Sports Drinks - Part 1
By Nanci S. Guest
| This article applies to athletes, but it may also apply to recreational exercisers participating in moderate-intensity activities lasting longer than 60 minutes or higher-intensity activities lasting longer than 30-45 minutes. |
WHO NEEDS THEM ANYWAY?
Almost everyone you talk to has an opinion on sports drinks. The spectrum ranges from pure skepticism (“they’re just another useless, over-marketed sugar-laden product”) to absolute endorsement (“sports drinks are my most valuable training aid, and I couldn’t live without them.”). So which is it?
Effects of Dehydration on Physiology and Performance
| Athletes regularly encounter dehydration and hyperthermia, and some fall victim to the consequences. These can range from slightly impaired performance to extreme heat illness. Hydration status is a critical determinant of an athlete’s physiological capacity to train, compete and recover successfully. Even slight dehydration (e.g., a 1%-2% loss in body weight, 1.5 lb.-3 lb. for a 150 lb. person) has a negative effect on physiological function and performance.
When individuals fail to replace body fluids and electrolytes, many adverse functional changes may ensue. These include: a higher plasma osmolality (due to decreased blood volume), a higher exercise heart rate (premature fatigue), lower blood flow to the skin (decreased ability to cool body) and a higher core temperature (which may lead to heat exhaustion). Heat stress and increasing body temperature can also impair mental performance, and this decrement is greater with increasing activity duration and increasing task complexity. Attention and vigilance are the first attributes affected, and this increases the risk of injury. In addition, dehydration negatively affects short-term memory, working memory, psychomotor and visual motor skills, arithmetic ability and mood. Consequently, mistakes in strategic game play, decreased mental tenacity (e.g., increased perceived exertion, inability to push yourself) and impaired focus and concentration may result. Athletes Usually Don’t Drink Enough – “Voluntary Dehydration”Even though the benefits of hydration have been clearly established by decades of scientific investigation, most athletes still experience dehydration during training and competition. In the literature, the incidence of dehydration in athletes during competition and/or training ranges from 20%-90%, depending on sport, environmental conditions and other factors Even the most experienced competitors can become dehydrated. Because most athletes underestimate their sweat loss and because the human thirst mechanism is an inaccurate short-term indicator of fluid needs, most of them don’t consume enough fluid. . |
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Unfortunately, there is no clear physiological indicator that signals dehydration is beginning until more obvious symptoms like thirst, growing fatigue, irritability, inability to mentally focus and hyperthermia present themselves. At this point, the negative impacts to performance tend to be irreversible, and the ability to “bounce back” is near impossible.
GETTING ATHLETES TO DRINK MORE
The Case for Water
The natural choice for hydration is water; it tends to be less expensive and more readily available than any other drink. However, water quenches the sensation of thirst before body fluid replacement is achieved. In addition, water doesn’t stimulate thirst or maintain fluid retention due to absence of electrolytes. It may also become bland and unappealing during prolonged exercise thereby reducing consumption.
The Case for Sports Drinks, * Increased Voluntary Fluid Intake
Keep in mind that sports drinks aren’t meant to be consumed outside of exercise or training nor are they meant to replace nutrient-rich beverages such as milk or 100% juice which are both part of a healthy diet. Sports drinks serve as a physiologically functional “training aid” to effectively rehydrate the body during exercise or competition. Numerous studies show that good-tasting sports drinks containing both carbohydrates and sodium chloride (salt) increase voluntary fluid intake compared with plain water in both occupational and athletic settings.
Thirst is driven by two key physiological changes: a rise in the concentration of plasma sodium levels and a drop in blood volume. Unfortunately, during acute thirst, just moistening the mouth provides a signal to the brain to stop drinking before the body’s fluids have been completely restored. In addition, the passage of fluids from the mouth to the stomach is also monitored by the nervous system. This movement of fluid causes drinking to stop before the deficit in body fluid volume is corrected. Therefore, although plain water is a good thirst quencher, it is a poor re-hydrator.
The sports drinks that are most effective in stimulating drinking must strike a balance between palatability and function. Sport drinks must taste best (e.g., chilled and not too sweet) when athletes are hot, sweaty and thirsty. They must also have the proper electrolyte profile to maintain the physiological drive to drink; this is absent in water. Whenever we sweat, part of that sweat comes from blood. Because we lose more water molecules from the blood than we do electrolytes, plasma-sodium concentration rises and stimulates thirst. But if sweat is replaced with plain water, the plasma sodium concentration falls and in turn reduces thirst before re-hydration has been achieved.
In addition, blood plasma levels are very tightly regulated, and continuous fluid replacement from water alone may lower plasma sodium concentration to a level that stimulates the kidneys to produce urine to bring the blood back to a safe sodium concentration. This process may further dehydrate the athlete, and in extreme or rare cases may cause the potentially fatal water hyponatremia (low blood sodium) that is sometimes seen in endurance events like marathons.
What to look for in a sports drink…
* The right amount of carbohydrate- 6%-8% carbohydrate (14-19 grams per 8 oz.)
* The right mix of carbohydrates– a combination of sucrose, glucose and fructose and/or glucose polymers
* The right amount of sodium– at least 100 mg. per 8 oz. (potassium levels are not as critical)
* Lightly sweetened and lightly flavoured– the taste people prefer when they’re hot and thirsty
* No carbonation, no caffeine and no amino acids
* Improved Performance
Research has consistently shown that there are numerous exercise occasions when sports drinks provide benefits to athletic performance that water cannot. During prolonged exercise (45 minutes or more) or high intensity intermittent exercise like team sports, sports drinks enhance performance when compared with water. The performance benefits of hydration and carbohydrate intake via sports drinks are independent and additive.
Ideally, the beverage that an athlete will the drink most of should be the beverage of choice. It’s the total volume of fluid intake that counts, and research clearly shows that athletes will indeed drink more when offered a sport drink compared to plain water. Bringing this awareness to athletes and coaches, and making sports drinks readily available (even in a diluted formula) will effectively aid in the prevention of dehydration to help keep athletes safe and performing at their best.
 | Make your own sports drink… |
| - 1 cup orange juice or cranberry juice | |
| - 1 Tbsp. sugar (optional) | |
| - a pinch of salt | |
| - 2 cups hot water | |
| Dissolve sugar and salt in hot water, add juice and chill. |
Download Client Handout (72kb PDF)
GO TO PART 2
Nanci S. Guest, M.Sc., C.S.C.S., owns Power Play: Nutrition, Fitness, Performance and has recently relocated to Toronto from Vancouver. Since 1995 she has provided the general public and athletes of all levels with nutritional counselling and personal training services. She conducts seminars for sports teams and athletic groups, teaches university-level sports nutrition and is the head sports nutrition consultant for the 2010 Winter Olympics being held in Vancouver/Whistler. Visit her at www.powerplayweb.
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