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EXB 101 Midterm 2 > 17-18. Exercise Metabolism > Flashcards

17-18. Exercise Metabolism Flashcards

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1
Q

What factors effect the metabolic response to exercise? Which are most important?

A
  • Intensity**
  • Duration**
  • Fitness
  • Exercise modality
  • Environmental factors
  • Nutritional factors (diet)
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2
Q

What are the 3 main objectives of substrate metabolism?

A
  • Maintain glucose homeostasis
  • Metabolize the most effective substrate based on ATP demand
  • Spare muscle glycogen
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3
Q

What hormones are responsible for regulating glucose at rest? Which one predominates after 12 hrs of fasting? Following a meal?

A
  • Insulin and glucagon
  • Fasting = glucagon
  • Following a meal = insulin
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4
Q

What are the factors acting to decrease blood glucose?

A
  • Insulin (decreases w/ exercise)

- Contraction stimulates increased muscle uptake of blood glucose during exercise in active muscle

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5
Q

What are the factors acting to increase blood glucose?

A
  • Epinephrine/Norepinephrine = increases insulin levels; decreases glucagon levels
  • Glucagon = activates gluconeogenesis (synthesis of glucose from liver)
  • Cortisol
  • Growth hormone
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6
Q

What accounts for the increase in glucose uptake by skeletal muscle w/ exercise?

A

Contraction (Ca2+) stimulates increased muscle uptake of blood glucose during exercise in active muscle

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7
Q

What 2 factors does hormone response during exercise depend on?

A

Intensity & duration of exercise

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8
Q

What organ is responsible for maintaining blood glucose levels?

A

Liver

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9
Q

What is the source of blood glucose?

A

Glycogen

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10
Q

What can one do during exercise to assist in maintaining blood glucose levels?

A

Use fat metabolism instead of CHO metabolism

-fatty acid conc increases –> muscle will start preferentially utilizing fatty acids instead of glucose

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11
Q

What does the choice of energy source depend on?

A

Intensity & duration of exercise

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12
Q

What are the primary energy sources used during high-intensity, short-duration exercise?

A
  • CP
  • Phosphagens
  • Glycogen
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13
Q

As exercise intensity increases, the concentration of catecholamines in the blood increases. How does this influence glycogen breakdown and utilization?

A

Catecholamines function to spare glucose utilization

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14
Q

How does the choice of energy source change as intensity & duration of exercise change?

A

Low to high intensity; High to low duration

  • LIpids
  • CHO, aerobic
  • CHO, anaerobic
  • CP
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15
Q

Whenever exercise intensity increases suddenly, what is the immediate response?

A

To maintain ATP levels through the rapid and full activation of CK and rapid depletion of CP

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16
Q

What is the role of membrane transporters?

A

Help regulate glucose uptake

17
Q

Name 2 transporters that are recruited to the plasma membrane of the fiber during exercise.

A
  • GLUT 4

- CPT

18
Q

What accounts for the increase in FFA conc in the blood following the onset of exercise?

A
  • Selective recruitment of oxidative fibers
  • Hormonal & non hormonal factors increase lipolysis, FFA release & uptake by the muscle
  • Activation of enzymes that favor oxidation of FFA over oxidation of pyruvate
19
Q

During low intensity exercise, why are FFAs the predominant energy source for oxidation rather than CHOs?

A

Glucose utilization is inhibited when FAs are available as alternate fuel

20
Q

Why is the availability of plasma FFA reduced w/ increase in exercise intensity?

A
  • Intensity increases –> start to restrict blood flow to gut & adipose sites which release FFA
  • Blood vessels constrict –> release of FFA into blood decreases
21
Q

Why do FG fibers produce a larger amount of lactate than FOG fibers when recruited?

A
  • FOG fiber oxidize substrate –> do aerobic glycolysis

- FG fibers don’t have oxidative capacity –> do anaerobic glycolysis to produce lactate

22
Q

As exercise intensity increases, there is a crossover in fuel utilization from primarily fat to CHOs. What is responsible for the increase in glycogen utilization w/ increases in exercise intensity?

