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Chemical pathways and reactions that result in the breakdown of molecules (catabolism) or synthesis of molecules (anabolism)
Set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP)
Fat, protein and carb metabolism ultimately leads to
- Electron carriers going to the electron transport chain
Reactions that require ATP
What factors determine how much energy is associated with carbs, fat, and protein?
- Chemical structure
- Number of hydrogen atoms, and strength of bonds
Electron is removed from an atom or molecule
Addition of electron from an atom or molecule
Role of enzymes
- Regulate the speed at which a reaction occurs
- Do not cause a reaction to occur
- Affected by pH and temperature
Muscle has limited storage capacity for fat and carbohydrate, the 2 most important fuels for contracting muscle. Thus, during exercise, muscle uses carbohydrate and fat stored from other organs. What are these organs?
- Liver supplied additional carbohydrates in the form of glucose
- Makes glucose moreso than stores
- Adipose tissue (subcutaneous) supplies additional lipids in the form of fatty acids
- Fat also secretes hormones and cytokines that can affect metabolism in lever and muscle (fat is endocrine organ)
- Nervous system - does not provide fuel, but needs constant supply of glucose; competes with muscle for glucose
Where is carbohydrate stored in the body?
- Muscle Glycogen (400 g)
- Liver glycogen (100 g)
- Blood glucose (3 g)
- There is also a small amount of glucose in some organs, but it is only available for the metabolic needs of those organs
Storage of carbohydrates
- Muscle glycogen
- Liver glycogen
- plasma glucose
Role of glycogen in the muscle
- To provide fuel to be oxidized
- Supplying energy for muscular contraction
Role of glycogen in liver
- Provides temporary storage for glucose; produce new glucose when body glycogen stores are compromised
- From glycerol and lactate
Oxidation of glucose to produce pyruvate
- Breakdown of glycogen to yield glucose, which is oxidized to pyruvate
- Catecholamines stimulate
- Insulin inhibits
- Synthesis of glycogen
- Catecholamines inhibit
- Insulin stimulates
Gram per gram, which form of carbohydrate contains the most energy?
- They all contain the same amount of kcal/g
- Chemically, all of these different forms of carbs are very similar
- Each contains approximately 4 kcals/g
What fraction of energy from the breaking of phosphate bonds from ATP is available as energy for mucular contraction?
Substrate level phosphorylation
- Does not require oxygen
- Occurs in both glycolysis and Kreb's
- 2 in glycolysis
- 1 in krebs
- Requires oxygen
- Reactions occur exclusively in the mitochondria
- Most important mechanism for synthesizing ATP
- ATP production is coupled to oxidation of the reduced hydrogen carriers NADH+H+ and FADH2
- Immediate energy system (phosphagen)
- Kreb's cycle
- Elextron transport
All energy systems are always being used, but the type of exercise and amount of product available changes the proportions of what energy pathways are being used
AMP as a cellular signal
- When lots of ATP are being hydrolyzed, we have an increasing number of AMP and ADP in the cell
- This high level signals the body to create more ATP to meet the demands of the skeletal muscle and other organ systems
Which of the bioenergetic pathways are used during each of these activites?
all are used for each activity, but the primary tank for short duration is phosphagen, 2-3 minutes of all out effort is lactate, and marathon is fatty acid oxidation
Can you think of a way to increase the size of the immediate energy tank and glycolytic tank?
- To incrase the phosphate system, you could supplement creatine or do short, high intensity training
- To increase glycogen, you could glycogen load, or could train by doing short, high intensity training of a quarter to a half mile in intervals
How many carbons are present in glucose, pyruvate, and acetyl CoA?
6, 3, and 2 respectively
How many net ATP do we get in glycogenolysis from SLP's?
3 net ATP
What is the effect of excess NADH in aerobic metabolism?
It feedsback to shut down the ETC
When is lactate produced?
When the demand of oxygen exceeds the availability
What causes the 'burn' of lactic acid?
The H+ ion that is carried with the lactic acid, which then reduces the body's pH
Fat of lactate
- Lactate shuttle - diffuse into adjacent fibers, converted back to pyruvate, and used as fuel
- Diffuse into blood stream and used as fuel by the heart, or sent to the cori cycle to synthesize glucose
Under what circumstances would there be inadequate oxygen supply and the formation of lactate?
