WK 8: Neuromuscular réponses to chronic exercise

Question 1

What are the neuromuscular adaptations to chronic training?

Answer 1

• muscle hypertrophy
• muscle strength and power
• muscle fibre size
• neural adaptations
• anaerobic capacity
• myofibrillar protein synthesis
• mitochondrial protein synthesis
• lactate tolerance
• capillarisation
• mitochondrial density and oxidative function
• endurance capacity

Question 2

What are the 3 principles of exercise training?

Answer 2

• overload, specificity, reversibility

Question 3

what are nqurmusucalr adaptions highly dependent on?

Answer 3

training type: resistance and endurance

Question 4

What is the definition overload?

Answer 4

Systems or tissues must be exposed to a set of stimuli beyond which it is normally accustomed in order for a training effect to occur (i.e., FITT principles)

Question 5

What is the definition specificity?

Answer 5

Training effects are specific to the muscles involved, the fibres recruited, the principle energy systems involved, the velocity of contraction and the type of contraction

Question 6

What is the definition of reversibility?

Answer 6

Consequence of the overload principle as gains can be quickly lost when the stimulus is removed

Question 7

What are the key stimuli responsible for exercise adaptation?

Answer 7

1. mechanical load
2. hormonal influences
3. neuronal activation
4. metabolic disturbances

Question 8

What are transcriptional activators?

Answer 8

• “turn on” key genes which increase exercise-related proteins

Question 9

What is the effect of stimuli on transcription factors?

Answer 9

they induce transcription factors. Some of these stimuli will make their way into the nucleus and so turn on more genes (increased mRNA - increased protein synthesis)

Question 10

What is the definition of muscular strength?

Answer 10

the maximal force that a muscle (or muscle group) can generate (as typically assessed by 1 RM)

Question 11

What are initial strength increases due to?

Answer 11

improvements in neural mechanisms

Question 12

what happens to strength after 4 weeks?

Answer 12

increase in muscle mass therefore an increase in Cross-SA.

Question 13

Over an 8 week period, neural factors account for 90% of strength gains, what happens after 4 weeks?

Answer 13

hypertrophy dominates.

Question 14

What are the neural improvements with resistance training?

Answer 14

• Motor unit synchronisation & firing rates
• Motor unit recruitment patterns (activating more motor units)
• Motor neurone excitability (the action potential and depolarisation)
• NMJ dispersion and size- helps propagation
• CNS activation, with reduced inhibitory reflexes e.g. golgi related inhibition

these all contribute to the initial improvements in strength

Question 15

What are the muscular changes of strength gains?

Answer 15

RT increases muscle fibre cross-sectional area (hypertrophy), which is directly linked to increased force production due to elevated myofibrillar proteins (more active myosin proteins).

Question 16

Force = myosin heads x force per cross-bridge x fraction in strong-bound state

Answer 16

that was the equation

Question 17

What increases muscle mass?

Answer 17

increase in myofibrillar protein content

This is due to the shift to type 2 glycolytic fibres and myosin heavy isoforms which generate higher force.

shifts in fibre type can occur with RT, but no substantial increases in capillarisation and mitochondrial density.

Question 18

What underpins muscle hypertrophy during resistance training?

Answer 18

PROTEIN SYNTHESIS.

• protein degradation is regulated by activation of the protein mTOR (decreases degradation)
• mTOR activates protein translation and thus hypertrophy.
• skeletal muscle size is largely due to increase in fibre see (hypertrophy) rather than fibre number (hyperplasia)
• during RT there is an increased production of IGF-1 which goes out of the cell and signals back onto the IGF-1 receptor and overall activates the mTOR.
• mTOR can be inhibited by RAP.

Question 19

What is the effect of resistance training on satellite cells and hypertrophy?

Answer 19

• RT can activate satellite cells (e.g. stem cells (SC) ), which are associated with skeletal muscle remodelling.
• SC are located in the basal lamina (between the sarcolemma and extra cellular space)
• once activated SC’s can integrate and fuse into current fibres to increase myonuclei number to increase high protein translation - thus increasing fibre hypertrophy.
• hypertrophy after approx. 15% 10 weeks of RT is associated with acute and chronic increase in SCs*

Question 20

What is endurance training?

Answer 20

the repetitive stimulation of muscles over extended periods of time, which is most often assessed by measuring VO2max.

Question 21

What is the relationship between endurance training and fibre type?

Answer 21

• induces a shift from fast to slow fibre phenotype (glycolytic to oxidative), but with little hypertrophy.
• fewer neural adaptations and more muscular.
• type 1 fibres have lower ATPase activity, but more efficient compared to type 2 fibres.

Question 22

What is the relationship between endurance training and capillarisation?

Answer 22

• increases the no. of capillaries surrounding each fibre, which improves O2 diffusion (Fick’s law) and substrate delivery to mitochondria, while also improving removal of waste products e.g. CO2.
• with increase in VO2max there is an increase in capillaries so an increase mitochondrial density. So O2 delivery must be increased to make use of the increased mitochondria.

Question 23

What is there relationship between endurance training and mitochondria?

Answer 23

• the most significant change to occur with endurance training is an increase in mitochondrial content and oxidative enzyme activities.

Question 24

What underpins improved muscle oxidative capacity during endurance training?

Answer 24

• the nuclear transcriptional coactivator PGC-1 regulates mitochondrial biogenesis.
• PGC-1 activates downstream transcription factors which control mitochondrial and fatty acid oxidation gene network.
• also controls expression of type 1 fibres and antioxidant enzymes.
• most improvements in performance are due to PGC-1.
• some factors in this pathway can inhibit the pathway that activates mTOR (resistance and endurance training improve one another).

Question 25

What is the effect of genetically over expressing PGC-1?

Answer 25

• shift towards type 1 fibres

- fatigue resistance improved.

Question 26

What is the relationship between endurance training and redox state?

Answer 26

Endurance training increases anti-oxidative enzymes to protect against reactive oxygen species (ROS)-induced damage

ROS are highly reactive oxygen-derived molecules (e.g., H2O2) that can increase in the muscle during exercise