Transcript Metabolism during Exercise

Exercise Physiology
MPB 326
David Wasserman, PhD
Light Hall Rm 823
3-7336
The Remarkable Thing about
Exercise
The Great Debate
• Top-down
• Feedback control
Energy Metabolism and the
Three Principles of Fuel
Utilization
The need for energy starts when calcium is released
from the sarcoplasmic reticulum of contracting muscle
The Working Muscle
Energy for Contraction
Muscle relaxation requires
energy too!
Where does this ATP come
from?
Sources of ATP
Stored in muscle cell (limited)
Synthesized from macronutrients
Common Processes for ATP production
Anaerobic System
a. ATP-PC (Phosphagen system)
b. Anaerobic glycolysis (lactic acid system)
Aerobic System
a. Aerobic glycolysis
b. Fatty acid oxidation
c. TCA Cycle
ATP-PCr (Phosphagen system)
1.
Stored in the muscle cells (PCr > ATP)
2.
ATP + H2O  ADP + Pi + E (ATPase hydrolysis)
3.
PCr + ADP  ATP + Cr (creatine kinase reaction)
4.
ADP + ADP  ATP + AMP (adenylate kinase)
5.
PCr represents the most rapidly available source of ATP
a) Does not depend on long series of reactions
b) No O2 transportation required
c) Limited storage, readily depleted ~ 10 s
Glycolysis
Glucose + 2 ADP + 2 Pi + 2 NAD+
2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
Lactate Dehydrogenase
Hypoxic conditions
Pyruvate + CoA + NADH + H+
Lactate + NAD+
Pyruvate Dehydrogenase
Lots of Oxygen
Pyruvate + CoA + NADP+
Acetyl-CoA + CO2 + NADPH
Pyruvate Dehydrogenase
Pyruvate + CoA + NADP+
Acetyl-CoA + CO2 + NADPH
TCA Cycle
Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 2H20
CoASH + 3 NADH + 3H+ + FADH2 +
GTP + 2CO2
Beta Oxidation of Fatty Acids
7 FAD + 7 NAD+ + 7 CoASH + 7 H2O +
H(CH2CH2)7CH2CO-SCoA
8 CH3CO-SCoA + 7 FADH2 + 7 NADH + 7 H+
Summary of ATP Production
via Lipid Oxidation
ATP Balance Sheet for Palmitic Acid (16 carbon)
ATP
•
•
•
Activation of FA chain
ß oxidation (16 Carbons / 2) –1 = 7 (at 5 ATP each)
Acetyl-CoA (16 Carbons / 2) = 8 (at 12 ATP each)
Total per chain
-1
35
96
130
Electrochemical Energy and ATP
Synthesis
Energy for “Burst” and Endurance Activities
Rate of ATP Production (M of ATP/min)
• phosphagen system ..............4
• anaerobic glycolysis..………2.5
• aerobic system.......................1
How long Can it Last?
