1. THE PHYSIOLOGY OF EXERCISE
Melissa J Arkinstall (Exercise Physiologist)

2. LECTURE OUTLINE I METABOLISM: Muscle Fuel Sources
II ENERGY SYSTEMS: Sport Specific
III STRATEGIES: Performance Enhancement

3. I METABOLISM: Muscle Fuel Sources
All physical activities require energy to be released to the
muscles in order to fuel contraction and prevent fatigue.
Important Questions
How is energy released?
What fuels sources exist in our body?
Where does ATP come from?
What pathways can we use to make ATP?
Why do we slow down?

4. METABOLISM: Energy Release
ATP or adenosine triphosphate is the energy currency used by our body everyday to perform a number of tasks:
Maintain body temperature
Repair damaged cells
Digestion of food
Mechanical work – movement
ATP ↔ ADP +
Energy

5. METABOLISM: Our need for Energy
Fact: Our muscles already contain ATP molecules
Problem: There are not enough!
Result: Find other ways to provide our body with ATP
In order to maintain exercise we need to supply our
muscles with an adequate amount of ATP or energy.
Physiology Principle: ATP Supply = ATP Demand
Energy

6. METABOLISM: Sources of Energy
Question: Where does the additional ATP come from?
The chemical breakdown of
the fuel sources in our body:
Muscle Glycogen
Blood Glucose (Liver)
Fats (Adipose Tissue)
Proteins (Amino Acids)*
ATP ↔ ADP +
Energy

7. ATP Triacylglycerol Intramuscular Glycogen (5,000 grams) Triglyceride
ADIPOSE TISSUE
BLOOD PLASMA
MUSCLE
Triacylglycerol
(5,000 grams)
Glycerol
FFA
Mitochondria O2
ATP
Acetyl -CoA
Krebs Cycle &
Electron Transport
Glycogen
(600 grams)
Glucose
(25 grams)
Intramuscular
Triglyceride
(350 grams)
FFA-Albumin FFA Fatty Acids
LIVER
( grams)

8. METABOLISM: Sources of Energy
Important: two factors determine the amount of ATP
required to perform exercise and the types of fuel used:
Exercise Intensity – rate of ATP production
Exercise Duration – amount of ATP production
In the next section we will learn to categorise sporting events
using exercise intensity and duration to determine the energy
systems that are being used to provide our bodies with ATP.
ATP ↔ ADP +
Energy

9. METABOLISM: Effects of Exercise Intensity
EFFECTS OF EXERCISE INTENSITY ON
FUEL SELECTION DURING EXERCISE
1500
1200
900
600
300
Plasma glucose
Plasma FFA
IMTG
Muscle glycogen
Energy expenditure (J/kg/min)
Relative exercise intensity (% of VO2max)
Romijn et al. Am. J Phsyiol. Endocrin. Metab. 265: E380-E391, 1993.

10. METABOLISM: ATP Production
ATP is able to be produced by more than one system/ pathway
A system can be categorised as either:
Anaerobic “O2 independent”
Does not require oxygen
2. Aerobic “O2 dependent”
Requires oxygen O2 O2

11. METABOLISM: Anaerobic Pathways
Remember: these pathways generate energy without using O2
ATP is produced by these energy systems:
ATP-CP system
ATP ‘reservoir’
Immediate energy system
2. Anaerobic Glycolysis system
Exclusively uses CHO
Short-term “lactic acid” system

12. METABOLISM: Aerobic Pathways
Remember: these pathways require O2 to generate energy
ATP is produced by these energy systems:
3. Aerobic glycolytic (CHO) system
Moderate- to high-intensity exercise
Finite energy source (CHO →ATP)
4. Aerobic lipolytic (Fat) system
Prolonged low-intensity exercise
Unlimited energy source (Fat →ATP)
CHO
ATP O2
FAT

13. II ENERGY SYSTEMS: Athletic Events
This section will enable you to identify the energy
demands of a sporting event and the pathways used.
Important Questions
How can we categorise sporting events?
What energy systems match these categories?
What systems provide energy for 800 m sprint?
What system has the greatest capacity?
What systems fuel an Hawaii Ironman triathlon?

