A Review of Fluid and Hydration in Competitive Tennis

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International Journal of Sports Physiology and Performance, 2008, 3, 413-423

2008 Human Kinetics, Inc.

A Review of Fluid and Hydrationin Competitive Tennis

Mark S. Kovacs

Hypohydration is known to impair performance and increases the risk of heat injury.

Therefore, the consumption of appropriate fluid volumes before, during, and aftertennis play is important to maintain physiological homeostasis and performance.

Tennis is a sport that typically has points lasting fewer than ten seconds, with short-

to-moderate rest periods between each work bout. This sequence is repeated over

hours. Most fluid and hydration research has focused on continuous aerobic exercise,

which provides vastly different physiological strain compared with tennis practice

and competition. Consequently, practical recommendations on maintaining hydration

status for aerobic continuous exercise may not be appropriate for tennis athletes.

Tennis players can sweat more than 2.5 Lh1and replace fluids at a slower rate during

competition than in practice. In warm and hot environments, electrolyte-enhanced

fluid should be consumed at greater than >200 mL per changeover and ideally closerto 400 mL per changeover. Tennis scientists, coaches, and players need to individual-

ize hydration protocols to arrive at the optimal hydration strategy.

Keywords:hypohydration, heat stress, dehydration, electrolytes, euhydration

Understanding fluid and hydration status is one aspect in optimizing tennisperformance. Tennis is a sport that typically has points lasting fewer than tenseconds, with short-to-moderate rest periods dispersed between each work bout.1Tennis is often played in warm-hot environments for multiple hours at a time. This

combination of repeated moderate-high intensity activity over a period of hourschallenges the tennis athlete to maintain adequate hydration status both forperformance enhancement as well as the health and safety of the tennis athlete.Exercise-related hypohydration (less than optimal hydration) can reduceperformance and lead to health risks.24Substantial research has been performedon fluid and hydration in aerobic-focused activities;2,58however, tennis playerscompete in an intermittent, highly anaerobic state, indicated by high maximaloxygen consumption (VO2max) and exercising heart rate (HR) that could classifytennis athletes as highly anaerobically trained athletes.9,10This may conceivablyrequire different fluid and hydration requirements than traditional aerobic activities(eg, marathon running). In this review, physiological mechanisms leading toperformance improvement/decrement will be examined in conjunction with

Kovacs is with Player Development, United States Tennis Association, Boca Raton, FL.

BRIEF REVIEW


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practical implications for the player and coach. For a general review of physiologicalmechanisms related to fluid ingestion and electrolytes, see the work of Sawka andCoyle.11

A MEDLINE database search found 14,423 entries using the search wordhydration; however, only 8 entries came up when hydration was followed by theword tennis. When the same search was performed in the SPORTDiscus database,1280 entries were found for hydration,and when tenniswas added, 30 responseswere found. It is clear that the knowledge and resources are available for in-depthhydration studies in tennis, but little research has been performed. However, thelimited research that has been performed provides a clear picture of the fluid andhydration challenges of competitive tennis play. The literature on hydration intennis was reviewed by using MEDLINE and SPORTDiscus database searchesand cross-referencing these articles using the search terms hydration, dehydra-

tion, fluid consumption, hypohydration, and tennis. The purpose of this reviewwas to develop practical recommendations for tennis athletes based upon the evi-dence-based scientific literature from both controlled laboratory studies as well asfield testing in both practice and competitive tennis situations.

Indicators of Fluid Loss

The initial drive to drink for most athletes is instigated by the thirst mechanism;however, thirst is not a good indicator of body water status.12Ad libitum (volun-

tary) drinking typically leads to involuntary hypohydration, as 1.5 L of body watercould be lost before thirst is perceived.13A tennis players environment and sweatrate both are vital factors in contributing to hypohydration; however, a playerson-court fluid intake routine is equally important.

