—Fluid Needs in
Endurance Athletes
—Pre-Test
—It is good to keep
drinking a lot of pure water during a long distance race, such as a marathon. T/F
—An athlete does not
need to drink fluids during intense endurance exercise as long as they drink
enough in the 24 hours before exercise. T/F
—Sodium helps retain
fluid during vigorous endurance exercise.
T/F
—It is ok if I train
in a semi-dehydrated state so that my body gets used to this and I don’t have
to worry about slowing my pace to drink during races. T/F
—I don’t need to drink
during endurance exercise in cold weather.
T/F
—
—
—
—What is Important for
Optimal Performance?
—Water is the most
important performance-enhancing nutrient when exercise and heat stress are
combined
—
—The question is, how much
is really needed before and during exercise
—
—AND how can the addition
of electrolytes in water or sports drinks improve performance?
—
—Intro to the
Importance of Fluid Before and During Exercise
—Excessive
sweating=more serious fluid loss and a reduction in plasma volume
—This leads to
circulation failure within the body and core temperature increases to dangerous
levels.
—
—Intro to the
Importance of Fluid Before and During Exercise
—During near-maximal
exercise in the heat, along with dehydration, relatively less blood diverts to
peripheral areas (skin, muscle) for heat dissipation.
—
—Reduced peripheral
blood flow reflects the body’s attempt to maintain cardiac output despite a
decreased plasma volume caused by sweating.
(McArdle, Katch, & Katch, 2009)
—
—Core
Temperature During Exercise
—Any loss of body
weight > 3% seriously disturbs body temperature regulation and performance (Wein, 2011).
—
—Hyperthermia
–increased core temp. by 5°C or
higher.
—Normal core
temperature during exercise can reach up to 40°C (104°F).
—
—It is dangerous when
core temp. reaches 41°C,
or 106° F
(Vella & Kravitz, 2004).
—
—Core
Temperature During Exercise
—Heat generated by the
active muscles raises core temperature
—
—Signs of heat related
illness can result if one is exercising in the heat, which increase core temp.
even further
—
—Rises in core
temperature even happen while swimming or running outside in cold weather! (McArdle, Katch, & Katch, 2009)
—
—On a hot day,
temperature receptors located in the skin send signals to the hypothalamus to
cool the body by increasing the sweat rate (Vella & Kravitz, 2004).
—
—
—Water
Loss in the Heat: Dehydration
—Dehydration=imbalance
in fluid dynamics when fluid intake does not replenish water loss (McArdle, Katch, & Katch, 2009).
—
—Any amount of
dehydration impairs exercise performance.
—
—A 2% loss of body
weight results in decreased performance and signs of disorientation/confusion (Wein, 2011).
—
—A loss of >3% seriously disturbs temperature regulation!
—
—The risk for
dehydration increases even during intense exercise in the cold, so don’t let the
cold weather fool you!
—
—Water
Loss in the Heat: Dehydration
—Health risks
associated with dehydration include:
—
1)increased
core body temperature
2)increased
cardiovascular strain
3) increased
glycogen use
4) altered metabolic function and possibly altered CNS (Central Nervous System)
function
—
—Water
Loss in the Heat: Dehydration
—The risk of heat
illness greatly increases when a person begins exercising in a dehydrated state
(McArdle, Katch, & Katch, 2009).
—
—Dehydration can slow
the stomach emptying rate and cause stomach cramps and feelings of nausea.
—
—Magnitude
of Fluid Loss
—During high-intensity
exercise in the heat, a person can lose up to 3L of water/hour (McArdle, Katch, & Katch, 2009).
—
—However, sweat rate
can vary depending on:
1)the
environmental temperature
2)humidity
3)
type of clothing worn
4)
intensity
5)
fitness level
6)acclimation
to the environment (Vella & Kravitz, 2004).
—
—Body fluid loss
results in these 5 negative factors on performance (McArdle, Katch, & Katch, 2009):
—Decreased
plasma volume
—Decreased
blood flow to the skin
—Decreased
stroke volume (the amount of blood pumped out each heart beat)
—Increased
heart rate
—General
deterioration in the efficiency of circulation and thermoregulation during
exercise
—
—Water
Replacement: Rehydration
—Properly scheduling
fluid replacement maintains plasma volume, so circulation and sweating progress
optimally (McArdle, Katch, & Katch, 2009)
—
—A well-hydrated
athlete always functions at a higher physiologic and performance level than a
dehydrated athlete.
—
—Achieving hyperhydration BEFORE exercising in
a hot environment protects against heat stress because it:
1) Delays
dehydration
2) Increases
sweating during exercise to help cool the body
3) Diminishes
rise in core temperature
—
—Pre-exercise
hydration
—It is recommended to
consume plenty of fluids in the 24 hours before exercise (Vella & Kravitz, 2004).
