Anaerobic Energy Systems

Learning Objectives:
1. To understand how the two anaerobic energy systems
2. To understand lactate threshold and its effect on
3. To know which energy system is predominant in
various sports.
Anaerobic Energy Systems
 When the body is unable to provide the oxygen required
to resynthesise ATP it must start to work anaerobically.
 There are two anaerobic energy systems:
Phosphocreatine (PC) energy system (or ATP-PC
2. Lactate anaerobic energy system
Anaerobic energy systems
Phosphocreatine (PC) Energy
System (or ATP-PC system)
PC → P + C + Energy AND Energy + P + ADP = ATP
 For every molecule of PC broken down, one molecule of ATP
can be resynthesised.
No oxygen is required.
Energy is released very rapidly and there are no waste products.
Stores only last for 5-8s of high intensity exercise.
It is therefore excellent for very high short intensity activities
(e.g. 100m sprint) but not for anything longer.
PC can be resynthesised quickly. 50% in 30s, 100% in less than 4
mins (this requires O2 so intensity must be reduced).
Lactate Anaerobic Energy System
 This system involves the partial breakdown of glucose
(oxygen is required for full breakdown).
2 molecules of ATP are produced (18 times less than
Lactic acid is produced as a by-product.
This system can therefore only be sustained for between
10 seconds and 3 mins.
Few chemical reactions involved so energy can be
produced quickly.
summary of anaerobic energy systems
Lactic Acid
 Hydrogen is released during both glycolysis and the Kreb’s
These H ions combine with oxygen (in the electron
transport chain).
At some point there becomes too many H ions for the
amount of O2 available. Excess H ions combine with
pyruvate to form lactic acid.
This point is the lactate threshold (2 mmol per litre of
lactic acid above resting levels).
The build up in lactate acid is a contributing factor for
fatigue. It produces an acidic environment which slows
down enzyme activity and stops the breakdown of
glucose. It also effects nerve endings causing some pain.
What happens to Lactic Acid?
Lactic acid is often seen as a ‘waste product’ but can be a
useful energy source. During recovery (when O2 is
available) lactic acid can take the following routes:
 1. conversion to water and carbon dioxide (after being
converted back to pyruvate and entering the Kreb’s cycle)
 2. conversion into glycogen and stored in liver / muscles
 3. conversion into protein
 4. conversion into glucose
 5. conversion into sweat and urine
Lactate Threshold / OBLA
 Onset of blood lactacid accumulation (OBLA) is the point at
which lactic acid starts to accumulate in the blood (above 4
mmol per litre).
This occurs when there is insufficient O2 available to break
down lactic acid.
As exercise intensity increases, O2 consumption increases
until VO2 max is reached. Any increase in intensity will then
cross the lactate threshold.
Predominantly aerobic ATP resynthesis switches to anaerobic
when there is insufficient oxygen in the mitochondria to
combine with the H released when glucose is broken down.
OBLA shows fitness levels as the longer a performer can hold
off lactate accumulation, the fitter they are.
Exam Question
Elite games players require high levels of fitness and psychological
preparation, therefore regular fitness testing and after-match
analysis are common.
Figure 1 illustrates the relationship between the concentration of blood
lactate and the workload.
a) Use Figure 1 to identify the workload level at which lactate threshold
occurs, and explain why lactate (lactic acid) tends to be produced when
a player is exercising. (3 marks)
(b) Explain how lactate is removed from the blood by the body. (4
1.Lactate threshold correctly identified as between 500
and 800 Watts;
2. Lactate from anaerobic (glycolosis)/lack of oxygen
(O2)/high demand/lack of supply;
3. High intensity/workload exercise/equiv.
1 Used as respiratory substrate/for respiration / energy /
using oxygen (O2)/ lactate to replenish ATP;
2 Converted to pyruvate/pyruvic acid;
3 then to Carbon Dioxide (CO2) and water;
4 In inactive muscle and various tissues/organs;
5 Converted to glycogen/glucose;
6 In liver;
7 Some excreted in sweat/urine/conversion to protein
Energy System Continuum
There are three energy systems that can regenerate ATP:
 the ATP–PC system (anaerobic)
 the lactic acid system (anaerobic)
 the aerobic system
The use of each of these systems depends on the intensity
and duration of the activity:
 If the activity is short duration (less than 10 seconds) and
high intensity, we use the ATP–PC system.
