Generations of competitive distance runners were able to set world records at a wide range of running distances without ever consuming anything (let alone maximal quantities) and without apparently suffering life-threatening complications (as is now frequently reported in those who drink too much). In a study undertaken in the Nevada desert during World War II, army conscripts exercised in the desert heat for as long as they could without any fluid indigestion at all. They usually lasted about eight hours. What they found was a man could suffer water deficit so incapacitating that he could neither talk nor stand; yet he recovered his walking ability within a few minutes of water ingestion, and his feeling of well-being within half an hour or less after he began drinking. With a meal or two intervening, his recovery is practically complete in 6-12 hours.(5)
Dr. Timothy D. Noakes has shown two factors that help predict likely diagnosis in exercisers who are admitted to the medical facilities at endurance events. The first is whether the collapse occurs before the finish of the race or after the athlete completes the event; the second is whether the athlete is fully conscious or has an altered level of consciousness. Athletes who collapse after finishing the race are almost always fully conscious and are suffering from the sudden onset of postural hypotension. Formerly, this condition was called heat exhaustion. When the exerciser does not finish the exercise bout and has an altered level of consciousness, the initial differential diagnosis would include hyponatremia, a cerebrovascular accident and heatstroke, probably in that order. The doctors then checked the exercisers rectal temperature to see if it fell in the normal range of 37 E - 40 E C. If it was normal, heatstroke was excluded.
Treatment
Nursing should be conducted in the head down Trendelenburg position(6). Care must be taken not to correct levels too rapidly. Rapid correction has caused central pontine myelinolysis in patients with long-standing hyponatremia.
What is the trainer to do?
Make sure your clients hydrate properly with a beverage that contains sodium chloride. Most sports drinks such as Gatorade and PowerAid contain this substance. If signs of heat exhaustion occur, dont rule out hyponatremia.
Have them consult a physician immediately. Be safe not sorry.
1. Stedmans Medical Dictionary: 3 rd edition;Williams and Wilkins, 1997
2. Seizure after Exercise in the Heat: Flinn, Scott D. MD, Sherer, Ryan J., MD; the Physician and Sportsmedecine, September, 2000
3. Seizure after Exercise in the Heat: Flinn, Scott D. MD, Sherer, Ryan J., MD; The Physician and Sportsmedecine, September, 2000
4. Hyponatremia in Endurance Athletes: Noakes, Timothy D., MB, ChB, MD, The Physician and sportsmedecine, September, 2000
5. Water Shortage in the Desert: Adolph EF (ed); New York City, Interscience Publishers, Inc., 1947
6. Collapsed Ultra Endurance Athlete, Proposed Mechanisms and an Approach to Management: Holtzhausen, LM, Noakes TD; Clin J Sport Med 1997;7 (4); 292-301
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