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hse303 > Module 4 > Flashcards

Module 4 Flashcards

Lipid Metabolism During Exercise

1
Q

What are Lipids?

A

All-encompassing term used to refer to all types of fats

incl. fatty acids, triglycerides, phospholipids and cholesterol

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2
Q

What are triglycerides?

A

The major storage lipid form that is composed of 3x fatty acids and 1x glycerol backbone

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3
Q

Structure of triglyceride

A

Glycerol molecule acts as backbone for attachment of 3x fatty acids

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4
Q

Where are triglycerides stored?

A

Within lipid droplets, which are found in most tissues. For example, adipose tissue is one organ specifically adapted for lipid storage.

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5
Q

Metabolism of TGs

A
  • CANNOT be directly metabolised for synthesis of ATP

1) It is broken down to its individual components

2) The released fatty acids can be metabolised to resynthesize ATP in the process of beta-oxidation and oxidative phosphorylation

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6
Q

Fatty acids are available for oxidation in skeletal muscle from 3 primary sources:

A

1) TG stored in adipose tissue is broken down and free fatty acids are transported to working muscle through the bloodstream

2) TG stored in skeletal muscle (Intramuscular Triglyceride or IMTG) is broken down and fatty acids released are immediately available to the muscle

3) TG stored in lipoproteins are present in the bloodstream (chylomicrons, HDL, LDL or VLDL)

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7
Q

How much energy is available from adipose tissue triglyceride

A

12kg

Equivalent of almost 5 days of continuous running

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8
Q

How much energy is available from plasma triglycerides

A

4g

Equivalent to ~2 mins of running

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9
Q

How much energy is available from plasma fatty acids

A

0.4g

Equivalent to <20s of running

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10
Q

How much energy is available from intramuscular triglycerides

A

300g

Equivalent of 2.5hr of running

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11
Q

At rest, the dominant energy source is…

A

Plasma fatty free acids (the remainder comes from plasma glucose)

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12
Q

The rate of oxidation _____ with the transition from rest to moderate intensity exercise

A

Increases

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13
Q

Fat oxidation rate ____ during moderate intensity exercise (with equal contribution from intramuscular triglyceride and plasma FFA)

A

Peaks

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14
Q

During high intensity exercise, the contribution of fat from both sources (IMTG and Plasma FFA) is _____

A

Reduced

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15
Q

What occurs during prolonged low-intensity exercise, in relation to fatty acid oxidation?

A

It gradually increases over the duration of exercise

Study: Watt et al., 2002 - 4hr of exercise @ 55% VO2max

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16
Q

In the study of trained males, that exercised at ~55% VO2max for 3hrs

  1. What happened to plasma fatty acid oxidation?
  2. What happened to IMTG use?
A
  1. There was a substantial increase in plasma FA oxidation over the 3hrs
  2. There was a decline in use of IMTG
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17
Q

The key steps, that regulate the rate of fatty acid oxidation

A
  1. Adipose tissue lipolysis
  2. Fatty acid transport into the muscle
  3. IMTG lipolysis
  4. Fatty acid transport across mitochondrial membrane
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18
Q

The adipose tissue is formed of specialised cells, called _______

A

Adipocytes

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19
Q

What are adipocytes specifically adapted to do?

A

Store triglyceride

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20
Q

The appearance of glycerol in the circulation is the better marker of…

A

Lipolysis

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21
Q

With the onset of low-intensity exercise (25% VO2max), adipose tissue lipolysis (rate of appearance of glycerol in the circulation; Ra glycerol)

A

Increases well above resting levels

At the same time, there is a decrease in the rate of fatty acid re-esterification, resulting in a greater proportion of released fatty acids entering the circulation

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22
Q

The rate of lipolysis (meaning the appearance of glycerol in circulation) plateaus at _____ intensity exercise, and remained elevated during ____ intensity exercise

A

Moderate, High

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23
Q

When examining the rate of appearance of fatty acids (i.e lipolysis), there is a decline, particularly during high intensity exercise.

