ENERGY SYSTEMS

ENERGY SYSTEMS

What you need to know…

• ATP-PC, Lactic Acid, Aerobic systems– Key points, how they work

• Summary of the three energy systems

• Energy systems interplay

The Three Energy Systems

• There are three pathways or energy systems responsible for the resynthesis (___________) of ATP and supply of energy

• Which of the three energy systems operates during exercise depends on:– ___________ of exercise– How urgently the energy is required– ___________ of exercise– Whether or not ___________ is present

The Three Energy Systems

• The energy for muscular contractions is produced either anaerobically or aerobically via three energy systems– Anaerobic systems

1. ATP-PC system2. Lactic Acid system

– Aerobic system3. Aerobic system

The Three Energy Systems

• The three energy systems do not function independently or one at a time; all three energy systems are activated at the start of exercise and their relative contribution is determined by intensity and duration of exercise

• At rest, our demands for ATP are ___________ and can be met ___________

• As we start to exercise, the demand for ATP ___________ rapidly, especially during maximal activities and the ATP demands are met ___________

• However, if the exercise is less intense and longer ATP demands can be mostly met aerobically

Energy for Rest and Activity

• The body can create energy (ATP) under two main conditions

1. Rest: where there is enough (sufficient) oxygen available for the body to continue to function at a resting level

2. Activity: where physical exertion means there is not enough (insufficient) oxygen available for the body to continue to function at a particular level without a large increase in oxygen intake

At Rest

• The body has lots of oxygen available

• 2/3 energy comes from ___________– More ___________ is contained in fat than

carbohydrate

• 1/3 energy comes from ___________• The end products of aerobic

metabolism are:– Carbon dioxide (CO2), water (H2O) and

heat

During Activity

• Increased oxygen supply needed to go to working ___________

• Exercise of short duration and high intensity the ___________ systems supply most of the required energy– Carbohydrate main fuel

• Exercise of longer duration and low intensity ___________ system supplies energy– Carbohydrate initial fuel, then fat main

fuel once CHO is used

ATP-PC System

• Also known as: phosphate, PC, CP, phosphocreatine systems

• It’s an anaerobic system = no oxygen

• A small amount of ___________ is stored in the muscles

• Primary system for maximal intensity efforts of 1-10 seconds duration– Eg:

ATP-PC SystemHow it works

• Once ATP (stored in muscles) is used ATP needs to be ___________

• As we learnt earlier ATP is reformed using ADP and a free phosphate molecule (Pi)

• This process requires energy– Phosphocreatine (PC) is the chemical

compound that provides this energy– There is ~4 times the amount of PC in muscles

than ATP• So, PC is broken down to create energy

and this energy is used to reform ATP from ADP– PC releases a free phosphate:– PC = P + C– ADP + P = ATP

ATP-PC SystemSummary

• Provides most rapidly available source of ATP for energy because it depends on short and simple chemical reactions

• Anaerobic system so it doesn’t rely on ___________ to release energy

• ATP & PC both stored in ___________ and available for immediate energy release

• Although, after 5 seconds ~50% is depleted

• Once PC is completely used, ATP must be reformed in other ways– Usually via glycogen (stored in muscles and

liver) using anaerobic glycolysis from the lactic acid system

Lactic Acid System

• Also know as: anaerobic glycolysis, lactacid systems

• It’s an anaerobic system = no oxygen

• Provides bulk of ATP production for high intensity, sub-maximal efforts– Eg:

• Duration: 10 sec – 2-3 mins• Intensity: 85 – 95% max HR

Lactic Acid SystemHow it works

• As we know, there is not enough PC in the muscles to continuously repair ADP ATP

• In the lactic acid system this resynthesis of ATP is done differently

• This energy comes from the breakdown of ___________ (process is known as glycolysis)

• Because oxygen is not present the glycogen is not totally broken down– Pyruvic acid is created and because there is no

oxygen it is converted to lactic acid– Hydrogen ions also released– See figure 2.10, p.69

• As by-products (lactic acid and hydrogen ions) increase in the muscles it decreases the rate of ATP rebuilding and leads to ___________

Lactic Acid SystemSummary

• Requires no oxygen• More complex reactions than the

ATP-PC system to release energy• Requires glycogen to be broken

down to release energy (glycolysis)• Produces lactic acid, which

contributes to fatigue• Is the system used for sub-maximal

activities when the PC is depleted until the aerobic system can be used

Aerobic System

• Also known as: aerobic glycolysis, oxygen systems

• Creates the most energy out of all three systems

• Is the ___________ at creating energy• Contributes majority of ATP production in

sub-maximal, longer efforts– Eg:

• Duration: >30 sec• Intensity: <85% max HR

Aerobic SystemHow it works

• Stage 1: Carbohydrates (glycogen) is broken down into glucose and pyruvic acid using oxygen (aerobic glycolysis)– Occurs in the mitochondria (aerobic

powerhouse)– See figure 2.11, p.70

• Because oxygen is present a more complete breakdown of glycogen occurs resulting in no lactic acid

• Stage 2: Instead of pyruvic acid becoming lactic acid it is further broken down in the citric acid cycle (Kreb’s cycle), releasing ___________ and CO2

• Stage 3: The electron transport chain also produces large amounts of ATP along with ___________ and ___________– See figure 2.12, p.71

Aerobic SystemSummary

• Requires oxygen• Dominant system for sub-maximal

activities• Many more complex reactions than the

ATP-PC & lactic acid systems• Prefers to break down CHO rather than

fats– Although ___________ can produce more ATP– However, fats require more oxygen to produce

the same amount of ATP as CHO• Releases no toxic by-products and can be

used indefinitely• Produces far more ATP than the anaerobic

systems• However, still contributes significant

amounts of energy during high intensity efforts lasting 1-2 minutes

Comparing the Three Energy Systems

• Complete the summary table

ATP (Energy) Production

• The ___________ and ___________ of the physical activity determine which of the energy systems is the dominant contributor to ATP (energy) production

• See figure 2.14, p.74 and figures 2.15 & 2.16, p.75

Energy System Interplay

• Virtually all physical activities receive energy from each of the three energy systems

• Each system is best suited to supplying energy for specific types of events or activities

• They overlap each other depending on the type of activity and exercise demands

• They do not turn themselves on and off

REVISION QUESTIONS

1/ The ATP-PC system is the quickest to supply energy because it:A has an indefinite supply of stored ATPB does not use oxygenC is immediately available, is the simplest and quickest system for breaking down PC to create ATP, and is stored in muscle cellsD is more powerful than fats

2/ Marcus runs a 100m heat at his school athletics carnival, qualifying for the final in 12 secs. Most of the PC depleted during the 100m will be resynthesised during:A the first 3 minutes of an active recoveryB 1 minute of active recovery and eating high GI foodC 30 secondsD the first part of EPOC

REVISION QUESTIONS

3/ Discuss the energy system contribution for a 200m swimming event lasting 1 minute 45 seconds.

4/ What are triglycerides? (2 marks)

5/ What are they broken down to? (1 mark)

6/ Why and when would a recreational marathon runner possibly rely on fat as a fuel? (2 marks)