- If you are producing NADH at a rate faster than oxygen is delivered to the muscle, lactate is formed
- Conversion of pyruvate to lactate permits ATP to be synthesized at a rate faster than possible from the availability of oxygen
- Found largely in the nervous system
- Does NOT require insulin
Found in liver, does not require insulin
- Found in muscle and fat cells
- Requires insulin to be active
- Can ALSO be stimulated by exercise
How is GLUT4 mobilized?
- Insulin is secreted by the pancreas, delivered through the blood stream, and activates a receptor causing the GLUT4 molecules to come off of their vesicles and translocate to the sarcolemma
- This activates GLUT4, allowing glucose to come into the cell
- Reduced ability of insulin to exert its effects on muscle, liver, and adipose tissue
- Precursor type 2 diabetes
- Insulin still binds to its receptor, but GLUT4 translocation is impaired
- Decreased glucose uptake, causing hypergylcemia
What does each turn of the Kreb's cycle produce?
1 molecule of ATP (SLP), 3 molecules of NADH + H+, 1 molecule of FADH2, and 2 molecules of CO2
Can acetyl CoA be converted into pyruvate?
No, because this step is a committed step, and therefore we cannot create carbohydrates from fat
Per molecule of glucose, we produce?
10 molecules of NADH, 2 FADH, 5 ATP, and 4 CO2
Where is O2 tranported into muscle
via myoglobin in complex 4 of the ETC
1 molecule of NADH+H+ =
1 molecule of FADH2 =
If an uncoupler were present and active, how much substrate (fat, carb, protein) would be oxidized per ATP (i.e., would you burn more or less substrate to produce the same amount of energy in the form of ATP)?
- More substrate to produce the same amount of ATP
- Metabloic rate also increases
- Exercise CAN stimulate brown adipose tissue
How many ATP are produced by the complete oxidation of 1 molecule of glucose?
The following reaction is an example of what?
1,3 DPT + ADP --> 3 DPG + ATP
Substrate Level Phosphorylation (SLP)
Where does glycolysis, the Kreb's cycle, and electron transport occur within the cell?
- Glycolysis - cytoplasm
- Kreb's cycle - mitochondrial matrix
- ETC - Inner mitochondrial membrane
The conversion of pyruvate to _______ permits _____ to be recycled as a reducing agent, thus permitting _______ to continue at a fast rate
List 2 factors that stimulate GLUT4 proteins?
- Muscle contraction
List 2 molecules that contain 3 carbon atoms, circulate the plasma, and can be evetually metabolized in the glycolytic pathway
Acetyl CoA can be formed from
- Fatty Acids
- Carbon skeletons of amino acids degraded from protein
When plasma glucose > 100 mg/dL
- Insulin is released from the beta cell of pancreas
- Promotes glucose uptake by muscle, liver, and fat
- Inhibits lipolysis in adipose tissue
- Inhibits glucose release from liver
When plasma glucose < 90 mg/dL
- Glucagon is released from alpha cells of the pancreas
- Inhibits glucose uptake by muscle, liver, and fat
- Stimulates lipolysis in adipose tissue
- Promotes glucose release from liver
Amine and polypeptide hormones
- Quick uptake at target tissues
- Typically secreted in a pulsatile manner
- Short half-life
- E.g. catecholamines, insulin, glucagon
How does exercise stimulate the release of catecholamines?
Exercise stimulates the sympathetic nervous system, which causes stimulation of the medulla, which secretes catecholamines
When anterior pituitary is stimulated...
- Triggers the release of 'releasing hormones'
- ACTH acts on the adrenal cortext to cause secretion of glucocorticoids (cortisol), which influences several target organs
- High levels of cortisol in the blood causes negative feedback by stopping the secretion of ACTH
Mechanisms of hormone action
- 1. Alter membrane transport
- 2. Activation of 2nd messenger systems to stimulate or inhibit enzyme activity (cAMP)
- 3. Modulating the rate of intracellular protein synthesis by stimulating DNA and gene transcription in the nucleus
- Example is to change transcription to increase muscle growth
2nd messenger cascade activating glycogenolysis
- 1. A molecule of adrenaline stimulates adenylate cyclase to form several molecules of cAMP
- 2. Each molecule of cAMP activates several molecules of active cAMP kinase
- Each molecule of cAMP kinase activates several molecules of phosphorylase and inactivates several molecules of glycogen synthase
What determines the activity of hormones
- Activity is determined by the free hormone concentration
- Many hormones are bound to transport proteins
- Hypothalamus reacts to a stimuli, and stimulates secretion of a releasing hormone
- Releasing hormone stimulates release of AP hormone
- AP hormones stimulate another endocrine organ to release another hormone
When ACTH acts on the adrenal cortex, what is most often released
What is the HPA axes hormonal response to exercise?