What does this mean for plasma fatty acid concentration?

A

Plasma fatty acid concentrations decline during high intensity exercise

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24
Q

The decline in rate of fatty acid appearance is attributed to __________________________________ during high intensity exercise

A

A decline in adipose tissue blood flow

Because blood flow to skeletal muscle is prioritised during high-int exercise, at the expense of other tissues, including adipose tissue

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25
Q

Why does adipose tissue blood flow decline during high intensity exercise?

A

The rising catecholamine concentrations, which inhibits adipose tissue blood flow

This decline is blood flow ‘traps’ fatty acids in the adipose tissue, preventing them from entering circulation

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26
Q

Immediately after exercise, there is a ________ ________ in plasma fatty acid concentration, once adipose tissue blood flow returns.

A

Rebound elevation

This is particularly evident following exercise at 85% VO2max

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27
Q

Does the reduction in plasma fatty acid concentration explain the reduction in fat oxidation at high intensities of exercise?

First evidence piece - examined the effect by infusing lipids into circulation to elevate plasma fatty acid concentrations during high intensity exercise and examined rate of fat oxidation.

A

Plasma FA elevated successfully in lipid infusion trial

Plasma FA concentrations achieved in this study are higher than during low and moderate intensities of exercise

Showed that raising plasma FA concentrations at 85% VO2max only partially increased fat oxidation rates

Therefore, the decline in fat oxidation at high intensities is only partially due to a decline in plasma FA availability to the muscle

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28
Q

Does the reduction in plasma fatty acid concentration explain the reduction in fat oxidation at high intensities of exercise?

Second evidence piece

A

Plasma FA availability is NOT the major limiting factor in the decline in fat oxidation rate during high intensity exercise, measured fatty acid concentration in muscle

Showed that as exercise intensity increased from 65% to 90% VO2max, there is an increase in muscle fatty acid concentration

Indicates that the limitation in plasma fatty acid oxidation is NOT due to the decline in fatty acid availability - there is plenty of fatty acid available in the muscle cell

The limitations must be elsewhere, probably relating to the oxidation of fatty acids in the mitochondria

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29
Q

With prolonged exercise, rates of adipose tissue lipolysis…

A

rises markedly and progressively

This high rate of adipose tissue lipolysis is important to supply the elevated plasma FA oxidation rates during prolonged exercise

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30
Q

With prolonged exercise, plasma FA and glycerol concentrations…

A

continue to rise throughout a 4hr moderate intensity (~60% VO2max) exercise bout

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31
Q

With prolonged exercise, the rates of adipose tissue lipolysis are supported by…

A

1) Substantial rises in catecholamines

2) Reductions in insulin concentrations

Both are related to exercise duration

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32
Q

Once plasma fatty acids are released into circulation…

A

they must be delivered to active skeletal muscle

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33
Q

Lipids can circulate as triglycerides, packed into _____, secreted from the ______ or ______, absorbed from the ___

A

Lipoproteins (e.g. HDL, LDL, VLDL)

Liver

Chylomicrons

Gut

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34
Q

Triglycerides in lipoproteins need to be _____ ______ to ________ the fatty acids, and this is done by a lipase located on the capillary surface called _______. This will increase the available fatty acids for transport into skeletal muscle.

A

Broken down

Liberate

Lipoprotein lipase (or LPL)

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35
Q

Lipoproteins only account for ____% of total energy expenditure during exercise, so most fatty acids taken up by the muscle circulate as fatty acids in the blood.

A

3%

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36
Q

True or false: Fatty acids poorly soluble (meaning they do not dissolve in the blood)

A

True

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37
Q

Majority of fatty acids are transport bound to _____

A

Albumin

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38
Q

What is albumin?

A

The most abundant protein in the blood

Each albumin molecule contains 3 high affinity binding sites for fatty acids (plus 7 low affinity binding sites)

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39
Q

The high affinity fatty acid binding sites on albumin saturates at around fatty acid concentrations of…

A

2 mmol/l

The highest plasma FA concentrations are seen during prolonged exercise

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40
Q

Fatty acids require transport from the ______, across the ______ ______, and across the ________ and into the muscle cell before they can undergo oxidation.