The production of sweat will cause an increase in plasma osmolality thatincreases the drive to drink fluid, owing to the partial plasma retention of Na+.14With the consequent increase in osmotic gradient (fluid moves to equalize soluteconcentrations) supported by an exercise-induced increase in intravascular albu-min and loss of free water,15fluid is mobilized from the intracellular compartmentto maintain the extracelluar fluid volume.14This relocation of fluid from the cells

into the vascular system reduces hypovolemia (an important stimulus for thirstand drinking). Notably, no substantial correlations between postmatch perceivedthirst and sweat rate or body weight percentage change were found in tennis play-ers.16This observation supports the notion that thirst is not a sensitive indicator ofbody water status or a sufficient stimulus to prevent a substantial net body waterloss during exercise in a hot environment.13

A players thermoregulatory capacity can be diminished if adequate fluidintake is not maintained.8,14,17A fully hydrated, average-sized male tennis player(mass ~80 kg) contains approximately 48 L of water.12Tennis practice and matchescan last up to five hours, and players sweat rates are often above 1.5 Lh1. It is

not uncommon for athletes to have sweat rates greater than 2.5 Lh1,12,18whichmay be more than twice that of the gastric emptying rate (1.2 Lhr1) forbeverages.1921Attempting to keep pace with a sweat rate of greater than 1.5 Lhr1is a practical and physiological challenge. During a study of collegiate tennisplayers, the athletes voluntary water consumption was approximate 1.0 Lhr1,16


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Hydration in Competitive Tennis 415

which is close to the typical gastric emptying rate of 1.2 Lhr1. The coupling ofvoluntary consumption and gastric emptying may be the subconscious desire ofthe athletes to avoid gastrointestinal discomfort. Another study examining ad libi-

tum fluid intake during tennis competition found that water intake representedonly 27% of the total fluid loss.22In a more recent study it was found that a sampleof tennis players consumed on average 1.6 Lh1of fluid.18Hopefully these obser-vations are evidence that contemporary hydration education is having some effecton tennis players fluid consumption habits. These consumption rates, even thoughimproved, still could lead to a body fluid deficit of approximately 1 Lh1or greaterin warm-to-hot environments (assuming a sweat rate > 2.5 Lh1). This level ofconsumption equates to a 12% reduction in bodyweight per hour. In a three hourmatch this would lead to hypohydration of 3 to 6%. This magnitude of hydrationdeficit may result in a reduce strength and endurance performance by greater than

30% and severely inhibit temperature regulation, inducing headache, nausea, andother hypohydration-related symptoms.3

Competitive factors, such as a close match or highly energized crowds, caninhibit the drive or motivation to consume fluids to a greater extent than duringpractice.24The volume of fluid consumed was less than required for replacementneeds, which would, if prolonged, lead to hypohydration. This finding has obvi-ous implications for players preparing for and competing in major tournaments.

Hypohydration and Tennis Performance

Exercise performance can be impaired when an individual is hypohydrated by aslittle as 2% of body mass, and a loss of 5% can decrease work capacity by about30%.13,25Given sweat rates of approximately 2.5 Lh1,12some tennis athletes losegreater than 3 Lh1.18Clearly, hypohydration is a constant threat to tennis perfor-mance as well as health and safety. Apart from lowering body fluid levels, a hypo-hydrated athlete has a reduced capacity to dissipate heat as a result of reducedblood flow to the skin, which usually results in an increased core bodytemperature21,26(see Figure 1). The combination of hypohydration and increasedcore temperature can reduce cardiac stroke volume by ~20% during exercise.27

This reduction results in an increased heart rate and requires the athlete to work ata greater intensity, which continues the cycle of rising core temperatures. There isevidence that for every 1% of body mass loss due to hypohydration, heart rateincreases 5 to 8 beatsmin1and core temperature by 0.2 to 0.3C11,21,26(see Figure1). However, when trying to offset hypohydration, for every 1 L of fluid ingested,core temperature reduces by ~0.3C and heart rate by 8 beatsmin1 28(see Figure2). When hypohydrated, it is clear the cardiovascular demands are increased tomaintain performance when fully hydrated.

Even a small reduction in body weight (


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Figure 1Effect of body fluid loss on heart rate and core temperature (informationadapted from [9] [12] [18][19]).

Figure 2Effect of rehydrated fluids on heart rate and core temperature of hypohydratedathlete (information adapted from [12]).