• phosphagen system...8 to 10 sec
• anaerobic glycolysis…1.3 to 1.6 min
• aerobic system.........unlimited time (as long as nutrients last)
Aerobic Energy
• During low intensity exercise, the
majority of energy is provided
aerobically
• Energy produced aerobically requires
O2
• Therefore, O2 uptake can be used as
a measure for energy use
Exercise Testing in Health and Disease
Oxygen Uptake and
Exercise Domains
INCREMENTAL
VO2 (l/min)
4
Severe
2
Heavy
Moderate
0
150
Work Rate (Watts)
300
Anaerobic Threshold Concept
Exercise
15
Blood
Lactate
mM
Heart
Disease
Onset of lactic acidosis
10
5
Athlete
0
50
Rest Period
150
100
Exercise
(watts)
200
250
Anaerobic Threshold in Some Elite Long
Distance Athletes can be close to Max
Exercise
15
Blood
Lactate
mM
Onset of lactic
acidosis
10
Bill
Rodgers
5
0
Basal
Oxygen
Uptake
20
60
40
Oxygen Uptake
(% maximum)
80
100
Oxygen Deficit and Debt
Oxygen Uptake and
Exercise Domains
CONSTANT LOAD
Severe
4
Heavy
2
0
Moderate
12
Time (minutes)
24
Lactate and Exercise
12
Blood Lactate
mM
6
0
0
12
Time (minutes)
24
Three Principles of Fuel Utilization during Exercise
• Maintaining glucose homeostasis
• Using the fuel that is most efficient
Storage
Metabolic
• Preserving muscle glycogen core
Glucose homeostasis is usually maintained despite
increased glucose uptake by the working muscle
Moderate
Exercise
100
80
Blood
Glucose
(mg/dl)
60
40
20
0
5
Rates of Glucose
Entry and
Removal from
the Blood
(mg•kg-1•min -1)
4
Entry
3
2
Removal
1
0
-30
0
30
Time (min)
60
Carbohydrate Stores after an Overnight Fast
Sedentary
Liver
Glycogen
Blood
Glucose
Muscle
Glycogen
400
grams
4 grams
100
grams
Carbohydrate Stores after an Overnight Fast
1 hr of Exercise
Liver
Glycogen
Blood
Glucose
Muscle
Glycogen
400
grams
4 grams
100
grams
Carbohydrate Stores after an Overnight Fast
2 hr of Exercise
Liver
Glycogen
Blood
Glucose
Muscle
Glycogen
400
grams
4 grams
100
grams
Carbohydrate Stores after an Overnight Fast
3 hr of Exercise
Liver
Glycogen
Blood
Glucose
Muscle
Glycogen
400
grams
4 grams
100
grams
Carbohydrate Stores after an Overnight Fast
4 hr of Exercise
Liver
Glycogen
Blood
Glucose
Muscle
Glycogen
400
grams
4 grams
100
grams
!!!
Contribution of different fuels to metabolism by the
working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficient
Storage
Metabolic
• Preserving muscle glycogen core
The Most Efficient Fuel depends on
Exercise Intensity and Duration
Metabolic Efficiency
CHO is preferred during high intensity exercise because its metabolism yields
more energy per liter of O2 than fat metabolism.
kcal/l of O2
CHO
Fat
5.05
4.74
CHO can also produce energy without O2!!!
Storage Efficiency
Fat is preferred during prolonged exercise because its metabolism provides
more energy per unit mass than CHO metabolism.
kcal/g of fuel
CHO
Fat
Fats are stored in the absence of H2O.
4.10
9.45
Effects of Exercise Intensity
• Plasma FFA (fat from
fat cells) is the
primary fuel source
for low intensity
exercise
• As intensity
increases, the source
shifts to muscle
glycogen
From: Powers & Howley. (2007).
Exercise Physiology. McGraw-Hill.
Effects of Exercise Duration
From: Powers & Howley. (2007). Exercise Physiology.
McGraw-Hill.
Fuel Selection
From: Powers & Howley. (2007). Exercise Physiology. McGraw-Hill.
• As intensity increases carbohydrate use
increases, fat use decreases
• As duration increase, fat use increases, carb use
decreases
Contribution of different fuels to metabolism by the
working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficient
Storage
Metabolic
• Preserving muscle glycogen core
Other fuels are utilized to spare muscle glycogen during
prolonged exercise thereby delaying exhaustion
Lactate
Pyruvate
Amino Acids
Adipose
NEFA
Glycerol
NEFA
Muscle
GLY
GNG
ATP
GLY
Glucose
Liver
As exercise duration increases:
• More energy is derived from fats and less from glycogen.
• Amino acid, glycerol, lactate and pyruvate carbons are
recycled into glucose.
Contribution of different fuels to metabolism by the
working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficient
Storage
Metabolic
• Preserving muscle glycogen core
Discussion Question
Can you accommodate all three principles
of fuel utilization?
Why not?
What is the Consequence?