- Release of:
- HP adrenal cortex axis (cortisol)
- HP growth hormone axis (GH)
- HP thyroid axis (thyroid hormones)
What is the non-HP axes hormonal response to exercise?
- Pancreas (Insulin and glucagon)
- Adrenal medulla (catecholamines)
- Adrenal cortex (aldosterone)
- Parathyroid gland (calcitonin and PTH)
- Posterior pituitary (antidiuretic)
Role of cortisol in exercise
- Maintains plasma glucose by increasing FFA supply by stimulating lipolysis in adipose tissue
- Also stimulates glucose release and production in the liver
- Attenuates/inhibits glucose uptake by skeletal muscle
- Aids in recovery and repair after strenuous exercise
ACTH has what effects on glucose?
Sparing, it stimulates lipolysis and gluconeogenesis/glycogenolysis
Growth hormone's effects
- Stimulates the release of insulin-like growth factors (IGF1 and IGF2) from liver
- This promotes growth and repair in skeletal muscle
Effects of HP thyroid axis on exercise
To enhance catecholamines effects
What happens when liver glycogen is full?
We produce VLDL
What happens to glucose, insulin, and glucagon during exercise (assuming no carbohydrate is consumed during exercise)?
As intensity of exercise increases, blood glucose will decrease first. Catecholamine release then stimulates the release of glucagon and inhibits insulin, keeping glucose levels at normal range
Why are NE levels higher than E levels during exercise
- NE is a neurotransmitter in skeletal muscle, which spills into the blood stream, making NE levels greather than E
- Epinephrine is the primary catecholamine regulating plasma glucose
Function of aldosterone
Regulates plasma volume and Na+/H20 balance by regulating Na+ and K+ secretion at the kidney
Aldosterone secretion during exercise is stimulated by?
- Increase in plasma [K+]
- Decrease in plasma volume
- Increase in sympathetic nervous system activity
How does exercise lead to decreases in plasma volume and increase in plasma [K+]
- Sweating causes plasma volume to decrease. The volume of potassium stays the same, but the concentration increases because of the reduced plasma volume
- Fluid shifts (more fluid to muscle, less to plasma) also causes plasma volume to fall and concentration of [K+] to increase
- These two factors cause the release of aldosteron
High serum calcium concentration stimulates?
Release of calcitonin from thyroid gland to block the release of calcium from bone; and stimulates calcium storage in bone and excretion at the kidneys
Low serum calcium concentration stimulates?
- Release of parathyroid hormone from teh parathyroid gland that acts to raise serum calcium by breakding down calcium in bone, releasing it into the blood
- Vitamind D helps the intestines take in calcium
Exercise stimulates release of PTH, why?
Low serum calcium caused by sweat loss
What is the action of ADH (vasopressin)
- Stimulates reabsorption of water in kidneys
- This preserves plasma volume, and reduces urin output
What is the action of oxytocin
Musce contraction in uterus and ejection of milk during lactation
Describe the difference in how hormones from the anterior and posterior pituitary are secreted
- AP - hypothalamus secretes a releasing hormone which signals the AP to release a specific hormone
- PP - hormones are stored and secreted when needed
Name 2 posterior pituitary hormones
Oxytocin and ADH
What are 2 stimuli that can promote an increase in aldosterone secretion? What organs are involved?
- Increase in [k+]
- Decrease in plasma volume
- Kidney, lung, and liver are affected
What is the role of ADH in exercise?
Helps maintain blood volume and blood pressure
Hormone that stimulates gulcose uptake
Hormones that inhibit glucose uptake
- Cortisol, GH, catecholamines
- These are known as counterregulatory hormones
Hormones that stimulate lipolysis
Cortisol, GH, catecholamines
Hormones that inhibit lipolysis
What are the actions of counter regulatory hormones
- Increase availability of other fuels
- Stimulate gluconeogenesis
- Block uptake of glucose into cells
3 situations where blood glucose falls and counter-regulatory hormones are released
During sleep, blood glucose is used by the brain and CNS. Where does this glucose come from?
Liver glycogen stores
What are your liver glycogen stores like when you wake up?