A

Capillary

Extracellular space

Sarcolemma

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41
Q

The transport of fatty acids across the sarcolemma is related to the concentration of ….

A

plasma fatty acids

The higher the concentration of plasma FA’s = the greater the rate of FA transport

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42
Q

Fatty acid translocase (FAT, CD36)

A

A fatty acid binding protein that is present in the sarcolemma

The most well characterised fatty acid transporter in muscle

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43
Q

Fatty acid translocase (CD36) and its expression

A

Highly dependent on muscle fibre type

FA transport capacity and content of CD36 and fatty acid oxidation = all higher in type 1 (slow twitch) muscle fibers

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44
Q

Fatty acid translocase (CD36) is crucial to enable the…

A

oxidation of plasma fatty acid during exercise

studies show that fatty acid transport is substantially reduced during exercise in CD36 “knocked out” mice, compared to wild type mice that contain the CD36/FAT protein at normal levels

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45
Q

The absence of CG36/FAT causes a…

A

Reduction in fat oxidation rates during exercise and a concomitant increase in CHO oxidation

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46
Q

CD36/FAT is also present in the _____ in the muscle

A

Cytosol

Strong evidence that CD36/FAT translocates between the cytosol and sarcolemma depending on contractile activity (i.e. exercise) of the muscle

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47
Q

Muscle contraction stimulates…

A
  1. Uptake of fatty acid palmitate; AND
  2. An increase in CD36/FAT content in the sarcolemma
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48
Q

To stimulate CD36/FAT translocation, it must come from signals generated during muscle contraction, which could be:

A

1) Increased activity of AMPK (due to breakdown of ATP and rises in intracellular concentrations of AMP and ADP)

2) Rises in intracellular calcium (Ca2+) and activation of Ca2+/calmodulin-dependent protein kinase (CAMK)

3) Activation of stress signalling pathways called extracellular signal-regulated kinase (ERK)

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49
Q

Fatty acid binding protein plasma membrane (FABPpm)

A

A protein present in the sarcolemma that interacts with CD36/FAT

Translocates to sarcolemma in response to muscle contraction

50
Q

Fatty acid transport proteins 1 and 4 (FATP1 and FATP4)

A

The third type of protein implicated in sarcolemmal fatty acid transport

The sarcolemma content of these proteins increases during exercise/muscle contraction (and in response to insulin)

51
Q

An important step for maintaining fatty acid uptake is the…

A

conversion of fatty acids into fatty acyl-CoA

Occurs through the addition of CoA molecule, which ‘traps’ the fatty acid within the cell, as fatty acid acyl-CoA cannot diffuse through the sarcolemma.

This aids in keeping intracellular concentrations of fatty acids low, maintaining gradient by which fatty acids can enter the cell

52
Q

The process of FA conversion to fatty acid acyl-CoA is controlled by a group of enzymes called…

A

Acyl-CoA synthetases (ACSs)

Skeletal muscle expresses several different ACS isoforms varying in subcellular localisation, and help to channel FAs within the cell.

53
Q

Fatty acid transport protein (FATP) 1 and 4 possess ACS activity

A

They facilitate FA uptake by maintaining a fatty acid gradient

54
Q

Fatty acid binding protein cytosolic (FABPc)

A

Another protein that is present in the cytosol

Believed to be important in fatty acid trafficking

55
Q

Cytosolic fatty acid binding protein (FABPc)

A

Interacts with proteins on cell membrane (i.e. CD36/FAT) and bind to deliver fatty acid to the mitochondria for oxidation

This process is important during exercise.