—
—In addition, the
athlete should drink 16 oz of fluid about 20 minutes before the start of
exercise (Vella & Kravitz, 2004).
—
—The athlete still
needs to consume fluids during exercise, especially in the heat (McArdle, Katch, & Katch, 2009).
—
—During
Exercise
—Fluid requirements
vary remarkably between athletes and between exercise situations.
—Fluid loss is
effected by (AIS Sports Nutrition):
1) Genetics-some people sweat
more (Myself-this note was not in my presentation, lol, but because I sweat a lot, I noticed I have to drink more to stay hydrated than others it seems.)
2) Body
size-larger
athletes vs. smaller athletes
3) Fitness-more fit people sweat earlier in exercise and in larger volumes
4) Environment-sweat losses are
higher in hot, humid conditions
5)
Exercise Intensity-sweat
losses increase as exercise intensity increases
—
—During
Exercise
— Better to start
drinking early and often during exercise (AIS Sports Nutrition).
—Every 15-20 minutes,
the athlete should consume between 200-300 mL
(about .85-1.25 cups) (AIS Sports Nutrition).
—
—Adequacy
of Rehydration
—Signs of dehydration
include (Vella & Kravitz, 2004) :
- dark urine with
strong odor
- muscle cramps
- decreased sweat
rate
- fatigue (Vella & Kravitz, 2004)
—The athlete drank
enough fluids during and before exercise if they excrete a large volume of
light colored, odorless urine (McArdle, Katch, & Katch, 2009)
—
—Sodium
Facilitates Rehydration
—A moderate amount of
sodium added to a rehydration beverage provides more complete rehydration.
—
—Maintaining a
relatively high plasma concentration of sodium helps (McArdle, Katch, & Katch, 2009):
- Sustain thirst
drive
- Promote
retention of fluids
- More quickly
restore lost plasma volume during rehydration
—
—Sodium
Facilitates Rehydration
—Restoring water and
electrolyte balance in recovery can help by adding moderate to high amounts of
sodium, such as 2300mg, to fluids or food (McArdle, Katch, & Katch, 2009).
—
—Add 1/3 tsp. of table
salt to 1L of water, especially if exercising for a prolonged period of time in
the heat.
—
——
—What About Potassium?
—A tiny amount of
potassium (36-90 mg) enhances water retention.
—
—This amount may
prevent any extra potassium loss that results from sodium retention by kidneys.
—
—However, even at
intense exercise levels, potassium lost in sweat is small and poses no
immediate danger.
—
—Can replace potassium
lost through sweat by increasing the amount of potassium-rich foods (McArdle, Katch, & Katch, 2009).
—
—Sodium
Facilitates Rehydration
—Fluid intake is
increased when beverages are cool, flavored, and contain salt (AIS Sports
Nutrition).
—
—This makes sports
drinks the perfect beverage to drink during exercise! They have the right amount of sodium and
potassium needed (AIS Sports Nutrition).
—
—Pure water absorbed
from the gut rapidly dilutes plasma sodium concentration, so it’s important to
drink fluids with sodium in them to prevent a condition called Hyponatremia (McArdle, Katch, & Katch, 2009).
—
—Hyponatremia: Reduced Sodium Concentration in Body Fluids
—Hyponatremia , or low blood
sodium levels, causes symptoms similar to dehydration and is potentially life
threatening.
—
—The sodium
concentration balance is disturbed which can cause swelling of the brain.
—
—Can often occur in
prolonged endurance events of 2 hours or more when large volumes of low sodium
drinks (like water) are consumed and sweat losses are small (from dehydration).
—
—Taking in
sodium-containing fluids helps match fluid intake to sweat loss since sodium
helps retain fluid and lowers the risk of hyponatremia (AIS Sports Nutrition).
—
—To Reduce the Risk of
Hyponatremia, an Individual Can
Follow These 5 Steps:
1) 2-3 hours before exercise drink 14-22 oz. of fluid
2) Drink 5-10 oz. of fluid about 30 min. before exercise
3) Drink no more than 32 oz. of plain water spread
over 15-minute intervals during or
after exercise
4) Add a small amt. of sodium (about ¼-1/2 tsp. of salt per 32 oz. to fluid. Commercial sports drinks are also effective
in providing water, carbohydrate fuel, and electrolytes.
5) Do not restrict dietary salt.
—
—References
AIS Sports Nutrition. (2009).
Fluid-who needs it?
Australian Sports
Commission. Retrieved from
McArdle, W. D., Katch, F. I., &Katch, V. L.
(2009). Sports and exercise
nutrition. (3rd ed.). Baltimore, MD: Lippincott Williams & Wilkins.
Vella, C., & Kravitz, L. (2004). Staying cool when your body is hot.
Retrieved from
Wein, Debra.
(2011). Nutrition for ultra
endurance events: fluid and
electrolytes
guidelines. Retrieved from
http://www.nsca-lift.org/Perform/article.asp?ArticleID=299
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