A
  • Increase demand for ATP
  • Increase rate of ATP utilization
  • Increase epinephrine release & increase levels of inorganic phosphate, ADP, AMP in muscle –> lead to increase phosphorylase and PFK activity, increase glycogen breakdown, increase glycolytic flux
  • Increase recruitment of fibers that rely primarily on CHO (FG fibers)
  • Decrease in fat oxidation
23
Q

How does diet influence fuel use & RQ during prolonged submaximal steady state exercise? (high carb vs. normal vs. high fat diet)

A 
HIGH CARB:
-high RQ to start --> drops drastically w/ increased duration of exercise
-Fuel = predominantly fat
MIXED DIET:
-RQ relatively constant 
-Fuel = predominantly fat
HIGH FAT:
-RQ starts low, but stays relatively constant
-Fuel = predominantly fat
24
Q

Under what circumstances is there a crossover in fuel use from mostly CHO to mostly fat?

A
  • Exercise is prolonged (>2-3 hrs)
  • Exercise is submaximal & steady state
  • RQ is close to 1.0 at start of exercise –> CHO is predominant substrate initially
25
Q

What can cause an increase in fat metabolism?

A
  • Increase in adipose tissue lipolysis, FA release from AT, FFA delivery to muscle
  • Increase in FFA movement across muscle membrane
  • Increase in movement of FAs across mitochondrial membrane due to activation of CPT
  • Activation of Krebs cycle and ETC in mitochondria
26
Q

What does enhanced delivery of glucose to contracting muscle depend on?

A
  • Increased blood flow and capillary recruitment
  • Increased transport across plasma membrane
  • Increase activation of glycolytic and oxidative pathways responsible for glucose metabolism
27
Q

What are the precursors for liver gluconeogenesis? Where do they come from?

A
  • Lactate from anaerobic glycolysis

- Amino acids from muscle

28
Q

What 2 cycles allow gluconeogenesis precursors to return to the liver?

A
  • Cori (lactate cycle)

- Glucose-alanine (amino acid) cygle

29
Q

The capacity to oxidize pyruvate depends on:

A
  • Aerobic capacity = # of mitochondria
  • availability of oxygen
  • total activity of LDH
30
Q

How does an acceleration in rate of glycolysis lead to lactate production?

A

Rate of ATP demand increases –> rate of glycolysis increases –> chooses anaerobic glycolysis (lactate production) to keep up with ATP demands

31
Q

How does the recruitment of FG fibers lead to lactate production?

A

FG don’t have oxidative capacity –> do anaerobic glycolysis –> produce lactate

32
Q

What does the Randle Theory state?

A

Inhibition of glucose utilization when FAs are available as an alternate fuel

33
Q

What are the mechanisms by which glycolysis is inhibited?

A
  1. Suppression of PDH by increases in acetyl CoA & NADH
  2. Inhibition of PFK by citrate leading to G6P which suppresses hexokinase & phosphorylase
  3. Reduced allosteric activation of phosphorylase due to decreased levels of AMP, ADP, and Pi
34
Q

What does absolute work rate or energy flux determine?

A

Total quantity of fuel required by the working muscle

35
Q

What does relative work rate dictate?

A

Proportion of CHO and fat based fuels for oxidation phosphorylation

36
Q

How does fuel selection & utilization correlate to exercise intensity (VO2max)?

A

80% VO2max = energy from CHO exceeds fat

37
Q

At higher work intensities, muscle glycogen can provide more than half the total energy used by the muscle. How?

A
  • Increase in SNS drive
  • Greater abundance of glycolytic as opposed to lipolytic enzymes in skeletal muscle
  • Increase recruitment of FG fibers that rely on glycogen
38
Q

Plasma concentration is maintained through what 4 processes?

A
  • Mobilize glucose from liver glycogen stores
  • Mobilize plasma FFA from adipose tissue to spare plasma glucose
  • Synthesize new glucose in the liver (gluconeogenesis) from amino acids, lactate, and glycerol
  • Block glucose entry into cells to force the substitution of FFA as a fuel

EXB 101 Midterm 2 (5 decks)

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