National Athletic Trainers' Association Position Statement: Fluid Replacement for Athletes

National Athletic Trainers’ Association

Position Statement:

Fluid Replacement for Athletes

Douglas J. Casa, PhD, ATC, CSCS (Chair)*;

Lawrence E. Armstrong, PhD, FACSM*; Susan K. Hillman, MS, MA, ATC, PT†;

Scott J. Montain, PhD, FACSM‡; Ralph V. Reiff, MEd, ATC§;

Brent S.E. Rich, MD, ATC储; William O. Roberts, MD, MS, FACSM¶;

Jennifer A. Stone, MS, ATC#

*University of Connecticut, Storrs, CT; †Arizona School of Health Sciences, Phoenix, AZ; ‡US Army Research

Institute of Environmental Medicine, Natick, MA; §St. Vincent Hospital, Indianapolis, IN; 储Arizona State University,

Phoenix, AZ; ¶MinnHealth Family Physicians, White Bear Lake, MN; #US Olympic Training Center, Colorado

Springs, CO

Objective: To present recommendations to optimize the

fluid-replacement practices of athletes.

Background: Dehydration can compromise athletic perfor-

mance and increase the risk of exertional heat injury. Athletes

do not voluntarily drink sufficient water to prevent dehydration

during physical activity. Drinking behavior can be modified by

education, increasing accessibility, and optimizing palatability.

However, excessive overdrinking should be avoided because it

can also compromise physical performance and health. We

provide practical recommendations regarding fluid replace-

ment for athletes.

Recommendations: Educate athletes regarding the risks of

dehydration and overhydration on health and physical perfor-

mance. Work with individual athletes to develop fluid-

replacement practices that optimize hydration status before,

during, and after competition.

Key Words: athletic performance, dehydration, heat illness,

hydration protocol, hydration status, oral rehydration solution,

rehydration

uring exercise, evaporation is usually the primary

mechanism of heat dissipation. The evaporation of

sweat from the skin’s surface assists the body in

regulating core temperature. If the body cannot adequately

evaporate sweat from the skin’s surface, core temperature rises

rapidly. A side effect of sweating is the loss of valuable fluids

from the finite reservoir within the body, the rate being related

to exercise intensity, individual differences, environmental

conditions, acclimatization state, clothing, and baseline hydra-

tion status. Athletes whose sweat loss exceeds fluid intake

become dehydrated during activity. Therefore, a person with a

high sweat rate who undertakes intense exercise in a hot,

humid environment can rapidly become dehydrated. Dehydra-

tion of 1% to 2% of body weight begins to compromise

physiologic function and negatively influence performance.

Dehydration of greater than 3% of body weight further disturbs

physiologic function and increases an athlete’s risk of devel-

oping an exertional heat illness (ie, heat cramps, heat exhaus-

tion, or heat stroke). This level of dehydration is common in

sports; it can be elicited in just an hour of exercise or even

more rapidly if the athlete enters the exercise session dehy-

drated. The onset of significant dehydration is preventable, or

at least modifiable, when hydration protocols are followed to

assure all athletes the most productive and the safest athletic

experience.

The purpose of this position stand is to 1) provide useful

recommendations to optimize fluid replacement for athletes, 2)

emphasize the physiologic, medical, and performance consid-

erations associated with dehydration, and 3) identify factors

that influence optimal rehydration during and after athletic

participation.

RECOMMENDATIONS

The National Athletic Trainers’ Association (NATA) rec-

ommends the following practices regarding fluid replacement

for athletic participation:

1. Establish a hydration protocol for athletes, including a

rehydration strategy that considers the athlete’s sweat rate,

sport dynamics (eg, rest breaks, fluid access), environmen-

tal factors, acclimatization state, exercise duration, exer-

cise intensity, and individual preferences (see Table 1 for

examples of potential outcomes).

Address correspondence to National Athletic Trainers’ Association,

Communications Department, 2952 Stemmons Freeway, Dallas, TX

75247.

212 Volume 35 • Number 2 • June 2000

Journal of Athletic Training 2000;35(2):212–224

www.journalofathletictraining.org

2. A proper hydration protocol considers each sport’s unique

features. If rehydration opportunities are frequent (eg,

baseball, football, track and field), the athlete can consume

smaller volumes at a convenient pace based on sweat rate

and environmental conditions. If rehydration must occur at

specific times (eg, soccer, lacrosse, distance running), the

athlete must consume fluids to maximize hydration within

the sport’s confines and rules.

3. Fluid-replacement beverages should be easily accessible in

individual fluid containers and flavored to the athlete’s

preference. Individual containers permit easier monitoring

of fluid intake. Clear water bottles marked in 100-mL

(3.4-fl oz) increments provide visual reminders to athletes

to drink beyond thirst satiation or the typical few gulps.

Carrying water bottles or other hydration systems, when

practical, during exercise encourages greater fluid volume

ingestion.

4. Athletes should begin all exercise sessions well hydrated.

Hydration status can be approximated by athletes and

athletic trainers in several ways (Table 2). Assuming

proper hydration, pre-exercise body weight should be

relatively consistent across exercise sessions. Determine

the percentage difference between the current body weight

and the hydrated baseline body weight. Remember that

body weight is dynamic. Frequent exercise sessions can

induce nonfluid-related weight loss influenced by timing

of meals and defecation, time of day, and calories ex-

pended in exercise. The simplest method is comparison of

urine color (from a sample in a container) with a urine

color chart (Figure). Measuring urine specific gravity

(USG) with a refractometer (available for less than $150)

is less subjective than comparing urine color and also

simple to use. Urine volume is another indicator of

hydration status but inconvenient to collect and measure.

