SPORTS MEDICINE ADVISOR
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Sports Drinks
by Pam Fitzergald, M.S., A. T. C.
Fluid replacement is a must before, during and after activity in order to safeguard your athletes' health and for optimizing athletes performance. A weight loss of greater than 2% resulting from dehydration can fatigue the athlete, cause a loss of concentration, increase heart rate and lead to circulatory collapse. What type of fluid is best to drink during exercise? Are sports drinks better than water? What is the best beverage? Water is the most common beverage consumed. The ideal fluid replacement beverage is one that tastes good to the athlete, does not cause gastrointestinal discomfort when consumed in large quantities, promotes rapid fluid absorption and maintenance of extracellular fluid volumes and provides energy to working muscles.
There is evidence that consumption of sports drinks, such as Gatorade, 10-K, Quick Kick, etc., maintains physiologic function as well as drinking plain water and provides performance benefits exceeding those of water. Research states that sports drinks containing 6-8 percent carbohydrate solution actually enter the bloodstream as rapidly as plain water. The 6 percent carbohydrate beverage not only entered the blood as fast as water but, was associated with improved exercise endurance. Both drinks had the same favorable influence on cardiovascular and thermoregulatory function.
While it is apparent that carbohydrate feeding during exercise can improve exercise performance, there tends to be confusion as to which carbohydrate type is best-glucose, glucose polymers, sucrose or fructose. The type of carbohydrate has a major influence on the rate of gastric emptying provided that the concentration is low. Glucose polymers are chains of glucose molecules that are shorter than starches, but longer than simple sugars. Polymers are more beneficial to the athlete than simple carbohydrates because they pass through the stomach more rapidly. Simple carbohydrates and glucose supply energy and maintain fluid balance in the range of 5-1 1O% carbohydrate concentration. Glucose and sucrose stimulate fluid absorption in the small intestine. When consumed during exercise they have similar effects on cardiovascular, thermoregulatory responses and performances. Fructose is absorbed more slowly than other carbohydrates and does not stimulate as much absorption of fluid.
Fructose is not associated with performance improvement, it can not be metabolized and released rapidly enough by the liver to provide adequate amounts of glucose to the working muscles. Gastrointestinal distress and diarrhea are common side effects of drinking solutions containing fructose during exercise, especially at 10% or greater concentrations. Fructose in high concentrations would not be beneficial in fluid replacing drinks because of the slow absorption rate. Carbohydrate loading drinks containing fructose used days prior to an event would give the body time to produce more glycogen.
According to research, performance improvement associated with carbohydrate beverages occurs when the athlete consumes at least 25-30 grams of carbohydrate each hour. This can be accomplished by drinking fluids with 6-8% carbohydrate, 4-8 ounces every 15-20 minutes, according to the American College of Sports Medicine.
How important are the electrolytes provided by sports drinks? The electrolyte requirements of most physically active people can be more than adequately met by consuming a balanced diet. Imbalances may occur under special circumstances such as during the initial stage of acclimation to a hot environment, during prolonged repeated exposure to exercise and heat, and during exercise lasting several hours. Among the important electrolytes are sodium, chloride, potassium, magnesium and calcium, which are often included in glucose-containing electrolyte drinks. Sodium helps maintain proper body fluid volume. Small amounts of sodium improve water and glucose absorption in the body. Glucose electrolyte solutions maintain body fluid balance better than glucose drinks alone. Sodium also plays an important role in muscle contraction and in the condition of nerve impulses. A slight deficiency of sodium may impair performance, cause nausea, vomiting, headache, loss of appetite, muscular weakness and leg and abdominal cramps.
If a high carbohydrate diet precedes athletic activity, the type of sports drink ingested has no affect on performance improvement. If glycogen stores are low prior to activity the carbohydrate consumed in a drink during activity will spare muscle glycogen.
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