Summer heat on the tennis court in arizona: how it raises body temperature and what can be done about it

SUMMERS IN SADDLEBROOKE:
KEEPING COOL ON THE COURT

DAVID LAMB
KEY POINTS
in contact with the skin; this is called convective heat gain. But the most important way the
Body temperature during a tennis match is a body gains heat during exercise is by its own
balance between how fast the body gains and metabolic activity. Roughly 75-80% of the
loses heat: In addition to air temperature, how energy the body produces by converting fats hard one plays and the dryness of the air are the two most critical factors in the control of triphosphate), the fuel for muscle contraction and other metabolic processes, is “wasted” as  Fatigue (mental and/or physical) and heat heat. During strenuous exercise, the muscles illness can be of concern as body temperature can produce 100 times more heat than they do rises, sweat production increases, and the at rest, and if most of this heat is not rapidly body loses too much water. Early fatigue is removed, the body will cook its own proteins. the most common effect of increased body (Most of us tennis players need not worry about temperature in SaddleBrooke tennis players, cooking our proteins; if we are not breathing hard and are spending lots of time complaining possible. Heat exhaustion, heat stroke and about line calls and joking with our opponents, low blood sodium levels can be deadly but are we are not participating in “strenuous exercise.”) highly unlikely for SaddleBrooke players. BODY HEAT LOSS DURING EXERCISE
The risk of heat illness can be minimized by The heat produced by the exercising muscles is playing early in the day, taking lots of rest rapidly transferred to the cooler blood that breaks, and by appropriate drinking during circulates through the muscles and eventually to the skin. On a cool day, this heat can then be  The vast majority of tennis players in transferred from the warm skin to the cooler air SaddleBrooke will gain nothing more than a by radiation and convection. But neither of these mechanisms can operate on a hot day when the environment is warmer than the skin. Thus, the evaporation of sweat from the skin
is the only way to lose body heat on a hot
before tennis might help you win a few more summer day. (Evaporation of sweat is the
process by which liquid water droplets on the skin are converted into gaseous water vapor. Heat from the skin drives this process—similar HOW THE BODY ATTEMPTS TO
to how heat on a burner can change a pan of MAINTAIN A NORMAL
TEMPERATURE
Evaporation of sweat from the skin is a very BODY HEAT GAIN DURING EXERCISE
effective way to rid the body of excess heat. For At rest, the body attempts to regulate its “core” every quart of sweat that is evaporated, nearly temperature—the temperature of the heart, 600 Calories of heat are removed. Interestingly, lungs, and other internal organs—at about 100 nationally-ranked players in their mid-40s F, but that temperature can rise several degrees generate approximately 580 Calories of heat per during intense exercise. On the tennis court on hour during a 2-hour singles match, and they a summer day, heat from the environment is produce a bit more than a quart of sweat each transferred to the body mostly by radiation from hour to offset that metabolic heat gain.6 Players the sun and from hot surrounding surfaces such in SaddleBrooke, especially doubles player, may as the court itself. Additionally, the body can lose sweat at a rate of 1 quart per hour on a hot absorb heat from warm air molecules that come day, but they would presumably generate less than half the heat that younger singles players beds in the skin to dissipate heat to the How the humidity in the air affects the
evaporation of sweat. The rate of evaporation
radiation). If we sweat profusely during tennis of a given amount of sweat is largely dependent on the amount of water vapor in the air that drinking, we risk losing too much body water, circulates next to the skin. In other words, if the leading to a diminished blood volume. Such a air is dry—as in the Arizona desert, the loss of body water can lead to deterioration in evaporation of sweat can easily keep the body tennis performance and possible heat illness. To summarize, there are two vital reasons for keeping body fluids high: to help cool the body ial S eat Loss during Prolonged
Exercise
