Chapter 4

Question 1

Bioenergetics

Answer 1

The study of
energy in the human body.

Question 2

Metabolism

Answer 2

All of the
chemical reactions that occur
in the body to maintain itself.
Metabolism is the process in
which nutrients are acquired,
transported, used, and disposed
of by the body

Question 3

Sources of Energy

Answer 3

The main sources of chemical energy for most organisms are carbohydrates, fats,
and protein. The energy from the oxidation of carbohydrates, fats, and proteins sustains
the biochemical reactions required for life.

Question 4

Exercise Metabolism

Answer 4

The
examination of bioenergetics as it
relates to the unique physiologic
changes and demands placed on
the body during exercise.

Question 5

Substrates

Answer 5

The material or substance
on which an enzyme acts.

Proteins, carbohydrates, and lipids (fats) constitute the main substrates
used to transfer metabolic energy to be used for all types of cellular activity and life

Question 6

Carbohydrates

Answer 6

Organic compounds
of carbon, hydrogen, and
oxygen, which include starches,
cellulose, and sugars, and are
an important source of energy.
All carbohydrates are eventually
broken down in the body to
glucose, a simple sugar.

A lack of
carbohydrates in the diet can cause fatigue, poor mental function, and lack of endurance
and stamina.

Question 7

Glucose

Answer 7

A simple sugar manufactured
by the body from carbohydrates,
fat, and to a lesser
extent protein, which serves as
the body’s main source of fuel.

Question 8

Glycogen

Answer 8

The complex carbohydrate
molecule used to store
carbohydrates in the liver and
muscle cells. When carbohydrate
energy is needed, glycogen is
converted into glucose for use by
the muscle cells

Question 9

Fat

Answer 9

One of the three main
classes of foods and a source of
energy in the body. Fats help the
body use some vitamins and keep
the skin healthy. They also serve
as energy stores for the body. In
food, there are two types of fats,
saturated and unsaturated.

Question 10

Triglycerides

Answer 10

The chemical or
substrate form in which most fat
exists in food as well as in the body.

Question 11

Protein

Answer 11

Amino acids linked by
peptide bonds, which consist of
carbon, hydrogen, nitrogen, oxygen,
and usually sulfur, and that
have several essential biologic
compounds.

Question 12

Gluconeogenesis

Answer 12

The formation
of glucose from noncarbohydrate
sources, such as amino acids.

Question 13

Adenosine Triphosphate (ATP)

Answer 13

Energy storage and transfer unit
within the cells of the body.

When the chemical bonds that hold ATP together are broken, energy is released
for cellular work (such as performing muscle contraction), leaving behind another
molecule called adenosine diphosphate (ADP) One of the functions of energy
metabolism is to harness enough free energy to reattach a phosphate group to an ADP
and restore ATP levels back to normal to perform more work.

Question 14

Adenosine Diphosphate (ADP)

Answer 14

A high-energy compound
occurring in all cells from which
adenosine triphosphate (ATP)
is formed.

Question 15

Energy and Muscle Contraction

Answer 15

Energy is used to form the myosin-actin cross-bridges that facilitate muscle contraction.
At these cross-bridges is an enzyme that separates a phosphate from the ATP, releasing
energy. The energy is needed to allow the cross-bridge to ratchet the thin actin fi lament
toward the center of the sarcomere. Once that process is complete, another ATP is needed
to release the cross-bridge so that it can fl ip back and grab the next actin active site
and continue the contractile process. Thus, for one cycle of a cross-bridge, two ATPs are
needed (6,8,9). When all the ATP is completely depleted, there is no energy to break the
connection between cross-bridges and actin active sites, and the muscle goes into rigor.

Question 16

Two Factors of Exercise

Answer 16

Intensity and duration

Question 17

Energy Usage from ATP

Answer 17

Only about 40% of the energy released from ATP is actually
used for cellular work, like muscle contraction. The remainder is released as heat

Question 18

ATP Processing

Answer 18

When the enzyme ATPase combines with an ATP molecule, it splits the last phosphate
group away, releasing a large amount of free energy, approximately 7.3 kcal per unit of
ATP (6,8,9). Once the phosphate group has been split off, what remains is ADP and an
inorganic phosphate molecule

Question 19

Three Metabolic Pathways to Generate ATP

Answer 19

Before ATP can release additional energy again, it must add back another phosphate
group to ADP through a process called phosphorylation. There are three metabolic
pathways in which cells can generate ATP

1. The ATP-PC system
2. The glycolytic system (glycolysis)
3. The oxidative system (oxidative phosphorylation)

Question 20

Metabolic Pathway: ATP-PC System

Answer 20

The process of creating a new ATP molecule from a phosphocreatine
molecule (ATP-PC system) is the simplest and fastest of the energy systems (Figure 4.3)
and occurs without the presence of oxygen (anaerobic)

The ATP-PC system provides
energy for primarily high-intensity, short-duration bouts of exercise or activity.
This can be seen in power and strength forms of training in which heavy loads are used
with only a few repetitions, or during short sprinting events.

