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Fluid Balance
Fluid Balance
Performance is optimized when fluid balance is
maintained throughout exercise. (A) Proper hydration has been
shown to decrease the risk of breast, colon and urinary tract
cancer, mitral valve prolapse, salivary gland function, and
urinary stone disease. (C) Dancers and athletes are at an
increased risk for dehydration because of the increased fluid
loss from sweat and respiratory water loss. As a result, much
research has been done to determine the optimal fluid intake
for athletes. The following is an overview of the results.
A majority of fluid lost during exercise is due to
sweating. The amount of sweat production varies from
individual to individual and is affected by environment, type
of exercise, and clothing.(B) The body attempts to replace
these fluids through increased absorption of fluid by the gut,
which is regulated by gastric emptying. It is believed that
maximal fluid absorption occurs when the amount and rate of
fluid intake matches that of gastric emptying.(A) The
American College of Sports Medicine along with the American
Dietetic Association and Dieticians of Canada have reviewed
current research and made recommendations based on these
findings. They recommend drinking 400-600ml (14-20 ounces) of
fluid before exercise and 150-300ml (5-10 ounces) every 15-20
minutes during exercise. After exercise, they recommend
additional fluid intake of up to 150% of the weight lost
during exercise.(A) A majority of the studies reviewed have
been on continuous exercise. Dance is often categorized as
intermittent exercise. A study by Shi and Gisolofi (E)
indicates that the amount of fluid and carbohydrate depletion
during intermittent exercise is at least comparable to that of
continuous exercise because of the high intensity. Shi and
Gisolfi’s study suggests the same fluid replacement for
intermittent and continuous exercise. Overall it has been
shown that the optimal amount of fluid replacement after
exercise is 450ml (15 ounces) of fluid per pound of weight
lost during the exercise bout.(D)
These guidelines are
general however, and adjustments need to be made as the
environment changes. In altitude above 2,500 meters fluid
loss increases due to diuresis, high respiratory water loss,
and decreased appetite.(A) To insure proper kidney function
at high altitudes, fluid intake should be increased to as much
as 3-4L (105-140 ounces) per day.(A)
Heat and humidity can have an enormous effect on the loss of
body fluids and thermoregulation. It is important to properly
hydrate to maintain plasma volume so the body can continue to
cool through sweating at optimal levels during heat and
humidity. It is more difficult for sweat to evaporate when
humidity is high; which decreases the rate of cooling through
sweating. Appropriate clothing helps the body’s
thermoregulation in heat and humidity. Wet clothing allows
sweat to evaporate more readily. Therefore, it is not a good
idea to switch to dry clothing mid workout because the body
will have an increased chance of over heating. Cotton and
linen in light colors are good to wear in the heat and
humidity because they readily absorb moisture and reflect heat
rays. Clothing made of rubber, plastic, and heavy cotton will
heat up the core temperature because it decreases the amount
of heat lost to evaporation.(D)
Exercise in cold weather is also a concern. When it is
cold a majority of the fluid loss during exercise is through
respiratory passages and sweating if very insulated clothing
is worn. To reduce fluid loss due to excessive insulated
clothing layers, light clothing made of synthetics and wool
can be effective in insulating while absorbing and wicking
away moisture as it is produced. Wearing layers is also
effective because they can be taken off as the core
temperature increases. The guidelines for the amount and type
of fluid replacement are the same throughout cold and heat and
should match the amount of fluid lost(A,D).
It is important to not only know how much to drink, but also
to know what to drink. During prolonged exercise
carbohydrates stores can be depleted as well. It has been
shown that the optimal drink should contain a carbohydrate
concentration of 4-8%,(A, D) It is important to note that
drinking caffeinated beverages may be more detrimental than
helpful. Research has shown that small amounts of caffeine can
increase performance(D); however, caffeine is a severe
diuretic and can increase the risk of dehydration. Therefore
it is not recommended to use caffeinated beverages for fluid
replacement(D).
|
Electrolyte |
Function |
Distribution |
| Sodium (Na+) |
Essential
role in fluid and electrolyte balance – accounts for half
the osmolarity of ECF.
Role in generation of
action potentials. |
Represents
about 90% of extracellular cations.
Level in blood controlled
by aldosterone, ANP, and ADH. |
| Potassium(K+) |
Establishes
resting membrane potential and essential in the
repolarisation phase of action potentials in nervous and
muscle tissue.
Aids maintenance of fluid
volume in cells.
Helps regulate pH. |
Most
abundant intracellular action.
Blood serum level
controlled by aldosterone. |
| Calcium(Ca2+) |
Roles in
blood clotting, neurotransmitter release, maintenance of
muscle tone, and excitability of nervous and muscle
tissue. |
Most
abundant mineral in the body due to bone content.
Principally extracellular.
Blood level controlled
chiefly by Parathyroid hormone (PTH). |
| Chloride (Cl-) |
Helps
balance anions in different fluid compartments. |
Most
prevalent extracellular anion.
Diffuses easily between
interstitial space and ICF.
Level controlled
indirectly by aldosterone – due to relationship with
sodium. |
| Bicarbonate
(HCO3-) |
Major
buffer of H+ in plasma.
Helps maintain correct
balance of anions and cations in ECF and ICF. |
Second most
prevalent anions in extracellular fluid.
A small amount found in
intracellular fluid.
Blood level controlled by
kidneys which can both form and excrete bicarbonate. |
Table 1
Five key electrolytes found in the body.
A.
American College of Sports Medicine, American Dietetic
Association, and Dieticians of Canada. Nutrition and athletic
performance: Joint position statement. Medicine and
Science in Sports and Exercise. 200:2130-2138.
Available at http://www.acsm-msse.org
B.
Naghii MR. The significance of water in sport and
weight control. Nutrition and Health. 2000;
14:127-132.
C.
Kleiner SM. Water: an essential but overlooked nutrient.
Journal of the American Dietetic Association. 1999;
99(2):200-206.
D.
McArdle WD. Katch FI. Katch VL. Exercise Physiology:
Energy, nutrition and Human Performance. 4th Ed.
Baltimore, Maryland: Williams and Wilkins; 1996.
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