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Hydration, Dehydration and Rehydration

Jani Macari Pallis, 
Ph.D. Photo
Jani Macari Pallis, Ph.D.

With warm weather on its way, I thought a review on hydration, the risks of dehydration and overhydration, and proper rehydration might be useful to all of us as Tennis Server readers. In this column we'll discuss how proper hydration enhances performance on the court, how to stay hydrated, getting rehydrated and concerns for special populations (kids, seniors, wheelchair players).

When I think of hydration issues and tennis, one person's name comes to mind as the expert -- Dr. Michael Bergeron. Dr. Bergeron is an applied physiologist and member of the USTA Sport Science Committee. As an assistant professor of pediatrics at the Medical College of Georgia in Augusta, Georgia and a fellow of the American College of Sports Medicine, his interests include sports performance and nutrition, with an emphasis on the effects of exercise in the heat on fluid and mineral balance. Dr. Bergeron has worked with junior, collegiate, and touring professional tennis players on various aspects of training, match preparation, nutrition, and playing in the heat.

I asked Dr. Bergeron if he would share the latest information on the effects of heat on tennis players.

The Balance Of Body Fluids
Body fluids account for over 70% of an average human's body (and even a larger percentage of an infant's body). Our body fluids are composed of water and substances called electrolytes. Dissolved in water these materials develop tiny electrical charges. Some electrolytes have positive charges (sodium, potassium, magnesium and calcium), others have negative charges (chloride, sulfate and phosphate). These electrical charges stimulate and regulate many of our body functions - like heart rate.

As long as the volume and chemical composition of our body fluids remain in a balanced prescribed range we enjoy health. Conversely when this balance is disturbed, disease can take over.

Our bodies have several mechanisms for eliminating fluids including tears, excretions from the bladder, bowels and through perspiration. Even our lungs expel water and electrolytes along with air as part of the respiratory process. Although the bladder and bowels are responsible for the removal of body waste products, the primary function of perspiration is the regulation of body heat. Our bodies create great quantities of heat from internal chemical reactions.

Perspiration or sweat is part of our body's mechanism of cooling itself. Sweat is primarily water and the electrolytes sodium and chloride. As the sweat is exposed to the air it evaporates, cooling our bodies. Evaporation is our body's major mechanism of dissipating heat when we exercise. This is why on hot, humid days we have more difficulty cooling down. The humid air is already saturated with moisture inhibiting the evaporation process. If our bodies can not cool down, our core body temperatures increase which in turn has a negative effect on different body functions.

Dehydration Affects Performance:
When sweat losses are greater than fluid intake players become dehydrated. Dehydration of 1-2% of your body weight begins to significantly affect some of your body's functions and negatively affects performance. (So if you normally weigh 150 pounds, that calculates to a loss of 1.5-3.0 pounds of fluids. Keep in mind, a cup of water weighs a little over half a pound.) A 3% loss of body weight increases the risk of developing heat cramps, heat exhaustion or heat stroke. These levels of dehydration are common in sports, including a 1-2.5 liter per hour fluid loss in tennis.

"Many athletes start an event already dehydrated", said Dr. Bergeron. When this happens you may experience the effects of dehydration rapidly. A common scenario for dehydration in tennis - you played a match earlier in the day but have not completely rehydrated yourself before playing again that same day.

Our body's systems are very interrelated -- one system affects another. In particular, dehydration affects our cardiovascular system. The heart rate rises 3-5 beats for every 1% of body weight lost! In the heat, heart rate goes up even more. The reduction in body fluids also affects the heart stroke volume (the amount of body fluids we pump through our body). Peformance implications include decreases in muscle strength and endurance, aerobic power, physical work capacity, and increased fatigue. There are also psychological effects such as decreased time to exhaustion, feelings of exertion and impaired mental functions.

Recognizing Hydration Problems In Yourself Or Others:
Players, parents and those supervising athletes should be able to recognize the basic signs and symptoms of dehydration.

Initially you may just feel thirsty. As dehydration progresses you may have a headache, grow irritable, begin to make errors in judgement, feel apathetic, confused, weak, experience decreased performance, dizziness or muscle twinges. In advanced stages you may experience heat sensations on the head and neck, chills, nausea, vomiting and muscle cramps or dyspnea (shortness of breath).

Staying Hydrated
Okay! We all agree. We need to stay hydrated! How do you do that? Dr. Bergeron provides these tips:

  • Drink water, juice, milk, or sports drinks throughout the day. Avoid alcohol or excessive caffeine (coffee, tea, soft drinks).
  • Drink regularly during practice and warm-up.
  • Check your urine: it should be light-colored or clear. If you need frequent bathroom breaks to urinate (every 45 minute) you may be drinking too much.
  • Drink at each changeover. Adults and older adolescents can comfortably drink 48 ounces per hour to prevent significant fluid deficits.
  • Weigh yourself before and after play. Drink about 150% of any remaining fluid deficit to rehydrate yourself.
  • If you are prone to heat-related muscle cramps, add salt to your diet by eating high-salt foods, or adding salt to your food or drinks. This will help your body retain fluid.

Proper Rehydration
As Dr. Bergeron has pointed out, a 1-2.5 liter per hour sweat loss in tennis is common. To become rehydrated, it is not enough to drink plain water. Water does not contain the electrolytes our bodies lose through sweat. The electrolytes sodium and chloride are necessary for proper body function and can prevent heat-induced muscle cramps. Adding potassium to your diet (for example, by eating bananas) will not prevent or resolve heat-related muscle cramps.

