1. ENERGY SYSTEMS
Week 10

3. 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

4. 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
Whether or not ___________ is present

5. The Three Energy Systems
The energy for muscular contractions is produced either anaerobically or aerobically via three energy systems
Anaerobic systems
1. ATP-PC system
2. Lactic Acid system
Aerobic system
3. Aerobic system

6. 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

7. Energy for Rest and Activity
The body can create energy (ATP) under two main conditions
Rest: where there is enough (sufficient) oxygen available for the body to continue to function at a resting level
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

8. 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

9. 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

10. 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:

11. ATP-PC System How 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

12. ATP-PC System Summary
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

13. 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

14. Lactic Acid System How 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 ___________

15. Lactic Acid System Summary
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

16. 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

17. Aerobic System How 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

18. Aerobic System Summary
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

21. Comparing the Three Energy Systems
Complete the summary table

22. 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

23. 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

24. Energy System Interplay
What does differ is the relative importance and contribution that each system makes to rebuilding ATP and supplying energy
See figure 2.7, p.66