Bolders Dad and musty have posted very good and reliable information
I recommend to my patients who weigh >120 lbs that they drink at least 24 oz of water 1-2 hours before sports participation in a sweaty sport then every 15-20 minutes they are getting a small drink.
The American Academy of Pediatrics recommendations:
The normal thirst mechanism is unreliable for determining how much fluid should be consumed;
about 120 to 180 mL every 15 to 20 minutes for a 40 kg (88lbs) child is a good starting point
http://www.aap.org/sections/sportsmedicine/PDFs/SportsShorts_02.pdf
also link for sports nutrition
http://www.aap.org/sections/sportsmedicine/PDFs/SportsShorts_06.pdf
Fluids: Children and teenagers are at increased risk for dehydration (lack of adequate body water) and heat illness. Risk is greatest in hot, humid weather during long and intense activities. Use these guidelines to ensure that young athletes get enough fluids during physical activity:
- Never restrict fluids for any reason. Make sure that drinks are available at all times.
-Plain water is the best drink for most athletes. Carbonated drinks should not be used. Offering flavored water or an
appropriate sport drink (check with your pediatrician) may encourage a young athlete to drink more.
- Athletes need to drink 4 to 8 ounces of water every 15 to 20 minutes during activity.
- Thirst is not a reliable guide to the need for water. An athlete may become dehydrated before he or she feels thirsty.
-Body weight should be about the same before and after activity.
Pre-exercise/Game Meal Guidelines:May include any reasonable foods that an athlete feels may help his or her performance
and do not cause any complaints.
Nutrition Pearls:
1. Failing to take in enough fluids and calories may lead to early fatigue, irritability, or a sudden drop in performance.
2. Pre-event liquid meals are safe and effective. They provide fluids, are easy to digest, and empty quickly from the stomach
(if they are not too concentrated).
3. Consuming carbohydrates within 30 minutes after intense exercise followed by more carbohydrates 2 hours later
helps athletes better prepare for future activities.
4. Avoid supplements that may include unproven and dangerous ingredients.
Also if you are interested (sorry this is lengthy)
Body temperature is maintained within a narrow range by balancing heat load with heat dissipation. Evaporation is the principal mechanism of heat loss in a hot environment, but this becomes ineffective above a relative humidity of 75 percent.
Up to 70 percent of the risk for heat illness is attributable to excess humidity, followed by elevated solar radiation (20 percent) and increased temperature (10 percent).
Children differ from adults with respect to their anatomical and physiologic response to heat stress. These differences translate into a potentially greater risk for severe heat illness in children, especially infants and young athletes (I will put differences at end if you are interested)
Heat exhaustion Patients with heat exhaustion have known heat exposure and an elevated core body temperature between 37C (98.6F) and 40C (104F). Additional symptoms include:
- Tachycardia
- Sweating (especially when associated with exercise)
- Nausea, vomiting
- Headache
- Fatigue, weakness
- Dizziness
- Syncope with prompt return of normal mental status
- Severe thirst
- Normal mental status or mild confusion that responds rapidly (within 30 minutes) to cooling
- Signs of mild to moderate dehydration
Children with symptoms of heat exhaustion should stop exercising immediately and be moved to a cooler environment (eg, natural shade, air conditioned vehicle, air conditioned building). Excess clothing should be removed, and the patient should be given chilled salt-containing liquids (eg, flavored sports drinks such as Gatorade?) to drink. Most patients with mild heat exhaustion respond to these measures and do not require further care
Recommended adaptations include more hydration breaks, more frequent player substitutions during organized competition, ensuring a shaded area for rest
Maintenance of hydration Scheduled hydration breaks with strong encouragement for drinking is very important in children because they are more likely to inadequately replenish fluid losses during prolonged exercise and have a higher rise in rectal temperature when dehydrated relative to adults
Flavoring water by adding both carbohydrates and sodium chloride increases fluid intake by as much as 90 percent versus offering unflavored water
The adequacy of hydration can be measured by comparing pre- and post-activity dry weight. One rule of thumb is to consume 240 mL (8 ounces) of fluid for every pound lost during the event. Athletes with persistent weight loss of 2 percent or more should be withheld from activity since unreplaced fluid losses over consecutive days of exercise markedly increase the risk for heat illness.
Appropriate clothing - Children should wear a single layer of absorbent, loose fitting clothing to maximize convective heat loss. Light colors help reduce absorption of solar radiation
Pediatric considerations - Several key anatomic and physiologic differences exist between children and adults. These differences theoretically place children at increased risk for heat-related illness, although direct comparison between adults and children has failed to show differences in heat dispersal or greater vulnerability to heat illness among children.
- Heat production -Children produce more metabolic heat per kilogram of body weight because they have a higher basal metabolic rate than adults.
- Body surface area -Younger children have a higher surface area to mass ratio, resulting in a greater rate of heat absorption in hot environments. However, body composition (especially an increase in body fat) and lack of fitness are likely more important contributors to susceptibility to heat illness in older children and adolescents.
- Blood circulation - Children have a smaller absolute blood volume which limits the potential of blood borne heat transfer from the body core to the body surface where this heat can be dissipated. In addition, children have a lower cardiac output at a given metabolic rate than adults, further limiting head dissipation during exercise
- Sweat production - Children have a lower rate of sweating than adults as a result of a lower sweat rate per gland and begin sweating at a higher body temperature
- Fluid replenishment - Children are more likely to inadequately replenish fluid losses during prolonged exercise and have a higher rise in rectal -Temperature when dehydrated
- Acclimatization - Physiologic changes that result in increased heat tolerance include increased rate of sweating, a lower temperature threshold for sweating, reduced electrolyte losses in sweat, lower heart rate, increased aldosterone production with decreased urinary sodium, and lower core and skin temperatures. Children achieve these adaptations to a hot environment more slowly than adults and typically require 10 to 14 days to achieve adequate acclimatization
