Transcript Chapter 4 - Fitness Mentors

Chapter 4
Exercise Metabolism and
Bioenergetics
Objectives
• After this presentation, the participant will be able to:
– Describe the primary methods of how the body produces energy for
exercise.
– Differentiate between and define aerobic and anaerobic metabolism.
– Distinguish which energy pathways are used for various intensities and
durations of exercise.
– Understand the interaction of carbohydrate, fat, and protein as fuels for
exercise.
– State the differences in the energy use during steady state and
exhaustive exercise.
– Describe basic training-induced adaptations in energy production.
Bioenergetics
• Bioenergetics is the study of how energy is
transformed through various biochemical
reactions
– Metabolism refers to all the chemical reactions that
occur in the body to maintain itself
– Exercise metabolism refers to the examination of
bioenergetics as it relates to the unique physiologic
changes and demands placed on the body during
exercise
Nutrient Substrates
• 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
• Carbohydrates provide the body with a
source of fuel and energy required for all
daily activities including exercise.
– The storage form of carbohydrates, called
glycogen
Nutrient Substrates
• Another important source of energy is fat. The chemical
or substrate form in which most fat exists in food as well
as in the body is called triglycerides. Fat is mainly used
as fuel during low intensity, long duration exercise.
• The third fuel source is protein. But protein rarely
supplies much energy during exercise. During a low
calorie diet, protein can be used as fuel to supply
carbohydrates via gluconeogenesis. This is why muscle
loss typically happens when using the low calorie
method of dieting.
• Gluconeogenesis: The formation of glucose from
noncarbohydrate sources, such as amino acids.
Energy and Work
• Adenosine Triphosphate is one of the primary sources
of immediate energy for cellular metabolism stored in
chemical bonds
– When the chemical bonds that hold ATP together are
broken, energy is released and utilized for cellular
work. This leaves behind another molecule called
adenosine diphosphate (ADP)
– To perform mechanical work ATP is required
Energy and Work
• ATP-PC system- Provides energy for short
duration high intensity work,* by replenishing
ATP rapidly (6-10 seconds)
• Glycolysis- Provides energy through the
breakdown of glucose to create ATP for
moderate intensity, moderate duration work (3050 seconds)
• Oxidative system-The most complex of the
three energy systems is the process that uses
substrates with the aid of oxygen to generate
ATP.
The Oxidative System
• The three oxidative or aerobic systems include:
–
–
–
–
1.
Aerobic glycolysis
2.
The Krebs cycle
3.
The electron transport chain (ETC)
Fat can also be metabolized aerobically. Fat is the
preferred fuel source for aerobic activities of long
duration like a marathon.*
– The first step in the oxidation of fat is a process
referred to as β-oxidation
• Produces lots of ATP, but very slowly
Energy During Exercise
• Intensity and duration of exercise are
inversely related.
– The amount of energy available from stored
ATP and phosphocreatine is small, whereas
the amount of energy from stored
carbohydrate has a greater capacity, but is
still limited
– The amount of available fuel for exercise from
fats is essentially unlimited.
Energy During Exercise
• Costs of exercise vary depending on
conditions
– Lying supine burns fewer calories than
standing exercise
– The body prefers oxidative metabolism
– Excess postexercise oxygen
consumption- Elevated oxygen consumption
after strenuous exercise
– During intermittent work glycolysis provides
energy for work, oxidative provides recovery
Fuel Contribution During
Exercise
• The bioenergetics of exercise can be indirectly
measured in a laboratory using various modes of
exercise by measuring the respiratory quotient.
• 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
– An RQ of 1.0 indicates that carbohydrate is supplying 100% of
the fuel
– An RQ of 0.7 indicates that fat is supplying 100% of the fuel.
– An RQ between 0.7 and 1.0 indicates a mixture.
Summary
• Bioenergetics is the study of how energy is
transformed through various biochemical
reactions
• Metabolism refers to all the chemical reactions that
occur in the body to maintain itself
• Proteins, carbohydrates, and lipids (fats) constitute
the main substrates used
• ATP is the chemical form of energy derived from
three pathways
• RQ determines percentage of fat, carbs, or protein
utilized in exercise