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Energy Systems
Fuel for Muscle Contraction
Carbohydrates, fats and protein are
broken down to form an energy rich
molecule called Adenosine
Triphosphate (ATP).
Fuel for Muscle Contraction
When a muscle is stimulated,
enzymes are released which cause
one of the phosphate bonds to be
broken, thus releasing energy
Fuel for Muscle Contraction
There is only a small amount of ATP
stored in the muscles (enough for
one or two contractions).
The body must use 3 different
energy systems to supply more ATP.
Food as the Source of Fuel
Carbohydrates (CHO)
– After digestion are broken down into
blood glucose
– Some CHO is also broken down into
glycogen which is stored in the liver and
muscles
– Blood and muscle glycogen are used
before liver glycogen
– Provides 16 Kj energy per gram
Food as the Source of Fuel
Fats
– After digestion , dietary fats are found
in the blood as free fatty acids and
triglycerides.
– Excess fat is stored in adipose tissue
and muscle
– Fat is used as fuel in low to moderate
activity exercise of a long duration
– Yields 37Kj per gram energy.
Food as the Source of Fuel
Protein
– Under normal circumstances, protein is
not used by the body to resynthesise
ATP.
– Only used in starvation type conditions.
– Protein is important for other body
repair and maintenance processes.
– Yields 17Kj per gram energy.
Energy Systems
So, we need ways
to resynthesise
(put back
together) the ATP
in muscles. There
are two general
types: aerobic
(with oxygen) and
anaerobic (without
oxygen).
Energy
Anaerobic
Phosphate
Lactic
Aerobic
Energy Systems
The ATP/PC system
– Also called alactacid system or
phosphate system
– The first part of this system is the
resident ATP molecules which are
always ready for break down.
– The second part involves the breakdown
of another molecule called
Phosphocreatine (or Creatine Phospate)
PC.
Energy Systems
PC
C + P + energy
this energy then resynthesises ATP
ADP + P + energy
ATP
Energy Sytems
There is only enough PC in the
muscles for about 10 seconds of
maximal or near maximal exercise.
No waste product produced
No oxygen used (anaerobic)
Examples of activities which
predominantly utilise ATP/PC system
include 100m sprint, high jump.
Energy Systems
The Lactic Acid System (anaerobic
glycolysis)
For high intensity activities lasting
between 10 and 90 seconds.
Body breaks down muscle stores of
glycogen (CHO)
No oxygen used
Energy Systems
Muscle glycogen
Pyruvic Acid
ATP
Lactic Acid
Muscle Fatigue
ADP
Energy Systems
Provides ATP very quickly but is
inefficient because of lactic acid build
up in muscles and blood.
Lactic acid contributes to muscle
fatigue and exhaustion.
Lactic Acid can take up to 2 hours to
be removed from bloodstream.
Typical event is 400m run.
Energy Systems
Aerobic Energy System
– After 2-3 minutes of exercise the body
is able to provide enough oxygen for a
the aerobic energy system to provide a
continuous supply of ATP.
– Oxygen + muscle glycogen
pyruvic acid + carbon dioxide + water + energy
Energy Systems
Efficient because water used for cooling,
CO2 is breathed out and oxygen limits
build up of lactic acid.
Fats can also be “burned” using aerobic
system
Complex system of chemical reactions are
used (aerobic glycolysis, Krebs cycle, and
Electron transport system).
All reactions occur within special cells
called mitochondria.
Energy Systems
Lower intensity (up to 70%
maximum)
Typical events include marathon,
cross country skiing.
Energy Systems
The Relationship Between Systems
– The systems do NOT work in isolation
– They each have a contribution in most
activities…the proportion of that
contribution varies depending upon the
duration and intensity.
Energy Systems
– Eg a marathon runner will initially use
ATP/PC during start and the lactic acid
system during the first minute or two
before the aerobic system “clicks in”.
They may also use the two anaerobic
systems for a couple of bursts of speed
during the race.
Energy Systems