56
Q

1

Proteins involved in fatty acid transport across the sarcolemma:

A

The concentration of fatty acids in the interstitial space

57
Q

2

Proteins involved in fatty acid transport across the sarcolemma:

A

Fatty acids can directly diffuse across the sarcolemma

58
Q

3

Proteins involved in fatty acid transport across the sarcolemma:

A

High rates of FA sarcolemmal transport are reliant on several proteins that facilitate this process

includes, FABPpm, CD36/FAT and FATP1/4

59
Q

4

Proteins involved in fatty acid transport across the sarcolemma:

A

CD36/FAT translocates from cytosolic stores to the plasma membrane during exercise to enable a higher rate of fatty acid transport

Due to signals that are generated by muscle contraction

60
Q

5

Proteins involved in fatty acid transport across the sarcolemma:

A

FABPc is a cytosolic isoform of FABP and is involved in delivery of fatty acids to the mitochondria

61
Q

6

Proteins involved in fatty acid transport across the sarcolemma:

A

Acyl CoA synthetases are enzymes which convert fatty acids to fatty acylCoA, a step which traps fatty acids in the cell and prepares them to undergo beta-oxidation

62
Q

Intramuscular triglyceride makes up an important energy source that contributes up to __% of total fat oxidation during exercise

A

50

63
Q

IMTG is stored in…

A

Lipid droplets

64
Q

The storage of IMTG

A

Highly muscle fibre type specific

Type 1: 2-3 fold more lipid droplets than type 2 fibers

65
Q

The breakdown of IMTG during exercise

A

Highly muscle fiber type specific

Reductions in IMTG content only seen in type 1 muscle fibers

66
Q

Reductions in IMTG content in type 2 muscle fibers are only seen during…

A

very demanding exercise, in very well trained individuals

due to a combo of:

1) A high oxidative capacity in highly trained individuals; AND

2) Type 2 muscle fiber recruitment during intense prolonged exercise

67
Q

Lipid droplets in skeletal muscle can be found in…

A

subsarcolemmal and intermyofibrillar regions of the cell

68
Q

Lipid droplets in intermyofibrillar regions are located…

A

next to the mitochondria

and only these lipid droplets are readily broken down during exercise

this mitochondrial location is highly advantageous, as fatty acids that are liberated from these lipid droplets can be efficiently oxidised in the mitochondria

69
Q

Lipolysis in skeletal muscle contains the following lipases…

A

Hormone Sensitive Lipase (HSL)

Adipose Triglyceride Lipase (ATGL)

70
Q

The abundance of skeletal muscle lipases (HSL and ATGL) are higher in which muscle fiber type?

A

Type 1

This explains why the breakdown of IMTG is predominantly restricted to type 1 muscle fibers

Studies show that content of HSL and ATGL are approx. double in type 1 muscle fiber compared to type 2.

71
Q

The key difference between lipolysis occurring in muscle compared to adipose tissue

A

In muscle - lipolysis can be activated by catecholamines and muscle contraction itself

72
Q

HSL - In response to adrenaline and muscle contraction

A

HSL is translocated (moves) from cytosolic locations to the lipid droplet

this is part of the mechanism that stimulates lipolysis

73
Q

In skeletal muscle, an increase in lipase activity (combined effect of HSL and ATGL)

A

Occurs very quickly at onset of exercise

74
Q

Activation of lipolysis:

ATGL

A

Phosphorylation of ATGL from adrenaline and contraction-mediated signals is an important part of ATGL activity

ATGL activity is dependent on binding with other ‘co-activator’ proteins that increase the activity of ATGL

75
Q

Activation of lipolysis:

HSL

A

Adrenaline stimulation of PKA activity (acting via cAMP) stimulates the phosphorylation of HSL to increase its activity

Muscle contractions stimulate HSL activity through phosphorylation mechanisms

Activation of a stress signalling kinase (extracellular signal-regulated kinase; ERK) during exercise stimulates the phosphorylation and activation of HSL

76
Q

Activation of lipolysis:

AMPK activity

A

Enhanced during intense and prolonged exercise

Reduces HSL activity and reduces fatty acid oxidation rates during high intensity exercise

Although, there are examples of situations where AMPK activity is elevated alongside high rates of IMTG utilisation