- They are nearly empty, because the body does not use muscle glycogen unless the muscles are active
- The liver can take up glucose from the blood and make it into pyruvate, or can take pyruvate, lactate, or glycerol, and turn it back into glucose
- Muscle CANNOT turn lactate, pyruvate, or glycerol back into glucose
As exercise intensity increases, what happens to levels of insulin, and all hormones that stimulate release of glucose, ffa, and protein?
- Insulin will drop as intensity of exercise increases, whereas epi, norepi, GH, cortisol, and glucagon will all increase as intensity increases
- Same effect when duration increases
Glucose uptake is increased during exercise many fold above resting values. Since insulin concentrations are falling during exercise, and the effects of the counter-regulatory hormones is to block glucose uptake, how does muscle maintain such a high rate of glucose uptake
- Muscle contraction stimulating GLUT4 mobilization
- Increased blood flow to muscle
What must blood glucose levels be maintained at to supply adequate fuel to brain and CNS
Name 4 ways that the body can maintain plasma glucose during exercise
- Upregulation of lipolysis
- attenuate glucose uptake (conserve plasma glucose)
What do catecholamines do to glycogenolysis in the liver and muscle?
- Directly stimulate it
- They will also cause release of glucagon, and inhibit the release of insulin
How do we make new glucose?
Gluconeogenesis, which is synthesizing glucose in the liver from carbon residues of other compounds such as amino acids, lactate, pyruvate, and glycerol
What stimulates HSL?
- Glucagon, GH, and cortisol
- HSL stimulates that breakdown of triglycerides
List hormones that decrease and increase during exercise
- Insulin decreases
- Epi/norepi, glucagon, cortisol, GH, and epinephrine increase
List the hormones that stimulate and attenuate glucose uptake into muscle
- Insulin stimulates glucose uptake into muscle
- Cortisol, GH, and epinephrine attenuate glucose uptake into muscle
Where is fat stored in the body?
- Adipose tissue and muscle as IMTG
- Adipose is both subcutaneous and visceral
What type of fat is most present in the body?
What is most fat in the blood stored as?
- TG in circulating lipoproteins (LDL, VLDL)
- Small fraction of lipid in plasma as FFA
What is a chylomicron?
A carrier of triglycerides
Why is HDL a 'healthy' fat?
It can take lipid out of an endothelial cell and bring it to the liver, where it can be secreted
Insulins relationship with fats
- Stimulates the uptake
- Also inhibits hormones such as HSL, which inhibits lipolysis
Side note on glucose
Can be used to make glycerol backgone of TG molecule, but not FFA
Where does visceral fat drain?
Into the portal vein, thus anything produced by visceral fat goes to the liver
How are IMTGs stored?
- As simple droplets, often near mitochondria
- Slow twitch fibers have larger droplets and larger mitochondria
- Stores increased by endurance training
Brown adipose tissue
- Man small lipid droplets
- Many mitochondria 'thermogenic'
- 1% of adult adipocytes
- Dense capillary network, similar to muscle
- Innervated by SNS, which releases NE to break down fat locally
- Large lipid droplet, occupying most of intracellular space
- No mitochondria
- 99% of adult adipocytes
- Innervated by SNS
Hydrolysis of triglycerides into free fatty acids
HSL stimluation and inhibition
- Stimulated by catecholamines
- Inhibited by insulin
LPL turnsVLDL into free fatty acids
VERY small energy store
What second messenger regulates lipolysis?
- Epinephrine binds to beta 1 receptor and activates the cascade, which activates HSL, which leads to lipolysis
- If alpha 2 receptor is activated, lipolysis is inhibited by shutting off this pathway
Epi/norepi binds to both beta 1 and alpha 2 receptors on adipose tissue. How do you think this effects lipolysis during low (<40% VO2max) and high intensity (>75% of VO2max) exercise
- During low intensity exercise, beta 1 is bound, and we stimulate lipolysis
- During high intensity exercise, alpha 2 is bound, and we inhibit lipolysis
What stimulates lipolysis?
- Growth hormone
- Thyroid hormones
- Cytokines (leptin)
- These all elicit a much slower response than catecholamines
If blood flow increases to adipose tissue
- More regulating hormones (catecholamines, insulin) and more carrier proteins (albumin) are delivered to adipocytes
- Lipolysis can be increased simply by increasing blood flow to fat cells
- Exercise at moderate intensity increases blood flow to adipose tissue by 2x
ATBF and lipolysis
- Have same characteristics and are both stimulated by catecholamines
- ATBF low at high intensity exercise
What happens to lipolysis if fasting insulin goes above 10 uU/mL?
