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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
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Korey Stringer1974-2001
Minnesota VikingsOffensive Tackle
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Water Balance: Normal
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Output Intake
MetabFoodFluidsStoolBreathSweatUrine
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Water Output:Normal vs.Exercise
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Normal Exercise
StoolBreathSweatUrine
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Water Intake: Normal vs Exercise
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Normal Exercise
MetabFoodFluids
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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
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Heat and Sweat Production During Exercise
70kg subject, running 1 hr900 Cal expended
mechanical efficiency = 20%180 Cal movement, 720 Cal
heat
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Heat and Sweat Production During Exercise
body specific heat = 0.83Cal/kg/deg
780 Cal -> 12.4 deg C = 22 deg F
death
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Heat and Sweat Production During Exercise
Evaporate 1 liter sweat = 580 Cal heat
720 Cal heat = evaporates 1.24 liters of sweat
Real conditions, approx. 2 liters or 4.4 pounds of water loss
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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
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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.
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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
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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
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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
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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
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Strategies for Avoiding Dehydration
Anticipate high risk conditions High temperature
Uniform/clothing effects
High humidity Indoor sports Uniform/clothing effects
Low air movement Uniform/clothing effects
Bright sun Dark colored clothing
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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
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Calculating hydration needs Hydration Worksheet
Available on course web page
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Example: Joe played tennis for two hours. He drank a 16oz bottle of water
during his workout. Initial weight = 180 lbs Post-exercise weight = 176 lbs
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 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
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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?
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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
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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.”
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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
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Prevalence of Hyponatremia in Elite Athletes
1999 New Zealand Ironman Ultradistance 18% of finishers were hyponatremic
45% female finishers hyponatremic 14% male finishers hyponatremic
Adequate water intake but inadequate electrolyte replacement
2002 Boston Marathon 13% with hyponatremia 0.6% with critical hyponatremia (3 runners)
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HyponatremiaCommon 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)
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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
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Electrolyte replacement after exercise
Electrolyte imbalances can occur with: Low salt intake Repeated days of hard training
4 liters of sweat contains 3-7g sodium 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)
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Sport DrinksWater, 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%
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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
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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)
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Sport Drinks Preferred tastes
Especially kids/teens
Particularly useful for: endurance athletes high heat stress environments heavy sweaters
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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
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Homemade Sport DrinkNancy 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
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Homemade Sport DrinkHilary 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