19-22. Metabolic Adaptations to Exercise Flashcards
What is muscle atrophy?
Diminished capacity to generate or maintain power in response to reduced physical activity
What is muscle hypertrophy?
Enhanced capacity to develop maximum strength and power following resistance training
What is increased oxidative metabolism?
Enhanced capacity to maintain power for long periods of time following endurance exercise –> increased oxidative metabolism
How are adaptations readily reversible?
When the stimulus for adaptation is diminished or eliminated
Define genotype.
Underlying genes that are expressed
Define phenotype.
Outward, observable characteristics of a muscle
How does a change in gene expression results in an altered phenotype?
Altered gene expression –> protein structure of a muscle is altered –> phenotype of muscle has been changed
What is meant by the statement: “the adaptive response of muscle is specific to the type of exercise”?
Aerobic vs. anaerobic exercise will result in diff adaptations in muscle metabolism
What comprises endurance training?
- High activation frequency of motor units
- Low force output
Name some of the adaptations to endurance training?
- 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
Why does the lactate threshold occur at a higher intensity of exercise following endurance training?
- 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
What adaptations occur in the muscle to increase fat utilization during endurance exercise?
- Higher conc of FFA in blood
- Higher FFA uptake
- Able to metabolize fat @ higher rate
What is the training effect?
Attenuated response at same work rate
What is the major adaptation to resistance training?
Increase in fiber CSA
How does the training effect affect the cross over point between fat and CHO metabolism?
- Shifts cross over point to the right
- Able to use fat metabolism @ higher workloads before switching to CHOs
What are the training-induced changes in muscle fiber type for deconditioned athletes? Conditioned? Endurance?
- 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
How do type IIa fibers adapt to greater loads? Why?
Don’t adapt much for greater loads b.c they’re fully recruited at the lightest load already
The increase in maximal oxygen uptake in muscles is due to what 2 factors?
- Increased cardiac output
- Increased oxygen extraction by muscle
What factors cause QO2 (respiratory capacity of muscle) to increase w/ training?
- Increased mitochondria w/ increased oxidative enzymes
- Increase in capillary density
How are intermyofibrilar mitochondria better than subsarcolemmal mitochondria?
- IMG has 2.5 fold greater respiration rate than SS
- IMF can produce 2-fold greater ATP than SS
What are the enzymatic adaptations to anaerobic training?
- Minimal increases in phosphagen and glycolytic system enzymes
- No increase in TCA, ETC, or fat metabolizing enzymes
What is resistance training?
Increase in the frequency of recruitment of motor units and a significant increase in the load against which motor units contract
Muscle mass is determined by the balance between what 2 processes?
- Protein synthesis
- Protein degredation
What is the key variable of muscle force production?
of cross bridges activated
In a muscle fiber, what determines the CSA?
of myofibrils
In a motor unit, what determines the innervation ratio?
Fiber CSA
What regulates force output of a muscle?
- Motor unit recruitment
- Frequency of stimulation
In what fiber types does hypertrophy occur?
ALL
In terms of protein turnover, what leads to atrophy? Hypertrophy? Maintenance?
- Atrophy = decrease in protein synthesis; increase in protein degradation
- Hypertrophy = increase in protein synthesis; decrease in protein degradation
- Maintenance = increase in protein synthesis & degradation
What causes the increase in protein synthesis leading to muscle hypertrophy?
- Increase in translational efficiency of existing myonuclei
- Addition of myonuclei through satellite cell proliferation and differentiation
What is a nuclear domain?
Area that a single myonucleus controls
What are the 3 theories as to the role of satellite cells in the growth of muscle fibers in adults?
- 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
For postnatal growth, how do satellite cells play a part in fiber growth?
- Myonuclear domain increases
- No need to add myonuclei
What is primarily responsible for changes in muscle mass during early life?
Hormones & other factors of puberty
What is IFG1? Role in increasing DNA in muscle?
- 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
How is # of nuclei related to amount of DNA?
Directly = increase # of nuclei –> increase amount of DNA in muscle
Is IGF1 necessary for growth in muscle mass as an adult?
No, not necessary in animals that have already reached optimal growth (adult size)
What is responsible for the increase in skeletal muscle mass in adults? What isn’t?
Increase in size of muscle fibers, not # of muscle fibers
What regulates the increase in muscle fiber size?
Increase in protein synthesis
What stimulates the increase in protein synthesis?
- Increase in loading
- Increase in recruitment (neural activity)
What is meant by the phrase: “use it or lose it”?
Must use muscles (train) in order to maintain muscle mass
What is a polysome?
Messenger RNA w/ multiple ribosomes associated w/ it
What is the role of resistance exercise for polysomes?
Resistance exercise –> increase in protein synthesis –> increase in # of polysomes
What is mTOR? Importance?
LOOKUP
What are the 2 downstream targets of mTOR? What is the primary way that this pathway is activated in adults?
LOOKUP
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?
- Endurance exercise = mitochondrial biogenesis –> increase in oxidative capacity
- Resistance = increase in protein synthesis –> hypertrophy
- Both = hypertrophy in oxidative fibers