Lipolysis can be suppressed by 50%
Insulin's affects on cAMP
- When insulin binds to its beta receptor, it stimulates PI3 Kinase, which then phosphorylates and activates phosphodiesterase
- Phosphodiesterase degrades cAMP, causing a decrease in cAMP activity
- By decreasing cAMP, insulin causes HSL activity to decline
After consumption of a meal, insulin increases. What happens to plasma FFA concentrations?
Plasma FFA concentration falls, because lipolysis is shut down, and the FFA in the blood is used up
Insulin resistance in skeletal muscle leads to a decrease in glucose uptake by the skeletal muscle. What are the effects of insulin resistance in adipose tissue?
- Higher levels of fat in bloodstream
- Can even become toxic
- Starts to deposit cells throughout the body, which begins to interfere with normal metabolism
What happens when we have excess fat in blood?
- We have to uptake fat into muscle
- This activates a couple Fatty acid bindng protein and CD36
- These proteins bring fat into muscle, and are eventually converted into acetyl-CoA, and are brought across the mitochondrial membrane by CPT, where we go through beta oxidation, whih leads to acetyl-CoA units brought to the krebs, leading to a significant amount of ATP
- If the muscle is not active, the fat can be stored as IMTG
Excessive FFA delivery to skeletal muscle can induce insulin resistance. Can you think of a potential mechanism?
- You get excess fat in the cell, which inhibits the pathway of GLUT4 mobilization
- Inhibition comes on the insulin side, insulin is prevented from binding GLUT4
Converts FFA into several molecules of acetyl CoA
Complete oxidation of oleic acid (18 c) yields how many ATP?
Complete oxidation of one TG molecule (1 molecule of glycerol + 3 moelcules of oleic acid) yields how many ATP?
Acetyl-CoA produces how many ATP in the Krebs?
In the Krebs, 1 acetyl-CoA also gives off
- 1 SLP, 1 NADH+, and 1 FADH2
- The NADH+ and FADH2 produce 4 ATP in the ETC
Where can you make fat from carbs?
- Only in the liver
- This only occurs when calories are consumed in excess
- 2% of carb calories can be turned into fat
Hierarchy of fuel oxidation
Several cytokines released from visceral adipocytes (aka adipokines) have been implicated in insulin resistance. Can you think of a way that a cytokine produced by adipocytes can affect insulin action in skeletal muscle?
Interferes with GLUT4 transporter
In obese humans, plasma leptin concentrations are actually higher than in lean individuals. Can you think of a reason why this might be?
What does leptin do?
- Stimulates thermogenesis in tissues such as muscle and liver
- Decreases energy intake by suppressing hunger and satiety (in hypothalamus)
Most fat is stored in subcutaneous adipose tissue, even in very obese individuals. During exercise,
Most of fatty acids delivered form muscle come from subcutaneous fat
What are the primary stimulators of lipolysis?
Catecholamines, glucagon, and cortisol
What is the primary inhibitor of lipolysis?
What determines the rate of lipolysis in different adipose tissues?
Blood flow and concentration of hormones
What does the liver use for energy?
- Beta-oxidation of free fatty acid
- Liver is also the primary cite of synthesis of cholesterol from dietary fat
How much glycogen does the liver store?
- 100g, which is about 25% of what muscles store
- This glucose can be delivered to muscle through glycogenolysis
How does the liver create new glucose?
HGO (hepatic glucose output)
The summed deliver of glucose from liver glycogenolysis and gluconeogenesis is called hepatic glucose output (HGO)
Does calcium play a role in regulating hepatic glycogenolysis?
No, only in skeletal muscle
- Pyruvate made from either lactate, glycerol, or alanine
- Only reason this can be done in the liver, is because we can reverse this last step in the liver, when phosphoenol pyruvate is acted upon by pyruvate kinase to give pyruvate
What would be the effect of insulin resistance in the liver?
