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Sports
Drinks Introduction
Depletion of the body's carbohydrate stores and dehydration are two
factors that will limit prolonged exercise. Dehydration
Sweating is the way in which the body maintains it's core temperature at
37 degrees centigrade. This results in the loss of body fluid and
electrolytes (minerals such as chloride, calcium, phosphate, magnesium,
sodium and potassium) and if unchecked will lead to dehydration and
eventually circulatory collapse and heat stroke. The effect of fluid loss on
the body is as follows:
Electrolytes
Electrolytes serve three general functions in the body:
The sweat that evaporates from the skin contains a variety of
electrolytes. The electrolyte composition of sweat is variable but comprises
of the following components:
Carbohydrate
Carbohydrate is stored as glucose in the liver and muscles and is the
most efficient source of energy as it requires less oxygen to be burnt than
either protein or fat. During exercise there is in an increased uptake of
blood glucose by the muscles and to prevent blood glucose levels falling the
liver produces glucose from the liver stores and lactate.
The body's carbohydrate stores are gradually depleted and if not checked
will result in reduced performance. Consuming carbohydrate before, during
and after exercise will help prevent blood glucose levels falling too low
and also help maintain the body's glycogen stores. Many athletes cannot
consume food before or during exercise and therefore a formulated drink that
will provide carbohydrate is required. Fluid
absorption
There are two main factors that affect the speed at which fluid from a
drink gets into the body:
The higher the carbohydrate levels in a drink the slower the rate of
stomach emptying. Isotonic drinks with a carbohydrate level of between 6 and
8% are emptied from the stomach at a rate similar to water. Electrolytes,
especially sodium and potassium, in a drink will reduce urine output, enable
the fluid to empty quickly from the stomach, promote absorption from the
intestine and encourage fluid retention. What's
wrong with water?
Drinking plain water causes bloating, suppresses thirst and thus further
drinking. It stimulates urine output and therefore is inefficiently
retained. A poor choice where high fluid intake is required. Water contains
no carbohydrates or electrolytes. Sports
Drinks
There are three types of Sports drink all of which contain various levels
of fluid, electrolytes and carbohydrate.
The osmolality of a fluid is a measure of the number of particles in a
solution. In a drink these particles will comprise of carbohydrate,
electrolytes, sweeteners and preservatives. In blood plasma the particles
will comprise of sodium, proteins and glucose. Blood has an osmolality of
280-330mOsm/kg. Drinks with an osmolality of 270-330mOsm/kg are said to be
in balance with the body's fluid and are called Isotonic. Hypotonic fluids
have fewer particles than blood and Hypertonic have more particles than
blood. Consuming fluids with a low osmolality, e.g. water, results in a fall in
the blood plasma osmolality and reduces the drive to drink well before
sufficient fluid has been consumed to replace losses. Which
is most suitable?
Isotonic - quickly replaces fluids lost by sweating and supplies a
boost of carbohydrate. This drink is the choice for most athletes - middle
and long distance running or team sports. Glucose is the body's preferred
source of energy therefore it may be appropriate to consume Isotonic drinks
where the carbohydrate source is glucose in a concentration of 6% to 8% -
e.g. High Five, SiS Go, Boots Isotonic, Lucozade Sport. Hypotonic - quickly replaces fluids lost by sweating . Suitable
for athletes who need fluid without the boost of carbohydrate - jockeys and
gymnasts. Hypertonic - used to supplement daily carbohydrate intake normally
after exercise to top up muscle glycogen stores. In ultra distance events
high levels of energy are required and Hypertonic drinks can be taken during
exercise to meet the energy requirements. If used during exercise Hypertonic
drinks need to be used in conjunction with Isotonic drinks to replace
fluids. Want
to make your own?
Isotonic - 200ml of orange squash (concentrated orange), 1 litre
of water and a pinch of salt (1g). Mix all the ingredients together and keep
chilled Hypotonic - 100ml of orange squash (concentrated orange), 1 litre
of water and a pinch of salt (1g). Mix all the ingredients together and keep
chilled. Hypertonic - 400ml of orange squash (concentrated orange), 1 litre
of water and a pinch of salt (1g). Mix all the ingredients together and keep
chilled. Food
for thought
In a trail conducted by scientists in the city of Aberdeen it was
determined that a 2% carbohydrate-electrolyte drink provided a more
effective combat to exercise fatigue in a hot climate when compared to a 15%
carbohydrate-electrolyte mixture. Associated
Pages
The following Sports Coach pages should be read in conjunction with this
page. Help
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