Exercise Physiology MPB 326 David Wasserman, PhD Light Hall Rm 823 3-7336.
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Transcript of Exercise Physiology MPB 326 David Wasserman, PhD Light Hall Rm 823 3-7336.
Exercise PhysiologyMPB 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 productionAnaerobic System
a. ATP-PC (Phosphagen system) b. Anaerobic glycolysis (lactic acid system)
Aerobic Systema. Aerobic glycolysisb. Fatty acid oxidationc. TCA Cycle
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 ATPa) Does not depend on long series of reactionsb) No O2 transportation required
c) Limited storage, readily depleted ~ 10 s
ATP-PCr (Phosphagen system)
Glycolysis
Glucose + 2 ADP + 2 Pi + 2 NAD+
2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
Lactate Dehydrogenase
Pyruvate + CoA + NADH + H+
Lactate + NAD+
Hypoxic conditions
Pyruvate Dehydrogenase
Pyruvate + CoA + NADP+
Acetyl-CoA + CO2 + NADPH
Lots of Oxygen
Pyruvate Dehydrogenase
Pyruvate + CoA + NADP+
Acetyl-CoA + CO2 + NADPH
Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 2H20
CoASH + 3 NADH + 3H+ + FADH2 + GTP + 2CO2
TCA Cycle
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 -1
• ß oxidation (16 Carbons / 2) –1 = 7 (at 5 ATP each) 35
• Acetyl-CoA (16 Carbons / 2) = 8 (at 12 ATP each) 96
Total per chain 130
Electrochemical Energy and ATP Synthesis
Energy for “Burst” and Endurance Activities
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)
Rate of ATP Production (M of ATP/min)• phosphagen system ..............4 • anaerobic glycolysis..………2.5 • aerobic system.......................1
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 DiseaseExercise Testing in Health and Disease
Oxygen Uptake and Exercise Domains
4
2
150 Work Rate (Watts)Work Rate (Watts)
INCREMENTAL
ModerateModerate
HeavyHeavy
300
VOVO 22 (l/min)
(l/min)
SevereSevere
00
Heart Disease
Anaerobic Threshold Concept
250
Exercise
(watts)
0
5
10
15
Exercise
20015010050
Rest Period
Onset of lactic acidosis
Blood
Lactate
mM
Athlete
Anaerobic Threshold in Some Elite Long
Distance Athletes can be close to Max
100
Oxygen Uptake
(% maximum)
Exercise
80604020Basal Oxygen Uptake
Onset of lacticacidosis
0
5
10
15
Blood
Lactate
mM
BillRodgers
Oxygen Deficit and Debt
Oxygen Uptake and Exercise Domains
2
00 1212Time (minutes)
24
CONSTANT LOAD
ModerateModerate
HeavyHeavy
SevereSevere
4
Lactate and Exercise
0
6
12
Blood LactatemM
12
Time (minutes)
0 24
Three Principles of Fuel Utilization during Exercise
• Maintaining glucose homeostasis
• Using the fuel that is most efficientStorageMetabolic
• Preserving muscle glycogen core
Glucose homeostasis is usually maintained despite increased glucose uptake by the working muscle
Time (min)
BloodGlucose
(mg/dl)
0
20
40
60
80
100
0
1
2
3
4
5
-30 0 30 60
Rates of GlucoseEntry and
Removal fromthe Blood
(mg•kg-1•min-1)
Entry
ModerateExercise
Removal
Liver Glycogen
BloodGlucose
MuscleGlycogen
Carbohydrate Stores after an Overnight FastSedentary
4 grams100
grams
400grams
Liver Glycogen
BloodGlucose
MuscleGlycogen
Carbohydrate Stores after an Overnight Fast 1 hr of Exercise
4 grams100
grams
400grams
Liver Glycogen
BloodGlucose
MuscleGlycogen
Carbohydrate Stores after an Overnight Fast 2 hr of Exercise
4 grams100
grams
400grams
Liver Glycogen
BloodGlucose
MuscleGlycogen
Carbohydrate Stores after an Overnight Fast 3 hr of Exercise
4 grams100
grams
400grams
Liver Glycogen
BloodGlucose
MuscleGlycogen
Carbohydrate Stores after an Overnight Fast 4 hr of Exercise
4 grams100
grams
400grams
!!!
Contribution of different fuels to metabolism by the working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficientStorageMetabolic
• Preserving muscle glycogen core
The Most Efficient Fuel depends on Exercise Intensity and Duration
Metabolic EfficiencyCHO is preferred during high intensity exercise because its metabolism yields more energy per liter of O2 than fat metabolism.
kcal/l of O2
CHO 5.05 Fat 4.74
CHO can also produce energy without O2!!!
Storage EfficiencyFat is preferred during prolonged exercise because its metabolism provides more energy per unit mass than CHO metabolism.
kcal/g of fuel
CHO 4.10 Fat 9.45
Fats are stored in the absence of H2O.
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
• As intensity increases carbohydrate use increases, fat use decreases
• As duration increase, fat use increases, carb use decreases
From: Powers & Howley. (2007). Exercise Physiology. McGraw-Hill.
Contribution of different fuels to metabolism by the working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficientStorageMetabolic
• Preserving muscle glycogen core
Other fuels are utilized to spare muscle glycogen during prolonged exercise thereby delaying exhaustion
GNGGLY
Adipose
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.
LactatePyruvate
Amino Acids
NEFAGlycerol
NEFA
GlucoseATP
GLY
Muscle
Liver
Contribution of different fuels to metabolism by the working muscle is determined by 3 objectives:
• Maintaining glucose homeostasis
• Using the fuel that is most efficientStorageMetabolic
• Preserving muscle glycogen core
Discussion Question
Can you accommodate all three principles of fuel utilization?
Why not?
What is the Consequence?