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The triathlon is an athletic event that involves
performers undertaking a long distance swim,
immediately followed by a cycle race and then finally a
run of several kilometres.
(a) What would be the major energy sources used by a
(3 marks)
(b) Briefly explain how these energy sources are used
for regeneration of ATP.
(5 marks)
2 (a) 1. Fats;
2. Fatty acids;
3. Glycerol;
4. Triglycerides.
Sub max 2 marks
Sub max 2 marks
3 marks
1. Carbohydrates/glycogen/glucose broken down
into pyruvate;
2. Anaerobic/glycolysis;
3. Some ATP produced;
4. Fats/triglycerides/fatty acids/glycerol broken down
into variety of
5. Beta oxidation;
6. Into mitochondria;
7. Krebs cycle;
8. Electron transport chain;
9. Oxidation/aerobic;
10. Large quantities of ATP produced.
5 marks
Anaerobic Respiration
Describe how ATP is produced
in the ATP-PC, and Lactic Acid
Give advantages and drawbacks
of these systems.
4c Molecule
Anaerobic Respiration
Does not require the presence
of oxygen!
There are two types of anaerobic
•ATP-PC system (alactic system)
• Lactic Acid (Lactate anaerobic)
Lactic Acid System
Quick Recap – what happens in Glycolysis?
Glyco = Glucose
Lysis = Splitting
• Occurs in the cytoplasm
• Glucose is converted into Glucose–6–Phosphate
• Enzyme involved = PFK (phosphofructokinase)
• Glucose–6–Phosphate is oxidised by the removal of 2 H2
• Glucose-6-Phosphate is split into 2 molecules of Pyruvate
• Energy is released and used to form 2 x ATP molecules
Lactic Acid System
• The Lactic Acid system is essentially the process of
• Occurs in the cell cytoplasm,
• Glucose is split into 2 x pyruvate molecules
• 2x ATP molecules are produced
• In aerobic respiration the pyruvate is then converted
into Acetyl Co A by pyruvate dehydrogenase, and this
enters Krebs Cycle.
• When exercise intensity is high, oxygen supply to the
muscles does not meet the demands for energy
• With insufficient oxygen, not all the pyruvate can enter
Krebs Cycle, so some builds up in the cytoplasm
•If too much puruvate builds up, the process of glycolysis
will stop and no more ATP will be produced.
• Instead, the enzyme lactate dehydrogenase converts the
pyruvate to lactic acid
• This keeps glycolysis going so that 2x ATP can still be
produced for each glucose broken down.
4c Molecule
Lactic Acid System Advantages
• Much faster to release energy than aerobic
• Does not require oxygen so can occur during very high
intensity exercise
• Any lactic acid produced can be converted back into
glycogen and stored, or into pyruvate and used for
aerobic respiration once exercise has finished
• Produced 2 ATP per glucose
• Muscles ability to buffer changes in pH can be
improved by training
Lactic Acid System Disadvantages
• Lactic acid accumulates which lowers the pH of the
muscle cell and blood, and can prevent glycolytic
enzymes working
• Due to lactic acid build up, the muscles will fatigue
within 1-3 mins
• Only releases 2 ATP compared to the 38 released by
aerobic respiration – only 5% of the energy in each
glucose can be harnessed.
Remember though before all this
takes place we are able to able to
obtain energy for short bursts (110 seconds) through
ATP-PC (alactic) System
• Phosphocreatine (PCr) is an energy-rich compound
found in cells.
• The breakdown of PCr releases enough energy to
resynthesise 1 ATP
• Occurs in cell cytoplasm
• Enzyme involved = creatine kinase
• Muscles can contain stores of PCr sufficient to
sustain around 10seconds of maximal exercise
• There is some evidence that creatine supplements can
increase muscle PCr stores.
ATP-PC (alactic) System
• Very quick to provide energy to resynthesise ATP
(almost immediate)
• Can sustain 10s intense exercise
• No fatiguing by-products produced
• PCr stores are recovered by aerobic respiration very
quickly after exercise finishes (within 2-3 mins)
• Anaerobic – does not rely on oxygen supply
• PCr levels can be improved by training and
ATP-PC System Disadvantages
• Only lasts for 8-10s
• When PCr stores depleted they cannot be replenished
until after exercise finishes, or if exercise intensity
drops significantly (as high levels of O2 availability are
required for aerobic respiration) – fatigue occurs.
•If exercise continues after the depletion of the PCr
stores then other energy systems must be used to
resynthesise ATP.
•Only 1 ATP resynthesised for every PCr broken down.
• Creatine supplementation has limited success, and
potential side effects of cramps, bloating and
The Energy Continuum
The energy systems are not used one at a time – all three
are continually being used together, but depending on the
activity some may be used more than others.
The factors that determine the predominant system:
• Availability of oxygen
• Exercise intensity
• How soon energy is required
The relationship between the 3 systems can be shown
Lactic Acid
% Energy
1 min
ATP-PC-LA Threshold
3 mins
LA-O2 Threshold
Activities can be plotted along an energy continuum line to
show the predominant energy systems being used:
over 3mins
Exam Questions:
Elite swimmers can complete a 200 metres free-style race
in just under 2 minutes.
(a) (i) Describe how the majority of energy will be produced
for this type of race.
(4 marks)
(ii) Explain the main cause of muscle fatigue during this
type of race.
(2 marks)
One popular form of training for Rugby Union is intermittent or
interval training. This involves periods of intense exercise broken up
with periods of rest.
The graph shows levels of ATP-PC stores during a period of interval
training. The player sprints 50 metres and then walks back to the
start of the sprint to recover before repeating the sprint.
(b) Use the graph to
describe and explain
the effects of
interval training on
ATP-PC levels.
(4 marks)