body core temperature will be O.K. as long as you continue to produce sweat and don’t athletes, this value can reach 3.5 quarts per exercise too strenuously.) However, when the humidity in the air is high, even if the air temperature is moderate, heat loss by the evaporation of sweat may be unable to keep pace with the heat gain generated by contracting muscles. It is in such conditions of high humidity that severe heat illness is most likely to occur. In SaddleBrooke, the most dangerous time to play tennis is during those days of the summer monsoon when the humidity rises. But even then, the relative humidity typically is less than dehydration if the fluid were not replaced by 50%, compared to 80-90% in other parts of the drinking. But few athletes can force them country. Note that the relative humidity (the amount of water vapor in the air relative to how On average, athletes replace only about half of much the air can hold at a given temperature) is their sweat loss during exercise when they drink usually greater in the early morning; the air can hold more moisture when it warms up, so the relative humidity is lower as the sun rises higher eat Do You Lose Playing
in the sky. This explains the counterintuitive sensation of feeling less sweaty as the air Let’s face it; even a brief observation of doubles spend the bulk of their time on the court THE IMPORTANCE OF MINIMIZING
standing still. Of course, there are except DEHYDRATION AND MAINTAINING
especially among highly competitive players. BLOOD VOLUME
Also, singles players are more likely to expend lots of energy and to lose lo On average, we have only about 5 quarts of are no scientific studies that describe the volume of blood is critical, especially during average sweat rate of club-level senior tennis exercise in the heat. Why? Because we need players in the desert, but one could hazard a to deliver lots of blood to the working mu guess that it is about one pint per hour for mo t 1) provide nutrients, 2) remove lactic acid, players at SaddleBrooke. You can determine your personal sweat rate by recording your nude ammonia and other byproducts of metabolism, and 3) to carry away the excess heat crea d by body weight before and after you play and muscle contraction. Also, adequate blood recording the volume of fluid that you drink during play. Your total sweat loss in quarts is the difference in body weight divided by 2.1 (to Effects of dehydration on the risk of heat
convert pounds to quarts) added to the volume illness. Heat illness begins to be a concern
of beverage consumed. Divide this value by the when dehydration exceeds 3-5% of body mass. duration of your match in hours to find your At this level of dehydration, sweat production, sweat rate in liters per hour. (This calculation assumes that you don’t take any bathroom HEAT ILLNESS3
Sweat Volume (quarts) =
Heat cramps and heat syncope (fainting) are the [weight before – we ht a
fter match (lbs)]/2.1
types of heat illness most likely to affect SaddleBrooke tennis players, especially those Volume of beverage consumed (quarts)
who are less fit or suffer from cardiovascular Sweat Rate (quarts/hour) =
Sweat Volume (quarts) t
/ ime of match (hours)
Heat cramps are muscle spasms, often in the
legs, arms, and abdomen, and are thought to be caused by dehydration and a loss of sodium due alcula
C
tion Example:
to heavy sweating. Heat cramps are more likely in tennis players who are not accustomed to strenuous tennis matches and/or have not become acclimatized to the hot environment. Treatment of heat cramps includes consumption of salty fluids and foods before, during, and after exercise, plus rest and stretching of the affected  Weight loss: 150 – 148 = 2 lbs Heat syncope (fainting) is preceded by
 Total sweat loss during 2-hour match: dizziness and weakness during standing in the 0.95 quarts + 1 quart of water = 1.95 quarts heat, especially when rising quickly from a  Sweat rate: 1.95 quarts/2 hours = 0.975 qts/h seated position. These symptoms are caused by blood collecting in the dilated veins and WHAT DEGREE OF DEHYDRATION IS
capillaries of the skin and legs; as more blood HARMFUL?
collects in these areas, less is available to be Effects of dehydration on athletic
returned to the brain. Fainting is more likely in performance. There are no data on senior
dehydrated, unfit players who have recently tennis players, but studies on fit young adults suggest that a weight loss of more than 2% of body weight can lead to impaired exercise For SaddleBrooke tennis players, dizziness or performance. Thus, a 150-pound tennis player fainting might occur when a player stands up could presumably lose 3 pounds during a match after being seated for a few minutes between without any adverse effects on tennis play. As games late in a match. This is a self-correcting dehydration progressively exceeds 2% loss of ailment because blood more easily returns to the brain when the person collapses. Players who feel dizzy should lie down with their legs elevated, preferably in the shade or in an air- cases it is likely that minor dehydration leads to conditioned room, and drink cool fluids. CAUTION: Be aware that a heart weakened by