- Inhibition of all glucose output
- Glucose levels in blood skyrocket
- Big issue for type II diabetics
Lactate to pyruvate
- Amino acids (alanine and glutamine)
- Lactate produced by muscles during exercise released in plasma
- Plasma lactate is taken up by the liver, and converted to pyruvate
- Pyruvate is run through the process of 'reverse glycolysis' to produce glucose
- Glucose produced by the liver can be stored as glycogen, or be released into the blood directly as glucose
- Conversion of alanine to plasma glucose
- Excessive pyruvate production during (prolonged) exercise leads to production of the amino acid alanine
- Alanine is transported to the liver, taken up, and converted to pyruvate
- Pyruvate is run through the process of "reverse glycolysis" to produce glucose
- Glucose produced by the liver can be stored as glycogen, or released to the blood directly as glucose
HGO (hepatic glucose output) during exercise
- increases up to 10x above resting levels, which is primarily due to gluconeogenesis
- Increase is proportional to exercise intensity and duration
HGO during exercise <60% VO2max
- Plasma glucose remains constant
- HGO= muscle glucose uptake
HGO during exercise >60% VO2max
- Plasma glucose increases slightly
- Hepatic glucose output > muscle glucose uptake
Given what we know about glycogen storage in the liver, how will exercise duration affect liver glycogenolysis and gluconeogenesis
- <1 hr, most HGO is from glycogenolysis
- >1 hr, most of HGO is from gluconeogenesis
Describe the changes in insulin and glucagon during exercise, and how this would effect hepatic glucose output
- Most of the increase in HGO during exercise is due to the decrease in insulin rather than the increase in glucagon
- Insulin drops dramatically at the onset of exercise, but glucagon doesn't increase much
What stimulates the release of glucagon during exercise?
Increase in catecholamines
During exercise, most of the glucose produced during gluconeogenesis is released to the plasma, rather than stored as liver glycogen, why?
FFA in the liver
difference between liver and skeletal muscle, is that the acetyl-CoA that is forme din the liver is converted to ketones rather than entering the TCA cycle as acetyl-CoA
During starvation, prolonged severe exercise, and uncontrolled diabetes, FFA is released form adipose tissue is delivered to liver and converted to ketones
- Can be used by brain and CNS as alternative fuel sources
- If produced in mass quantities, can produce acidosis
Effect of endurance training on HGO
- increased liver glycogen storage (~20%)
- Increased gluconeogenic capacity
- Enhanced insulin sensitivity
As a result of endurance training, what happens to hepatic glucose output during exercise at the same absolute workload?
- It decreases
- The liver will have greater capacity for gluconeogenesis, but will not need to put out as much glucose, because muscle is using more fat
Gluconeogenesis is stimulated by what?
Glycogenolysis is stimulated by what?
Catecholamines, glucagon, and cortisol
What are 2 indirect but easy methods of measuring how much ATP the body is using at any given time?
VO2 and heat production
Measurement of heat production
- Measurement of oxygen consumption
- Burn 5 calories per liter of oxygen
subject inspires ambient air, and rate of oxygen consumption determined by changes in O2% and CO2% in expired air
reflects measurements made at mouth
- Reflects measurement made at tissue
- RER=RG during steady state exercise
Is RER lower when fasted (i.e. first thing in the morning before breakfast) or after eating a meal?
RER is lower when fasted, mostly because liver glycogen is depleted overnight
When is RER higher - during walking or running?
At the start of exercise, where do we get most of our ATP?
- From nonaerobic pathways, because ATP is not being produced fast enough at the start
- Trained person gets to steady state much quicker
In type 2 diabetes, there is mitochondrial dysfunction. Compared to sedentary and trained healthy individuals, what will VO2 at the onset of exercise look like?
VO2 inreases much quicker in a healthy, trained individual than in a diabetic. This quicker increase in VO2 means that the trained individual will use less anaerobic pathways, making exercise more efficient
What are the clinical implications for exercise in people with type 2 diabetes?
Takes longer for a diabetic to meet steady state
What are some factors that affect the magnitude of O2 deficit
- Intensity of exercise
- Training status
- Health status
Recovery from exercise
Fast portion of EPOC (first 2-3 minutes)
O2 is used to restore ATP and PC to resting levels, and restore muscle and blood O2 stores
Slow portion of EPOC
- Used to support heart and muscles of respiration (elevated heart rate and breathing)
- Reduce body temperature back to normal
- Oxidize excess lactate back to glucose
EPOC is proportional to exercise intensity. Can you think of a means to increase EPOC
- Train at altitude
- Train in heat
- Exercise in cold
- Increase duration
What type of post exercise recovery is best to facilitate lactate removal
Moderate intensity exercise
What is the largest portion of total daily energy expenditure?
