Sensing mechanical signals for muscle hypertrophy

Question 1

What is the role of mechanosensors in muscle hypertrophy?

Answer 1

Triggered by force, they trigger an early signalling response that initiates hypertrophic (mTORC1) signalling and muscle hypertrophy

Mechanosensors modify in response to force, leading to muscle growth.

Question 2

What structures make up the myofiber?

Answer 2

Sarcomeres in parallel and series

Sarcomeres are the basic contractile units of muscle.

Question 3

What is lateral transmission of force?

Answer 3

It occurs predominantly from the collagen structure surrounding muscle tissue, down through the basal lamina

This type of force transmission is essential for muscle response to exercise.

Question 4

What are DGC and Integrins classified as?

Answer 4

Mechano-transducers/sensors for lateral transmission of force

They play a crucial role in force transmission and muscle signaling.

Question 5

What does longitudinal transmission of force involve?

Answer 5

It occurs through structures within the myofiber, such as actin, myosin, Z-lines

This transmission is vital for muscle contraction and response.

Question 6

Which proteins are considered mechano-transducers/sensors for longitudinal transmission of force?

Answer 6

Dystrophin, Desmin, a-actinin

These proteins help in sensing mechanical stimuli and triggering muscle growth.

Question 7

What is the meaning of transduced?

Answer 7

to turn tension signal into something that drives muscle growth through protein synthesis

Question 8

What is the function of phosphatidic acid (PA) in muscle hypertrophy?

Answer 8

It activates mTORC1, which drives muscle growth in response to resistance training

PA synthesis is stimulated by mechanical signals.

Question 9

How long did hypertrophy-inducing eccentric contractions (EC) increase phosphatidic acid concentration? (O’Neil et al, 2009)

Answer 9

For up to 60 minutes in tibialis anterior muscle

This indicates a prolonged response to mechanical stimuli.

Question 10

What was the effect of Butanol on PA signalling? (O’Neil et al, 2009)

Answer 10

It blocked mTORC1 signalling that controls protein synthesis

This highlights the importance of PA in the hypertrophic process.

Question 11

How do integrins affect skeletal muscle?

Answer 11

They sensitise skeletal muscle to mechanical strain and subsequent growth

This sensitivity is crucial for effective muscle adaptation.

Question 12

What effect does overexpression of ⍺7β1-integrin have on muscle growth?

Answer 12

It results in greater muscle growth after eccentric exercise training (Zou at al, 2011)

This suggests integrins are important for muscle adaptation.

Question 13

What is a>Tg?

Answer 13

A protein that controls the expression of the integrins in the muscle

Question 14

What is ‘the pump’ in muscle physiology?

Answer 14

Muscle fibre swelling as a potential trigger for mechano-sensors and hypertrophy

This phenomenon is associated with exercise-induced changes.

Question 15

When does whole-muscle swelling occur?

Answer 15

right after resistance exercise (Farup et al, 2015)

Question 16

What prevents the muscle swelling?

Answer 16

Integrin and Cytoskeleton inhibitors
(Low and Taylor, 1998)

Question 17

What does exercise-induced muscle damage (EIMD) refer to?

Answer 17

Damage ranging from macromoles of tissue to tears in the sarcolemma

EIMD is a significant factor in muscle adaptation.

Question 18

What is exercise-induced muscle damage (EIMD) dependent on?

Answer 18

volume, intensity and velocity of exercise

Question 19

What type of contractions induce greater muscle damage?

Answer 19

Eccentric contractions, during which the muscle is forcibly lengthened

This form of contraction is particularly effective in stimulating muscle repair and growth.

Question 20

What happens to EIMD levels with repeat bouts of the same exercise?

Answer 20

They result in markedly reduced levels of EIMD

This protective effect can last several weeks to months.

Question 21

What did Moore et al (2005) discover regarding exercise-induced muscle damage (EIMD)?

Answer 21

-6 sets of lengthening contractions = increased levels of z-line streaming and muscle protein synthesis compared with shortening contractions
-protein synthesis was greater when muscle damage was present.

Question 22

What is z-line streaming?.

Answer 22

a way of measuring muscle damage

Question 23

How long do the protective effects of prior exercise last after the initial training?

Answer 23

up to 6-9 months (Nasaka et al, 2001)

Question 24

Does lactate drive resistance exercise-induced muscle anabolism?

Answer 24

No, lactate infusion did not alter intramuscular pH or muscle protein synthesis

This suggests lactate is not an anabolic signalling molecule.

Question 25

What did Moberg et al, 2020, find regarding blood lactate?

Answer 25

MPS levels in the hours of recovery were identical between conditions (lactate and saline), suggesting blood lactate is not a driver of metabolic responses to exercise

Question 26

What was the effect of long-term supplementation with 2% α-ketoglutarate?

Answer 26

It resulted in significant gastrocnemius skeletal muscle hypertrophy and increased markers of mTORC1 activity (more larger muscle fibres after supplement regime (in animals) ## Footnote This indicates potential for α-ketoglutarate in muscle growth.

Question 27

Did L-arginine-ketoglutarate supplementation increase 1 RM strength in humans?

Answer 27

No, it did not increase strength over a placebo in trained or untrained humans ## Footnote This suggests limitations in the effectiveness of this supplementation for muscle mass.