Energy Systems

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.

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.

Energy SystemsThere are 3 energy systems:• The aerobic systemThis 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 lactate systemThis is the primary energy system for middle distance events. ATP is produced quite quickly but there is a harmful by-product.• The ATP-PC systemThis system produces energy extremely quickly but can only fuel around 10 seconds of activity.

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.

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).

Kreb’s Cycle

• 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.

• At this stage we gain another NADH for each Acetyl Coenzyme A.

• 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

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 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).

GLYCOLYSIS• 2ATP are used to split glucose into two 3-carbon molecules.• For each of the 3-carbon molecules, 2ATP and 1NADH are produced when

forming pyruvic acid.

KREBS CYCLE• Pyruvic acid is not able to enter the Krebs Cycle, so coenzyme A is added to

form acetyl coenzymeA.• For each acetyl coA that enters the Krebs Cycle 1ATP, 3NADH and 1FADH2 are

produced.

ELECTRON TRANSPORT CHAIN• The NADH and FADH2 molecules produced during Glycolysis and the Krebs

Cycle enter the Electron Transport Chain, yielding 34ATP.

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.

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 and increased number and size of mitochondria.

• 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.

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).

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.

Factors affecting VO2 MaxVO2 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

Exam Question

• Describe the changes that occur in the body to make the aerobic energy systems more efficient following prolonged endurance training. (4 marks)

1. Cardiac hypertrophy – larger heart creates a stronger contraction (pump).

2. Increased resting stroke volume – volume of blood leaving the left ventricle per beat.

3. Decreased resting heart rate – number of beats per minute at rest.

4. Increased blood volume and haemoglobin levels – higher volume of oxygen able to be transported at one time.

5. Increased muscle glycogen stores – greater amount of glucose available for energy production from converted glycogen.

6. Increased myoglobin content in muscles – greater initial receptors of oxygen from the circulatory system before it is transported to the mitochondria.

7. Increased capilliarisation of muscle – more O2 can be diffused into working muscle from circulatory system.

8. Increased number and size of mitochondria – more ATP can be resynthesized in the muscle cell.

9. Resulting increase in VO2 max overall (maximal oxygen consumption).

O2 Consumption – Rest & Exercise

Post ExerciseFollowing 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 lactate and excess H ions.

EPOC

• 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/heart 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.

EIMD & DOMS• Exercise induced muscle damage (EIMD)• Delayed onset of muscle soreness (DOMS) is a symptom

of this.• EIMD is most severe during different or high intensity

training (this is why overload is a key principle of training)• One reason these is damage to the sarcomeres

(actin/myosin filaments). Protein intake in the 2-hour window of opportunity helps minimise this.

• Glucose depletion is also a contributing factor so a high carb diet is important.

Does muscle soreness mean that training is working?

Exam QuestionDuring 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.

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/oxygenB. Glycolysis/Anaerobic glycolysisC. Carbohydrates/glycogen/glucoseD. broken down into pyruvate/ pyruvic acidE. Some ATP produced/2 ATPF. Krebs cycleG. Fats/triglycerides/fatty acids/glycerolH. Beta oxidationI. Oxidation of acetyl-coenzyme-A/Citric acid/ production of CO2J. Electron transport chainK. Water/H2O formed/hydrogen ions formed (H+)/ hydrogen/protonsL. Large quantities of ATP produced or resynthesised/34- 36 ATP

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

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.

Mark Scheme

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:

1. Phosphocreatine (PC) energy system (or ATP-PC system)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 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.

summary of anaerobic energy systems

Lactate

• Hydrogen is released during both glycolysis and the Kreb’s cycle.• 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 lactate.

• If high intensity exercise continues then excess H ions continue to build up. This 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.

Lactate and Lactic Acid

• These terms are often used interchangeably but are actually different things.

• Lactate is produced by the body during anaerobic exercise. It is not a negative by-product and actually helps to provide the body with energy.

• Lactic acid is a slightly different substance and isn’t actually produced by the body.

• That said, you can probably use either term although lactate is technically correct.

What happens to Lactate?

Lactate is often seen as a ‘waste product’ but can be a useful energy source. During recovery from intense exercise (when O2 is available) lactate 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 lactate accumulation (OBLA) is the point at

which lactate starts to accumulate in the blood (above 4 mmol per litre).

• This occurs when there is insufficient O2 available to break down lactate.

• 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.

100m Sprinting

It is often said that the winner of a 100m race is the person who slows down the least. Is this true?Usain Bolt 100m world record50-60m 0.82 seconds60-70m 0.82 seconds70-80m 0.82 seconds80-90m 0.83 seconds90-100m 0.90 seconds

Energy System ContinuumThere are three energy systems that can regenerate ATP:• the ATP–PC system (anaerobic) • the lactate system (anaerobic) • the aerobic systemThe 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 lactate system

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

Which energy system?

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 Continuum

It is the duration of the activity not the distance covered which determines the energy sources. E.g. Mo Farah can run 3000m in 7.30mins. Another person may take that long to run 1500m. They would both be using a similar percentage of aerobic / anaerobic energy.

Distance 200 400 800 1500 5000 10000

Time 22 49 1m53 3m55 14m00 30m00

% aerobic

% anaerobic

Think about the tactics involved in races such as 5000m.Mo Farah 5000m last raceThe percentage of aerobic/anaerobic is dependant on how quickly the race is run. E.g. a 200m race could be sprinted anaerobically or jogged aerobically.

Distance 200 400 800 1500 5000 10000

Time 22 49 1m53 3m55 14m00 30m00

% aerobic 29 43 66 84 95 97

% anaerobic

71 56 34 16 5 3

A = ATP-PC System

B = Lactiate Energy System

C = Aerobic Energy System

FatigueMuscle fatigue is the inability to maintain muscle contractions. There are numerous causes including:• An increasingly acidic environment caused by the build

up of 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.).• Damage to muscle fibres (micro tears)

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

Lactate Tolerance

• The ability to withstand the effects of lactate accumulation.

• This may be related to the amounts of bicarbonate in the blood (which can combine with lactate to reduce its acidity).

• May just be down to motivation/determination levels.

Energy System Fuel Used Intensity / Duration Contribution Sporting

Examples

ATP-PC ATPPC High / Short Up to 10s

(approx)

DivingGym vault

100m sprint

Lactic Acid(Anaerobic Glycolysis)

Glycogen / Glucose

High Intensity

Short – Moderate Duration

10s – 3mins

Depending on intensity

200m sprint400m sprint50m swim

Aerobic(Glycolysis)

CarbohydratesFats

Proteins (extreme circumstances)

Submaximal

Extended

Peak efficiency achieved in 1-2 mins. Dominant system when HR

<85%

1500mMarathonTriathlon

Exam QuestionMany 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 4 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;

EXAM QUESTIONSuccessful 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)

Different Forms of Energy

• Discuss with the person next to you – how many different forms of energy can you name?

• Mechanical energy• Electrical energy• Potential energy• Chemical energy• Kinetic energy

• Electrical energy – the energy in electrical charges

• Potential energy – the energy possessed by an object because of its position

• Chemical energy – the energy stored in food• Kinetic energy – the energy in moving objects

(also called movement energy)• Mechanical energy – the sum of potential

energy and kinetic energy

1. The hammer has potential energy but no kinetic energy.2. Lifting the hammer up increases its potential energy.3. The force applied to the hammer gives it kinetic energy.

The sum of the potential and kinetic energy is mechanical energy which is the force applied to the nail.

Energy

• Messages sent around the body are in the form of electrical energy.

• When a message travels along a motor neurone it changes to chemical energy as it passes across the synaptic cleft