Energy for Muscular
Activity
Chapter 5
1
Where do we get Energy for our
working muscles?
The Three Energy Nutrients
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 Fats
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 Carbohydrates
 Proteins
Carbohydrates
Carbohydrates are broken down into
glucose and stored into the muscle as
glycogen.
 Most easily broken down into this state
which is why they are the first thing our
body uses as a form of energy.

Proteins
Proteins are broken down into amino acids.
 Proteins are used for energy when the body
is in starvation mode.

Fats
Fats are broken down in to fatty acids and a
glycerol.
 Fats are the LAST energy source which is
used.

Metabolism
Metabolism
• All the chemical reactions in the body that
occur in the production of energy to do
work (i.e. muscle work,
7
Bioenergetic Conversion
The process by which our body converts the
energy found in carbohydrates, proteins and
fats into a more usable form, Adenosine
Triphosphate (ATP).
8
ATP = Adenosine TRI Phosphate
3 phosphates are present
Adenosine Triphosphate (ATP)
 Adenosine triphosphate (ATP)
 ATP is a usable form of energy for
the body.
 Made in the mitochondrion
 Resynthesized in two ways
Aerobically
Anaerobically
ATP
ADP + Pi + ENERGY
Recall the Hydrolysis of
ATP Equation
ATP + H20
ADP + Pi + Energy
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 ATP
is the molecule that gives every cell in
our body energy to function.
 All things in our body require energy in
order to be able to function properly.
– Food metabolism
– Heart beat
– Muscles contract
 When
you need energy it is on.
 When you don’t need energy it is being
stored and not used.
2 ways to re-synthesize ATP
Aerobic System
Two Energy Systems
 Aerobic System
In the presence of oxygen (O2)
All of its metabolic activity will involve O2
Occurs in the mitochondria
Leads to the complete breakdown of glucose
Lag period (slow to reach peek production)
Longer duration activities
 With
the presence of oxygen you are able to
perform an activity over a long period of
time with a balanced intensity.
 What
is an example of “aerobic activity”
– Requires oxygen
 How
does your body react?
– Heart rate increases
– Breathing increases
Anaerobic
Without oxygen (O2)
 Occurs in cytoplasm
 Produces ATP immediately when needed
 Fast rate of ATP production
 Quick burst & shorter duration activities
 Needed for short and medium length
activities.

– Ex: weight lifting, short shifts in hockey
Energy spectrum:
Anaerobic <------------------------------> Aerobic
• These systems are not in opposition
• These systems do not work in isolation, both
systems are always contributing to some extent.
• All sporting events require some contribution
from both systems.
• The body has three (3) primary metabolic
pathways to resynthesizing ATP as it is used up
and/or needed during exercise.
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Three Metabolic
Pathways
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Three Metabolic Pathways

Within the ANAEROBIC and AEROBIC
systems, there are 3 metabolic pathways by
which ATP energy reserves are restored:
– ATP-PC pathway (anaerobic alactic)
– Glycolysis pathway (anaterobic lactic)
– Cellular respiration (aerobic)
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High Energy Phosphate System
P
ENERGY
Creatine
ADP + Pi  ATP
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ATP-PC System
 ATP-PC System (anaerobic alactic)
 First of two anaerobic energy
pathways
 Relies on the action of stored
ATP and phosphocreatine
 Yields enough ATP for 7-12
seconds of energy
 Provides highest rate of ATP
synthesis
PC + ADP
ATP + CREATINE
ATP-PC

Plays an important role in sporting events
which only last a few seconds, but require
large bursts of energy.
– Ex: Olympic weight lifting, high jump, 50-100
m dash.

HOWEVER – muscles do not have large
supplies of phosphocreatine, and after about
10-15 seconds, body begins to rely on the
second system.
High Energy Phosphate System
Overview
Primary energy source:
Stored ATP, CP
Duration of activity:
7 to 12 s
Sporting events:
Weightlifting, high jump, long jump, 100
m run, 25 m swim
Advantages:
Produces very large amount of energy
in a short amount of time
Limiting factors:
Initial concentration of high energy
phosphates (ATP, PC)
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The Anaerobic Glycolytic System
Glycogen
ENERGY
Lactic Acid
ADP + Pi  ATP
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Glycolysis



A biochemical process that releases energy in the form of
ATP from glycogen and glucose
anaerobic process (in the absence of oxygen)
The products of glycolysis (per molecule of glycogen):
- 2 molecules of ATP
- 2 molecules of pyruvic acid

The by-product of glycolysis (per molecule of glycogen):
- 2 molecules of lactic acid
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The Anaerobic Glycolytic System

Starts when:
– the reserves of high energy phosphate
compounds fall to a low level
– the rate of glycolysis is high and there is a
buildup of pyruvic acid
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Anaerobic Threshold



The exercise intensity at which lactic acid begins to accumulate within
the blood
The point during exercise where a person begins to feel discomfort and
burning sensations in the muscles
Lactic acid is used to store pyruvate and hydrogen ions until they can
be processed by the aerobic system
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Substrates for the anaerobic energy system


The primary source of
substrates is carbohydrate
Carbohydrates:
– primary dietary source
of glucose
– primary energy fuels for
brain, muscles, heart,
liver
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Carbohydrate breakdown and storage
Complex
Carbohydrates
Digestive
system
Glucose
Blood
Stream
Circulation of glucose
throughout body
Glucose stored
in blood
Glucogenesis
Glycogen
Glycogen stored
in muscle or liver
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LACTIC ACID CHALLENGE 
What is lactic acid challenge?

This is a class challenge.
– Find an place on the wall, and the person who
can perform a wall sit for the longest – will win
a prize!

Describe what you felt that made you want
to stop?
What is lactic acid?

After 2 or 3 minutes of a sustained activity
the body can not break down glucose fast
enough to keep up.

Lactic Acid builds up in the muscle fibers

You are forced to slow down/stop – as it
causes pain/discomfort in the muscle.
The Anaerobic Glycolytic System Overview
Primary energy source:
Stored glycogen, blood glucose
Duration of activity:
12 s to 3 min
Sporting events:
800 m run, 200 m swim, downhill ski
racing, 1500 m speedskating
Advantages:
Ability to produce energy under
conditions of inadequate oxygen
Limiting factors:
Lactic acid build up, H+ ions build
up (decrease of pH)
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The Role of Three Energy Systems During an All-out
Exercise Activity of Different Duration
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