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WHAT IS ATP ?
Carbohydrates, Fats and Protein – contain energy,
however we can’t use it directly. These nutrients are
used to form a chemical compound called ATP
(adenosine triphosphate). When broken down it releases
energy for body functions eg. muscle contraction, nerve
impulse transmission, cell division, secretion by organs).
THE FUNCTION OF ATP
When an electrical impulse arrives at the muscle, it
stimulates the ATP to break down into ADP and
phosphate and to release its energy. The energy is used
to power the rowing motion of the myosin crossbridges,
making the muscle contract. Only a small amount of ATP
is stored in the muscle, so chemical reactions take place
to produce more ATP to allow
the muscles to keep
contracting.
THE FUNCTION OF ATP
To produce or re-synthesise ATP, energy is obtained
from food or from Creatine Phosphate (CP) (also known
as phosphocreatine or phosphagen)
ATP production during resting conditions
* Demand for ATP is low so produced aerobically.
Major food fuels is fats (2/3) and carbohydrates (1/3).
* ATP is produced in the mitochondria and transported
to the myosin crossbridges.
THE ENERGY SYSTEMS
The body has three different ATP manufacturing
systems or energy pathways:
• ATP-PC system
• Lactic acid system
• Aerobic or oxygen system
Each of these systems have the same purpose – to
produce or re-synthesise ATP that is used for energy.
ATP-PC SYSTEM
ATP stored in the muscle is broken down to
release energy for muscle contraction. There is a
large amount of energy that is released from the
breakdown of the bond between the 2nd and 3rd
phosphate molecules.
ATP-PC SYSTEM
If you continue to exercise, the left over ADPs and
phosphates must be recombined to produce ATP. Initially
this is done by creatine phosphate. This does not require
O2.
To re-synthesise ATP to it’s original state, creatine (stored in
the muscle) and energy obtained from food provides the
energy to allow the free phosphate molecule to reattach to
the adenosine and 2 phosphates.
Creatine phosphate stores are exhausted after about 10
seconds of high intensity exercise and so are not
replensished until after 2 mins of rest.
LACTIC ACID SYSTEM
• Provides energy for events of up to 3 minutes.
• Carbohydrates (glycogen/glucose) are the
primary fuel for re-building ATP.
•Produces 1-3 ATP molecules for each glucose
molecule.
ADP + Pi
Glycogen
Glucose
Pyruvic acid
Lactic acid
Energy
ATP
LACTIC ACID SYSTEM
MAIN STEPS:
•Glycogen is broken down chemically by a series of
reactions into pyruvic acid.
•Energy is released which is used to re-synthesise ATP
(ADP + Pi = ATP).
•Absence of oxygen = pyruvic acid converted to lactic
acid.
THE AEROBIC SYSTEM
•After 2-3 mins of vigorous activity the body is able to
take in sufficient oxygen to meet it’s energy
requirements aerobically – provided the intensity of
the activity does not exceed 85% of maximal heart
rate. This is the point at which lactic acid starts to
accumulate – known as the anaerobic threshold.
•Activity between 85-100% HR max = accumulation
of lactic acid, fatigue of muscles, cannot continue
exercise.
•Reduce intensity to enable individual to continue
(reduce to 60% HR max).
THE AEROBIC SYSTEM
RESPIRATION
•Process of breaking down glycogen in cells using O2 to
produce ATP. Aerobic glycolysis occurs in the
mitochondria (specialised components in aerobic muscle
cells).
•ATP produced in mitochondria – transported to myosin
crossbridges to provide energy for muscular contraction.
STAGES IN AEROBIC ENERGY PRODUCTION
Glycogen/Glucose
Fats
ATP
Kreb’s
Cycle
ATP
C02
ATP
Pyruvic acid
Protein
CO2
Electron transport
chain
H20
H20
ATP
ATP
Heat
Heat
ATP
ADP + Pi
MAIN STEPS OF AEROBIC ENERGY PRODUCTION
First Stage – Breakdown of glycogen and glucose to
pyruvic acid in the presence of O2 , with some energy
released for ATP re-synthesis.
Second Stage – Kreb’s cycle. Pyruvic acid is broken
down into CO2 with further energy release.
Third Stage – Electron transport system. Water (H20) in
the form of perspiration, heat and substantial ATP is
formed (total 38 moles of ATP from 1 mole of glycogen)
During prolonged events, in the presence of O2, fat and
protein can be broken down to CO2 and H2O to provide
energy for ATP re-synthesis. This only happens after
glycogen stores have been exhausted first.
FACTORS LIMITING THE AEROBIC SYSTEM
FACTORS LIMITING THE AEROBIC SYSTEM
Oxygen Deficit = the period after the onset of exercise where
O2 consumption is below that required to produce all the ATP
required aerobically.
Steady State = the point during exercise when oxygen supply
equals oxygen demand.
Oxygen Debt = oxygen consumed during recovery. The amount
consumed is above what is required at rest to repay the O2
deficit and replenish the body’s energy stores.
Hitting the wall = when glycogen is depleted in endurance
events, the body is able to use fats for ATP production. Fats
require more O2 to produce the same amount of ATP. The
cardio-respiratory system has to work harder and the athlete
will have to slow down and fight hard to keep going.
ENERGY CONTRIBUTION OF EACH SYSTEM