For color analysis or specific gravity, use midstream urine

collection for consistency and accuracy. Remember that

body weight changes during exercise give the best indica-

tion of hydration status. Because of urine and body weight

dynamics, measure urine before exercise and check body

weight (percentage of body weight change) before, during,

and after exercise sessions to estimate fluid balance.

5. To ensure proper pre-exercise hydration, the athlete should

consume approximately 500 to 600 mL (17 to 20 fl oz) of

water or a sports drink 2 to 3 hours before exercise and 200

to 300 mL (7 to 10 fl oz) of water or a sports drink 10 to

20 minutes before exercise.

6. Fluid replacement should approximate sweat and urine

losses and at least maintain hydration at less than 2% body

weight reduction. This generally requires 200 to 300 mL (7

to 10 fl oz) every 10 to 20 minutes. Specific individual

recommendations are calculated based on sweat rates,

sport dynamics, and individual tolerance. Maintaining

hydration status in athletes with high sweat rates, in sports

with limited fluid access, and during high-intensity exer-

cise can be difficult, and special efforts should be made to

minimize dehydration. Dangerous hyperhydration is also a

risk if athletes drink based on published recommendations

and not according to individual needs.

7. Postexercise hydration should aim to correct any fluid loss

accumulated during the practice or event. Ideally com-

pleted within 2 hours, rehydration should contain water to

restore hydration status, carbohydrates to replenish glyco-

gen stores, and electrolytes to speed rehydration. The

primary goal is the immediate return of physiologic

function (especially if an exercise bout will follow). When

rehydration must be rapid, the athlete should compensate

for obligatory urine losses incurred during the rehydration

process and drink about 25% to 50% more than sweat

losses to assure optimal hydration 4 to 6 hours after the

event.

8. Fluid temperature influences the amount consumed. While

individual differences exist, a cool beverage of 10° to

15°C (50° to 59°F) is recommended.

9. The Wet Bulb Globe Temperature (WBGT) should be

ascertained in hot environments. Very high relative hu-

midity limits evaporative cooling; the air is nearly satu-

rated with water vapor, and evaporation is minimized.

Thus, dehydration associated with high sweat losses can

induce a rapid core temperature increase due to the

inability to dissipate heat. Measuring core temperature

rectally allows the athlete’s thermal status to be accurately

determined. See the NATA position statement on heat

illnesses for expanded information on this topic.

10. In many situations, athletes benefit from including carbo-

hydrates (CHOs) in their rehydration protocols. Consum-

ing CHOs during the pre-exercise hydration session (2 to

3 hours pre-exercise), as in item 5, along with a normal

daily diet increases glycogen stores. If exercise is intense,

then consuming CHOs about 30 minutes pre-exercise may

also be beneficial. Include CHOs in the rehydration

beverage during exercise if the session lasts longer than 45

to 50 minutes or is intense. An ingestion rate of about 1

g/min (0.04 oz/min) maintains optimal carbohydrate me-

tabolism: for example,1Lofa6%CHOdrink per hour of

exercise. CHO concentrations greater than 8% increase the

rate of CHO delivery to the body but compromise the rate

of fluid emptying from the stomach and absorbed from the

intestine. Fruit juices, CHO gels, sodas, and some sports

drinks have CHO concentrations greater than 8% and are

not recommended during an exercise session as the sole

beverage. Athletes should consume CHOs at least 30

minutes before the normal onset of fatigue and earlier if

the environmental conditions are unusually extreme, al-

though this may not apply for very intense short-term

exercise, which may require earlier intake of CHOs. Most

CHO forms (ie, glucose, sucrose, glucose polymers) are

suitable, and the absorption rate is maximized when

multiple forms are consumed simultaneously. Substances

to be limited include fructose (which may cause gastroin-

testinal distress); those to be avoided include caffeine,

alcohol (which may increase urine output and reduce fluid

retention), and carbonated beverages (which may reduce

voluntary fluid intake due to stomach fullness).

11. Those supervising athletes should be able to recognize the

basic signs and symptoms of dehydration: thirst, irritabil-

ity, and general discomfort, followed by headache, weak-

ness, dizziness, cramps, chills, vomiting, nausea, head or

neck heat sensations, and decreased performance. Early

diagnosis of dehydration decreases the occurrence and

severity of heat illness. A conscious, cognizant, dehy-

drated athlete without gastrointestinal distress can aggres-

sively rehydrate orally, while one with mental compromise

from dehydration or gastrointestinal distress should be

transported to a medical facility for intravenous rehydra-

tion. For a complete description of heat illnesses and issues

Journal of Athletic Training 213

related to hyperthermia, see the NATA position statement

on heat illnesses.

12. Inclusion of sodium chloride in fluid-replacement bever-

ages should be considered under the following conditions:

inadequate access to meals or meals not eaten; physical

activity exceeding 4 hours in duration; or during the initial

days of hot weather. Under these conditions, adding

modest amounts of salt (0.3 to 0.7 g/L) can offset salt loss

in sweat and minimize medical events associated with

electrolyte imbalances (eg, muscle cramps, hyponatremia).

Adding a modest amount of salt (0.3 to 0.7 g/L) to all

hydration beverages would be acceptable to stimulate

thirst, increase voluntary fluid intake, and decrease the risk

of hyponatremia and should cause no harm.