77
Q

During high intensity exercise, there is a clear ____ in utilisation of IMTG

A

Reduction

78
Q

During initial stages of high intensity exercise, there is an ___ in lipase activity

A

Increase

There is no inhibition of lipase

Due to hormonal changes with higher intensity exercise

79
Q

Lipase activity - At onset of exercise at 90% VO2max

A

Higher adrenaline concentrations

Lower insulin concentrations

Reduction in IMTG use at higher intensities is NOT due to reduced lipase activity, which is maintained at higher intensities

80
Q

In order for fatty acids to undergo beta-oxidation in the mitochondrial matrix…

A

they need to be transported from the cytosol and across the outer and inner membranes of the mitochondria

  • Final point of control over rates of fatty acid oxidation
81
Q

Mitochondrial FA transport

A

A complex process involving a group of carnitine palmitoyl transferase I, CPT-I and CPT-II, which together utilise free carnitine to transport LCFA-CoA into the mitochondrial matrix

82
Q

Mitochondrial FA transport

Fatty acids need to pass across…

A

the inner and outer mitochondrial membranes in order to be broken down through the process of beta-oxidation in the mitochondrial matrix

83
Q

Mitochondrial FA transport

Long chain fatty acids cannot…

A

pass through the mitochondrial membranes so a mechanism is needed to enable fatty acid oxidation in the matrix

84
Q

Mitochondrial FA transport

Fatty acids are transported into the mitochondria with…

A

the assistance of a series of proteins

85
Q

Mitochondrial FA transport

Fatty acids ‘activated’

A

conversion to fatty acyl-CoA

This is a preparatory step ahead of beta-oxidation

86
Q

Mitochondrial FA transport

Fatty acyl-CoA is jointed with carnitine to form…

A

acyl-carnitine

This is catalysed by the enzyme carnitine palmitoyl transferase-I (CPT-I)

87
Q

Mitochondrial FA transport

Once acyl-carnitine is formed, is can then…

A

pass through the mitochondrial membranes into the matrix

88
Q

Mitochondrial FA transport

Once the acyl-carnitine can pass through the mitochondrial membranes into the matrix, the carnitine is then…

A

removed by the enzyme CPT-II to reform the fatty-acyl-CoA

89
Q

Mitochondrial FA transport

Final step

A

The reformed Fatty acyl-CoA is now located in the mitochondrial matrix and can enter the pathway of beta-oxidation

90
Q

Importance of CPT-I to fatty acid oxidation

A

A study that used a specific CPT-I inhibitor (etomoxir)

In this study they stimulated muscle to contract electronically in the absence or presence of etomoxir

Findings:
- High rates of oxidation of fatty acid palmitate during muscle contraction, which is reduced when CPT-I activity is inhibited

91
Q

Mitochondrial fatty acid transport at high exercise intensities:

Mitochondrial fatty acid transport is…

A

The major limiting factor in fat oxidation at high intensities

92
Q

What are fatty acids?

A

Characterised by a long chain of carbon atoms, and one of the key characteristics of fatty acids is related to the length of this chain

Fatty acids can either be short, medium or long, depending on the number of carbons in the chain region of the molecule

93
Q

Chain length classifications:

Short chain fatty acids (SCFA)

A

Contain 5 or less carbon atoms

94
Q

Chain length classifications:

Medium chain fatty acids (MCFA)

A

Contain 6-12 carbons

95
Q

Chain length classifications:

Long chain fatty acids (LCFA)

A

Contain 13 or more carbons (e.g. palmitic acid, stearic acid are 2 of the most common fatty acids in the body)

96
Q

What is an important difference in short and medium chain fatty acids?

A

They can diffuse across the mitochondrial membrane independently of CPT-I/II and does not require carnitine

97
Q

What is different about the long chain fatty acids?

A

When they diffuse across the mitochondrial membrane, they ARE dependent on CPT-I/II and the availability of carnitine

98
Q

How do these differences in fatty acid chain lengths appear?

