If the past few weeks are any indication we are in store for
scorching conditions the remainder of the summer. And believe it or not the start of the fall sport practice season
in Michigan is right around the corner.
This means many children will soon be out in the extreme heat and humid
conditions. Heat stroke is one of the common causes of exercise-related death
in high school students in the United States. Water is the one nutrient children should consume abundantly
throughout the day. The primary method
the body deals with the heat is by the evaporation of sweat. This evaporative cooling, if excessive
or prolonged, can lead to relatively large losses in body water. Consider that only a 2% loss in body weight of adults (only
about 3 lbs. for a 150 lb. adult) via sweating can lead to increased perceived
exertion and central fatigue, a decrease in sweat rate and cooling, a decrease
in mental performance, a decrease in fine motor skills and precision, and a
decrease in endurance and work capacity,
preventing dehydration is critical for optimal performance and health
during training and competition.
Voluntary dehydration, or dehydration occurring when fluids
are in abundance, is of concern during both intermittent activities and
prolonged activities in the heat for several reasons. First, our thirst mechanisms often underestimate our fluid
needs during exercise and we simply fail to drink enough to replace fluid
losses. Secondly, as water
absorption from the gastrointestinal tract is limited, at the highest sweat
rates and in the most extreme conditions, it is difficult to actually replace
all the fluid that is lost.
Further, electrolyte insufficiencies/imbalances can occur if fluid
replacement practices do not include the addition of sodium and potassium, as
these (and other) electrolytes are lost during the sweating/cooling process.
Interestingly, children may actually experience greater heat
stress when exercising in hot environments than adults do. There are quite a few basic
differences in the chemical makeup of children that make it harder for them to
regulate body temperature than adults.
Children have more body surface area than body weight, so
when the outside temperature is higher than body temperature, children tend to
gain heat faster than adults. Don’t let their smaller size deceive you.
During exercise, children generate up to 20% to 25% more
heat for their body weight than adults. Youngsters’ higher metabolic rates also
contribute to the higher amounts of heat that kids can generate with exercise
and activities.
Movements that are unrefined and inefficient produce more
heat in kids than older athletes who have mastered their techniques and have
more smooth movements.
The amount of blood pumped during exercise is less in
children than adults, so there is less ability to move heat to the skin to give
off heat.
Children have immature sweating mechanisms and also sweat
less than adults, so they have less ability to get rid of heat by evaporation
of sweat. They do not have as many sweat glands, and those sweat glands are not
as efficient as adults. Getting sunburned also decreases the ability of the
sweat glands to perform, so wearing sunscreen is a must (in addition to
protecting their skin from premature aging and skin cancer).
Children adjust to the heat more slowly, so it will take
longer for them to get used to summer temperatures and humidity than adults.
This process of adaptation is called acclimatization. This ability to adapt is
what allows your Baby Bear not to get
too hot or too cold, but to be just right.
Core body temperature in children rises higher and more
quickly with dehydration, so it is even more important to provide drink breaks
for young active children. The thirst drive in a child is not as good as an
adult’s thirst drive, so taking frequent breaks to drink fluids should be
mandatory.
Children who are overweight are even more at risk for heat
illness because extra weight can compound most of these problems. They have to
generate more heat to move the larger body mass, it is harder to give off heat
(so they retain more heat), and they adjust even more slowly to the heat.
As little as a 1% loss in of body mass (1lb. in a 100 lb.
child) during exercise can decrease endurance performance. Therefore, voluntary dehydration is of
particular concern to young athletes.
In order to prevent voluntary dehydration, a few things are
clear. First, young athletes must
drink during athletic events/activities, even when they are not thirsty. One good strategy is to drink every
15-20 minutes during activity. Chilled sports drinks such as Gatorade and
PowerAde (both contain electrolytes) enhance thirst and rate of fluid
absorption. In some studies, the
use of such drinks has completely prevented voluntary dehydration. It must be stated that in most cases
plain water is a better hydrating option than sports drinks. Sports drinks with electrolytes are
recommended in extreme heat and after intense and consistent activity of an
hour or more in duration. Sugar
laden beverages like fruit juice are not good hydrating options!
According the American Dietetic Association young athletes
should consume at least 16 ounces of fluid two hours prior to exercise, and 5
to 10 ounces during exercise, taken every 15 to 20 minutes. Athletes should get
into the habit of weighing themselves before and after exercise to determine
how much water weight they lose through activity—and consume 16 to 24 ounces of
water for every pound lost.
According to a study last year at Indiana State University
80% of NCAA Division 1 and 50% of NFL players were dehydrated as determined by
their preseason physicals. Even at
the highest levels of competition and even though teams have dedicated training
staffs to monitor the athletes dehydration can be a problem. [1]
It’s important for coaches and parents to make their
athletes aware and monitor their own hydration status. How do you know if you’re
properly hydrated? Take a look at
your urine. Generally speaking,
the clearer the urine, and the better hydrated you are. If it is a clear-pale lemonade color,
you are hydrated. If it is darker
lemonade to apple juice color, you are dehydrated. And if it is dark and cloudy, you are severely dehydrated
and should notify medical staff immediately.
Over the next few months many children will be playing
sports and many others will be enjoying the rest of their summer vacation by
swimming and riding bicycles.
Make sure they get the fluids they need to keep them safe and maximize
their potential on the field of play whether that’s on the baseball field,
tennis court, backyard or playground.
Food For Thought:
Many fruits and vegetables are also excellent sources of hydration. In fact, about 80 percent of our water
intake comes from drinking. The other 20 percent comes from food. When I was a kid my dad didn’t lug
a around a water bottle when working the farm. He would simply jump off the tractor and pull a cucumber off
the vine and use it to hydrate.
Don’t neglect the water bottle but you can also add some of
the delicious water-filled foods below to your diet to stay hydrated this
summer.
Cucumber - 96% (water content)
Lettuce - 95%
Celery - 95%
Zucchini- 95%
Tomato - 94%
Spinach - 92%
Watermelon - 92%
Strawberries - 92%
Broccoli - 91%
Grapefruit - 91%
Cantaloupe - 90%
Peach - 88%
100% Orange Juice - 88%
Carrots - 87%
Pineapple - 87%
Raspberries- 87%
Apricot - 86%
Blueberries- 85%
Yogurt - 85%
Apple - 84%
Cherries - 81%
Banana - 74%
Afterthought:
This hydration related information is from natural health
doctor Joseph Mercola. In a recent
article Dr. Mercola highlights the following:
·
Scientific evidence to support the
recommendation to drink 8 8-ounce glasses of water a day is lacking.
·
Some experts have suggested that the ongoing
advice to drink 8 cups of water a day is “thoroughly debunked nonsense” being
spread by bottled water companies in order to churn up more profit.
·
If you drink too much water, the sodium levels
in your blood may drop to dangerously low levels, causing hyponatremia -- a
dangerous condition in which your cells swell with too much water.
·
Many people are dehydrated, however, and could
benefit from drinking more water, and especially from swapping sugar-sweetened
beverages like soda with water.
·
Commercial sports drinks are unnecessary for the
vast majority of people; the best rehydrating agents are plain water and
coconut water, which is naturally rich in electrolytes.
·
Your body will tell you when it's time to
replenish your water supply, because once your body has lost between one to two
percent of its total water, your thirst mechanism lets you know that it's time
to drink some water; if you drink when you’re thirsty and your urine is a pale
yellow or lighter in color, you’re probably staying well hydrated. [2]
[1] http://www.indstate.edu/news/news.php?newsid=1950
Phil Loomis
Youth Fitness/Nutrition Specialist
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