13. Calculate each athlete’s sweat rate (sweating rate ⫽

pre-exercise body weight ⫺ postexercise body weight ⫹

fluid intake ⫺ urine volume/exercise time in hours) for a

representative range of environmental conditions, prac-

tices, and competitions (Table 3). This time-consuming

task can be made easier by weighing a large number of

athletes before an intense 1-hour practice session and then

reweighing them at the end of the 1-hour practice. Sweat

rate can now be easily calculated (do not allow rehydration

or urination during this 1 hour when sweat rate is being

determined to make the task even easier). This calculation

is the most fundamental consideration when establishing a

rehydration protocol. Average sweat rates from the scien-

tific literature or other athletes can vary from 0.5 L/h to

more than 2.5 L/h (0.50 to 2.50 kg/h) and are not ideal to

use.

14. Heat acclimatization induces physiologic changes that

may alter individual fluid-replacement considerations.

First, sweat rate generally increases after 10 to 14 days of

heat exposure, requiring a greater fluid intake for a similar

bout of exercise. An athlete’s sweat rate should be reas-

sessed after acclimatization. Second, moving from a cool

environment to a warm environment increases the overall

sweat rate for a bout of exercise. The athlete’s hydration

status must be closely monitored for the first week of

exercise in a warm environment. Third, increased sodium

intake may be warranted during the first 3 to 5 days of heat

exposure, since the increased thermal strain and associated

increased sweat rate increase the sodium lost in sweat.

Adequate sodium intake optimizes fluid palatability and

absorption during the first few days and may decrease

exercise-associated muscle cramping. After 5 to 10 days,

the sodium concentration of sweat decreases, and normal

sodium intake suffices.

15. All sports requiring weight classes (ie, wrestling, judo,

rowing) should mandate a check of hydration status at

weigh-in to ensure that the athlete is not dehydrated. A

USG less than or equal to 1.020 or urine color less than or

equal to 4 should be the upper range of acceptable on

weigh-in. Any procedures used to induce dramatic dehy-

dration (eg, diuretics, rubber suits, exercising in a sauna)

are strictly prohibited.

16. Hyperhydration by ingesting a pre-exercise glycerol and

water beverage has equivocal support from well-controlled

studies. At this time, evidence is insufficient to endorse the

practice of hyperhydration via glycerol. Also, a risk of side

effects such as headaches and gastrointestinal distress

exists when glycerol is consumed.

17. Consider modifications when working with prepubescent

and adolescent athletes who exercise intensely in the heat

and may not fully comprehend the medical and perfor-

mance consequences of dehydration. Focus special atten-

tion on schedules and event modification to minimize

environmental stress and maximize time for fluid replace-

ment. Make available the most palatable beverage possi-

ble. Educate parents and coaches about rehydration and the

signs of dehydration. Monitor and remove a child from

activity promptly if signs or symptoms of dehydration

occur.

18. Large-scale event management (eg, tournaments, camps)

requires advance planning. Ample fluid and cups should

be conveniently available. With successive practice ses-

sions during a day or over multiple days (as in most

summer sport camps), check hydration status daily before

allowing continued participation. Be aware of unhealthy

behaviors, such as eating disorders and dehydration in

weight-class sports. Use extra caution with novice and

unconditioned athletes, and remember, many athletes are

not supervised on a daily basis. If the WBGT dictates,

modify events (change game times or cancel) or change

game dynamics (insert nonroutine water breaks, shorten

game times). Recruit help from fellow athletic trainers in

local schools, student athletic trainers, and athletes from

other sports to ensure that hydration is maintained at all

venues (ie, along a road race course, on different fields

during a tournament). Be sure all assistants can commu-

nicate with the supervising athletic trainer at a central

location. For successive-day events, provide educational

materials on rehydration principles to inform athletes and

parents of this critical component of athletic performance.

19. Implementing a hydration protocol for athletes will only

succeed if athletes, coaches, athletic trainers, and team

physicians realize the importance of maintaining proper

hydration status and the steps required to accomplish this

goal. Here are the most critical components of hydration

education:

● Educate athletes on the effects of dehydration on physical

performance.

● Inform athletes on how to monitor hydration status.

● Convince athletes to participate in their own hydration

protocols based on sweat rate, drinking preferences, and

personal responses to different fluid quantities.

● Encourage coaches to mandate rehydration during practices

and competitions, just as they require other drills and

conditioning activities.

● Have a scale accessible to assist athletes in monitoring

weight before, during, and after activity.

● Provide the optimal oral rehydration solution (water, CHOs,

electrolytes) before, during, and after exercise.

● Implement the hydration protocol during all practices and

games, and adapt it as needed.

● Finally, encourage event scheduling and rule modifications

to minimize the risks associated with exercise in the heat.

BACKGROUND AND LITERATURE REVIEW

Dehydration and Exercise

Physiologic Implications. All physiologic systems in the

human body are influenced by dehydration.

1,2

The degree of

214 Volume 35 • Number 2 • June 2000

dehydration dictates the extent of systemic compromise. Iso-

lating the physiologic changes that contribute to decrements in

performance is difficult, as any change in 1 system (ie,

cardiovascular) influences the performance of other systems

(ie, thermoregulatory, muscular).

The body attempts to balance endogenous heat production

and exogenous heat accumulation by heat dissipation via con-

duction, convection, evaporation, and radiation.

The relative

contribution of each method depends on the ambient temper-

ature, relative humidity, and exercise intensity. As ambient

temperature rises, conduction and convection decrease mark-

edly, and radiation becomes nearly insignificant.

