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Creatine is one of the most talked-about ergogenic aids around.
A number of supplement companies offer creatine monohydrate (CrH2O) as a new tool for increasing strength and muscle mass.
The Role of ATP
All of the energy produced by the body is generated through
a series of chemical reactions within the body’s tissues.
The raw materials for these reactions are the foods we eat:
the carbohydrates, fats and proteins. These foods are by and
large digested in the stomach and assimilated in the intestines.
Many go through additional chemical changes in the liver.
These components are then converted by a series of reactions
into a chemical called adenosine triphosphate, or ATP
ATP is known as the body’s “energy currency”
It’s used for building new tissue, nerve transmission,
digestion, gland secretions and, of course, for muscle contraction.
As its name implies, ATP has three phosphate molecules bonded
to an adenosine molecule. When one of the bonds connecting
these phosphate molecules is broken through a process known
as hydrolysis, a great deal of energy is created. It is this
breaking of bonds between molecules that produces all of the
energy utilized by the body. In muscle the energy activates
specific sites on the contractile elements of the muscle fiber,
causing them to shorten.
There are three main pathways for the energy production the
body needs to live and grow. This energy is produced by complex
reactions that occur within the cell, and all involve the
use of ATP in differing ways. Two of these three pathways
are called anaerobic, which means that the chemical processes
producing the energy do not utilize oxygen. The anaerobic
pathways include the ATP-CP system and glycolysis. The third
pathway utilizes oxygen in its chemical reactions and is referred
to as the aerobic system. Only the ATP-CP system uses creatine
to create energy.
The ATP-CP Energy Pathway
The ATP-CP pathway is the body’s only immediate source
of energy. Activities such as weightlifting and the 100-yard
dash, which require rapid and immediate energy, are heavily
dependent on this pathway. The ATP-CP system involves an interaction
between two molecules, ATP and creatine phosphate, or CP,
within the cell. When ATP’s outermost phosphate bond
is broken off, adenosine diphosphate, or ADP, is formed, along
with a great deal of energy. Since the body has only about
three ounces of ATP at any one time, however, it runs out
of its supply rapidly. Creatine phosphate comes to the rescue.
The CP molecule also releases a large amount of energy when
the bond between its creatine and phosphate molecules is split.
As a result, its phosphate is donated directly to ADP to re-form
ATP in the presence of the catalytic enzyme creatine kinase.
This process is known as rephosphorylation. ATP is now available
to begin the energy cycle again. Since the cell’s concentration
of CP is three to five times higher than that of ATP, creatine
phosphate functions as the cell’s energy reservoir.
The ATP-CP pathway provides enough energy for a one-minute
walk or six seconds of sprinting, after which the other pathways
take over. The main advantage of this energy system is that
it can go to work immediately, something the others can’t
do. If it weren’t for the ATP-CP system, we wouldn’t
be able to lift heavy weights or do any other work that requires
immediate full effort. We’d have to start lifting in
slow motion.
The Other Energy Pathways
The second anaerobic system is glycolysis. This system provides
most of the energy for medium-duration activities like bodybuilding,
wrestling and sprint swimming. During glycolysis a glucose
molecule enters the cell from the blood and is transformed
into a product called pyruvic acid through a series of complex
reactions. These reactions allow a significant amount of energy
to be produced quickly for muscular contraction just as the
ATP-CP system begins to phase out. Glycolysis can also use
muscle glycogen (the stored form of glucose) and the glycerol
formed when a fat molecule is broken down as raw material
for energy production.
In the absence of adequate oxygen the pyruvic acid is converted
into lactic acid and alanine, which actually helps keep glycolysis
going by removing excess hydrogen ions that would normally
bring it to a halt. The lactic acid escapes into the bloodstream
and away from the muscle. This escape mechanism is only temporary,
however, because
the level of lactic acid in the blood and muscle eventually
increases. This increased acidity inactivates some of the
enzymes used in glycolysis, which reduces the ability of the
muscles to contract. Fatigue sets in and exercise must stop.
The third type of energy production is the aerobic system,
which is used for vigorous exercise beyond two to three minutes.
This system releases 95 percent of the potential energy in
each glucose and fat molecule through a complex set of processes
called the Krebs cycle, which can only function in the presence
of oxygen. This aerobic system makes use of the mitochondria
in the cells, which are also known as the cells’ energy
factories
All three energy systems are interrelated. Rather than switching
on and off like the lights of a traffic signal, they overlap
to provide a smooth transition from one means of energy production
to another. This allows the body to perform at its best through
all levels of exercise intensity. Creatine compounds play
an important role in the process by providing large amounts
of energy for immediate use.
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