Physiology of Strength + Power II (S2)

Question 1

What two factors characterise muscle performance?

Answer 1

Neural activation and muscle-tendon unit force

Question 2

According to this hypothesis, what would an increase in strength or muscle performance mean?

Answer 2

We would need to augment neural activation and augment muscle tendon unit force

Question 3

What drives early strength gains in untrained individuals?

Answer 3

Augmentation of neural activation

Question 4

What contributes more to long-term strength gains?

Answer 4

Muscle hypertrophy (increased muscle size)

Question 5

Does neural activation continue to improve with training over time?

Answer 5

Yes, but improvements become less efficient

Question 6

Can someone be strong without large muscle mass? Why?

Answer 6

Yes – due to the neural element

• it is particularly important from the expression of strength as a skill

Question 7

Which parts of the CNS adapt to resistance training?

Answer 7

Augment certain structures in motor cortex, brain stem, and spinal cord

Question 8

How much can previously untrained individuals typically increase strength after 4 weeks of resistance training?

Answer 8

About 10–15 %

Question 9

What is discharge rate in a motor unit?

Answer 9

Speed at which action potentials propagate along the sarcolemma

Question 10

How does a ~2 pulses per sec increase in discharge rate affect force?

Answer 10

Small increase in discharge rate leads to a a large increase in force production shown by a leftward shift of the force-rate curve

Question 11

How does early training change motor-unit recruitment?

Answer 11

Units are recruited at lower % of maximal force and therefore fire for longer during a task

Question 12

Which combined neural changes explain rapid strength gains in the first 4–8 weeks?

Answer 12

EARLIER recruitment of MORE motor units plus HIGHER discharge rates

Question 13

What is the role of antagonist coactivation during movement?

Answer 13

Protects joints and helps coordinate movement

Question 14

How can reducing antagonist coactivation improve force production in theory?

Answer 14

In theory there would be less resistance from antagonist allowing agonist to produce more force

Question 15

What does the 1a afferent sensory neuron detect?

Answer 15

Sits in the muscle spindle and muscle length and rate of change in length

Question 16

What happens when the 1a afferent is activated by a rapid stretch (e.g. tendon tap)?

Answer 16

It projects excitation onto spial cord + alpha motor neuron, exciting the agonist muscle + triggering a reflex contraction in the agonist

Question 17

How can you bypass the tendon tap reflex in research?

Answer 17

By electrically stimulating the 1a afferent directly to measure the stretch-reflex

Question 18

What training effect is often seen in the stretch reflex after strength training?

Answer 18

An increase in the stretch reflex, showing enhanced agonist activation

Question 19

What effect does strength training have on antagonist muscle activation?

Answer 19

Often decreases activation or increases inhibition of the antagonist

Question 20

Why is inhibition of the antagonist important during strength training?

Answer 20

It allows maximal force expression by reducing counterforce

Question 21

So in summary - In the first 4–6 weeks of strength training, what primarily explains strength gains?

Answer 21

Neural adaptations, not muscle hypertrophy

Question 22

What two factors determine the estimated force of a muscle?

Answer 22

Specific tension of the muscle and its cross-sectional area (CSA)

• if have more fibres constructed in parallel = greater force production

Question 23

What is the relationship between CSA and force production?

Answer 23

Linear – bigger muscles generally produce more force

Question 24

What factors influence the degree of muscle hypertrophy from strength training?

Answer 24

1. Intrinsically - Genetics, sex
2. Can be influenced somewhat - nutrition, recovery
3. Measurement methods - MRI for CSA is gold standard

Question 25

What is muscle hypertrophy?

Answer 25

An increase in muscle size by adding more contractile property

Question 26

SO how does muscle hypertrophy occur exactly - What is the role of satellite cells in muscle hypertrophy?

Answer 26

They differentiate to add nuclei and to increase the number of proteins located in muscles and there's a number of processes that need to take place...

Question 27

What are the 2 processes that therefore need to take place for satellite cell differentiation?

Answer 27

1. Need to stimulate protein synthesis / increase ratio of synthesis:breakdown to be in favour of synthesis 2. We do that through activation of certain signalling pathways (will go through later), which trigger gene expression = differentiation of satellite cells

Question 28

What happens if satellite cells are blocked?

Answer 28

Muscle size cannot increase to the same extent

Question 29

What triggers satellite cell differentiation and protein synthesis?

