1. Energy Systems

2. Energy Production
We can produce energy in 2 main ways: Aerobically Glucose + O2 → energy + CO2 + H2O Anaerobically Glucose → energy + lactic acid Can you remember the formula for each one?

3. Adenosine Triphosphate (ATP)
Our body uses ATP to produce energy.
The body transforms the food we eat into ATP.
When ATP is broken down it releases ADP + P + energy.
The body can resynthesise ATP by the reverse reaction: ADP + P + energy = ATP.
The body cannot store much ATP (only enough for about 2-3s of intense activity) so any energy required needs to be produced immediately.

4. Sources of Energy
ATP can be resynthesised from the breakdown of carbohydrates (into glucose), fats (into fatty acids and glycerol), and protein (into amino acids).
Excess glucose is stored as glycogen in the muscles and liver.
Glycerol can be converted into glucose when glycogen stores have been depleted (e.g. marathon).
At rest most of our energy comes from fats, during exercise energy is mostly supplied from carbohydrates.

5. Energy Systems There are 3 energy systems: The aerobic system
This is the primary energy system for endurance events. It produces lots of ATP and no fatiguing by-products but it cannot produce energy quickly.
The lactic acid system
This is the primary energy system for middle distance events. ATP is produced quite quickly but there is a harmful by-product (lactic acid).
The ATP-PC system
This system produces energy extremely quickly but can only fuel around 10 seconds of activity.

6. Aerobic Energy Production from Glucose
When oxygen is present glucose can be broken down completely.
This occurs in the mitochondria and produces CO2, H2O, and energy (ATP).
The advantages of aerobic energy production is that there are no fatiguing by-products, the energy sources are usually abundant and lots of ATP can be produced.
The breakdown of glucose into energy (ATP) involves 3 stages: Glycolysis, Kreb’s cycle, and the Electron Transport Chain.

7. Glycolysis The initial stage of glucose breakdown.
This stage is identical in both the aerobic and anaerobic systems.
Some complicated reactions take place but the basics you need to know are….
Pyruvic acid is produced (pyruvate).
2 ATP are used and 4 ATP produced, so there is a net gain of 2 ATP during this stage.
As well as ATP we also gain NADH, which becomes important at a later stage (Electron Transport Chain).
As ATP is required to start this process what happens when we totally run out of energy?

8. This follow’s on from glycolysis, using the products from Glycolysis.
It only occurs in the presence of oxygen.
The pyruvic acid from glycolysis is added to coenzyme A, producing Acetyl Coenzyme A in preparation for the Kreb’s Cycle.
Again, lots of complicated reactions take place but all that you need to know is that 2 ATP are produced.
In the Krebs cycle we also gain a further 6NADH and 2FADH2
Kreb’s Cycle

9. Electron Transport Chain
The final stage of glucose breakdown.
Once again, numerous complicated chemical reactions take place but all that you need to know is;
Large amounts of oxygen are required at this stage (thus it is aerobic energy production). The oxygen binds to Hydrogen to form H2O
The NADH and FADH2 from previous stages are utilised here.
34 ATP molecules are produced.
So, at the end of these 3 stages 40 molecules of ATP are produced and 2 are used (net production = 38 ATP).
Electron Transport Chain

10. Aerobic Energy Production from Fat
Fatty acids are broken down by a process called beta-oxidation to acetyl CoA which enters the Kreb’s cycle (and eventually electron transport chain).
More ATP can be produced from fat than from glucose (during electron transport chain) but far more O2 is required.
Fat is therefore an excellent energy source at rest or low intensity exercise but cannot be used during high intensity exercise when a lack of O2 becomes a limiting factor.

11. Summary of Aerobic System

12. 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 system)
Lactate anaerobic energy system
Anaerobic energy systems

13. 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).

14. Lactate Anaerobic Energy System
This system involves the partial breakdown of glucose (oxygen is required for full breakdown) as only glycolysis occurs (Kreb’s cycle and ETC require O2).
2 molecules of ATP are produced for every molecule of glucose (19 times less than aerobic!).
Lactate 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.

15. How is Lactic Acid Produced?
Hydrogen is released during both glycolysis and the Kreb’s cycle (as part of NADH and FADH).
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.
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.

