Get the Splash on Fluids for Youth Athletes
By Maria R. Lambert, MS, RD, and Brenda M Malinauskas, PhD, RD
From late spring to early fall, hot and humid weather is common, which makes staying properly hydrated increasingly important. As compared to adult athletes, youth athletes sweat less, produce more heat, and are less able to transfer heat from muscles to skin ("Timely Statement", 1996) while exercising. Additionally, children have a greater ratio of surface area to body volume as compared to adults, and therefore are exposed to a faster influx of heat when environmental temperature exceeds skin temperature (Bass & Inge, 2001). Thus, youth athletes are at especially high risk for exercise-induced dehydration. The following reviews characteristics of dehydration and provides guidance to promote proper hydration for the youth athlete.
Although dehydration can occur any time of the year, dehydration and heat illness, including muscle cramps, syncope (fainting), heat exhaustion, and life-threatening heat stroke, are most prominent when environmental temperature and humidity are high. It is more difficult for the body to release the heat that is generated during exercise as the temperature and humidity rise (Augustine, 2003). Whereas high temperature alone can be detrimental to the athlete, high humidity slows the evaporation of perspiration, the body's natural "cooler," and thus humidity deserves consideration in regard to effect on hydration status, independent of environmental temperature ("Heat and humidity add up to danger", 2005). On a day when humidity is 85% and temperature is 85" F, the apparent temperature (how hot the temperature and humidity combination makes it feel) can exceed 105" F ("Heat and humidity add up to danger"). As a health professional who works with athletes, recognize that more aggressive hydration strategies are needed for youth athletes who practice and compete in hot, humid weather.
Dehydration can be acute, occurring from a single bout of intense exercise, or chronic, which occurs when an athlete does not rehydrate adequately over a period of time, most commonly days to weeks. Dehydration, whether acute or chronic, is defined as 1% body weight loss resulting from fluid loss (Kleiner, 1999). The degree of dehydration associated with exercise can be determined by sweat loss, estimated by body weight change ("Dehydration", n.d.). Comparison of body weight before and after exercise is the most practical method to ensure an athlete is adequately rehydrated because short-term changes in body weight are caused by changes in body fluid content (Bar-Or, 2000). Mild dehydration is loss of up to 6% of body weight, moderate is 7% to l0%, and severe dehydration is in excess of 10% body weight loss. Although the thirst mechanism is activated at 2% to 3% body weight loss, as low as a 2% body weight loss can increase core body temperature (a precursor of heat illness), stress the circulatory system, impair thermoregulation and muscle contractile activity, and decrease oxygen supply to muscle from low blood volume that is associated with a dehydrated state. Collectively, these physiologic changes associated with mild dehydration compromise athletic performance and increase physical injury risk (Augustine, 2003, Kleinman, 2004).
Unfortunately, thirst is not an accurate gauge of hydration. In fact, when thirst becomes apparent, mild dehydration is present (Bass & Inge, 2001). Insufficient fluid consumption can lead to "voluntary dehydration," that being dehydration occurring even when sufficient fluids are offered and available (Bar-Or, 2000). Youth athletes should be encouraged and reminded to drink fluids throughout the day, throughout exercise sessions, and drink fluid to replace sweat loss after exercise. Daily fluid recommendations, excluding additional needs associated with exercise, are 3 to 6 cups (8 ounces is 1 cup) for 4 to 6 year olds and 5 to 8 cups for 7 to18 year olds (Nevin-Folino, 2005).
In regard to additional fluid requirements associated with exercise, youth athletes should have an established drinking schedule that is used for practice as well as competition sessions. The following is a suggested guide. Keep in mind, however, that the drinking schedule should be tailored to individual needs, which are affected by environmental conditions, exercise intensity, and fitness level of the athlete. In general, 7 to 10 year olds should drink 1 ½ to 2 cups of fluid 2 hours before exercise, ½ to 1 cup 15 minutes before exercise, and ¼ to ½ cup every 15 minutes during exercise. Fluid needs are slightly greater for 11 to 18 year olds; recommendations are 2 to 2 ½ cups 2 hours before exercise, 1 to 1 ½ cups 15 minutes before exercise, and ½ cup every 15 minutes during exercise. Regardless of age, athletes should drink 2 cups for each pound of weight loss after exercise (Nevin-Folino, 2005).
