Carbohidrates and Exercise
Apoina Kartini

Carbohydrate :
1. Polysaccharides (starches),
2. Disaccharides (sucrose and lactose),
3. Monosaccharides (glucose and fructose).

These carbohydrates (CH) must be:
1. Digested,
2. Absorbed,
3. Transported to appropriate cells for
metabolism.
What the happens to the carbohydrate after
it is absorbed into the body?

Digested to glucose for absorption into the
blood
 Fructose and galactose are converted to
glucose by the liver.
 Glucose is the blood sugar.

A high-CH meal will lead to a rather rapid
increase in the blood sugar level, usually
within an hour.
 The glycemic index represents the effect a
particular food has upon the rate and amount
of increase in the blood glucose level.
 Foods containing high amount of refined
sugars have a high glycemic index because
they lead to a rapid rise in the blood sugar,
But, some starchy foods also have a
high glycemic index
 Foods high in fiber, such as beans,
generally have a low glycemic index,
 Fructose has a low glycemic index,
which is one of the reasons its use had
been advocated for endurance athletes.

Normoglycemia:
60-100 mg/dl, or mg/100 ml, or mg%).
 The rise in blood  stimulates the
pancreas to secrete insulin into the
blood.
 Insulin is a hormone that facilitates the
uptake and utilization of glucose by
various tissue in the body, most notably
the muscle and adipose tissue.


Foods with a high glycemic index may lead
rapidly to high blood glucose levels, possibly
hyperglycemia (>140 mg%), which will cause
an enhanced secretion of insulin from the
pancreas.
 High serum levels of insulin will then lead to a
rapid, and possibly excessive, transport of the
blood glucose into the tissues
 This may lead in turn to a reactive
hypoglycemia (<40-50 mg%)
The fate of blood glucose : (Figure 4.6)
1.
May be used for energy, particularly by the brain
and other parts of the nervous system that rely
primarily on glucose for their metabolism.
2.
May be converted to either liver or muscle
glycogen. Liver glycogen may later be reconverted
to blood glucose.
3.
May be converted to and stored as fat in the
adipose tissue. When the dietary CH exceeds the
energy demands of the body and the storage
capacity of the liver and muscles for glycogen.
4.
May be excreted in the urine if an excessive
amount occurs in the blood because of rapid
ingestion of simple sugars.
The fate of blood glucose

The body has three energy sources of
CH :
1. Blood glucose,
2. Liver glycogen,
3. Muscle glycogen.

One hour of aerobic exercise uses
over half of the liver glycogen supply

Fifteen hours or more of starvation will
deplete the liver glycogen.

The greatest amount of CH stored in the body
is in the form of muscle glycogen. Because
the muscle compose such a large proportion
of the body mass as contrasted to the liver.

Muscle glycogen is about 12 grams/kg of
muscle tissue.

As liver glycogen, the muscle glycogen stores also
may be decreased or increased, with considerable
effect on physical performance.
 A trained endurance athlete may have twice the
amount of stored muscle glycogen than an untrained
sedentary individual has.
 Approximate CH stores in the body of a normal,
sedentary adult:
Source
Blood glucose
Liver glycogen
Muscle glycogen
Amount in grams
Calories
5
75-100
300-400
20
300-400
1.200-1.600
Gluconeogenesis = the new formation of glucose





Some body cell (nerve cells in the brain and retina
and red blood cells) are normally totally dependent
upon glucose for energy and require a constant
source.
CH can be used to produce energy either aerobically
or anaerobically.
In the lactic acid system, ATP is produced rapidly via
anaerobic glycolysis (the end product: lactic acid)
In the oxygen system (aerobic glycolysis), the
production of relatively large amount of ATP.
For the same amount of CH, anaerobic metabolism
yields only two ATP, whereas aerobic metabolism
yields thirty-six to thirty-eight ATP.

Some body cell (nerve cells in the brain and
retina and red blood cells) are normally totally
dependent upon glucose for energy and
require a constant source.

CH can be used to produce energy either
aerobically or anaerobically.

In the lactic acid system, ATP is produced
rapidly via anaerobic glycolysis (the end
product: lactic acid)

In the oxygen system (aerobic glycolysis), the
production of relatively large amount of ATP.

For the same amount of CH, anaerobic
metabolism yields only two ATP, whereas
aerobic metabolism yields thirty-six to thirtyeight ATP.

Hypoglycemia and depleted muscle glycogen
may precipitate fatigue.

CH supplies approximately 40% of the body’s
energy needs during rest.

In mild to moderate exercise  50% or more

When exercise becomes more intense, such
as at 70-80% of capacity  CH is the
preferred fuel

At maximal or supramaximal exercise efforts,
it is used almost exclusively.

A well-conditioned person may be able to
exercise:
– for many hours at 40-50% of VO2 max,
– for 1-2 hours at 70-80% of VO2 max,
– but only for minutes at maximal or supramax level
of VO2 max.

CH more efficient fuel than fat, by about 7 %

More oxygen is needed to metabolize the fat

From one liter of oxygen, we will find that CH
yields about 5,05 and fat gives only 4,69
Calories

CH is able to produce ATP for muscle
contraction up to three times as rapidly as fat.

The primary CH source of energy for physical
performance is muscle glycogen, specifically
the glycogen in the muscle that are active.

As the muscle glycogen is being used during
exercise, blood glucose may enter the muscle
and also enter the energy pathways,

The liver will release some of its glucose to
help maintain blood glucose levels, and
prevent hypoglycemia

Exercise  facilitates the transport of
blood glucose into the muscle.