affects motivation and coordination. Also, as cardiovascular disease can also cause blood volume is diminished due to dehydration, dizziness. If there is any question about the quality of a player’s cardiovascular health, a adequate amounts of blood to the muscles an physician should be consulted before the athlete Heat exhaustion is similar to heat syncope, i.e.,
the affected person fails to maintain an adequate pumping of blood by the heart, resulting in collapse, but heat exhaustion is WHAT PLAYERS SHOULD DO TO
accompanied by a high core temperature (101oF MINIMIZE THE RISK OF HEAT ILLNESS
to 104oF). It is possible that a SaddleBrooke  Get accustomed to living in the heat and player with a compromised cardiovascular system could suffer heat exhaustion. Treatment  Play early in the day or later in the evening is the same as with heat syncope with the  Wear light-colored clothing and a wide- addition of the application of cold towels to the  Don’t play as hard or as long as you do when cardiovascular disease may be a contributor to any collapse of a player on the tennis court. Finally, if there are any signs of delirium or appears to be heat exhaustion may actually be Players who feel ill during a match should heat stroke; emergency personnel should be conditioned room, lie down, and consider scenario is highly unlikely in SaddleBrooke having a friend or relative drive them home or Heat stroke is a serious illness and is
Adapting to Tennis Play in a Hot
accompanied by confusion, disorientation, Environment to Minimize the Risk of Heat
impaired judgment, and a very high core body temperature (>105oF). Heat stroke can lead to How should beginning players who have just kidney failure, brain and liver damage, and widespread blood clotting. Risk factors for heat environment prepare for regular play in the stroke include poor fitness, lack of adaptation to summer heat? It only requires a week or two of a hot environment, dehydration, and excess heat exposure for 90-120 minutes daily plus a body weight. It is highly improbable that 2 hours gradual increase in duration of tennis play to of typical doubles play in SaddleBrooke would become acclimatized to exercise in the heat. In bring on heat stroke unless a player had been other words, players need both heat exposure working in the heat for several hours before and tennis training. Leisurely walking or cycling playing tennis. Heat stroke is a medical for 90 minutes in the hottest part of the day provides the heat exposure, and playing tennis immediately if heat stroke is suspected. in the cool part of the day or in the evening is the best way to achieve the tennis training. One Exertional hyponatremia is a rare condition
might begin the tennis training part of the characterized by an abnormally low level of regimen with 45 minutes of play for the first 2 sodium (Latin: natrium) in the blood. Although days, 60 minutes for days 3 and 4, 90 minutes not strictly a heat illness, hyponatremia is seen for days 5 and 6, and then 2 hours each day. in endurance athletes in hot environments and in military trainees. The most common cause of Are You Drinking Enough? Too Much?
hyponatremia in athletes is the drinking of For most people who exercise, thirst is sufficient to stimulate only enough drinking to replace beverages that contain little or no sodium. about half of the sweat they lose during Military recruits undergoing basic training in hot, exercise. If you don’t sweat much, this is O.K., humid environments have died after they drank but if you are a heavy sweater, you should more than 20 quarts of water in a few hours in a probably be drinking more than your thirst tells misguided attempt to counteract the heat. This you to. By recording your body weight before and after a match, you can easily tell if you are concentration in the blood, which can lead to drinking too much or too little. If you find that brain swelling, seizures, coma, and death. It is you are losing more than 2% of your body highly unlikely that SaddleBrooke tennis players weight after your usual drinking during tennis, would suffer from hyponatremia unless they you need to drink more; if you are gaining consumed huge volumes of water before they weight, you need to drink less (each quart of water weighs about 2.1 lbs). If you are losing weight even when you are drinking as much as comfortable during exercise, drink more than you normally would during the first few hours of concentration above 10% and are thus more recovery until your weight returns to normal. likely to trigger gastrointestinal discomfort if Is Water O.K., or Do I Need a Sports Drink?
