Post on 23-Dec-2015
THE PHYSIOLOGY OF EXERCISE
Melissa J Arkinstall (Exercise Physiologist)
LECTURE OUTLINE
I METABOLISM: Muscle Fuel SourcesI METABOLISM: Muscle Fuel Sources
II ENERGY SYSTEMS: Sport SpecificII ENERGY SYSTEMS: Sport Specific
III STRATEGIES: Performance EnhancementIII STRATEGIES: Performance Enhancement
All physical activities require energy to be released to the
muscles in order to fuel contraction and prevent fatigue.
I METABOLISM: Muscle Fuel Sources
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?
ATP or adenosine triphosphate is the energy currency used by our body everyday to perform a number of tasks:
METABOLISM: Energy Release
• Maintain body temperature
• Repair damaged cells
• Digestion of food
• Mechanical work – movement
ATP ↔ ADP + Energy
Fact: Our muscles already contain ATP molecules
METABOLISM: Our need for Energy
Problem: There are not enough!
Physiology Principle: ATP Supply = ATP DemandEnergy
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.
Question: Where does the additional ATP come from?
METABOLISM: Sources of Energy
The chemical breakdown of
the fuel sources in our body:
a. Muscle Glycogen
b. Blood Glucose (Liver)
c. Fats (Adipose Tissue)
d. Proteins (Amino Acids)*
ATP ↔ ADP + Energy
ADIPOSE TISSUE BLOOD PLASMA MUSCLE
Triacylglycerol(5,000 grams)
Glycerol
FFA
FFAMitochondria
O2
ATP
Acetyl -CoA
Krebs Cycle &Electron Transport
Glycogen (600 grams)
Glucose(25 grams)
IntramuscularTriglyceride (350 grams)
FFA-Albumin FFA Fatty Acids
LIVERLIVER
Glycogen(100-120 grams)
Important: two factors determine the amount of ATPrequired to perform exercise and the types of fuel used:
METABOLISM: Sources of Energy
a. Exercise Intensity – rate of ATP production
b. Exercise Duration – amount of ATP production
ATP ↔ ADP + Energy
In the next section we will learn to categorise sporting eventsusing exercise intensity and duration to determine the energysystems that are being used to provide our bodies with ATP.
Ene
rgy
expe
nditu
re (
J/kg
/min
)EFFECTS OF EXERCISE INTENSITY ONFUEL SELECTION DURING EXERCISE
1500
1200
900
600
300
Plasma glucosePlasma FFAIMTGMuscle glycogen
25 65 85
Relative exercise intensity (% of VO2max)
Romijn et al. Am. J Phsyiol. Endocrin. Metab. 265: E380-E391, 1993.
METABOLISM: Effects of Exercise Intensity
ATP is able to be produced by more than one system/ pathway
METABOLISM: ATP Production
1. Anaerobic “O2 independent”
Does not require oxygen
2. Aerobic “O2 dependent”
Requires oxygen
O2
O2
A system can be categorised as either:
Remember: these pathways generate energy without using O2
METABOLISM: Anaerobic Pathways
1. ATP-CP system
• ATP ‘reservoir’
• Immediate energy system
2. Anaerobic Glycolysis system
• Exclusively uses CHO
• Short-term “lactic acid” system
ATP is produced by these energy systems:
Remember: these pathways require O2 to generate energy
METABOLISM: Aerobic Pathways
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)
ATP is produced by these energy systems:
CHO
FAT
O2
ATP
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?
II 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: Athletic Events
The body has 4 distinct systems it can use to supplyenergy for these different types of events:
Event Energy System
ENERGY SYSTEMS: Pathways
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
Event Type: Maximal strength & speed Event Duration: 0 - 6 sec (Dominant System)
Energy Sources1. ATP ↔ ADP + Pi + H+ 2. CP + ADP + H+ ↔ ATP + Cr
Availability: Immediate- stored in muscleAnaerobic Power: LargeAnaerobic Capacity: Small
ENERGY SYSTEMS: ATP-CP (Phosphagen)
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: Anaerobic (O2 independent)
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 Glycolytic (CHO)
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: LowAerobic Capacity: Unlimited
ENERGY SYSTEMS: Aerobic Lipolytic (Fat)
So we can see that the contribution of these systemsto energy production will depend on the event type:
ENERGY SYSTEMS: Effects of Exercise Duration
49.6%
44.1%
6.3%
60%50%
35%
40%50%
65%
92%
8%
50%
50%
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)
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.