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blood volume, and plasma osmolality,29it is more important to prevent hypohy-dration than trying to rehydrate. This requirement highlights the importance fortennis athletes to have a planned fluid ingestion schedule before and throughout

the tennis match to prevent, rather than react to, fluid imbalances.Apart from the detrimental physiological effects that hypohydration has on

tennis athletes, their cognitive function, decision making, and proper execution ofcomplex skills can also be impaired.30Tennis is a sport that requires fast reactionsand consistent concentration over an extended period of time. Top performancealso requires players to choose and execute high percentage tennis strokes over anextended period. Maintaining high cognitive function may be more of a concernin tennis than in some of the sports that have received the majority of hydrationresearch (eg, cycling and running).

During tennis play, as the magnitude of hypohydration increases, there is an

accompanying increase in core temperature of between 0.10 and 0.40C for eachpercent decrease in body weight14(Figure 1). The aim of training programs, ergo-genic aids, and recovery time is to optimize training time and performance whilelimiting the deleterious effects of increased body temperature and hypohydration.A homeostatic explanation for hypohydration is that thermoregulation is sacri-ficed for cardiovascular stability on the assumption that the hypohydrated athletewill stop playing and move to a cooler environment.14This strategy may be effec-tive for typical individuals; however, it would not be effective in competitive situ-ations, wherein the inherent desire of athletes to deal with adversity and pushthrough physiological barriers is at the core of their success.

Electrolytes and Tennis

Because tennis induces large sweat rates, maintaining electrolyte levels is para-mount in order to limit the negative effects of hypohydration. Under typical physi-ologic conditions for acclimated athletes, potassium (K+) and magnesium (Mg+)concentrations will not be high in sweat.12Contrary to the belief of many coachesand athletes that K+ depletion is a major cause of heat-related muscle cramps,some research supports the relationship between heat-related muscle cramps andextracellular Na+depletionnot K+depletion.12,31Potassium loss in sweat duringexercise is rather small, relative to whole-body K+stores and, consequently, hasminimal physiological or performance consequence.32 Magnesium is anotherelectrolyte that many health professionals recommend, mainly as a deterrent toheat-related muscle cramps. Magnesium sweat loss is also minimal, but reducedlevels of Mg+have been seen in people who suffer from muscle cramping; there-fore, a noncausation link has been made.33However, a lower plasma Mg+ levelduring exercise is more likely due to compartmental fluid redistribution ratherthan to sweat loss.33So supplementing with Mg+or K+may not reduce the likeli-

hood of exercise-induced muscle cramping and is not recommended as a benefi-cial supplement for hydration purposes,33 but in appropriate doses should beharmless.

Although exercise-induced muscle cramping has multiple causes, the repeatedhigh Na+losses (due to sweating), which reduce extracellular Na+content, espe-cially if daily Na+ingestion (through diet) is low, may partly explain why some


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players may cramp in the later rounds of tournaments or toward the end of astrenuous training or match day. Hypohydration and electrolyte loss are not thesole reasons for muscle cramping.31Although exercise-induced muscle cramping

is still not fully understood, it is plausible that psychological stress may contrib-ute, as anecdotal reports indicate a large number of muscle cramping incidents intennis players take place during stressful situations in matches.

The combined effect of large sweat Na+losses with ingestion of a large quan-tity of hypotonic fluid (eg, unsalted water), could significantly dilute plasma Na+(hyponatremia).34 Hyponatremia can have serious consequences, includingfatigue, rises in core temperature, muscle cramping, and reduced performance.35Hyponatremia is not as common in tennis play as in other sports such as marathonrunning. More prominent problems are hypohydration-related fatigue, rises incore temperature, muscle cramping, and reduced performance.35

Gender has a large affect on fluid loss during tennis play. A study evaluatinga broad range of fluid-electrolyte responses in males and females to competitivematch play in a hot environment found that sweat rates of males were consistentlyhigher than those of females, even when the per-hour sweat rates were expressedrelative to estimated body surface area.16Males, as would be expected, had largerfluid losses than the female subjects, but the fluid intake was similar. Males havebeen shown to have greater sweat rates in other, nontennis, exercise research.36,37As a result, fluid consumption guidelines should be different between the genders.Males should attempt to consume greater relative fluid levels during training andcompetition. At the current time, no gender-specific guidelines for tennis areavailable for tennis and research in both the laboratory and field settings isneeded.