4,5

Heat loss

from evaporation is the predominant heat-dissipating mecha-

nism for the exercising athlete. In warm, humid conditions,

evaporation may account for more than 80% of heat loss. In

hot, dry conditions, evaporation may account for as much as

98% of cooling.

If sufficient fluids are not consumed to offset

the rate of water loss via sweating, progressive dehydration

will occur. The sweating response is critical to body cooling

during exercise in the heat. Therefore, any factor that limits

evaporation (ie, high humidity, dehydration) will have pro-

found effects on physiologic function and athletic perfor-

mance.

Water is the major component of the human body, account-

ing for approximately 73% of lean body mass.

Body water is

distributed within and between cells and in the plasma. At rest,

approximately 30% to 35% of total body mass is intracellular

fluid, 20% to 25% is interstitial fluid, and 5% is plasma.

6,7

Water movement between compartments occurs due to hydro-

static pressure and osmotic-oncotic gradients.

6,7

Because sweat

is hypotonic relative to body water, the elevation of extracel-

lular tonicity results in water movement from intracellular to

extracellular spaces.

6–9

As a consequence, all water compart-

ments contribute to water deficit with dehydration.

6,10

Most of

the resultant water deficits associated with dehydration, how-

ever, come from muscle and skin.

The resulting hypovole-

mic-hyperosmolality condition is thought to precipitate many

of the physiologic consequences associated with dehydration.

A major consequence of dehydration is an increase in core

temperature during physical activity, with core temperature

rising an additional 0.15 to 0.20°C for every 1% of body

weight lost (due to sweating) during the activity.

13,14

The

added thermal strain occurs due to both impaired skin blood

flow and altered sweating responses,

15–21

which is best illus-

trated by the delayed onset of skin vasodilation and sweating

when a dehydrated person begins to exercise.

These thermo-

regulatory changes may negate the physiologic advantages

resulting from increased fitness

21,22

and heat acclimatiza-

tion.

21,23

Additionally, heat tolerance is reduced and exercise

time to exhaustion occurs at lower core temperatures with

hypohydration.

Accompanying the increase in thermal strain is greater

cardiovascular strain, as characterized by decreased stroke

volume, increased heart rate, increased systemic vascular

resistance, and possibly lower cardiac output and mean arterial

pressure.

25–31

Similar to body temperature changes, the mag-

nitude of cardiovascular changes is proportional to the water

Table 1. Sample Hydration Protocol Worksheet

Parameter to Consider

Example A: College

Soccer, Katie (60 kg)*

Example B: High School

Basketball, Mike (80 kg)*

1) WBGT 28.3°C (83°F) 21.1°C (70°F)

2) Sweat rate† 1.7 L/h 1.2 L/h

3) Acclimatized Yes No

4) Length of activity 2 45-minute halves 4 10-minute quarters

5) Intensity Game situation (maximal) Game situation (maximal)

6) Properly prehydrated No (began ⫺2% body weight) Yes

7) Individual container Yes No (just cups)

8) Type of beverage 5% to 7% CHO‡ solution 5% to 7% CHO solution

9) Assess hydration status At halftime (with scale) No

10) Available breaks Halftime Quarters, half, timeouts

11) Amount given Maximal comfortable predetermined amount

given at half time (about 700 to 1000 L)

200 mL at quarter breaks

400 mL at half time

100 mL at 1 timeout/half

12) End hydration status ⫺4.8% body weight Normal hydration

13) Hydrated body weight 60 kg 80 kg

Pre-exercise body weight 58.8 kg 80 kg

Halftime body weight 57.5 No measure

Postexercise body weight 57.1 80.1 kg

*Assumptions: Both are starters and play a full game.

†Sweat rate determined under similar parameters described in example (ie, acclimatization state, WBGT, intensity, etc) under normal game

conditions (ie, no injury timeouts, overtime, etc).

Note: Keep results on record for future reference.

‡CHO, carbohydrate.

Table 2. Indexes of Hydration Status

Condition

% Body Weight

Change* Urine Color USG†

Well hydrated ⫹1to⫺1 1 or 2 ⬍1.010

Minimal dehydration ⫺1to⫺3 3 or 4 1.010–1.020

Significant

dehydration

⫺3to⫺5 5 or 6 1.021–1.030

Serious dehydration ⬎5 ⬎6 ⬎1.030

*% Body weight change ⫽ [(pre-exercise body weight ⫺ postexercise

body weight)/pre-exercise body weight] ⫻ 100.

†USG, urine specific gravity.

See Figure for urine color chart and references. Please note that

obtaining a urine sample may not be possible if the athlete is seriously

dehydrated. These are physiologically independent entities, and the

numbers provided are only general guidelines.

Journal of Athletic Training 215

deficit. For example, heart rate rises an additional 3 to 5 beats

per minute for every 1% of body weight loss.

The stroke-

volume reduction seen with dehydration appears to be due to

reduced central venous pressure, resulting from reduced blood

volume and the additional hyperthermia imposed by dehydra-

tion.

6,14,25,32–34

Both hypovolemia

7,17,35,36

and hypertonicity

7,35,37–39

have

been suggested as mechanisms for the altered thermoregulatory

and cardiovascular responses during dehydration. Manipula-

tion of each factor independently has resulted in decreased

blood flow to the skin and sweating responses.

