During physical activity the body loses water primarily through sweat, even in
cold weather or in water. The body has several mechanisms to protect itself
from the negative effects of dehydration, but thirst does not occur until the
person is already dehydrated!
The American College of Sports Medicine (ACSM) points out that as we get older,
drinking enough water is especially important because with age our body is less
able to regulate our temperature, putting us at increased risk of heat-related
illness. Age also affects our ability to stay hydrated during exercise and our
ability to recognize when we need more water.
A key to successful workouts is keeping well hydrated before, during and after
exercise. The length of your workouts, heat, humidity and the amount you sweat
are all major considerations for keeping your body in proper fluid balance.
Hydration Tips
Water vs. Sport Drinks
For exercise lasting under 45 minutes, water is your best choice. For the
recreational athlete who may exercise 30-40 minutes per session, water is
sufficient for hydration:
Research suggests that for workouts consisting of at least 45 minutes of
continuous exercise or high-intensity workouts of any duration running,
aerobics, biking and intense weight training a sports drink may be beneficial
in delaying muscle fatigue by providing your body with additional energy:
carbohydrates and electrolytes
and enhances performance by fueling the muscles
absorbed more quickly and helps to retain fluids consumed after prolonged
intense exercise
Over-hydration
Drinking too much water can cause problems such as water intoxication and,
although this is not something most of us have to worry about, it does happen
among many exercisers and should be something to be aware of. As the water
content of the blood increases, the salt content is diluted; consequently, the
amount of salt available to body tissues decreases, which can lead to problems
with brain, heart and muscle function.
Symptoms include:
These symptoms can also be attributed to dehydration, so it is important to
know your body and know how much you are drinking.
Remember that you can get your daily water requirements from sources other than
pure water. Your cup of tea counts! Water is the main ingredient in all drinks
carbonated drinks, fruit juices and even coffee. All these contribute to your
daily fluid intake. Fruit and vegetables also have high water content, so
proper nutrition is just as important.
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Eating for Exercise
By Timothy M. Brewi, B.A., D.T.R.
July/August 2002
1. Food Before Exercise
performance suffers with as little as 2 percent loss of body weight due to
dehydration. Drink at least 2 cups of water about 2 hours before exercise.
Drink another 2 cups of water within 20 minutes of exercise.
breakfast). Note that performing aerobic exercise on an empty stomach or when
you're hungry does not increase the amount of fat you burn; rather, it may
cause protein to be sacrificed as fuel.
diet all through the day! (For more information on healthy food choices, click
here.)
from muscles and into the gastrointestinal tract during digestion. The ideal
time for fitness activities is about ...
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o 1/2 hour after a light snack.
o 1 hour after a light meal, heavy snack, or meal replacement drink.
o 2 hours after a regular meal.
o 3 hours after a Thanksgiving-type feast.
does not provide a quick burst of energy, but may cause a rise in insulin
followed by a drop in blood sugar resulting in fatigue.
2. Food During Exercise
water during exercise does not cause upset stomach or cramps; whereas
restricting water during exercise may cause severe dehydration and limit
performance. Be aware that exercise blunts the sense of thirst. "If you wait
until you notice your thirst, you're already becoming dehydrated." So whether
you feel thirsty or not, drink 1/2 cup of water every 10-15 minutes. Ideally,
exercisers should consume adequate fluids during activity so that body weight
remains relatively unchanged before and after exercise.
excess water loss through perspiration. Salt tablets will aggravate dehydration
by drawing fluids into the stomach. Prevent muscle cramps during exercise by
keeping well hydrated.
the most appropriate fluid to drink is cool water. The typical American diet
provides ample electrolytes (sodium, potassium, chloride, and magnesium) to
replace what is lost by sweat. However, persons who exercise strenuously for
more than an hour or exercise in extreme environmental conditions (neither of
which is recommended!) may require a sports beverage containing carbohydrates
and electrolytes.
muscles and into the gastrointestinal tract for digestion.
3. Food After Exercise
during exercise, weigh yourself immediately before and after exercise. The
difference is water loss. Ideally, exercisers should consume adequate fluids
during activity so that body weight remains relatively unchanged before and
after exercise.
but to losing water. Consume 2 cups of water for every pound of body weight
lost during exercise.
excess water loss through perspiration. Salt tablets will aggravate dehydration
by drawing fluids into the stomach. Prevent muscle cramps after exercise
(especially the night after exercise) by keeping well hydrated.
post-exercise snack is light and nutritious, containing mainly carbohydrates
and protein in a ratio of about 2:1. Examples:
o 1 cup of fruit juice with protein powder.
o 1 cup of 1 percent milk, fat-free ice cream, or nonfat yogurt.
o 1 apple with 1 inch cube of low-fat cheese.
o 2 slices of whole wheat bread with 2 thin slices of turkey, optional mustard.
well-balanced diet all through the day!