A

When examining the oxidation rate of individual fatty acids during moderate and high intensity exercise

A long chain fatty acid (e.g. Oleate) is inhibited during exercise at 80% VO2max, compared to 40% VO2max

Where, the oxidation rate of a medium chain fatty acid (e.g. Octanoate), which does not require CPT, is the same at both 40% and 80% VO2max

99
Q

One theory behind the inhibition of CPT-I activity at high intensity exercise

Changes in muscle pH

A

At a lower pH - activity of CPT-I is inhibited and mitochondrial fatty acid transport is suppressed

  • pH is minimally affected during prolonged submaximal exercise when lactate accumulation is minimal and fat oxidation rates are high
  • muscle lactate accumulation and reductions in muscle pH and fat oxidation occur during higher intensity exercise
  • this theory is supported by more direct evidence when CPT-I activity is assessed under difference pH that reflect the changes during high intensity exercise
100
Q

Metabolic changes that occur after endurance training

A
  • Increased fat oxidation; AND
  • Sparing of carbohydrate
  • This was observed during a steady state exercise bout performed at the same workload after 12wks of endurance training
  • The increase in fat oxidation is due to an increase in contribution of IMTG
101
Q

Endurance trained individuals exhibit higher fat oxidation rates at the same relative exercise intensities (i.e. same % VO2max)

A

Observed when maximal rates of fat oxidation are measured during an incremental exercise test

  • The absolute workload (i.e. power output) is markedly higher in the trained individuals
102
Q

Underlying reasons for this increase in fat oxidation in the endurance trained state:

When exercise is performed at same absolute workload (i.e. same power output), the hormonal response to exercise is…

A

…suppressed in the trained state

  • The increase in catecholamines and the reduction in insulin concentrations are less marked post-training - this creates conditions that provide lower stimulus for adipose tissue lipolysis
103
Q

Underlying reasons for this increase in fat oxidation in the endurance trained state:

There is little evidence that the adipose tissue adapts to endurance training (other than reductions in size brought about extended periods of negative energy balance). Therefore, as the catecholamine response is suppressed…

A

the release of FFA from adipose tissue is lower in the endurance trained state

  • Results in lower plasma FFA concentrations and unchanged, or even lower, plasma FFA oxidation during exercise
104
Q

In the table below (4.6.2) that examines metabolic responses to the same exercise bout (same workload, watts) before and after a period of exercise training. You can see that…

A
  1. Plasma concentrations of glycerol and free fatty acids are lower after training - indicative of suppressed adipose tissue lipolysis
  2. The rate of palmitate appearance (palmitate Ra, a direct measure of adipose tissue lipolysis) is lower after training
  3. The rate of palmitate disappearance (palmitate, Rd, a direct measure of fatty acid uptake) is lower after training
  4. Ultimately, the oxidation rate of fatty acid palmitate is lower after training, indicating lower use of plasma fatty acid as a fuel during exercise post-training
105
Q

When comparing trained vs untrained individuals performing at the same % of VO2max (i.e. same relative intensity):

Catecholamine responses

A

Trained individuals may exhibit higher catecholamine responses

Due to the higher overall force production and higher metabolic rate

106
Q

When comparing trained vs untrained individuals performing at the same % of VO2max (i.e. same relative intensity):

The rate of lipolysis

A

Plasma FFA and Plasma FFA oxidation is higher in trained individuals

An increase in adipose tissue blood flow during exercise may also contribute to this enhancement in adipose tissue lipolysis

107
Q

The enhancement in plasma FFA uptake into skeletal muscle of trained individuals is thought to be partly due to…

A

enhanced skeletal muscle blood flow and increased availability of plasma FFA

108
Q

The most important adaptation post-endurance training is within the skeletal muscle itself

A

An increase in the content of the fatty acid transporters is a well-recognised muscle adaptation to regular endurance training that likely explains the increased capacity to transport fatty acids into skeletal muscle

109
Q

Muscle specific adaptations promoting IMTG storage and utilisation

A

There is direct evidence that endurance training increases utilisation of IMTG sources during exercise

Studies show net use of IMTG during exercise is greater post-training

Occurs with a corresponding reduction in the net use of muscle glycogen (i.e glycogen sparing)

110
Q

The increased use of IMTG is specific in which type of muscle fiber - 1 or 2?