III STRATEGIES: Performance Enhancement
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
STRATEGIES: To increase fat availability
ADIPOSE TISSUE BLOOD PLASMA MUSCLE
Triacylglycerol(5,000 grams)
Glycerol
FFA
FFAMitochondria
O2
ATP
Acetyl -CoA
Krebs Cycle &Electron Transport
Glycogen (600 grams)
Glucose(25 grams)
IntramuscularTriglyceride (350 grams)
FFA-Albumin FFA Fatty Acids
LIVERLIVER
Glycogen(100-120 grams)
STRATEGIES: Effect of 3-d diet on capacity
Tim
e to
exh
aust
ion
(min
)
HIGH-CHO HIGH-FAT
250
200
150
100
50
Christensen EH & E Hansen. Scand. Arch. Physiol. 81: 161-171, 1939.
“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)
STRATEGIES: Effect of 3-d diet on capacity
Rat
ings
of
perc
eive
d ex
erti
on 18
16
14
12
10
*
D-1 D-1 D-4 D-4
High-CHO High-fat
Stepto NK et al. Med. Sci Sports Exerc. 34: 449-455, 2002.
Ratings of Perceived Exertion during intense exercise
“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: 241-257, 1998
STRATEGIES: Effect of 3-d diet on metabolism
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
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)
LAB Easy ride Hills HIT Easy ride LAB EXP
HIT 3-4 h 2-3 h 3-4 h
Overview of Experimental Protocol: Burke et al. 2000
Ene
rgy
expe
ndit
ure
(%)
HIGH-CHO HIGH-FAT
100
80
60
40
20
Burke LM et al. J. Appl. Physiol. 89: 2413-2421, 2000.
Fat
Fat
Muscle glycogen
Muscle glycogen
Glucose Glucose
*
*
Fuel metabolism during 2 h cycling at 70% VO2max
TIME-TRIAL PERFORMANCE AFTER2 HR CYCLING AT 70% VO2max
Tim
e to
com
plet
e 7
kJ/k
g B
M
(min
)
HIGH-CHO HIGH-FAT
50
40
30
20
10
Burke LM et al. J. Appl. Physiol. 89: 2413-2421, 2000.
34:10±2:37
30:44±1:07
Time trial performance after 2 h cycling at 70% VO2max
FA
T/C
D36
(A
rbit
rary
uni
ts)
PRE HIGH-CHO HIGH-FAT
50
40
30
20
10
*
Effect of fat adaptation (6-d) on gene expression
1. Five days exposure to a high-fat, low-CHO diet caused markedchanges 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 markedchanges in fuel substrate oxidation during 2 h of submaximal exercise at 70% of VO2max
2. These changes were independent of CHO availability becauseenhanced 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 markedchanges in fuel substrate oxidation during 2 h of submaximal exercise at 70% of VO2max
2. These changes were independent of CHO availability becauseenhanced rates of fat oxidation persisted despite the restoration of muscle glycogen stores
3. Despite promoting “glycogen sparing” during submaximalexercise, 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 markedchanges in fuel substrate oxidation during 2 h of submaximal exercise at 70% of VO2max
2. These changes were independent of CHO availability becauseenhanced rates of fat oxidation persisted despite the restoration of muscle glycogen stores
3. Despite promoting “glycogen sparing” during submaximalexercise, fat-adaptation strategies did not provide a clearbenefit 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-adaptationstrategies by endurance athletes competing in events lasting2-3 h in duration
Conclusions: Burke et al. 2000
•
QUESTIONS
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