However, this system is activated at the onset of activity, regardless of intensity,
because of its ability to produce energy very rapidly in comparison with the other
systems

recovery of the
ATP-PC cycle is complete in approximately 90 seconds.

Question 21

The Glycolytic System (Glycolysis)

Answer 21

The other anaerobic means of producing ATP is through the chemical breakdown
of glucose, a process referred to as anaerobic glycolysis.

The end result of glycolysis in which glucose or glycogen is
broken down to either pyruvic acid (aerobic glycolysis) or lactic acid (anaerobic glycolysis)

Although this system can produce a signifi cantly greater amount of energy than the
ATP-PC system, it too is limited to approximately 30 to 50 seconds of duration (1–3,6–9).
Most fi tness workouts will place a greater stress on this system than the other systems
because a typical repetition range of 8 to 12 repetitions falls within this time frame.

Question 22

The Oxidative System (Oxidative Phosphorylation)

Answer 22

The most complex of the three energy systems is the process that uses substrates with
the aid of oxygen to generate ATP. All three of the oxidative processes involved in theproduction of ATP involve oxygen and are thus referred to as aerobic processes. The
three oxidative or aerobic systems include:
1. Aerobic glycolysis
2. The Krebs cycle
3. The electron transport chain (ETC)

The body prefers aerobic or oxidative metabolism because carbon dioxide and
water are more easily eliminated

Question 23

Aerobic Vs. Anaerobic Glycolysis

Answer 23

Whether glycolysis is aerobic or anaerobic, the process is the same; the presence of oxygen
only determines the fate of the end product, pyruvic acid (without oxygen the end
product is lactic acid), but in the presence of oxygen, pyruvic acid is converted into an
important molecule in metabolism called acetyl coenzyme A (acetyl CoA)

Question 24

Metabolism During Steady State Exercise

Answer 24

The body prefers aerobic or oxidative metabolism because carbon dioxide and
water are more easily eliminated

At the start of exercise aerobic
metabolic pathways are too slow to meet these initial demands, so the body relies on
the ATP-PC cycle (resulting in a reduction of ATP and PC levels and an increase in ADP
and creatine) as well as from anaerobic metabolism of glucose early into the exercise
period.

Gradually, the rate of aerobic ATP production
increases, and less and less energy is derived from anaerobic sources. Once the plateau
has been reached, the energy demands of the exercise are being met by aerobic production
of energy

Question 25

Excess Postexercise Oxygen
Consumption (EPOC)

Answer 25

The
state in which the body’s metabolism
is elevated after exercise.

ATP above and beyond what is needed (as evidenced by the still elevated
oxygen consumption) for recovery is produced to help reestablish baseline levels
of ATP and PC and to assist with clearing metabolic end products.

Question 26

Estimating Fuel Consumption During Exercise

Answer 26

The respiratory quotient (RQ) is the amount of carbon dioxide (CO2) expired divided
by the amount of oxygen (O2) consumed, measured during rest or at steady state of
exercise using a metabolic analyzer (6,9). When V
O2 and V CO2 are measured and the RQ
calculated during steady-state exercise, the relative contribution of fats and carbohydrates
as fuel sources can be determined. During steady-state exercise, an RQ of 1.0 indicates
that carbohydrate is supplying 100% of the fuel, whereas an RQ of 0.7 indicates that fat
is supplying 100% of the fuel for metabolism. Any RQ between 0.7 and 1.0 indicates a
mixture of carbohydrates and fats are fueling metabolism.

Question 27

Fat Burning Zone Myth

Answer 27

This increase in intensity raised the total caloric expenditure from fats, for the same
time investment, above that of the low-intensity walk, to the tune of about a 50% increase.
Thus, the marketing statement that decreasing intensity puts one into a fat-burning zone
is not entirely accurate. In this example, a slightly higher intensity resulted in a greater
contribution from fat despite the increased reliance on carbohydrates as a fuel source.