Tommy Boone, PhD, MPH, FASEP, EPC and Larry Birnbaum, PhD, MA, EPC
Energy is necessary for muscle contraction, which is critical for human movement.
Chemical substances such as carbohydrates, lipids, and proteins provide the energy
for movement by muscle contraction.
The nutrients yield usable forms of energy (a
process called catabolism) from the chemical activities (i.e., metabolism) that take
place in the muscle fibers.
Since the body’s metabolism is increased with exercise,
the oxidation or breakdown of the nutrients is increased to provide more energy in
the form of adenosine triphosphate, ATP.
The catabolism of glucose by way of
supplies the electrons that produce energy within the
electron transport chain
Fats can also be converted to compounds that are
intermediate products in the catabolism of glucose.
Depending upon the work that is
required of the fiber, not all the glucose undergoes glycolysis.
Some is combined
with other glucose molecules to form glycogen (this process is called
When there is an increased need for glucose as a source for energy, the stored
glycogen is broken down into glucose to undergo glycolysis.
This process of
converting glycogen into glucose is called
The purpose of bioenergetics (i.e., the conversion of foodstuffs into usable energy-rich
phosphate compounds, ATP) is to insure cellular energy production.
In regards to
exercise, the energy within the ATP molecule is used for muscle contraction.
compound itself is a combination of a molecule of adenine and ribose (referred to as
adenosine) linked to three phosphates.
The bonds of the two outer phosphates represent
When the enzyme ATPase breaks these bonds, energy is released to do
Indeed, the hydrolysis of ATP to adenosine diphosphate (ADP), inorganic
), and energy is critical to the sliding of filaments, known as myofibrils, and
muscle contraction (see the Skeletal Muscle chapter).
Because ATP is the universal energy donor for cellular work, cells must be able to
Fortunately, there are several pathways to insure a constant supply.
immediate is the
PC stands for phosphocreatine, which is also written
as creatine phosphate (CrP).
PC hydrolysis regenerates ATP by giving its phosphate to
ADP to form ATP (figure 1).
The enzyme creatine kinase
(CK) is involved in the
donation of phosphate to ADP.
This process does not require oxygen.
It is entirely
All forms of intense exercise, such as sprinting, weight lifting, and
gymnastics, are possible because of the phosphagen system.
Another metabolic pathway
that produces ATP is
It is an anaerobic pathway that ends with the breakdown
of glucose into two, 3-carbon molecules of lactic acid.
The third pathway is defined as