THE PHYSIOLOGY OF EXERCISE Melissa J Arkinstall (Exercise Physiologist)

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)*


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


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


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




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


•

QUESTIONS

THANK YOU

THE PHYSIOLOGY OF EXERCISE Melissa J Arkinstall (Exercise Physiologist)

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