28,34

Some

authors

17,35

have argued that hypovolemia is primarily respon-

sible for the thermoregulatory changes by reducing cardiac

preload and may alter the feedback to the hypothalamus via the

atrial pressure receptors (baroreceptors). The hypothalamic

thermoregulatory centers may induce a decrease in the blood

volume perfusing the skin in order to reestablish a normal

cardiac preload. Some studies

40,41

have provided support for

this hypothesis, but it is clearly not the only variable influenc-

ing thermoregulation during hypohydration. Two hypotheses

explain the role of hyperosmolality on the thermoregulatory

system. Peripheral regulation may occur via the strong osmotic

pressure influence of the interstitium, limiting the available

fluid sources for the eccrine sweat glands.

However, while

this peripheral influence is likely, it seems more feasible that

central brain regulation plays the largest role.

The neurons

surrounding the thermoregulatory control centers in the hypo-

thalamus are sensitive to osmolality.

43,44

Changes in the

plasma osmolality of the blood perfusing the hypothalamus

affect body water regulation and the desire for fluid consump-

tion.

28,32,45

It is likely that both hypovolemia and hypertonicity

contribute to body fluid regulation.

Potential changes at the level of the muscle tissue include a

possible increased rate of glycogen degradation,

18,46,47

elevated

muscle temperature,

and increased lactate levels.

These

changes may be caused by a decrease in blood perfusion of the

muscle tissue during the recovery between contractions.

The psychological changes associated with exercise in a

dehydrated state should not be overlooked. Dehydration in-

creases the rating of perceived exertion and impairs mental

functioning.

14,51

Dehydration also decreases the motivation to

exercise and decreases the time to exhaustion, even in in-

stances when strength is not compromised.

52–54

These are

important factors when considering the motivation required by

high-level athletes to maintain maximal performance.

Performance Implications. Studies investigating the role of

dehydration on muscle strength have generally shown decre-

ments in performance at 5% or more dehydration.

15,33,55–58

The greater the degree of dehydration, the more negative the

impact on physiologic systems and overall athletic perfor-

mance.

Most studies

30,55,59–62

that address the influence of dehy-

dration on muscle endurance show that dehydration of 3% to

4% elicits a performance decrement, but in 1 study,

this

finding was not supported. Interestingly, hypohydrated wrest-

lers who were working at maximal or near-maximal muscle

activity for more than 30 seconds had a decrease in perfor-

mance.

The environmental conditions may also play an

important role in muscle endurance.

33,48

The research concerning maximal aerobic power and the

physical work capacity for extended exercise is relatively consis-

tent. Maximal aerobic power usually decreases with more than

3% hypohydration.

In the heat, aerobic power decrements are

exaggerated.

Even at 1% to 2% hypohydration in a cool

environment,

64,65

loss of aerobic power is demonstrated. Two

important studies have noted a decrease in physical work capacity

with less than 2% dehydration during intense exercise in the

heat.

66,67

When the percentage of dehydration increased, physical

work capacity decreased by as much as 35% to 48%,

and

physical work capacity often decreased even when maximal

aerobic power did not change.

46,64,65

Hypohydration of 2.5% of

body weight results in significant performance decrements while

exercising in the heat, regardless of fitness or heat acclimation

status, although enhanced fitness and acclimation can lessen the

effects of dehydration.

Partial rehydration will enhance perfor-

mance during an ensuing exercise session in the heat, which is

important when faced with the reality of sports situations.

49,70

The

performance decrements noted with low to moderate levels of

hypohydration may be due to an increased perception of fatigue.

Rehydration and Exercise

Factors Influencing Rehydration. The degree of environ-

mental stress is determined by temperature, humidity, wind

speed, and radiant energy load, which induce physiologic

changes that affect the rehydration process.

71–73

Fluid intake

Table 3. Sample Sweat Rate Calculation*

ABCDE F G HIJ

Name Date

Body Weight

⌬BW (C-D) Drink Volume Urine Volume†

Sweat Loss

(E⫹F⫺G)

Exercise

Time

Sweat Rate

(H/I)

Before

Exercise

After

Exercise

kg kg g mL mL mL min mL/min

(lb/2.2) (lb/2.2) (kg ⫻ 1000) (oz ⫻ 30) (oz ⫻ 30) (oz ⫻ 30) h mL/h

kg kg g mL mL mL min mL/min

(lb/2.2) (lb/2.2) (kg ⫻ 1000) (oz ⫻ 30) (oz ⫻ 30) (oz ⫻ 30) h mL/h

kg kg g mL mL mL min mL/min

(lb/2.2) (lb/2.2) (kg ⫻ 1000) (oz ⫻ 30) (oz ⫻ 30) (oz ⫻ 30) h mL/h

kg kg g mL mL mL min mL/min

(lb/2.2) (lb/2.2) (kg ⫻ 1000) (oz ⫻ 30) (oz ⫻ 30) (oz ⫻ 30) h mL/h

Kelly K.‡ 9/15 61.7 kg 60.3 kg 1400 g 420 mL 90 mL 1730 mL 90 min 19 mL/min

(lb/2.2) (lb/2.2) (kg ⫻ 1000) (oz ⫻ 30) (oz ⫻ 30) (oz ⫻ 30) 1.5 h 1153 mL/h

*Reprinted with permission from Murray R. Determining sweat rate. Sports Sci Exch. 1996;9(Suppl 63).

†Weight of urine should be subtracted if urine was excreted prior to postexercise body weight.

‡In the example, Kelly K. should drink about 1 L (32 oz) of fluid during each hour of activity to remain well hydrated.

216 Volume 35 • Number 2 • June 2000

increases substantially when ambient temperature rises above

25°C; the rehydration stimulus can also be psychological.

74,75

An athlete exercising in the heat will voluntarily ingest more

fluid if it is chilled.

