macronutrient metabolism in exercise and training chapter 5
TRANSCRIPT
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Macronutrient Metabolism in Exercise and Training
Chapter 5
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Fuel for Exercise
The fuel mixture that powers exercise generally depends on:• The intensity of effort• The duration of effort • The exerciser’s fitness status• The exerciser’s nutritional status
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Bioenergetics
• Cells need constant supply of ATP• Minimal amounts stored for cellular processes
– Intramuscular
• Muscular contraction-exercise– Constant, large supply
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Bioenergetics
• Formation of ATP (3 metabolic pathways)– 1. Phosphocreatine (PC) breakdown
• ATP-PC system (phosphagen system)
– 2. Degradation of glucose and glycogen • Glycolysis (Glycolytic system)
– 3. Oxidative phosphorylation • Tricarboxylic cycle, Krebs cycle
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Bioenergetics
• Anaerobic pathways (do not involve O2)
– 1. ATP-PC breakdown – 2. Anaerobic glycolysis
• Aerobic pathway– Requires O2
– 2. Aerobic glycolysis– 3. Oxidative phosphorylation
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Bioenergetics
• ATP-PC ATP-PCr (30 sec)
• Activities (examples)– Sprints (< 30 sec)– High jumping– Weight lifting
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Bioenergetics
• Anaerobic Glycolysis –– Lactic acid system (20 or 30 sec to 120 sec) Intermediate in duration
Examples:• Middle distance running • Swimming• Basketball
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Bioenergetics
High intensity exercise – 2 minutes ATP-PCr (30 sec) Lactic acid systems (30-120 sec) Provide 50% of the energy
Aerobic sources• Provide 50% of the energy
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Aerobic Energy
Longer duration Requires a steady energy supply Examples:
• Marathon running• Distance swimming or cycling• Jogging, hiking, or backpacking
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Energy Continuum
100%
% C
apacity of E
nergy S
ystem
10 sec 30 sec 2 min 5 min +
Energy Transfer Systems and Exercise
Aerobic Energy System
Anaerobic Glycolysis
ATP - CP
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Relative Aerobic & Anaerobic Contributions
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Sources of Energy for ATP Synthesis
Sources of energy for ATP synthesis include:• Liver and muscle glycogen• Triacylglycerols within adipose tissue and
active muscle• Amino acids within skeletal muscle donate
carbon skeletons
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Carbohydrate Use During Exercise
Intense anaerobic exercise Muscle glycogen Blood glucose
Sustained high levels - aerobic exercise. Glycogen stores Blood glucose –
Glycogen breakdown - released from liver
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Macronutrient Contributions
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Intense Exercise
Change in hormone release Epinephrine Norepinephrine Glucagon Decreased insulin release
Stimulation Glycogen phosphorylase - glycogenolysis
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Intense Exercise
Early stages• Stored muscle glycogen
• Later stages• Glycogenolysis of liver stores
• Blood glucose
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Moderate and Prolonged Exercise
As exercise continues• Glucose from the liver becomes major
contributor (as muscle glycogen falls; about 2-3 hrs)
• Fat use increases
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CHO & Exercise
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Glycogen Depletion
Blood glucose levels fall. Level of fatty acids in the blood increases. Proteins provide an increased contribution
to energy. Exercise capacity progressively
decreases.
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Moderate and Prolonged Exercise
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Fatigue
• “hitting the wall”– Fall in muscle/liver glycogen
• Results – CNS used blood glucose as energy (central
fatigue)– Increased fat metabolism – Fat provides energy at a slower rate
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Trained Muscle
Trained muscle Increased ability to produce ATP (inc.
mitochondrial volume) Increased blood supply (capillary density) Increased glycogen storage
So, trained individuals Maintain a higher work rate Maintain that workrate for longer periods of
time
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Dietary Influence
• Condition 1 (Low carb)– Normal caloric intake – 3 days– CHO 5%– Lipid 95%
• Condition 2 (normal)– Recommended % CHO, Fat, Pro
• Condition 3 (high carb)– CHO 82%
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Dietary Influence
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Influence of Diet
A carbohydrate-deficient diet Rapid depletion of muscle and liver glycogen.
Low carbohydrate levels Intensity decreases to level determined by
how well the body mobilizes and oxidizes fat. So, this diet reduces performance
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Fat as an Energy Substrate
Fat supplies about 50% of the energy Light and moderate exercise.
Stored fat Important during the latter stages of
prolonged exercise (greater than 2 hours)
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Caloric Equivalents
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Sources of Fat During Exercise
Fatty acids released from adipocytes• Delivered to muscles as FFA bound to plasma
albumin
Circulating plasma triacylglycerol Very low-density lipoproteins Chylomicrons
Triacylglycerol Within active muscle itself
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Lipolysis
Hormones activate lipase. • These hormones are secreted more during
exercise.• Epinephrine, Nor-epinephrine, GH
Mobilization of FFAs from adipose tissue Trained muscle has an increased ability to
utilize fat due to the higher volume of mitochondria
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Exercise Training
Regular aerobic exercise:• Increases the ability to oxidize long-chain fatty acids• Improves the uptake of FFAs• Increases muscle capillary density • Increases size and number of muscle mitochondria• SO, at the same workload, after training
• Fat metabolism is up and CHO metabolism is down
• Same relative workload (% max), CHO and Fat utilization is the same
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Exercise Training
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Protein Use During Exercise
Carbohydrate-depleted state Causes significant protein catabolism.
Protein utilization rises Endurance Resistance-type exercise.
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Protein Use During Exercise
Greater use as energy fuel than previously thought• Nutritional status • Intensity of exercise training or competition.• Duration of exercise• Certain AAs, the branched-chain amino acids
• Leucine, Iso-leucine and valine• Oxidized directly in skeletal muscle
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Exercise and Protein Metabolism
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Protein Use During Exercise
• Branched-chain amino acids • Oxidized in skeletal muscle not the liver.• Leucine, isoleucine, valine
• Make up 1/3 skeletal muscle• Important in protein synthesis
– Seem to be oxidized during longer term endurance exercise
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Exercise and Protein Metabolism
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Exercise and Protein Metabolism
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Exercise and Protein Metabolism