A

Type 1

Increases in net IMTG breakdown during exercise observed during exercise post-training, occurs in type 1 NOT type 2 muscle fibers

111
Q

Other adaptations in skeletal muscle that contribute to elevated breakdown and oxidation of IMTG during exercise following a period of endurance training

A

1) IMTG storage is elevated

2) Pre-exercise IMTG content is directly related to utilisation of IMTG during exercise

3) Increase in IMTG content is also due to increase in number of lipid droplets in contact with the mitochondria - enables efficient transfer of FA’s contained within the lipid droplet across the mitochondria to undergo beta-oxidation

4) Endurance training increases content of lipolytic enzymes - increases ATGL, HSL content stays unchanged, phosphorylation of HSL increases HSL activity

112
Q

Muscle adaptations promoting fatty acid oxidation:

The final aspects are other skeletal muscle adaptations that promote fat oxidation are:

A

1) muscle fiber type

2) mitochondrial content

113
Q

Muscle adaptations promoting fatty acid oxidation:

Muscle fiber type and endurance trained individuals

A
  • Greater proportion of type 1 (slow twitch) muscle fibers
  • Type 1 fibers are suited to oxidise fatty acids - have greater content of proteins needed for transport, storage, breakdown and oxidation of FA’s
  • Hugh fat oxidation rates (with years of training) is partially due to greater proportion of type 1 fibers
  • However, fiber type proportion is unchanged with short-term endurance training (<3 months)
  • Therefore, elevated fat oxidation rates seen following typical training interventions is unlikely due to muscle fiber type shifts
114
Q

Muscle adaptations promoting fatty acid oxidation:

Mitochondrial content - first shown in classic exercise physiology paper by John Holloszy in 1967

A
  • Showed that running rats on a treadmill for 12wks increased the activity of mitochondrial enzymes in the electron transport chain
115
Q

Muscle adaptations promoting fatty acid oxidation:

The ‘gold standard’ measure of mitochondrial volume/density is…

A

Electron microscopy

116
Q

Muscle adaptations promoting fatty acid oxidation:

Numerous studies have shown that mitochondrial density is…

A

…enhanced with endurance training

  • This is due to an increase in the size of mitochondria
117
Q

Muscle adaptations promoting fatty acid oxidation:

Markers used to assess mitochondrial density/volume

A
  • mtDNA
  • Citrate synthase
  • Oxidative phosphorylation (i.e. electron transport chain) proteins
  • Cardiolipin
  • Most commonly used is citrate synthase activity - shows good correlation with electron microscopy assessments of mitochondrial volume
118
Q

The increase in mitochondrial volume is not thought to be the most important factor for elevating VO2max. However the increase in mitochondrial density with training is very important to…

A

support elevated rates of fat oxidation

119
Q

Enhanced mitochondria volume elevates fat oxidation in several ways:

A

1) Increased rate of mitochondrial fatty acid transport

2) Increased capacity for beta-oxidation

3) Increased capacity for oxidative phosphorylation

120
Q

Mitochondrial adaptations to endurance training:

1) Increased rate of mitochondrial fatty acid transport

A
  • Elevated surface area of mitochondria membrane available for fatty acid transport
  • Increased content and activity of CPT1
  • CPT1 activity correlates with fatty acid (palmitate) oxidation
121
Q

Mitochondrial adaptations to endurance training:

2) Increased capacity for beta-oxidation

A
  • Elevated content and activity of beta-hydroxyl-CoA dehydrogenase - the rate limiting enzyme of beta-oxidation
  • Increased rate of acetylCoA generation from fatty acids to enter the TCA cycle
122
Q

Mitochondrial adaptations to endurance training:

3) Increased capacity for oxidative phosphorylation

A
  • Greater surface area of the inner mitochondrial membrane
  • Elevations in content of protein complexes in the electron transport chain

hse303 (6 decks)

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