16. Summary of Energy Systems
Aerobic system – the slow bus Anaerobic system – the family car ATP-PC system – the super fast sports car

18. (Anaerobic Glycolysis) 200m sprint 400m sprint 50m swim
Energy System
Fuel Used
Intensity / Duration
Contribution
Sporting Examples
ATP-PC
ATP PC
High / Short
Up to 10s
(approx)
Diving
Gym vault
100m sprint
Lactic Acid
(Anaerobic Glycolysis)
Glycogen / Glucose
High Intensity
Short – Moderate Duration
10s – 3mins
Depending on intensity
200m sprint
400m sprint
50m swim
Aerobic
(Glycolysis)
Carbohydrates
Fats
Proteins (extreme circumstances)
Submaximal
Extended
Peak efficiency achieved in 1-2 mins. Dominant system when HR <85%
1500m
Marathon
Triathlon

19. 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 system
If the activity is long duration and submaximal pace, we use the aerobic system.

20. Which energy system?

21. 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
Aerobic or Anaerobic?

22. A = ATP-PC System B = Lactic Acid Energy System C = Aerobic Energy System

23. The Energy Continuum Remember that it is how long the event takes, not the distance that is important.

24. Lactate Threshold / OBLA
As exercise intensity increases, O2 consumption increases until VO2 max is reached. Any increase in intensity will then cross the lactate threshold.
Onset of blood lactic acid 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.
OBLA shows fitness levels as the longer a performer can hold off lactate accumulation, the fitter they are.

26. 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 in endurance events.
As an individual becomes fitter they will be able to work at a higher percentage of their VO2 max (higher intensity) before crossing the lactate threshold (and moving to anaerobic energy systems).
The Brownlee Brothers

27. Lactate Tolerance
The ability to withstand the effects of lactic acid accumulation.
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.

28. O2 Consumption – Rest & Exercise

29. Post Exercise
Following exercise, bodily processes do not immediately return to resting levels, especially after intense exercise.
Consuming O2 at higher than resting levels after exercise is called Excess Post-exercise Oxygen Consumption (EPOC). There are 2 components:
Fast (alactacid) component
O2 used to resynthesise ATP and phosphocreatine levels, re-saturates myoglobin (which transports O2 from blood to muscle fibres). This component will be very short after highly aerobic exercise.
Slow (lactacid) component
O2 used to remove lactic acid.

30. During the alactacid (fast) component 75% of PC stores are restored within 1min and nearly 100% in 4mins. It takes 2mins to reload myoglobin with oxygen.
The removal of lactic acid (slow component) can take up to several hours.
As O2 is vital during these processes it is essential to perform a cool down – breathing rate is raised slightly above resting level to ensure more oxygen is provided.
Fitness levels along with exercise intensity levels determine the duration of EPOC.
EPOC

31. 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)
i) 1- Exercise has become anaerobic;
2- Lactic acid accumulates in blood;
3- 2 mmol/L of blood.
(ii) 1 Lactate threshold is some proportion/percentage of VO2 max;
2 Proportion/percentage increases as fitness increases.
(iii) 1 Accurately measures intensity of training;
2 Elite performers need to train close to their Lactate threshold/VO2 max;

32. 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 marks)
2. Explain how the differing energy sources of these systems are used during:
(i) a series of javelin throws; (2 marks)
(ii) a long-distance run of increasing intensity. (4 marks)

33. Effects of Training on Aerobic Energy Systems
Cardiac hypertrophy and increased resting stroke volume (SV).
Decreased resting HR.
Increased muscle stores of glycogen and triglycerides.
Increased capilliarisation of muscle, increased number and size of mitochondria, more RBC.
More efficient transport and effective use of O2 means that fat is used more during exercise (carbs saved for higher intensity).
Maximal oxygen consumption (V02 max) increases.

34. Oxygen Consumption (VO2)
The amount of oxygen used by our body is called oxygen consumption.
During exercise we need more ATP so O2 consumption increases.
Often when we begin exercise there is insufficient O2 available to produce ATP aerobically as it takes time for the body to adjust.
When 02 consumed is lower than 02 used, there is an ‘oxygen deficit’.
O2 consumption increases with exercise intensity until the point of max O2 consumption (VO2 max).

35. VO2 Max
VO2 max is the maximum amount of O2 that the body can consume and use.
A higher VO2 max means a higher level of aerobic fitness.
If exercise intensity is submaximal (below VO2 max) then O2 consumption reaches a ‘steady state.’ – O2 consumption matches O2 required.
VO2 max can be assessed by measuring amount of O2 consumed in comparison to amount of CO2 breathed out during exercise with ever increasing intensity.