14. ENERGY SYSTEMS: Athletic Events
Sporting events can be classified into 4 main categories listed below:
1. Power Events
2. Speed Events
3. Endurance Events
4. Ultra-Endurance Events

15. ENERGY SYSTEMS: Pathways
The body has 4 distinct systems it can use to supply
energy for these different types of events:
Event Energy System
1. Power (Jump)
2. Speed (Sprint)
3. Endurance (Run)
4. Ultra-Endurance
ATP-CP system (phosphagen)
Anaerobic system (O2 independent)
Aerobic glycolytic (CHO) system
Aerobic lipolytic (Fat) system

16. ENERGY SYSTEMS: ATP-CP (Phosphagen)
Event Type: Maximal strength & speed
Event Duration: sec (Dominant System)
Energy Sources
1. ATP ↔ ADP + Pi + H+
2. CP + ADP + H+ ↔ ATP + Cr
Availability: Immediate- stored in muscle
Anaerobic Power: Large
Anaerobic Capacity: Small
The best way to describe energy is to define what it does.

17. ENERGY SYSTEMS: Anaerobic (O2 independent)
Event Type: Maximal speed or high-intensity efforts
Event Duration: sec (Dominant System)
Energy Sources
Muscle Glycogen ↔ 2 ATP + 2 Lactate + 2H+
Availability: Rapid- via glycogen breakdown (glycolysis)
Anaerobic Power: Moderate
Anaerobic Capacity: Larger than ATP-CP
The best way to describe energy is to define what it does.

18. ENERGY SYSTEMS: Aerobic Glycolytic (CHO)
Event Type: Moderate and High-intensity exercise
Event Duration: 2 min – 1.5 hours (Dominant System)
Energy Sources
Carbohydrates + O2 ↔ 38 ATP + by-products
Availability: Fast- via breakdown CHO
Aerobic Power: Large
Aerobic Capacity: Large but limited
The best way to describe energy is to define what it does.

19. ENERGY SYSTEMS: Aerobic Lipolytic (Fat)
Event Type: Low-intensity exercise
Event Duration: 4 hours+ (Dominant System)
Energy Sources
Fats + O2 ↔ ATP + by-products
Availability: Slow- via fat breakdown (lipolysis)
Aerobic Power: Low
Aerobic Capacity: Unlimited
The best way to describe energy is to define what it does.

20. ENERGY SYSTEMS: Effects of Exercise Duration
So we can see that the contribution of these systems
to energy production will depend on the event type:
49.6%
44.1%
6.3%
60%
50%
35%
40%
65%
92% 8%
ATP CP
Anaerobic Glycolytic
Aerobic Glycolytic
Aerobic Lipolytic
6 sec
30 sec
60 sec
2 min
1 hour
4 hours
Peak Performance, Hawley & Burke (1998)

21. III STRATEGIES: Performance Enhancement
Athletes and coaches are
constantly searching for new
ways to improve training and
competition performance.
Sports science has been very
successful in identifying many
strategies that are currently
used by athletes and coaches.

22. STRATEGIES: To increase fat availability
Fasting
2. Caffeine ingestion
(6-9 mg/kg BM)
3. Fat ingestion
Medium-chain fatty acids (MCFA)
Long-chain fatty acids (LCFA)
Intralipid (& heparin) infusion
5. Short-term fat-adaptation

23. ATP Triacylglycerol Intramuscular Glycogen (5,000 grams) Triglyceride
ADIPOSE TISSUE
BLOOD PLASMA
MUSCLE
Triacylglycerol
(5,000 grams)
Glycerol
FFA
Mitochondria O2
ATP
Acetyl -CoA
Krebs Cycle &
Electron Transport
Glycogen
(600 grams)
Glucose
(25 grams)
Intramuscular
Triglyceride
(350 grams)
FFA-Albumin FFA Fatty Acids
LIVER
( grams)

24. STRATEGIES: Effect of 3-d diet on capacity
Time to exhaustion (min)
HIGH-CHO HIGH-FAT
250
200
150
100 50
Christensen EH & E Hansen. Scand. Arch. Physiol. 81: , 1939.

