1. Chapter 9: Water Requirement and Fluid Balance Lecture 6.1

2. Fluid Requirements for Athletes
Athletes must be fully hydrated before they train or compete
Cannot adapt to dehydration
Performance will diminish as the athlete becomes dehydrated during competition

3. Ensuring Adequate Hydration Before Exercise
Adequate hydration can be accomplished in the last few days leading up to competition
Methods to check:
Urine should be pale in color - not reliable as athletes may be taking supplements that contain B vitamins that color urine yellow
Measuring urine osmolality – most reliable
> 900 mOsmol/kg – dehydrated
100 – 300 mOsmol/kg – well hydrated
Measuring body weight after rising before and after voiding – moderately reliable
Sudden drop in body mass any given day can indicate dehydration

4. Ensuring Hydration During Exercise
Thirst
Relying on thirst as a signal to drink is unreliable
Dehydration can occur before the thirst sensation
Goals
Consume enough fluids to keep body weight constant before and after
Athletes need to acclimatize to drinking and regular intervals during exercise
American and Canadian Dietetic Associations recommendations
Before Exercise: 15 minutes before consume ~ 500 ml of fluid
Hot and humid environments: frequent consumption, every 15 to 20 minutes of small volumes of 120 – 180 ml
Exercise lasting between 30 – 60 minutes water is sufficient to maintain hydration

5. Fluid Ingestion During Exercise
Benefits
Supplies exogenous fuel substrate – usually in the form of carbohydrates
Helps maintain plasma volume
Prevents dehydration
Gastric emptying
Availability of fluids ingested is limited by the rate of gastric emptying (intestinal absorption)
The faster gastric emptying = decreased absorption
Addition of carbohydrates to fluids decreases gastric emptying = increased absorption

6. Water Absorption in Small Intestine
Osmosis
Promoted by coupled transport of glucose and sodium

7. Composition of Sports Drinks
Dependent upon relative needs to replace water and provide fuel substrate
Main goal is rehydration i.e. heat
Carbohydrate (i.e. glucose) = g/L
Sodium = mmol/L
Not exceed isotonicity of 290 mOsmol/L
Substrate provision to maintain endurance i.e. cooler environment
Carbohydrate (i.e. glucose polymers) = g/L
Gastric emptying can be minimized by adding glucose polymers
Minimize osmolarity
Keep volume of the fluid in stomach as high as is comfortable for the athlete

8. Composition of Sports Drinks cont.
Commercially available sports drinks
Carbohydrate (i.e. glucose, glucose polymers, and some fructose) = g/L,
Sodium = mmol/L
Ideal fluid Replacement
Tastes good
Does not cause GI discomfort when consumed in large volumes
Promotes rapid gastric emptying and fluid absorption to maintain extracellular fluid volume
Provides energy in the form of carbohydrates for working muscles
Presence of sodium promotes consumption by maintaining thirst

9. Jeukendrup, Gleeson. Sport Nutrition: An Introduction to Energy Production and Performance 2e. Human Kinetics Inc, 2010.

10. Drinking During Training
Often neglected
Practice will accustom athletes to feeling of fluids in the stomach
Opportunity to experiment with different volumes and flavorings
Measure fluid consumption and body mass changes before and after
Provides an idea of athlete’s sweat rate under different environmental conditions
Help determine athlete’s requirement for fluid intakes during competition

11. Rehydration after Exercise
Progressive Dehydration with repeated bouts of exercise
Imparied thermoregulation
Increased cardiovascular strain
Loss of thermoregulatory advantages conferred by heat acclimation and high aerobic fitness
Loss of intracellular and extracellular volume during recovery
Reduced intracellular volume reduces rates of glycogen and protein synthesis
Main factors influencing effectiveness of postexercise rehydration
Volume and composition of fluid consumed

12. Sodium in Sports Drink Major cation in intracellular fluid
Euhydration is achieved when sodium intake is greater than sodium loss (Schirreffs et. al, 1996)
Promotes rapid fluid absorption in small intestine
Allows plasma sodium concentration to remain elevated during rehydration proces
Maintains thirst
Delays stimulation of urine output

13. Potassium in Sports Drink
Enhance replacement of intracellular water
Promote rehydration
Further studies need to be done to confirm hypothesis

14. Optimal Rehydration Beverage
Carbohydrates
Glucose
Glucose polymers
Stimulates fluid absorption in stomach

15. Fluid Consumption Post Exercise
Post Regular Exercise
Any fluid deficit incurred during one exercise can compromise the following exercise session
Ingestion of 150 % of weight loss for every kilogram of weight loss during exercise
Intake of caffeine and alcohol is discouraged
Diuretic actions
Consume solid fluids
Replace sodium and potassium losses

16. Recommendations on Exercise and Fluid Replacement
American College of Sports Medicine Guidelines on Fluid Intake for Exercise (2002)
Adequate fluid replacement maintains hydration and promotes health, safety and optimal performance
Consume a nutritionally balanced diet and drink adequate fluids 24 hours before an event
Consume approximately 6-8 ml of fluid per kg of body weight about 2 hours before exercise

17. Recommendations on Exercise and Fluid Replacement Cont.
During exercise drink early and at regular intervals to prevent excesses of 2 % of body weight
Fluids consumed should be below ambient temperature
Add carbohydrates and sodium when exercising longer than 60 minutes
Exercise bouts > 60 minutes
Add carbohydrates at a rate of g/hour to maintain oxidation of carbohydrate and delay fatigue

18. Recommendations on Exercise and Fluid Replacement Cont.
Addition of sodium during exercise bouts lasting > 60 minutes
500 – 700 mg/L water
Enhance palatability
Promote fluid retention
Prevent hyponatremia (in people who drink excessive amounts of fluid during prolonged exercise)
Rapid recovery from excessive dehydration
1.5 L of fluid for each kilogram of body weight loss
Addition of sodium will assist rapid and complete rehydration by stimulating thirst and fluid retention