 If the activity is longer than 10 seconds and up to
3 minutes at high intensity, we use the lactic acid
 If the activity is long duration and submaximal pace, we
use the aerobic system.
Muscle fatigue is the inability to maintain muscle contractions. There
are numerous causes including:
 An increasingly acidic environment caused by the build up of lactic
acid and excess H ions results in a breakdown in chemical reactions.
 Glucose stores being depleted.
 A change in the balance of chemicals that instigate muscle
 Dehydration causing increased blood viscosity (leading to increased
HR, overheating etc.).
The cause of fatigue depends on the type of activity being performed
and is still very much being researched and more fully understood.
What would be the cause of fatigue during the latter stages of a
marathon compared to those during 100m sprint or a 400m race?
VO2 Max Differences
A higher VO2 max means a higher lactate threshold.
Several factors affect an individuals VO2 max:
 Age – VO2 max decreases with age.
 Gender – woman have a 20% lower VO2 max.
 Training
 Genetic inheritance
Lactate Threshold / VO2 Max
and Exercise
 When an athlete crosses their lactate threshold fatigue
will quickly set in.
 Pacing themselves to work near, but not over, their lactate
threshold is key to success.
 As an individual becomes fitter they will be able to work
at a higher percentage of their VO2 max before crossing
the lactate threshold (and moving to anaerobic energy
Exam Question
Many elite swimmers use blood lactate sampling during training as a means
of establishing their training load.
(i) What do you understand by the term lactate threshold ?
(2 marks)
(ii) How is lactate threshold related to VO2 max?
(2 marks)
(iii) Explain how knowing blood lactate levels during a swim might assist an
elite performer.
(2 marks)
1 Levels at which lactate;
2 Lactic acid accumulates in blood;
3 Exercise has become anaerobic.
1 Lactate threshold is some proportion/percentage of VO2 max;
2 Proportion/percentage increases as fitness increases.
1 Accurately measures intensity of training;
2 Elite performers need to train close to their Lactate threshold/VO2
3 Accuracy in determining Lactate threshold/VO2 max is difficult.
Lactate Tolerance
 The ability to withstand the effects of lactic acid
 This may be related to the amounts of bicarbonate in
the blood (which can combine with lactic acid to
reduce its acidity).
 May just be down to motivation/determination levels.
After Exercise
To recover from intense exercise the body needs to:
 Restore ATP levels
 Restore phosphocreatine levels
 Deal with excess lactic acid (either by oxidating lactic acid
into pyruvate, or by converting lactic acid into glycogen in
the liver – both create ATP)
 Reloading myoglobin with oxygen
 Restoring muscle glycogen levels (high carb diet)
All, but the last of these requires oxygen as energy is required
from the complete breakdown of glucose.
Aerobic or Anaerobic?
 During nearly all activities both systems will be
involved at the same time, the one which is more
predominant depends on:
 The level of intensity
 The duration
 Your level of fitness
energy systems used - youtube clip
See p28/29 of textbook
Exam Question
Successful track and field performance is dependent upon an effective energy supply. Figure 3 shows how the
supply of each energy system varies according to the duration of a task.
1. Identify each of the energy systems A, B and C.
2. Explain how the differing energy sources of these systems are used during:
 (i) a series of javelin throws;
 (ii) a long-distance run of increasing intensity.
1. A- ATP-PC/phosphocreatine system/ATP system/alactic system;
B – lactate/lactic acid system/anaerobic glycolytic system;
C – aerobic/oxidative system.
2. (i) Immediate energy supplied/ATP system;
PC/CP (broken down); (credit equation)
Energy for ATP formation;
Aerobic system used for recovery/restoration of PC levels.
(ii) Low intensity – aerobic systems/oxidation;
Fats/glucose/glycogen/carbohydrates (CHO’s);
Krebs cycle/mitochondria;
Carbon dioxide (CO2) produced;
Increasing/high intensity – lack of oxygen (O2)/anaerobic;
ATP produced by glycolosis/lactic acid system;
Lactate accumulates/Hydrogen ions (H+)/acidity;
(2 marks)
(2 marks)
(4 marks)

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