Fluid and Electrolyte
Replacement in Athletes
Dr. David L. Gee
FCSN/PE 446
Required readings:
Williams: Chapter 9 (focus on p340-356)
ADA/ACSM Sports Nutrition Position Paper
Korey Stringer
1974-2001
Minnesota Vikings
Offensive Tackle
Water Balance: Normal
2500
2000
Metab
Food
Fluids
Stool
Breath
Sweat
Urine
1500
1000
500
0
Output
Intake
Water Output:
Normal vs.Exercise
5000
4000
Stool
Breath
Sweat
Urine
3000
2000
1000
0
Normal
Exercise
Water Intake:
Normal vs Exercise
5000
4000
Metab
Food
Fluids
3000
2000
1000
0
Normal
Exercise
In comparison to non-athletes:

Athletes greatly increase their water loss



Large increases in sweat loss
Some decreases in urine loss
Athletes need to greatly increase water intake



Large increases in fluid consumption
Smaller increases in food water and metabolic
water
Athletes often fail to consume adequate amounts
of fluids to maintain optimal hydration status
Heat and Sweat Production
During Exercise
 70kg
subject, running 1 hr
 900 Cal expended
mechanical
 180
heat
efficiency = 20%
Cal movement, 720 Cal
Heat and Sweat Production
During Exercise
body
specific heat =
0.83Cal/kg/deg
780 Cal -> 12.4 deg C =
22 deg F
death
Heat and Sweat Production
During Exercise
 Evaporate
 580
 720
1 liter sweat =
Cal heat
Cal heat = evaporates 1.24
liters of sweat
 Real conditions, approx. 2 liters
or 4.4 pounds of water loss
Effect of Dehydration on
Physiological Function
 2-4%
wt loss - reduced muscular
endurance time
 4-6% wt loss - reduced muscular
strength & endurance, heat cramps
 > 6% wt loss - severe heat cramps,
heat exhaustion, heat stroke, coma,
death
Strategies for Avoiding Dehydration

NATA Position Statement: Fluid
Replacement for Athletes
J. Athletic Training 35:212-224 (2000)
 “Athletes do not voluntarily drink sufficient
water to prevent dehydation during
physical activity.”


Thirst is a delayed response to
dehydration. Thirsty athletes are
already dehydrated.
Sports Nutrition Exam –
Friday, May 5

Format


multiple choice/true false
Short essay (2 – 2.5 pages)



Hypothetical case study
calculate exchange diet
Calculate fluid replacement needs



During exercise, after exercise (rehydration)
Bring calculator and pencils (no cell phone
calculators)
Required readings


ADA/ACSM Position Paper: Sports Nutrition
Williams textbook
Strategies for Avoiding Dehydration
Establish a hydration protocol for
athletes
 Determine individual sweat rate


Changes in body weight (pre-post
weighings)




1 pound = 1 pint additional fluids during exercise
May also account for urine volume
Goal: no weight loss (or < 2% wt loss)
Urine color or urine specific gravity
Strategies for Avoiding Dehydration
Emphasize continual fluid replacement
 Replace fluids as they are lost
 Practice fluid replacement





Gradually increase fluids
Body adapts to increase fluid consumption
Generally, cold fluids more rapidly absorbed
Use individual clear bottles for visual
monitoring
Old Rule of Thumb:


0.5-1 cup per 10-15 min
Individualize is far better
Strategies for Avoiding Dehydration

Understand each athlete’s sport
dynamics
Rest breaks/time outs
 Fluid accessibility


Establish athlete’s acclimatized state

Non-Acclimatized athletes
sweat more
 lose more electrolytes

Strategies for Avoiding
Dehydration


Anticipate high risk conditions
High temperature


High humidity



Indoor sports
Uniform/clothing effects
Low air movement


Uniform/clothing effects
Uniform/clothing effects
Bright sun

Dark colored clothing
Strategies for Avoiding
Dehydration


Hyperhydration
 1 pint, 15-30 minutes prior to exercise
 Limited benefits
Post-exercise rehydration


Ideally completed within 2 hrs
1 pound wt loss = 1.5-2 pts fluid replacement

ACSM/ADA rec: 16-24 oz per pound weight loss


1-1.5 pts per pound weight loss
Replace CHO and electrolytes at same time to speed
rehydration
Calculating hydration needs

Hydration Worksheet

Available on course web page
Example:

Joe played tennis for two hours. He drank a 16oz bottle of
water during his workout.






Water loss = 180-176 = 4 lbs
% body weight loss = 4/180 = 2.2% (dehydrated)
Total sweat loss = 4 pts + 1pt = 5 pts = 80 oz
To stay hydrated within 2% (minimum fluid replacement
rate)




2% x 180 = 3.6 lbs allowed wt loss = 3.6 pts allowable sweat loss
5 pts – 3.6 pts = 1.4 pts = 22.4 oz
22.4 oz/120 min = 0.19 oz/min = 2.8 oz every 15 min
Maximum fluid replacement rate


Initial weight = 180 lbs
Post-exercise weight = 176 lbs
80 oz / 120 min = 0.67 oz/min = 10 oz every 15 min
Recommended fluid replacement (per 15 min)

2.5-10 oz every 15 min
Practice Hydration Problem

LeBron participates in a 90
minute basketball workout
each day.




