19-22. Metabolic Adaptations to Exercise

Question 1

What is muscle atrophy?

Answer 1

Diminished capacity to generate or maintain power in response to reduced physical activity

Question 2

What is muscle hypertrophy?

Answer 2

Enhanced capacity to develop maximum strength and power following resistance training

Question 3

What is increased oxidative metabolism?

Answer 3

Enhanced capacity to maintain power for long periods of time following endurance exercise –> increased oxidative metabolism

Question 4

How are adaptations readily reversible?

Answer 4

When the stimulus for adaptation is diminished or eliminated

Question 5

Define genotype.

Answer 5

Underlying genes that are expressed

Question 6

Define phenotype.

Answer 6

Outward, observable characteristics of a muscle

Question 7

How does a change in gene expression results in an altered phenotype?

Answer 7

Altered gene expression –> protein structure of a muscle is altered –> phenotype of muscle has been changed

Question 8

What is meant by the statement: “the adaptive response of muscle is specific to the type of exercise”?

Answer 8

Aerobic vs. anaerobic exercise will result in diff adaptations in muscle metabolism

Question 9

What comprises endurance training?

Answer 9

• High activation frequency of motor units

- Low force output

Question 10

Name some of the adaptations to endurance training?

Answer 10

• Increased hexokinase activity
• Size, # of mitochondria
• Increase in all mitochondrial enzymes proportionate to increase in mitochondrial density
• Increase in intramuscular glycogen & lipid stores
• Increase in sarcolemmal FA transport proteins

Question 11

Why does the lactate threshold occur at a higher intensity of exercise following endurance training?

Answer 11

• More fibers are now FOG –> better oxidative capacity –> muscles don’t have to utilize anaerobic glycolysis (to produce lactate) to meet ATP demands
• Accumulation of lactate in blood doesn’t occur til higher work rate

Question 12

What adaptations occur in the muscle to increase fat utilization during endurance exercise?

Answer 12

• Higher conc of FFA in blood
• Higher FFA uptake
• Able to metabolize fat @ higher rate

Question 13

What is the training effect?

Answer 13

Attenuated response at same work rate

Question 14

What is the major adaptation to resistance training?

Answer 14

Increase in fiber CSA

Question 15

How does the training effect affect the cross over point between fat and CHO metabolism?

Answer 15

• Shifts cross over point to the right

- Able to use fat metabolism @ higher workloads before switching to CHOs

Question 16

What are the training-induced changes in muscle fiber type for deconditioned athletes? Conditioned? Endurance?

Answer 16

• Deconditioned = decreased oxidative capacity
• Conditioned = increased oxidative capacity of type I and IIa fibers
• Endurance = increased oxidative capacity for all fiber types b/c type IIx (FG) fibers adapted to have oxidative capacity

Question 17

How do type IIa fibers adapt to greater loads? Why?

Answer 17

Don’t adapt much for greater loads b.c they’re fully recruited at the lightest load already

Question 18

The increase in maximal oxygen uptake in muscles is due to what 2 factors?

Answer 18

• Increased cardiac output

- Increased oxygen extraction by muscle

Question 19

What factors cause QO2 (respiratory capacity of muscle) to increase w/ training?

Answer 19

• Increased mitochondria w/ increased oxidative enzymes

- Increase in capillary density

Question 20

How are intermyofibrilar mitochondria better than subsarcolemmal mitochondria?

Answer 20

• IMG has 2.5 fold greater respiration rate than SS

- IMF can produce 2-fold greater ATP than SS

Question 21

What are the enzymatic adaptations to anaerobic training?

Answer 21

• Minimal increases in phosphagen and glycolytic system enzymes
• No increase in TCA, ETC, or fat metabolizing enzymes

Question 22

What is resistance training?

Answer 22

Increase in the frequency of recruitment of motor units and a significant increase in the load against which motor units contract

Question 23

Muscle mass is determined by the balance between what 2 processes?

Answer 23

• Protein synthesis

- Protein degredation

Question 24

What is the key variable of muscle force production?

Answer 24

of cross bridges activated

Question 25

In a muscle fiber, what determines the CSA?

Answer 25

of myofibrils

Question 26

In a motor unit, what determines the innervation ratio?

Answer 26

Fiber CSA

Question 27

What regulates force output of a muscle?

Answer 27

• Motor unit recruitment

- Frequency of stimulation

Question 28

In what fiber types does hypertrophy occur?

Answer 28

ALL

Question 29

In terms of protein turnover, what leads to atrophy? Hypertrophy? Maintenance?

Answer 29

• Atrophy = decrease in protein synthesis; increase in protein degradation
• Hypertrophy = increase in protein synthesis; decrease in protein degradation
• Maintenance = increase in protein synthesis & degradation

Question 30

What causes the increase in protein synthesis leading to muscle hypertrophy?

Answer 30

• Increase in translational efficiency of existing myonuclei

- Addition of myonuclei through satellite cell proliferation and differentiation

Question 31

What is a nuclear domain?

Answer 31

Area that a single myonucleus controls

Question 32

What are the 3 theories as to the role of satellite cells in the growth of muscle fibers in adults?

Answer 32

• Myonuclear domain is inflexible = need to add myonuclei as fiber grows
• Fiber grows = no need to add myonuclei; increase in nuclear domain
• Myonuclear domain is flexible = can grow to a certain extent w/o adding myonuclei, past which you need to add myonuclei

Question 33

For postnatal growth, how do satellite cells play a part in fiber growth?

Answer 33

• Myonuclear domain increases

- No need to add myonuclei

Question 34

What is primarily responsible for changes in muscle mass during early life?

Answer 34

Hormones & other factors of puberty

Question 35

What is IFG1? Role in increasing DNA in muscle?

Answer 35

• Insulin-like growth factor 1
• Loading exercise –> IGF1 increases –> activates satellite cells & causes them to proliferate into muscle fibers –> contribute to increase in mRNA in muscle

Question 36

How is # of nuclei related to amount of DNA?

Answer 36

Directly = increase # of nuclei –> increase amount of DNA in muscle

Question 37

Is IGF1 necessary for growth in muscle mass as an adult?

Answer 37

No, not necessary in animals that have already reached optimal growth (adult size)

Question 38

What is responsible for the increase in skeletal muscle mass in adults? What isn’t?

Answer 38

Increase in size of muscle fibers, not # of muscle fibers

Question 39

What regulates the increase in muscle fiber size?

Answer 39

Increase in protein synthesis

Question 40

What stimulates the increase in protein synthesis?

Answer 40

• Increase in loading

- Increase in recruitment (neural activity)

Question 41

What is meant by the phrase: “use it or lose it”?

Answer 41

Must use muscles (train) in order to maintain muscle mass

Question 42

What is a polysome?

Answer 42

Messenger RNA w/ multiple ribosomes associated w/ it

Question 43

What is the role of resistance exercise for polysomes?

Answer 43

Resistance exercise –> increase in protein synthesis –> increase in # of polysomes

Question 44

What is mTOR? Importance?

Answer 44

LOOKUP

Question 45

What are the 2 downstream targets of mTOR? What is the primary way that this pathway is activated in adults?

Answer 45

LOOKUP

Question 46

Cell signaling pathway activated during endurance exercise vs. Signaling pathway activated w/ resistance training. How does the activation of both pathways together affect muscle growth in response to resistance exercise?

Answer 46

• Endurance exercise = mitochondrial biogenesis –> increase in oxidative capacity
• Resistance = increase in protein synthesis –> hypertrophy
• Both = hypertrophy in oxidative fibers