caffeine in energy drinks may have some value With some exceptions, water is a suitable if the drink is ingested 1 hour before exercise beverage for SaddleBrooke tennis players. The Electrolytes in sports drinks: Sodium is the
important one. Sports drinks also contain
sodium and other electrolytes and are designed to replace some of the electrolytes lost in sweat. Sodium is the only electrolyte lost in substantial amounts in sweat (880-1350 mg/quart of sweat), although the amounts lost are highly variable among individuals. The sodium content of the most popular sports drinks is quite low, i.e., 450 mg/quart (166 mg/12 oz) or less. Thus, 12 oz of High-level players in SaddleBrooke may get a a sports drink contains less sodium than the 200 small performance advantage by consuming a mg found in 12 oz of skim milk. In fact, even if sports drink rather than water during their tennis one drank a sufficient volume of a sports drink during exercise to replace all sweat losses, only carbohydrate for energy, and intense play can about half the sodium would be replenished decrease the availability of the carbohydrate fuel (about 900 mg sodium/quart of sweat versus in muscles. Sports drinks like Gatorade® and 450 mg sodium/quart of sports drink). (There is wide agreement among experts that an optimally carbohydrate and small amounts of sodium, formulated sports drink would contain more potassium, and other electrolytes. There is abundant research proving that sports drinks manufacturers don’t put more sodium in sports have beneficial effects on exercise performance drinks: First, more sodium makes the drink taste —typically a 5-7% improvement—for fit athletes too salty. Second,many consumers believe that dietary sodium is harmful). Still, if an athlete is continuous prolonged exercise such as cycling hot and sweaty, the sodium present in sports on a laboratory ergometer for 60 minutes or drinks can enhance the flavor of the beverage longer.5, 8 Also, there is a report of a simulated and may increase fluid consumption. Moreover, tennis match in which carbohydrate ingestion in the sodium does help the body retain the fluid a sports drink improved stroke performance concentration of sodium in sports drinks may be Sports drinks that are effective in improving of some value in minimizing muscle cramps during and after exercise. However, making concentrations ranging from about 5-7%, i.e., 5- sure that the diet has adequate salt is probably 7 grams/100 ml of liquid. Less concentrated more important in preventing cramps. High-level drinks provide too little carbohydrate to be of athletes who regularly suffer severe cramps can significant value, and more concentrated drinks often minimize cramping by adding extra salt tend to empty too slowly from the stomach and (sodium chloride) to their sports drinks. can cause gastrointestinal upset. Accordingly, drinks marketed as low-calorie options, e.g., Should Sports Drinks Include Vitamins?
Powerade Zero®, G2 Low Cal®, Propel®, may No. Although food companies have been trying taste good and stimulate drinking somewhat, but for decades to find it, there is no reliable they will not improve exercise performance scientific evidence that supplementary vitamins Likewise, diluting a sports drink with water will erase any potential benefit of the beverage drinks, fruit juices, and the so-called “energy drinks” such as Red Bull® have a carbohydrate Do Bananas and Potassium/Electrolyte
doubles players and especially singles players Powders Help Avoid Cramps?
may have difficulty reigning in their core body Because only small amounts of potassium are lost in sweat, eating bananas for their potassium SaddleBrooke tennis players should undergo heart disease. Before undertaking strenuous tennis competition, those who are unfit and to the heat for 90 min each day for a week or carbohydrates and can be useful as an energy The goal for maintaining the proper body fluid than 2% of body weight during match play. Because of taste problems in attempts to formulate an effective product, electrolyte poor performance; losing more than 3% can powders and most electrolyte solutions contain lead to heat illness. Heat cramps and fainting SaddleBrooke players, but heat exhaustion or even potentially deadly heat stroke are po Does Caffeine Enhance Exercise
in highly competitive players in the summer Performance and Does It Cause Greater
Dehydration?
weighing oneself before and after tennis. If Caffeine ingestion equivalent to a few cu s of weight loss is greater than 2%, drink more; if coffee or a caffeine tablet an hour before exercise is one of the few dietary supplement regimens that actually works to improve exercise performance, especially in exercise lasting 45 minutes or longer.7 But contrary to conventional For most SaddleBrooke players, water is an wisdom, consuming caffeinated beverages does not lead to more urine formation during exercise Highly competitive players may benefit from that is at least moderately strenuous.13 It is sports drinks. There is no reliable evidence that that caffeine consumption at rest does tend to provide any benefit to tennis players, but (although the main culprit is the volume of caffeine ingested 1 hour before tennis may help coffee, tea, or cola consumed), but during exercise the blood flow to the kidneys is reduced by as much as 80% so that little urine is To minimize the risk of heat illness, players should wear light-colored clothing and a wide-brimmed hat, play less strenuously, take SUMMARY
breaks between games, drink plen of cool If a player’s body temperature gets too high during a tennis match, performance is likely to deteriorate and the risk of heat illness incre ses. Body temperature during tennis play in the playing, move to the shade or air conditioned room, lie down, and consider having a fri the intensity of play and the dryness of the air. doubles players in SaddleBrooke will have no problem keeping their body temperatures in bounds because the intensity of play is low and the air is very dry. But higher-level competitive REFERENCES
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(2001). Physiological responses in tennis and running with similar oxygen uptake. Eur J Appl David Lamb is an emeritus professor of exercise physiology at The Ohio State University and a past president of the American College of Sports Medicine. He was chairman of the Gatorade Sports Science

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