Pre-workout weight = 240 lbs
Drinks 8 oz during workout
Post-workout weight = 234 lbs
To avoid dehydration and
overhydration, how much fluid
should LeBron consume during
his next workout?
Practice Problem Solution





Weight loss = 240-234 = 6 lbs (pts)
% weight loss = 6/240 = 2.5% (dehydrated)
Total sweat loss = 6pts + 0.5pts = 6.5pts =
104 oz.
Allowable sweat loss = 2% x 240 = 4.8 lbs
Minimum fluid replacement = 6.5 – 4.8 = 1.7
pts = 27.2 oz



27.2 oz/90min = .30oz/min x 15 = 4.5 oz/15min
Maximum fluid replacement = 104oz/90 =
1.15 oz/min x 15 = 17 oz/15min
Rec Intake ~ 4-16 oz/15min
Electrolyte Replacement


Sweat from extracellular fluids
Major electrolytes are Na and Cl


Potassium and calcium are minor components
Sweat is hypo-osmolar (hypotonic) compared
to plasma


Dehydration (with no/limited fluid replacement)
leads to hypernatremia
Williams: “Thus, electrolyte replacement during
exercise is not necessary.”
Electrolyte Strategies for Athletes



Most athletes do NOT need additional
electrolytes
Exception is for very high sweat losses (> 1hr
or heat stress conditions)
Replacement with excessive amounts of pure
water can lead to hyponatremia (water
intoxication)
 Dizziness, fainting, seizures, death

Swelling of the brain

Or asymptomatic
 Symptoms

mimic dehydration
Lack of ability to spit, dry skin, high body temperature
indicates dehydration
Prevalence of Hyponatremia in
Elite Athletes

1999 New Zealand Ironman Ultradistance

18% of finishers were hyponatremic



Adequate water intake


45% female finishers hyponatremic
14% male finishers hyponatremic
but inadequate electrolyte replacement
2002 Boston Marathon


13% with hyponatremia
0.6% with critical hyponatremia (3 runners)
Hyponatremia
Common Causes


excessive fluid consumption
excessive sodium loss in sweat



excessive sweating
“salty sweaters”
Risk Factors





heat stress environment
long duration
slower athletes
non-acclimatized athletes
small body weight (females)
Hyponatremia: Key Points



Hyponatremia unusual compared to
prevalence of dehydration
Know risk factors/situations
Watch out for ‘too much of a good thing’


fluid intake should not exceed losses
Sodium content of sport drinks are useful in
preventing hyponatremia

Sodium concentration in sports drink is more dilute
than in sweat

Palatability issues
Electrolyte replacement after exercise

Electrolyte imbalances can occur with:



4 liters of sweat contains 3-7g sodium



Low salt intake
Repeated days of hard training
Additional losses in urine, stools
Average US intake 6-9g sodium
Increase sodium consumption



salty foods
Salt (2g Na/tsp)
Salt tablets (during acclimatization, 1-2 wks)
Sport Drinks
Water, CHO, electrolytes replacement during exercise
 Provide
water
 Provide dilute carbohydrates
 should
be < 10% (<8% optimal)
 Gatorade: G+S @ 6%
 Powerade: F+GP @ 8%
 Fruit juice: F+S @ 11-15%
 Soft drinks: F @ 11%
Carbohydrates in Sport Drinks

Glucose


rapidly absorbed and utilized by muscle
Fructose

more slowly absorbed and utilized by liver
to replace liver glycogen
Sucrose (G-F)
 Glucose Polymers


lower osmolarity than simple sugars and
may allow for more rapid water absorption
Sport Drinks
 Provide
electrolytes during
exercise
replace Na and Cl lost in sweat
 enhances water uptake


[NaCl] < 1000mg/L
Gatorade: Na,Cl,K,P (460mg/L)
 Powerade: (Na,Cl) (300mg/L)
 Orange Juice: (10 mg Na/L)
 Soft drinks: (40 mg Na/L)

Sport Drinks
 Preferred

tastes
Especially kids/teens
 Particularly
 endurance
useful for:
athletes
 high heat stress environments
 heavy sweaters
Specialty Sports Drinks

Gatorade Endurance Formula



Nearly double sodium content + other electrolytes
May be beneficial for athletes at risk for
hyponatremia
Gatorade Propel


Dilute (3g CHO), “vitamin enhanced”, electrolytes
?
Flavored drinks may be more readily consumed
Homemade Sport Drink
Nancy Clark’s Sport Nutrition Guidebook, 2nd ed.

Yield: 1 quart







4 Tbl sugar
1/4 tsp salt
1/4 c boiling water
1/4 c orange juice (not concentrate) or 2 Tbl lemon
juice
3 3/4 c cold water
dissolve sugar,salt in hot water, add juice &
cold water, chill
50Cal, 12gCHO, 110mgNa, 30mgK per cup
Homemade Sport Drink
Hilary Warner, Nutrition Works!
2/3rd cup lemonade mix
 2.25 quarts water
 ¼ - ½ tsp salt
 8oz contains

65 Cal
 15g CHO (6%)
 65-130 mg Na