76–78

Individual differences in learned

behavior also play a role in the rehydration process.

athlete who knows that rehydrating enhances subsequent per-

formance is more apt to consume fluid before significant

dehydration occurs, so appropriate education of athletes is

essential.

The physical characteristics of the rehydration beverage can

dramatically influence fluid replacement.

71,75,78

Salinity, color,

sweetness, temperature, flavor, carbonation, and viscosity all

affect how much an athlete drinks.

16,75,79–85

Since most fluid

consumed by athletes is with meals, the presence of ample

fluid during meals and adequate amount of time to eat are

critical to rehydration.

When access to meals is limited, a

CHO-electrolyte beverage will help maintain CHO and elec-

trolyte intake along with hydration status.

Other factors that contribute to fluid replacement include the

individual’s mood (calmness is associated with enhanced

rehydration) and the degree of concentration required by the

task.

For example, industrial laborers need frequent breaks to

rehydrate because they must remain focused on a specific task.

This need for concentration may explain why many elite

mountain bikers use a convenient back-mounted hydration

system instead of the typical rack-mounted water bottle. The

back-mounted water reservoir may allow the cyclist to enhance

rehydration while remaining focused on terrain, speed, gears,

braking, and exertion.

Accessibility to a fluid and ease of

drinking may explain why athletes consume more fluid while

cycling compared with running in a simulated duathlon.

Hydration before Exercise. An athlete should begin exer-

cising well hydrated. Many athletes who perform repeated

bouts of exercise on the same day or on consecutive days can

become chronically dehydrated. When a hypohydrated athlete

begins to exercise, physiologic mechanisms are compro-

mised,

64,89,90

and the extent of the dysfunction is related to the

degree of thermal stress experienced by the athlete.

Athletes

may require substantial assistance in obtaining fluids as evi-

denced by the phenomena of voluntary (when individuals drink

insufficient quantities to replace fluid losses) and involuntary

dehydration.

Athletes should ingest 500 mL of fluid 2 hours before the

event (which allows ample time to urinate excess fluid) to

ensure proper hydration and physiologic function at the onset

of exercise.

79,93,94

Mandatory pre-exercise hydration is physi

ologically advantageous and more effective than hydration

dictated by often insufficient personal preference.

95,96

Ingest

ing a nutritionally balanced diet and fluids during the 24 hours

before an exercise session is also crucial. Increasing CHO

intake before endurance activity may be beneficial for perfor-

mance

97–99

and may even enhance performance for activities

as short as 10 minutes,

100

but it may have a limited effect on

resistance exercise.

101

There has been recent interest in potential benefits of

purposefully overhydrating before exercise to postpone the

onset of water deficit.

33,102–108

While an enhanced hydration

state is often reported with glycerol use, this does not always

translate into a performance improvement.

109

A recent study

110

found increased exercise time and plasma volume during

exercise to exhaustion in the heat when subjects were rehy-

drated with water and glycerol before exercise as compared

with rehydration using an equal volume of water without

glycerol. However, another study

111

found no benefits of

glycerol ingestion when the ensuing exercise took place in a

thermoneutral environment. Hyperhydrating before exercise,

even without glycerol, may enhance thermoregulatory func-

tion

112

and limit the performance decrements normally noted

with dehydration

109

while exercising in the heat (WBGT ⬎

25°C). A key point is that the benefits associated with glycerol

use seem to be negated when proper hydration status is

maintained during exercise.

113

However, many athletes are

unable to maintain hydration, so hyperhydration may be

beneficial in extreme conditions when fluid intake cannot

match sweat loss.

Rehydration during Exercise. Proper hydration during

exercise will influence cardiovascular function, thermoregula-

tory function, muscle functioning, fluid volume status, and

exercise performance. This topic has been extensively re-

viewed through the years, but some recent compilations are

especially notable.* Proper hydration during exercise enhances

heat dissipation (increased skin blood flow and sweating rate),

limits plasma hypertonicity, and helps sustain cardiac out-

put.

79,119,120

The enhanced evaporative cooling that can occur

(due to increased skin blood flow and maintained perfusion of

working muscles) is the result of sustained cardiac filling

pressure.

Rehydration during exercise conserves the centrally

circulating fluid volume and allows maximal physiologic

responses to intense exercise in the heat.

Two important purposes of rehydration are to decrease the

rate of hyperthermia and to maintain athletic perfor-

mance.

35,121

A classic study

122

showed that changes in rectal

temperature during exercise depended on the degree of fluid

intake. When water intake equaled sweat loss, rise in core

temperature was slowest when compared with ad libidum

water and no-water groups. This benefit of rehydration on

thermoregulatory function is likely due to increased blood

volume,

123

reduced hyperosmolality,

124

reduced cellular dehy

dration,

125

and improved maintenance of extravascular fluid

volume.

126

Some studies

127,128

have not shown a physiologic

or performance benefit when rehydration occurred during a

1-hour intense exercise session in mild environmental condi-

tions. The likely reason for a lack of benefit in these studies

was the fact that the exercise session did not elicit enough

sweat loss to cross the physiologic threshold of percentage of

body weight loss (eg, ⫺2%) that would negatively influence

performance and physiologic function. For example, in 1 of the

studies,

127

the subjects had only lost 1.5% of body weight at

the completion of the exercise session.

Athletes generally do not rehydrate to pre-exercise levels

during exercise due to personal choice,

75,129

fluid availability,

129

the circumstances of competition,

or a combination of these

factors. Athletes should aim to drink quantities equal to sweat and

urine losses, and while they rarely meet this goal, athletes can

readily handle these large volumes (⬎1 L/h).