A child's metabolic heat production per kilogram of body weight is greater than that of adults, but their ability to transfer heat from the center of the body to the skin is less effective; therefore, acclimatization to exercising in the heat is more gradual for youth versus adult athletes (Bass & Inge, 2001). To prevent dehydration and heat illness among youth athletes, acclimatization, in addition to a more aggressive hydration regimen during the acclimatization process, is warranted. Acclimatization is the process of physiologic and psychological adaptation to a new environment (Sparling & Millard-Stafford, 1999). Acclimatization allows the body to maintain a stable internal core temperature at higher humidity and environmental temperatures (Augustine, 2003). This occurs because of physiologic adaptations, namely sweat rate increases, sweating starts earlier in the exercise session, and the electrolyte content of sweat decreases. Although 75% of the adaptation from a cooler to a warmer environment can occur within five days, acclimatization usually takes 10 to 14 days (Sparling & Millard-Stafford). Intense and prolonged exercise undertaken before acclimatization can deter physical performance and health (Committee on Sports Medicine and Fitness, 2000).
From a physiologic standpoint, identifying the appropriate fluid for an athlete means finding the beverage that approximates the fluid that is lost from the body (sweat) during exercise. Sweat is mainly composed of water; the primary electrolytes that are in sweat are sodium and chloride (that is why sweat tastes salty). However, when you sweat, the body loses more water than it does electrolytes. In fact, blood concentrations of sodium increase as athletes lose sweat. If athletes do not drink enough water while exercising, dehydration occurs and sodium concentration in the blood increases (hypernatrernia). For the majority of athletes, hydrating (i.e., replacing water) during and after exercise is more important than is replacing electrolytes. The correct fluid choice to promote hydration during and immediately after exercise depends on the length of time of physical activity and how much someone sweats. If exercise is less than one hour, the goal is to replace the water that is lost as sweat, whereas for activity greater than one hour, the goal is to provide an energy substrate (sugar) to the muscles in addition to replacing water that is lost as sweat. Athletes producing copious amounts of sweat and ultraendurance athletes are those for whom electrolyte concerns may necessitate sports beverages containing greater amounts of electrolytes.
Americans spend $5.4 billion dollars on sports drinks each year and that number is likely to escalate as sports drinks are increasingly becoming the beverage of choice among youth athletes (Lallanilla, 2005). The basic sport drink (Gatoradea, PowerAdea) is noncaffeinated, contains between 100 and 110 milligrams of sodium per cup, 6% to 8% carbohydrate from a combination of sugars (glucose, sucrose, maltodextrin) that are absorbed from the gastrointestinal tract into the blood quickly, and provides 36 to 77 calories per cup (Nelson Steen, 2004). Interestingly, the sodium that is provided in sports beverages functions to facilitate the transport of glucose across the gastrointestinal tract rather than to replace sodium losses from sweat. Beverages containing greater than 8% carbohydrate, such as fruit juices and soft drinks, should be avoided during exercise because the water from these fluids is absorbed slowly and gastrointestinal distress (cramps, diarrhea) is common (Starling & Millard-Stafford, 1999). From a physiologic standpoint, slightly cool water is the beverage of choice to promote hydration for exercise lasting less than one hour (Murphy, 2004). Although sports drinks should not be expected to improve performance in youth athletes who exercise within this time frame, sports drinks may be more readily consumed than water due to the "flavor appeal". In summary, sports drinks are most beneficial during competition when youth athletes may be preoccupied and are not as likely to consume adequate amounts of fluids; otherwise, cool water is an appropriate source of fluid for hydration throughout the day.
Youth athletes who are overweight may be more vulnerable to dehydration compared to nonoverweight counterparts because they are less efficient in dissipating body heat (Bass & Inge, 2001). Youth athletes who are overweight should be encouraged to drink water, flavored water, or dilute sports drinks to encourage adequate fluid intake while restricting caloric intake. It is recommended that a Registered Dietitian work with youth athletes who are overweight and their families to identify appropriate dietary changes to promote a healthy body weight rather than simply restricting sports beverage consumption among the overweight athlete.
Appropriate hydration is paramount to the health of youth athletes, especially when exercising in hot, humid weather. Youth athletes should have an established hydration schedule that allows them to hydrate adequately throughout practice and competition sessions. Although water is the preferred fluid for youth athletes to promote hydration throughout the day and exercise sessions, flavored water and sports drinks may promote better hydration than water during training and competition because of the slightly sweet flavor. Coaches and parents should monitor pre- and post-exercise weight changes among youth athletes to determine the amount of fluid the athlete should drink to replace the water loss associated with an exercise session.
Maria Lambert is a graduate of the Master of Science degree in Nutrition program, Brenda Malinauskas (malinauskasb@ecu.edu) is an Assistant Professor, Department of Nutrition and Hospitality Management, East Carolina University, Greenville, North Carolina.
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| Title |
Get the Splash on Fluids for Youth Athletes. |
| Author |
Maria Lambert |
| Source |
Virginia journal (Radford, Va.) |
| Publisher |
Virginia Association for Health, Physical Education, Recreation and Dance |
| Date |
Fall 2006 |
| Vol(iss) |
28(2) |
| SIRC ID # |
S-1086388 |
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