25. STRATEGIES: Effect of 3-d diet on capacity
“There is clear evidence that short-term (1-3 days) “fat loading” is detrimental to endurance capacity and the performance of prolonged exercise. Such impairment is likely to result from a combination of the premature depletion of (lowered) muscle glycogen stores and the absence of any worthwhile increase in the capacity for fat utilization during exercise to compensate for the reduction in available carbohydrate fuel.”
Burke LM & JA Hawley. Med. Sci. Sports & Exerc. (in press 2002)

26. Ratings of Perceived Exertion during intense exercise18 16 14 12 10
High-CHO
High-fat *
Ratings of perceived exertion
D D D D-4
Stepto NK et al. Med. Sci Sports Exerc. 34: , 2002.

27. STRATEGIES: Effect of 3-d diet on metabolism
“Optimal performance in endurance and ultra-endurance events might be obtained if an athlete trains for most of the year on a high-CHO diet, then undergoes a short-term period of fat-adaptation followed by the traditional CHO-loading regimen in the final days before an event. Nutritional periodisation for ultra-endurance events should aim to enhance the contribution from fat to oxidative energy metabolism, thus potentially sparing endogenous carbohydrate stores.”
Hawley JA et al. Sports Med. 25: , 1998

28. Overview of Experimental Protocol: Burke et al. 2000
Day Day 2 Day 3 Day 4 Day 5 Day Day 7
LAB Easy ride Hills HIT Easy ride LAB EXP
HIT h h h
High-CHO or High-Fat diet LAB % VO2max
High-CHO diet (11 g/kg BM) HIT 8 x 5 85% VO2max
Experimental trial (2 70% VO2max then 7 kJ/kg BM time-trial)

29. Fuel metabolism during 2 h cycling at 70% VO2max
100 80 60 40 20
Glucose
Glucose
Muscle
glycogen *
Muscle
glycogen
Energy expenditure (%)
Fat *
Fat
HIGH-CHO HIGH-FAT
Burke LM et al. J. Appl. Physiol. 89: , 2000.

30. Time trial performance after 2 h cycling at 70% VO2max
2 HR CYCLING AT 70% VO2max 50 40 30 20 10
Time to complete 7 kJ/kg BM
(min)
34:10
±2:37
30:44
±1:07
HIGH-CHO HIGH-FAT
Burke LM et al. J. Appl. Physiol. 89: , 2000.

31. Effect of fat adaptation (6-d) on gene expression50 40 30 20 10 *
FAT/CD36 (Arbitrary units)
PRE HIGH-CHO HIGH-FAT

32. Conclusions: Burke et al. 2000
1. Five days exposure to a high-fat, low-CHO diet caused marked
changes in fuel substrate oxidation during 2 h of submaximal
exercise at 70% of VO2max

33. Conclusions: Burke et al. 2000
1. Five days exposure to a high-fat, low-CHO diet caused marked
changes in fuel substrate oxidation during 2 h of submaximal
exercise at 70% of VO2max
These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores

34. Conclusions: Burke et al. 2000
1. Five days exposure to a high-fat, low-CHO diet caused marked
changes in fuel substrate oxidation during 2 h of submaximal
exercise at 70% of VO2max
These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores
Despite promoting “glycogen sparing” during submaximal
exercise, fat-adaptation strategies did not provide a clear benefit
to the performance of a 30 min time-trial undertaken after
2 h of continuous cycling at 70% of VO2max

35. Conclusions: Burke et al. 2000
1. Five days exposure to a high-fat, low-CHO diet caused marked
changes in fuel substrate oxidation during 2 h of submaximal
exercise at 70% of VO2max
These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores
Despite promoting “glycogen sparing” during submaximal
exercise, fat-adaptation strategies did not provide a clear
benefit to the performance of a 30 min time-trial undertaken
after 2 h of continuous cycling at 70% of VO2max
The results of this study do not support the use of fat-adaptation
strategies by endurance athletes competing in events lasting
2-3 h in duration

36. QUESTIONS
THANK YOU