There are so many individual differences that it is hard to generalize a rehydration plan that will work for every tennis player. Players sweat at varying rates under the same conditions - in part, due to a difference in individual genetics. Environmental conditions (temperature), length, frequency and intensity of play and how acclimatized you are should all be incorporated into your rehydration plan.

The National Athletic Trainers' Association provides some examples of creating an individual rehydration plan. One key element is understanding your fluid losses. One simple way to calculate this is by weighing yourself before and after a match.

Yes, it is possible to drink too much water. As we've learned, sweat is composed of water and electrolytes. Subsequently, simply drinking water does not replace the electrolytes lost through sweating. Excessive water or low-sodium fluid consumption teamed with heavy sweating rates can lead to "hyponatremia" (low blood sodium), a dangerous and potential threat to all tennis players. This can easily happen in tennis, particularly when playing multiple, long matches on successive days in the heat," said Bergeron.

He reported "a 17-year old, nationally ranked tennis player drank an excessive amount of water, after playing a 4-hour tournament match in the heat. The player had a seizure, slipped into a coma, and spent 2 days in the hospital, before he recovered and his serum electrolytes were stabilized."

Special Populations (Kids, Seniors, Wheelchair Players):
Certain player populations -- kids, seniors and wheelchair tennis players -- may be at greater risk for dehydration.

Adolescents: As we have discussed, the primary purpose of sweating is to regulate body temperature. Hydration is especially important for pre-adolescent children. Generally smaller in stature, children have a larger surface area to body mass ratio than adults and are more vulnerable to heat absorption and increasing body temperature. Their sweat glands are not fully developed and are not as active, so body cooling through sweating is not as effective. Alternative measures to reduce the core body temperature during play in adolescents include: drinking cool liquids, shade, proper clothing (loose, cotton/polyester mix, white clothing) and monitoring the environmental conditions.

Seniors: As we age some of our body functions are often not as effective, including our ability to sweat. Muscle mass and body fluid volume is reduced. As well, seniors may voluntarily choose to restrict fluid consumption due to urinary incontinence concerns. All of these create a higher potential for dehydration.

Wheelchair Players: Based on the neurological level of injury, some wheelchair players (often quad players) lack the ability to sweat. Although tournament directors often try to schedule quad matches early or late in the day or evening, players always have to be prepared to play. Players should drink fluids, wear appropriate clothing, stay in the shade during changeovers, use spray bottles to mist themselves, or keep a container filled with ice and cold towels. One ingenious wheelchair player sewed pockets into a towel attached to his cap. He placed ice in the pockets which lay on the back of his neck. As the ice melted, it trickled down his back to cool him.

"More research needs to be conducted to find other effective ways to keep these players [kids, seniors and wheelchair players] cool," says Bergeron.

A Good Source of Information:
The National Athletic Trainers' Association has a position statement on fluid replacement which can be downloaded from their website. The statement includes a great deal of practical information, excellent overview material on the physiological and performance degradation caused by dehydration and outlines and provides additional references on developing a personal rehydration program.

Ellen Satlof from the NATA tells us that the NATA will be releasing a position statement on heat illness this fall. (I'll include a note in this column when this is available.)

Larry Armstrong's book, Performing in Extreme Environments (Human Kinetics) includes a urine color chart. Based on urine color you are able to determine whether you are well hydrated or not (the darker the urine the less hydrated you are)."

I also like the Sports Science Center at the Gatorade Sports Science Institute web site. They have a lot of practical information on the latest research written by many of the top experts in the field.

High Tech Monitoring Device
I did want to mention one other interesting aspect of hydration research and a little space age technology used in monitoring athletes. How do you measure core body temperatures on the court or field? One way is through a wireless sensor originally developed for NASA to monitor core body temperatures of astronauts.

An encapsulated sensing crystal is ingested - yes - you swallow the sensor like a pill. The ingested sensor monitors the body temperature and transmits the core body temperature data to an external receiver. What happens to the sensor in your body? It passes through and out your body via the bowels. (Yes - we definitely refer to this as a disposable and nonretrievable sensor.) The device is available through HQ, Inc. of Palmetto, Florida.

I hope we've included some useful information for you on hydration, dehydration and rehydration. I want to thank Mike Bergeron again for his knowledge, time and assistance in the preparation of this column.

Until next month --- Jani

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This column is copyrighted by Jani Macari Pallis, Ph.D., all rights reserved.

Dr. Jani Macari Pallis is the founder and CEO of Cislunar Aerospace, Inc., an engineering and research firm in San Francisco. In addition to her engineering practice, she has led two collaborations between NASA and Cislunar, creating educational materials on the aerodynamics of sports for pre-college students and educators. As the head of NASA's "Aerodynamics in Sports" project, she has led a team of researchers investigating the aerodynamics, physics and biomechanics of tennis. The group has conducted high speed video data capture at the US Open and research of ball/court interaction, footwork, serve speeds, trajectories and ball aerodynamics. Pallis received a BS and MS from the Georgia Institute of Technology, an MS in mechanical engineering from the University of California, Berkeley and a Ph.D. in mechanical and aeronautical engineering from the University of California, Davis. She is a member of the Executive Committee of The International Sports Engineering Association.

Questions and comments about these columns can be directed to Jani by using this form.


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