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Energy Systems
for Exercise
Energy Sources

From Food:
– CHO = 4 kcal
– Fat = 9 kcal
– Protein = 4 kcal

For Exercise:

ATP  ADP + P + energy
(for muscle contraction)
Adenosine Triphosphate



Energy-carrying molecule found in the cells of
all living things.
ATP captures chemical energy obtained from
the breakdown of food molecules and releases
it to fuel other cellular processes.
Cells require chemical energy for three general
types of tasks: to drive metabolic reactions
that would not occur automatically; to
transport needed substances across
membranes; and to do mechanical work, such
as moving muscles.
Methods of Supplying ATP For
Energy
Stored ATP + PC (Creatine
Phosphate) or ATP-PC
 Anaerobic metabolism/
glycolysis/lactic acid system
 Aerobic metabolism

ATP-PC System
Short duration (<10 secs)
anaerobic
 Uses stored ATP
 Strength/power movements
 Replenishes rapidly

The ATP-PC system
Active at the beginning of all forms of
activities
 Especially important in high intensity
exercises like weight lifting that require
short bursts of energy.
 The source of fuel for the ATP-PC
system is ATP and PC that is stored in
the muscles. Only a small quantity can
be stored, so this energy source is only
effective for activities that last ten
seconds or less.

Glycolysis
Breakdown of carbohydrates for fuel
 Fuel stored in the muscle as glycogen /
delivered to the muscle as blood
glucose
 Glycolysis can produce fuel for 30
seconds to a minute for moderate heavy
resistance training

Fast (Anaerobic) Glycolysis
(The lactic acid system)
Fast glycolysis is used when oxygen is
in short supply.
 Fast glycolysis results in the formation
of lactic acid
 An increase in lactic acid in the muscle
can involve muscular fatigue and
ultimately cessation of exercise.

Active Recovery from
Exercise (Cool down)

Facilitates lactate removal because of:
– increased perfusion of blood through the
liver and heart
– increased blood flow in muscles because
muscle tissue oxidizes lactate
Slow (Aerobic) glycolysis
(The aerobic system)
Slow glycolysis is used if there is
enough oxygen to allow a continuous
supply of fuel.
 The byproduct of this form of glycolysis
is pyruvate, which is not converted to
lactic acid but is transported elsewhere.
 Pyruvate is eventually dissipated as
sweat/urine

Aerobic/Oxidative System

Supplies energy to the muscle through the
use of continuous oxygen transport.
 System works at rest and during very low
intensity exercise such as walking
 This form of energy primarily utilizes fats
(70%) and carbohydrates (30%) as fuel
sources, but as intensity is increased there is
a switch in substrate majority from fats to
carbohydrates
Oxygen Uptake During
Aerobic Exercise

Increases sharply at
onset
 Levels off within a
few minutes if pace
is constant (steady
state)
 Oxygen demand
met by supply
Maximal Oxygen Uptake
(VO2 max)

The region where
oxygen uptake
plateaus and does
not increase despite
an additional
increase in exercise
intensity.
Oxygen Deficit

Difference between
oxygen consumed
during exercise and
amount that would
have been
consumed had a
steady rate, aerobic
metabolism
occurred at onset of
exercise.
Order of energy production
Initial energy comes form ATP stored in
muscles about 2 seconds
 Then the ATP-PC system about 10
seconds
 Then the Lactic acid system about 1
minute
 Then the Aerobic system 1minute
onwards


120
100
80
60
40
20
13
5
14
03
:4
5
45
0
10
% of energy from aerobic
The Energy-Time Continuum
Work Time (Minutes)
As the work time
increases, the
percentage of
energy contributed
by the aerobic
system increases.
Blood Lactate Threshold




Exercise intensity at the
point of lactate buildup.
Predicts aerobic
exercise performance.
Untrained ~ 55% of VO2
max.
Trained ~ 75% of VO2
max.