Answer 29

Mechanical stimulus from resistance training - this triggers the cascade if processes to signal protein synthesis which signals muscles to repair + get bigger

Question 30

What key signalling pathway regulates protein synthesis in muscle growth?

Answer 30

Muscle stimulus → increase conc IGF-1 → acts on Protein Kinase B → activates mTOR pathway

Question 31

What are the 3 main ways to increase muscle size to increase muscle force?

Answer 31

1. Mechanical tension 2. Muscle damage 3. Metabolic stress

Question 32

What does mechanical tension do in the muscle?

Answer 32

Causes stress that increases protein synthesis and triggers hypertrophy through sarcomere disruption

Question 33

What sarcomere structure is disrupted to trigger the hypertrophy process?

Answer 33

The Z-disk — tension causes an oblique pull of thin filaments, leading to Z-disk rupture + triggering of protein synthesis / repair process

Question 34

Is high load (e.g. near 1RM) necessary to trigger hypertrophy via mechanical tension?

Answer 34

No, but higher loads are more economical in producing greater increases in protein synthesis

Question 35

How does aging affect protein synthesis in response to mechanical tension?

Answer 35

Older individuals have a blunted protein synthesis response, contributing to muscle loss with age

Question 36

What causes soreness after unfamiliar exercise?

Answer 36

Micro-damage in the muscle fibres, triggering an inflammatory repair response

Question 37

Does muscle damage significantly contribute to hypertrophy long term?

Answer 37

It's unclear – damage may initiate hypertrophy but doesn't appear to be essential after adaptation (e.g. repeated bout effect)

Question 38

What is the "repeated bout effect" regarding muscle damage?

Answer 38

Reduced soreness/damage after repeating the same exercise, showing that muscle damage's contribution to hypertrophy is limited

Question 39

What is metabolic stress in strength training?

Answer 39

Accumulation of metabolites from repeated muscle contractions, especially under limited blood flow

Question 40

How can you increase metabolic stress during training?

Answer 40

Use blood flow restriction (BFR) with low loads to trap metabolites and enhance protein synthesis

Question 41

Why can’t mechanical tension and metabolic stress be maximized together?

Answer 41

High tension = low reps (low metabolic stress), High metabolic stress = low tension (e.g. BFR), - So you must prioritize one or the other in a given set

Question 42

What is hypertrophy?

Answer 42

Increase in the size of existing muscle fibres

Question 43

What is hyperplasia?

Answer 43

Increase in the number of muscle fibres or cells within a muscle

Question 44

Has hyperplasia been shown to occur in humans?

Answer 44

Evidence in humans is weak and limited but has been evidenced in animals

Question 45

Why is hyperplasia unlikely to occur significantly in humans?

Answer 45

Humans are born with a set number of muscle cells and satellite cells with limited capacity for new fibre formation

Question 46

How do genetics influence muscle growth potential?

Answer 46

Genetics determine the baseline number of muscle fibres and satellite cells available for growth

Question 47

What does the specificity of strength principle suggest?

Answer 47

The way you train will determine how you express strength

Question 48

Training with different contraction types... What strength gains were seen in eccentric-only training / concentric-only training?

Answer 48

Improvements only in eccentric contractions for eccentric-only groups Improvements only in concentric contractions for concentric-only group

Question 49

Why is contraction type important in strength training?

Answer 49

Strength improvements are specific to the type of contraction used in training - so, yes, size matters but need to express strength in particular ways for athletes

Question 50

Training with different intent... What training method led to greater early force production?

Answer 50

Explosive strength training (ECT) compared to strength training (SCT) and control (CON)

Question 51

How did ECT compare to SCT and control in torque production?

Answer 51

ECT showed significantly greater torque in early phase of force-time curve - so ECT improved ability to generate force rapidly

Question 52

The type of movement also matters... (control did nothing vs intervention did squats on knee extension strength) Did squat training improve isolated knee extension strength?

Answer 52

No, despite knee extension being involved partially in squats

Question 53

Where was strength improvement seen after squat training?

Answer 53

In isometric squat position (improved massively), not isolated knee extension

Question 54

However what was a downside to this 4 week intervention?

Answer 54

Beginners were used to most of the improvement in strength would have been due to neural activation - beginners learnt to squat better - shut down activity of antagonists + increases activity of agonist

Question 55

What three training variables influence how strength is gained?

Answer 55

1. Contraction type 2. Intent behind force production 3. Movement specificity