Reduced hydration status, susceptibility to low electrolyte levels, and resul-tant performance decrements are more commonly experienced by athletes in thelater stages of tennis tournaments. During a four-day tournament, more than halfthe tennis athletes had less-than-acceptable hydration status as measured by urinespecific gravity (USG) readings of >1.025.16Tennis athletes should have a USGof


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is added to the change in body weight providing the approximate sweat rate andfluid volume change for the athlete. Addition of Na+ concentrations above 20mmolL1 are recommended since urine production is much lower and more

ingested fluid is retained. Hydration protocols should be tested in practice, as afull bladder could hamper concentration during competition. Likewise, a higherosmolality prolongs the thirst and results in greater voluntary hydration.43

Fluid Intake and RequirementsAfter a Match or Practice

Postpractice or match hydration is not only important for immediate recovery, butalso for performance during play in a subsequent session on the same or the fol-

lowing day. Rehydration after exercise has three major purposes: 1) to replacefluid volume to an equal or greater extent than the volume lost while sweating, 2)to ingest liquid and/or solid carbohydrates to aid in glycogen resynthesis,45and 3)to replace electrolytes lost during sweating. Water cannot be the only fluid con-sumed after tennis play because the athlete is typically in a hypohydrated state andan increase in plain water will dilute the lowered electrolyte concentration in theblood and plasma even further. This fall in plasma osmolality and Na+concentra-tion reduces the athletes drive to drink and stimulates urine output, which couldlead to serious consequences (ie, hypohydration and hyponatremia).43,46The addi-tion of Na+ in postexercise beverages has been supported by multiple position

stands.40,47 Sodium supplementation after tennis play should be consumed at arate of ~1.5 gL1.18Although the incidence of hyponatremia is rare in tennis, itdoes occur and the consequences are life threatening. Athletes and coaches shouldbe educated on the need to consume sodium-rich fluid and food postmatch to limitthe possibility of hyponatremia.

Conclusions and Practical Applications

Maintaining appropriate fluid levels before, during, and after tennis practice and

competition is vital for performance, as well as health and safety of the athlete. Asvoluntary fluid ingestion does not provide enough fluid to offset the losses duringplay, tennis players should employ a structured fluid intake program during prac-tice and match sessions. Tennis players can sweat more than 2.5 Lh1, yet it isdifficult for athletes to comfortably drink substantially more than 1.2 Lh1. Thislarge difference makes consuming adequate fluids during tennis play difficult.Athletes consume fluids at approximately 1.2 to 1.6 Lh1, the rate of gastric emp-tying. Tennis players typically consume fewer fluids during matches than practice.Subsequently, the later stages of matches and tournaments are when athletes aremore susceptible to hydration problems. Preventive measures are more effective

than reactive responses to hydration-related performance and safety decrements.Electrolyte balance is an area of interest for tennis, due to the possibility of

large electrolyte losses in sweat. The major electrolyte lost during exercise is Na+,not K+, and this reduction in Na+has been linked to muscle cramping. A typicaltennis player who may sweat more than 10 L of sweat with an average sodiumconcentration (50 mmolL1) will need to replace at least 29 g of sodium chloride


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per day.33 Therefore, Na+ supplementation is recommended in regular diet (eg,sodium-rich foods), or sodium supplementation to fluid ingested before, during,and after tennis play. Tennis athletes should drink more than 200 mL every change-

over in mild temperatures, 27CWBGT). Each athlete should employ a specific hydration routine developedthrough a deliberate and specifically designed program throughout practice andmatch sessions. A CHO and electrolyte drink promotes fluid absorption to agreater degree than water alone. However, water consumption has been shown tobe sufficient for tennis practice and matches lasting less than 90 minutes. Theathlete should consume a CHO-electrolyte drink if matches or practices are longerthan 90 minutes, not only for performance enhancement possibilities, but also toaid in fluid palatability. Future research on tennis hydration should investigate

methods to increase fluid consumption during matches to limit the losses associ-ated with excess sweat rates, without increasing gastrointestinal distress. It mayalso be beneficial to monitor changes of ad libitum fluid consumption rates duringclose matches as opposed to easier matches, and if the hydration rate changesfrom the beginning to the end of matches. One area of research that should beexplored is whether hydration guidelines should be based on gender. Becausemales typically sweat at a higher rate than females, it would be reasonable to sug-gest that they consume larger amounts of fluids than females.

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A Review of Fluid and Hydration in Competitive Tennis