THE PHYSIOLOGY OF EXERCISE
Melissa J Arkinstall (Exercise Physiologist)
LECTURE OUTLINE
I
METABOLISM: Muscle Fuel Sources
II ENERGY SYSTEMS: Sport Specific
III STRATEGIES: Performance Enhancement
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
1. How is energy released?
2. What fuels sources exist in our body?
3. Where does ATP come from?
4. What pathways can we use to make ATP?
5. Why do we slow down?
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
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
Energy
Principle: ATP Supply = ATP Demand
METABOLISM: Sources of Energy
Question: Where does the additional ATP come from?
The chemical breakdown of
the fuel sources in our body:
a.
b.
c.
d.
Muscle Glycogen
Blood Glucose (Liver)
Fats (Adipose Tissue)
Proteins (Amino Acids)*
ATP ↔ ADP +
Energy
ADIPOSE TISSUE
BLOOD PLASMA
MUSCLE
Intramuscular
Triglyceride
(350 grams)
Triacylglycerol
(5,000 grams)
Glycogen
(600 grams)
Glycerol
FFA
FFA-Albumin
FFA
Fatty Acids
Acetyl -CoA
Mitochondria
Krebs Cycle &
Electron Transport
LIVER
Glycogen
(100-120 grams)
FFA
Glucose
(25 grams)
ATP
O2
METABOLISM: Sources of Energy
Important: two factors determine the amount of ATP
required to perform exercise and the types of fuel used:
a.
b.
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
Energy expenditure (J/kg/min)
EFFECTS
OF EXERCISE
ON
METABOLISM:
Effects ofINTENSITY
Exercise Intensity
FUEL SELECTION DURING EXERCISE
1500
1200
900
Plasma glucose
Plasma FFA
IMTG
Muscle glycogen
600
300
25
65
85
Relative exercise intensity (% of VO2max)
Romijn et al. Am. J Phsyiol. Endocrin. Metab. 265: E380-E391, 1993.
METABOLISM: ATP Production
ATP is able to be produced by more than one system/ pathway
A system can be categorised as either:
1. Anaerobic “O2 independent”
O2
Does not require oxygen
2. Aerobic “O2 dependent”
Requires oxygen
O2
METABOLISM: Anaerobic Pathways
Remember: these pathways generate energy without using O2
ATP is produced by these energy systems:
1. ATP-CP system
•
ATP ‘reservoir’
•
Immediate energy system
2. Anaerobic Glycolysis system
•
Exclusively uses CHO
•
Short-term “lactic acid” system
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)
CHO
O2
4. Aerobic lipolytic (Fat) system
•
Prolonged low-intensity exercise
•
Unlimited energy source (Fat →ATP)
FAT
A
T
P
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
1. How can we categorise sporting events?
2. What energy systems match these categories?
3. What systems provide energy for 800 m sprint?
4. What system has the greatest capacity?
5. What systems fuel an Hawaii Ironman triathlon?
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
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)
ATP-CP system (phosphagen)
2. Speed (Sprint)
Anaerobic system (O2 independent)
3. Endurance (Run)
Aerobic glycolytic (CHO) system
4. Ultra-Endurance
Aerobic lipolytic (Fat) system
ENERGY SYSTEMS: ATP-CP (Phosphagen)
Event Type: Maximal strength & speed
Event Duration: 0 - 6 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
ENERGY SYSTEMS: Anaerobic (O2 independent)
Event Type: Maximal speed or high-intensity efforts
Event Duration: 6 - 60 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
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
ENERGY SYSTEMS: Aerobic Lipolytic (Fat)
Event Type: Low-intensity exercise
Event Duration: 4 hours+ (Dominant System)
Energy Sources
Fats + O2 ↔ 456 ATP + by-products
Availability: Slow- via fat breakdown (lipolysis)
Aerobic Power: Low
Aerobic Capacity: Unlimited
So we can see that the contribution of these systems
ENERGY
Effects
Exercise
to energySYSTEMS:
production will depend
on theof
event
type:
6.3%
Duration
8%
40%
44.1%
50%
50%
65%
92%
60%
49.6%
6 sec
ATP
30 sec
CP
50%
60 sec
Anaerobic
Glycolytic
50%
35%
2 min
1 hour
4 hours
Aerobic
Glycolytic
Peak Performance, Hawley & Burke (1998)
Aerobic
Lipolytic
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.
STRATEGIES: To increase fat availability
1. Fasting
2. Caffeine ingestion
•
(6-9 mg/kg BM)
3. Fat ingestion
•
•
Medium-chain fatty acids (MCFA)
Long-chain fatty acids (LCFA)
4. Intralipid (& heparin) infusion
5. Short-term fat-adaptation
ADIPOSE TISSUE
BLOOD PLASMA
MUSCLE
Intramuscular
Triglyceride
(350 grams)
Triacylglycerol
(5,000 grams)
Glycogen
(600 grams)
Glycerol
FFA
FFA-Albumin
FFA
Fatty Acids
Acetyl -CoA
Mitochondria
Krebs Cycle &
Electron Transport
LIVER
Glycogen
(100-120 grams)
FFA
Glucose
(25 grams)
ATP
O2
Time to exhaustion (min)
STRATEGIES: Effect of 3-d diet on capacity
250
200
150
100
50
HIGH-CHO
HIGH-FAT
Christensen EH & E Hansen. Scand. Arch. Physiol. 81: 161-171, 1939.
STRATEGIES: Effect of 3-d diet on capacity
“There is clear evidence that shortterm (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)
Ratings of perceived exertion
Ratings of Perceived Exertion during intense exercise
18
16
High-CHO
High-fat
*
14
12
10
D-1
D-1
D-4
D-4
Stepto NK et al. Med. Sci Sports Exerc. 34: 449-455, 2002.
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 fatadaptation 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: 241-257, 1998
Overview of Experimental Protocol: Burke et al. 2000
Day 1
LAB
HIT
Day 2 Day 3 Day 4 Day 5 Day 6
Easy ride Hills
3-4 h
2-3 h
HIT
Easy ride LAB
Day 7
EXP
3-4 h
High-CHO or High-Fat diet
LAB
20 min @ 70% VO2max
High-CHO diet (11 g/kg BM)
HIT 8 x 5 min @ 85% VO2max
Experimental trial (2 h @ 70% VO2max then 7 kJ/kg BM time-trial)
Energy expenditure (%)
Fuel metabolism during 2 h cycling at 70% VO 2max
100
Glucose
Glucose
80
60
Muscle
glycogen
Muscle
glycogen
*
Fat
*
40
20
Fat
HIGH-CHO
HIGH-FAT
Burke LM et al. J. Appl. Physiol. 89: 2413-2421, 2000.
Time to complete 7 kJ/kg BM
(min)
TIME-TRIAL PERFORMANCE AFTER
Time trial performance after 2 h cycling at 70% VO 2max
2 HR CYCLING AT 70% VO2max
50
40
30
20
34:10
±2:37
30:44
±1:07
HIGH-CHO
HIGH-FAT
10
Burke LM et al. J. Appl. Physiol. 89: 2413-2421, 2000.
FAT/CD36 (Arbitrary units)
Effect of fat adaptation (6-d) on gene expression
50
*
40
30
20
10
PRE
HIGH-CHO
HIGH-FAT
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
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
2. These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores
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
2. These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores
3. 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
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
2. These changes were independent of CHO availability because
enhanced rates of fat oxidation persisted despite the restoration
of muscle glycogen stores
3. 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
4. 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
QUESTIONS
•
THANK YOU