36. Factors affecting VO2 Max
VO2 max is the body’s ability to get O2 to the lungs, transfer it to the blood, transport it to muscle cells and mitochondria, and use the O2 in energy processes.
It is dependant on:
The surface area of alveoli (genetically determined)
Red blood cell and haemoglobin levels
The capillary density in the lungs
The efficiency of the heart and circulatory system
The capillary density in muscle cells
The transfer of O2 to mitochondria via myoglobin
The take-up and use of O2 by mitochondria

37. Fatigue – What’s the cause?
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 contraction.
Dehydration causing increased blood viscosity (leading to increased HR, overheating etc.).

38. What happens to Lactic Acid?
Lactic acid is often seen as a ‘waste product’ but can be a useful energy source. During recovery from intense exercise (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

39. Describe the changes that occur in the body to make the aerobic energy systems more efficient following prolonged endurance training. (4 marks)
Cardiac hypertrophy – larger heart creates a stronger contraction (pump).
Increased resting stroke volume – volume of blood leaving the left ventricle per beat.
Decreased resting heart rate – number of beats per minute at rest.
Increased blood volume and haemoglobin levels – higher volume of oxygen able to be transported at one time.
Increased muscle glycogen stores – greater amount of glucose available for energy production from converted glycogen.
Increased myoglobin content in muscles – greater initial receptors of oxygen from the circulatory system before it is transported to the mitochondria.
Increased capilliarisation of muscle – more O2 can be diffused into working muscle from circulatory system.
Increased number and size of mitochondria – more ATP can be resynthesized in the muscle cell.
Resulting increase in VO2 max overall (maximal oxygen consumption).
Exam Question

40. Exam Question Fast component - resynthesis of ATP / PC levels;
During recovery from exercise, Excess Post-exercise Oxygen Consumption (EPOC) occurs. Explain the differing functions of the fast and the slow components of EPOC, and how EPOC varies with intensity of exercise. (7 marks)
Fast component - resynthesis of ATP / PC levels;
Alactacid component
Resaturation of myoglobin with oxygen
75% PC restored within one min, 100% within 4 mins;
Slow component - removal of lactate / lactic acid;
By oxidation / energy production;
Conversion to replenishment of glycogen (glucose) by reconverting lactic acid into pyruvate and continuing through the aerobic processes of Kreb’s cycle and electron transport chain;
Some converted to protein / some excreted in sweat and / or urine;
Oxygen used to maintain high work rates of heart / breathing muscles;
Extra oxygen used as temperature remains high;
More recovery time with higher intensities;
Greater oxygen consumption with higher intensity;
EPOC is larger with higher intensity.

41. At the 2008 Beijing Olympic Games, David Davies won the silver medal in the swimming 10 kilometre marathon event, in a time of 1 hour 51 minutes and 53.1 seconds. Explain how the majority of energy used during the race would be provided. (7 marks)
A. Majority produced by the aerobic system/oxygen B. Glycolysis/Anaerobic glycolysis C. Carbohydrates/glycogen/glucose D. broken down into pyruvate/ pyruvic acid E. Some ATP produced/2 ATP F. Krebs cycle G. Fats/triglycerides/fatty acids/glycerol H. Beta oxidation I. Oxidation of acetyl-coenzyme-A/Citric acid/ production of CO2 J. Electron transport chain K. Water/H2O formed/hydrogen ions formed (H+)/ hydrogen/protons L. Large quantities of ATP produced or resynthesised/ ATP

42. Figure 4 shows the effects of daily 10-mile runs on the concentration levels of glycogen in muscles. (a) Explain what Figure 4 shows, and briefly explain the role of glycogen in endurance performance. (4 marks) (b) How could elite endurance performers try to artificially increase their glycogen stores in an attempt to improve performance? (2 marks)
Exam Question

43. Mark Scheme a)
Shows that levels of stored glycogen are depleted during 10 mile run;
Limited glycogen stores;
1 day / 24 hours insufficient time for complete replenishment / equivalent;
Lack of glycogen causes fatigue or deterioration in performance;
Provides energy (store);
For ATP resynthesis;
Through oxidation / aerobic;
(b) Either –
1 Dietary manipulation – (3-4 days) prior to competition ingest no carbohydrates;
2 (Day) before competition – high carbohydrate diet, e.g. pasta / carbo loading;
Or –
3 Exercise plus diet – 4-6 days prior to competition take exhausting run;
4 Maintain low carbohydrate diet until day before competition – then carbo load;
Or -
5 Reduce intensity of training leading up to event;
6 Maintain high carbohydrate diet.