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Proper Hydration for Exercise - Water or
What and when athletes drink depends upon exercise duration and intensity
By Elizabeth Quinn, About.com Guide
Updated: June 29, 2009
Water is the most essential ingredient to a healthy life. Water has many
important functions in the body including:
Importance of Water During Exercise
Proper hydration is especially important during exercise. Adequate fluid intake
for athletes is essential to comfort, performance and safety. The longer and
more intensely you exercise, the more important it is to drink the right kind
of fluids.
Dehydration
Athletes need to stay hydrated for optimal performance. Studies have found that
a loss of two or more percent of one's body weight due to sweating is linked to
a drop in blood volume. When this occurs, the heart works harder to move blood
through the bloodstream. This can also cause muscle cramps, dizziness and
fatigue and even heat illness including:
Causes of Dehydration
Hyponatremia - Water Intoxication
Although rare, recreational exercisers are also at risk of drinking too much
water and suffering from hyponatremia or water intoxication. Clearly, drinking
the right amount of the right fluids is critical for performance and safety
while exercising.
Adequate Fluid Intake for for Athletes
Because there is wide variability in sweat rates, losses and hydration levels
of individuals, it is nearly impossible to provide specific recommendations or
guidelines about the type or amount of fluids athletes should consume.
Finding the right amount of fluid to drink depends upon a variety of individual
factors including the length and intensity of exercise and other individual
differences. There are, however, two simple methods of estimating adequate
hydration:
1. Monitoring urine volume output and color. A large amount of light colored,
diluted urine probably means you are hydrated; dark colored, concentrated urine
probably means you are dehydrated.
2. Weighing yourself before and after exercise. Any weight lost is likely from
fluid, so try to drink enough to replenish those losses. Any weight gain could
mean you are drinking more than you need.
Things that Affect Fluid Loss in Athletes
therefore increases you fluid needs.
sweating and exercise in the cold can impair you ability to recognize fluid
losses and increase fluid lost through respiration. In both cases it is
important to hydrate.
greater risk for dehydration. Again, weigh yourself before and after exercise
to judge sweat loss.
means you need to drink more and more frequently to avoid dehydration.
To find the correct balance of fluids for exercise, the American College Of
Sports Medicine suggests that "individuals should develop customized fluid
replacement programs that prevent excessive (greater than 2 percent body weight
reductions from baseline body weight) dehydration. The routine measurement of
pre- and post-exercise body weights is useful for determining sweat rates and
customized fluid replacement programs. Consumption of beverages containing
electrolytes and carbohydrates can help sustain fluid-electrolyte balance and
exercise performance."
According to the Institute of Medicine the need for carbohydrate and
electrolytes replacement during exercise depends on exercise intensity,
duration, weather and individual differences in sweat rates. [They write,
"fluid replacement beverages might contain ~20 30 meqILj1 sodium (chloride as
the anion), ~2 5 meqILj1 potassium and ~5 10% carbohydrate."] Sodium and
potassium are to help replace sweat electrolyte losses, and sodium also helps
to stimulate thirst. Carbohydrate provides energy for exercise over 60-90
minutes. This can also be provided through energy gels, bars, and other foods.
What about Sports Drinks?
Sports drinks can be helpful to athletes who are exercising at a high intensity
for 60 minutes or more. Fluids supplying 60 to 100 calories per 8 ounces helps
to supply the needed calories required for continuous performance. It's really
not necessary to replace losses of sodium, potassium and other electrolytes
during exercise since you're unlikely to deplete your body's stores of these
minerals during normal training. If, however, you find yourself exercising in
extreme conditions over 3 or 5 hours (a marathon, Ironman or ultramarathon, for
example) you may likely want to add a complex sports drink with electrolytes.
General Guidelines for Fluid Needs During Exercise
While specific fluid recommendations aren't possible due to individual
variability, most athletes can use the following guidelines as a starting
point, and modify their fluid needs accordingly.
Hydration Before Exercise
Hydration During Exercise
(with no more than 8 percent carbohydrate) every 15 - 30 minutes.
Hydration After Exercise
exercise to replenish glycogen stores.
Source:
Consensus Statement of the 1st International Exercise-Associated Hyponatremia
Consensus Development Conference, Cape Town, South Africa 2005. Clinical
Journal of Sport Medicine. 15(4):208-213, July 2005.
Exercise and Fluid Replacement, ACSM Position Stand, American College Of Sports
Medicine, Medicine and Science In Sports & Exercise, 2007.
Institute of Medicine. Water. In: Dietary Reference Intakes for Water, Sodium,
Cholride, Potassium and Sulfate, Washington, D.C: National Academy Press, pp.
73 185, 2005.