Saturday, July 7, 2012

Drink Up to Maximize Performance

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%


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]


Hydration Status Chart

Phil Loomis
Youth Fitness/Nutrition Specialist

No comments:

Post a Comment