Download Macronutrient Metabolism in Exercise and Training

Macronutrient Metabolism in
Exercise and Training
Chapter 5
Fuel for Exercise
 The fuel mixture that powers exercise
generally depends on:
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The intensity of effort
The duration of effort
The exerciser’s fitness status
The exerciser’s nutritional status
Bioenergetics
• Cells need constant supply of ATP
• Minimal amounts stored for cellular processes
– Intramuscular
• Muscular contraction-exercise
– Constant, large supply
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
Bioenergetics
• Anaerobic pathways (do not involve O2)
– 1. ATP-PC breakdown
– 2. Anaerobic glycolysis
• Aerobic pathway
– Requires O2
– 2. Aerobic glycolysis
– 3. Oxidative phosphorylation
Bioenergetics
• ATP-PC
 ATP-PCr (30 sec)
• Activities (examples)
– Sprints (< 30 sec)
– High jumping
– Weight lifting
Bioenergetics
• Anaerobic Glycolysis –
– Lactic acid system (20 or 30 sec to 120 sec)
 Intermediate in duration
 Examples:
• Middle distance running
• Swimming
• Basketball
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
Aerobic Energy
 Longer duration
 Requires a steady energy supply
 Examples:
• Marathon running
• Distance swimming or cycling
• Jogging, hiking, or backpacking
Energy Continuum
Relative Aerobic & Anaerobic
Contributions
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
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
Macronutrient Contributions
Intense Exercise
 Change in hormone release
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Epinephrine
Norepinephrine
Glucagon
Decreased insulin release
 Stimulation
 Glycogen phosphorylase - glycogenolysis
Intense Exercise
 Early stages
• Stored muscle glycogen
• Later stages
• Glycogenolysis of liver stores
• Blood glucose
Moderate and Prolonged Exercise
 As exercise continues
• Glucose from the liver becomes major
contributor (as muscle glycogen falls; about 23 hrs)
• Fat use increases
CHO & Exercise
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.
Moderate and Prolonged Exercise
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
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
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%
Dietary Influence
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
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)
Caloric Equivalents
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
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
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
Exercise Training
Protein Use During Exercise
 Carbohydrate-depleted state
 Causes significant protein catabolism.
 Protein utilization rises
 Endurance
 Resistance-type exercise.
Protein Use During Exercise
 Greater use as energy fuel than previously
thought
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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
Exercise and Protein Metabolism
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
Exercise and Protein Metabolism
Exercise and Protein Metabolism
Exercise and Protein Metabolism