130–132

Additionally,

athletes may not need to exactly match fluid intake with sweat loss

to maintain water balance given the small contribution of water

from metabolic processes.

133

Appealing to individual taste preferences may encourage

athletes to drink more fluids. In addition, including CHOs

and electrolytes (especially sodium and potassium) in the

rehydration drink can maintain blood glucose, CHO oxida-

tion, and electrolyte balance and can maintain performance

*References 6, 27, 71, 76, 79, 107, 108, 114–118.

Journal of Athletic Training 217

if the exercise session exceeds about 50 minutes in dura-

tion.

79,118,130,134–152

Also, recent evidence

153,154

indicates

that athletes performing extremely intense intermittent ac-

tivity with total exercise times of less than 50 minutes may

benefit from ingestion of CHOs in the rehydration beverage.

Rates of gastric emptying and intestinal absorption should

also be considered.

118,155–160

Fluid volume,

161

fluid calorie

content, fluid osmolality, exercise intensity,

162

environmental

stress,

162

and fluid temperature

107

are some of the most

important factors

in determining the rates of gastric emptying

and small intestine absorption (the small intestine is the

primary site of fluid absorption). The single most important

variable may be the volume of fluid in the stomach.

163,164

Maintaining 400 to 600 mL of fluid in the stomach (or the

maximum tolerated) will optimize gastric emptying.

If CHOs

are included in the fluid, the concentration should be 4% to 8%.

Concentrations higher than 8% slow the rate of fluid absorp-

tion.

165,166

Intense exercise (⬎80% of VO

max) may also

decrease the rate of gastric emptying.

155

Frequent ingestion

(every 15 to 20 minutes) of a moderate fluid volume (200 mL)

may be ideal, but it is not feasible in sports with extended

periods between breaks. The rates of gastric emptying and

intestinal absorption likely influence the speed of movement of

the ingested fluids into the plasma volume.

167

Since the gastric

emptying and intestinal absorption rates are not compromised

with the addition of a 6% carbohydrate solution as compared

with water, fluid replacement and energy replenishment are

equally achievable.

116,167–171

The rate of gastric emptying is

slowed

163,172

by significant dehydration (⬎4%), which com-

plicates rehydration and may increase gastrointestinal discom-

fort.

163,172

Regardless, rehydration will still benefit the ath-

lete’s hydration status.

172

Rehydration during exercise is also influenced by the state of

acclimatization of the athlete. Heat acclimatization is achieved

after 5 to 10 days of training in a hot environment and will

increase sweat rate, decrease electrolyte losses in the sweat,

and allow athletes to better tolerate exercise in the heat.

173,174

Heat acclimatization modestly increases rehydration needs due

to greater sweating. Fortunately, an athlete who is heat accli-

matized has fewer deficits associated with dehydration

175

and

tends to be a “better” voluntary drinker (ingests fluid earlier

and more often).

1,34

An athlete who exercises for more than 4 hours and hydrates

excessively (well beyond sweat loss) only with water or

low-solute beverages may be susceptible to a relatively rare

condition known as symptomatic hyponatremia (also known as

water intoxication).

76,108,176,177

Ultimately, the body cannot

excrete the consumed fluid rapidly enough to prevent intracel-

lular swelling, which is sufficient to produce neuropsycholog-

ical manifestations. Patients present with serum sodium levels

below 130 to 135 mmol/L, and the sequelae of hyponatremia

can result in death if not treated.

177

The condition can most

likely be avoided if sodium is consumed with the rehydration

beverage and if fluid intake does not exceed sweat

losses.

76,79,108

Every athlete will benefit from attempting to match intake

with sweating rate and urine losses. Individual differences exist

for gastric emptying and availability of fluids during particular

sports. Rehydration procedures should be tested in practice and

individually modified to maximize performance in competi-

tion.

97,108,116,156

Rehydration after Exercise. Replenishing fluid vol-

ume

178,179

and glycogen stores is critical in the recovery of

many body processes, including the cardiovascular, thermo-

regulatory, and metabolic activities.

71,97,178,180,181

Based on volume and osmolality, the best fluid to drink after

exercise to replace the fluids that are lost via sweating may not

be water.

71,182–184

Consuming water alone decreases osmolal-

ity, which limits the drive to drink and slightly increases urine

output. Including sodium in the rehydration beverage (or diet)

allows fluid volume to be better conserved and increases the

drive to drink.

71,125,178,184–186

Including CHOs in the rehydra-

tion solution may improve the rate of intestinal absorption

of sodium and water

118,178

and replenishes glycogen

stores.

118,187,188

Replenishing glycogen stores can enhance

performance in subsequent exercise sessions

189,190

and may

enhance immune function.

191

While a normal diet commonly

restores proper electrolyte concentrations,

192

many athletes are

forced to rehydrate between exercise sessions in the absence of

meals.

178

In addition, some athletes’ meals are eaten as long as

6 hours after an exercise session, which may compromise

electrolyte availability during rehydration after intense exercise

in hot conditions.

While replenishing fluid to equal sweating losses is often

recommended, this formula does not replace urine losses.

Ingestion equal to 150% of weight loss resulted in optimal

rehydration 6 hours after exercise.

185

Assessment of Hydration Status. Body weight changes,

urine color, subjective feelings, and thirst, among other indi-

cators, offer cues to the need for rehydration.

193

When prepar-

ing for an event, an athlete should know the sweat rate, assess

current hydration status, and develop a rehydration plan.

Determinations of sweat rate can be made.

