Transcript Fluid Retention/Regulation

Fluid Retention/Regulation
Pages
275-279
Water Loss in Heat:Dehydration
• Dehydration is an imbalance in fluid dynamics
when fluid intake does not replenish water loss
– No matter what type of exercise there is always water
lost
– Even non-exercise induced water loss also occurs, such
as when “power” athletes attempt to “make weight”
through rapid weight loss induced by common
dehydration techniques, such as a sauna or steam room.
– The risk of heat illness increases when a person begins
exercising in a dehydrated state.
Magnitude of Fluid Loss
• In an acclimatized person, water loss by sweating
averages nearly 12 liters (26 lbs) on a daily basis
• Several hours of exercise can cause the sweat
glands to become fatigued, which can in turn,
impair core temperature.
• Marathon runners lose about 5 liters of fluid
during competition, which accounts for 6-10 % of
body mass
• Wrestlers usually compete in a dehydrated state in
order to make their weight
Consequences of Fluid Loss
• Just about any degree of dehydration impairs
physiologic function and thermoregulation.
• As dehydration progresses and plasma volume
decreases, peripheal blood flow and sweating rate
diminish and thermoregulation becomes difficult
• Increased Heart rate
• Decreased blood flow to the skin
• Reduction in circulatory and temperatureregulating capacity to meet metabolic and thermal
demands of exercise.
Fluid Loss in Winter
• Colder air contains less moisture, thus there is a
greater fluid volume leaving the respiratory
passages as incoming air becomes humidified and
warmed to body temp.
• Causes up to 1 liter of fluid loss
• Cold stress stimulates an increase in urine
production.
• Some people overdress
Diuretic Use
• Plasma provides a greater percentage of water loss
from diuretic-induced dehydration
• Diuretic drugs can also impair neuromuscular
function
• Vomiting and diarrhea are not good ways to “make
weight” because they produce dehydration and
cause excessive mineral loss.
Rehydration
• Adequate fluid replacement sustains the
exceptional potential fro evaporative cooling of
acclimatized humans
• Athletes/people should properly schedule fluid
replacement to maintain plasma volume so that
circulation and sweating progress at optimal levels
• Drinking water can increase blood flow to the skin
for more effective cooling
– This prevents dehydration and its associated
consequences
Rehydration
• For wrestlers, dehydration is a way of life
so they can compete at a lower weight. This
is also seen in ballet dancers
• A well-hydrated athlete always functions at
a higher physiologic and performance level
than a dehydrated one
Pre-Exercise Hydration
• Drinking extra water before exercising in a hot
environment provides some protection against
heat stress because it delays dehydration, increases
sweating during exercise, and minimizes use in
core temp.
• Recommended consumption is between 400 and
600 mL (13-20 oz) of cool water 20 minutes
before exercise in heat.
– This increases stomach volume, but does not replace
fluid uptake during exercise
Adequacy of Rehydration
• Changes in body weight indicate the extent of
water loss during exercise and the adequacy of
rehydration during and after exercise or athletic
competition.
• Dark yellow urine with strong odor indicates
inadequate hydration.
• Each lb of weight loss after exercise represents
450 mL (15 fl oz).
• Water must be available during practice and
competition.
Sodium Facilitates Rehydration
• A small amount of sodium added to a
rehydration beverage facilitates more
complete rehydration than plain water
• Restoring water and electrolyte balance in
recovery occurs by:
– Adding moderate to high amounts of sodium to
the drink
– Combining solid food with plain water
Sodium Facilitates Rehydration
• Because the kidneys continually form urine, the volume of
ingested fluid following exercise must be larger (usually
by 25-50%) than exercise sweat loss to restore balance.
• If too much sodium, the excess fluid intake merely
increases urine output with no benefit to rehydration.
• With prolonged exercise in heat, sweat loss can deplete the
body of 13-17 g of salt per day.
• A glass of OJ or tomato juice replaces almost all the
potassium, calcium, and magnesium excreted in about 3
liters of sweat.