Exercise trainings affects on submax or resting VO2
Little to no effect unless body composition changes, Max VO2 is strongly influenced
RMR's greatest fraction
Maximal capacity of the cardiovascular system to deliver oxygenated blood to a large muscle mass involved in dynamic work
- 3.5 L/min (45 ml/kg/min) in untrained male
- 2.0 L/min (38 ml/kg/min) in untrained female
Criteria for achieving VO2max
- Leveling of oxygen consumption (VO2) with increasing exercise intensity
- <2 mL/kg/min increase in VO2 with an increase in intensity
- RER > 1.15
- >85% of age-predicted max HR
- Blood lactate > 8-10 mmol
Why does RER > 1.0?
Buffering of lactic acid by sodium bicarbonate results in production of non-metabolic CO2
Estimating energy expenditure based on measurement of respiratory gas exchange is called
For every liter of oxygen consumed, approximately how many kcals are expended?
During the end stages of a maximal exercise test, why does RER increase above 1.0?
The largest component of total daily expenditure is
The largest contributor to resting metabolic rate is
In general, the highest VO2max values are observed during which mode of exercise testing?
Treadmill running on a grade
Lipid, as a sole fuel, can support exercise at what % VO2max
cannot support exercise at intensities greater than 50-60% of VO2max
Name 2 strategies for enhancing carbohydrate availability
- 1.) Consume more carbohydrate before exercise
- 2.) Consume more carbohydrate during exercise
What promotes glycogenolysis?
Phosphorylase A, the active form (activated by Ca2+)
What slows the rate of glycolysis?
Phosphorylase b - inactive form
Where does glycogenolysis primarily occur at the onset of exercise?
In type I (slow twitch) fibers
As glycogen stores in type I fibers are depleted, glycogenolysis in what type of fibers then increases?
Type IIx and IIa, althought there is limited stores in these fibers
How long does it take to fully deplete muscle glycogen stores?
- 1-2 hours of high intensity exercise
- Low intensity takes over 3 hours
Plasma glucose uptake increases as glycogen stores become depleted because
There is a decreased availability of muscle glycogen, and increased glucose delivery to muscle due to increased blood flow to muscle and increased glucose extraction
Role of glycogen synthase
- Enzyme responsible for resyntehsizing glycogen
- Post exercise, our body is very sensitive to storing carbs. This is known as supercompensation
Exercise effects on GLUT4 and insulin
- GLUT4 protein is increased for ~24 hours
- Insulin sensitivity is enhanced for ~2 days
What is the importance of using fatty acids as a fuel? If you can increase utilization of fatty acids, what happens to glycogen utilization? How might this affecte endurance?
By using fat, you can sustain exercise longer and give you a kick at the end by preserving muscle glycogen, but always using SOME glycogen
During low intensity exercise, how is lipolysis regulated?
Epi concentrations are low, but beta-1 receptors have high affinity for epi; therefore most epi binds to beta-1 receptors and lipolysis is stimulated
During high intensity exercise, what happens to lipolysis?
Epi begins to bind to alpha-2 receptor, and lipolysis is inhibited
What increases lipolysis?
increased blood flow to adipocytes and muscle
Which sex burns more fat?
Female burn SLIGHTLY more
For exercise lasting longer than a few seconds in duration, what is the primary fuel burned?
During what type of exercise is fat oxidation the greatest?
- Moderate intensity exercise (50-60% VO2max)
- Rate of blood flow is highest at these intensities
- Epi/norepi concentrations low
What is the affect of consuming carbs within a few hours before exercise?
It substantially reduces fat oxidation
What is the effect of consuming carbohydrate during exercise on fat and carbohydrate oxidation? How does this occur?
If you consume carbohydrates during exercise, you activate GLUT4, and mass action, and will have relatively little insulin release
Exercise that recruit muscles with primarily slow twitch fibers will burn more?
Describe the effects of increasing exercise duration and intensity on fat and carbohydrate oxidation?
- Increased duration, more fat is burned
- Over time you will have a greater reliance
- Increasing intensity shifts to increased dependence on carbohydrates
How does exercise intensity affect the oxidation of IMTG and plasma FFA
- Plasma ffa is highest at lowest intensities
- IMTG is highest at moderate intensity
What are some possible reasons why total fat oxidation is reduced when exercise intensity is increased from 60% to 85% of VO2max
High epi/norepi concentrations decreases blood flow to adipocytes (reducing lipolysis, and thus FFA delivery)