18,134

Hydration

status can be assessed by measuring body weight before and

after exercise sessions; monitoring urine color, USG, or urine

volume; or using a combination of these factors.

194,195

A urine

color chart is included in this manuscript (Figure).

196

The

general indexes of hydration status are provided in Table 3. A

refractometer offers a precise reading of USG and can be used

as a general indicator of hydration state. A reading of less than

1.010 reflects a well-hydrated condition, while a reading of

more than 1.020 reflects dehydration.

134

Urine osmolality and

urine conductivity may also be useful tools in assessing

hydration status.

197

The hydration plan should take into account the length of the

event, the individual’s sweat rate, exercise intensity, the

temperature and humidity, and the availability of fluids (is

fluid constantly available, as in cycling, or is it consumed in a

large bolus during a break?). Habits of the coach or athlete, or

both, may need to be altered in order to maximize the hydration

process. Any plan for rehydrating during competition should

be instituted and perfected during practice sessions; it should

also be individually implemented, given the large variation

among people in what constitutes a “comfortable” amount of

rehydration.

198,199

A sample hydration protocol for preparing

an elite athlete for an event has been documented.

200

Composition of Rehydration Fluid. During exercise, the

body uses 30 to 60 g of CHOs per hour that need to be replaced

to maintain CHO oxidation and delay the onset of glycogen

depletion fatigue.

201–205

Thus, including 60 g of CHOs in 1 L

of fluid will not hinder fluid absorption and provides an

adequate supply of CHOs during or while recovering from an

exercise bout. The CHO concentration in the ideal fluid-

replacement solution should be in the range of to 6% to 8%

(g/100 mL).

117

The simple sugars, glucose or sucrose in simple

or polymer form, are the best additives to the replacement

218 Volume 35 • Number 2 • June 2000

fluid. Absorption is maximized if multiple forms of CHO are

ingested simultaneously (ie, fluid is absorbed more quickly

from the intestine if both glucose and fructose are present than

if only glucose is present).

107,116,206

The amount of fructose in

the beverage should be limited to about 2% to 3% (2 to 3 g/100

mL of the beverage), since larger quantities may play a role in

decreasing rates of absorption and oxidation and causing

gastrointestinal distress.

107,207

Ultimately, CHO composition

depends on the relative need to replace fluids or CHOs. During

events, when a high rate of fluid intake is necessary to sustain

hydration, the CHO composition should be kept low (eg, ⬍7%)

to optimize gastric emptying and fluid absorption. During

conditions when high rates of fluid replacement are not as

necessary (ie, during recovery from an exercise session, mild

environmental conditions, etc), the carbohydrate concentration

can be increased to optimize CHO delivery with minimal risk

of jeopardizing the hydration status.

Small quantities of sodium may enhance palatability and

retention, stimulate thirst, and prevent hyponatremia in a

susceptible individual.* Sodium concentration should be

approximately 0.3 to 0.7 g/L.

72,80,108,157,208

Other valuable

sources of practical information concerning the composition

of rehydration beverages and rehydration in general are

available.†

Recognizing Dehydration in Athletes. The early signs and

symptoms of dehydration include thirst and general discomfort

and complaints. These are followed by flushed skin, weariness,

cramps, and apathy. At greater water deficits, dizziness,

headache, vomiting, nausea, heat sensations on the head or

neck, chills, decreased performance, and dyspnea may be

present.

5,79,211,212

The degree of dehydration, the mental status,

and the general medical condition of the athlete will dictate the

mode, amount, type, and rate of rehydration. Identifying the

early signs of dehydration can limit the onset or degree of an

exertional heat illnesses.

5,79,211,212

A comprehensive review of

the prevention, identification, and treatment of the exertional

heat illness can be found in the position stands by the NATA

and the American College of Sports Medicine.

211,213

Event Management. Some events are conducted under

environmental conditions that are extreme and force the athlete

to reduce intensity or risk a heat illness. These hazardous heat

stresses can be avoided by scheduling athletic events during the

coolest part of the day or a cooler time of the year.

211,214

The

reality of sport administration is that many events take place

regardless of the environmental conditions. Individuals super-

vising an event in a hot humid environment must ensure that

athletes have ample access to fluids, are encouraged to match

fluid intakes with sweat losses, and are monitored for dehy-

dration and exertional heat illness. Whenever possible, mini-

mize the exercise intensity of athletes in the extreme heat, since

this is the largest contributor to dehydration and heat illness.

When successive exercise sessions occur on the same day or on

ensuing days, hydration status, sleep, meals, and other factors

that maximize performance and enhance safety should be

maintained. Given the variety of events an athletic trainer may

supervise, we cannot formulate an event management recom-

mendation for all sports. However, the general concepts are

interchangeable across sports and venues. For example, game

modifications such as decreasing the length of play or inserting

nontraditional water breaks (especially in youth sports and

practice situations) will reduce the rate of heat illness. Closely

monitoring environmental conditions via the WBGT or the

heat index will allow an informed approach to hydration and

sweat modification. Athletes who are educated on how to

prevent and recognize dehydration are empowered to partici-

pate actively in implementing their own hydration protocols,

thereby enhancing both performance and safety. The person

responsible for the medical supervision of an event should have

a detailed plan to address facilities, equipment, supplies,

staffing, communication systems, education, and implementa-

tion of event policy.

213,215–220

ACKNOWLEDGMENTS

This position statement was reviewed for the NATA by the Pro-

nouncements Committee and reviewers Kristine L. Clark, PhD, RD,

David Lamb, PhD, and Jack Ransone, PhD, ATC.

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