Physiology of Strength and Power

Question 1

How is a muscle action produced?

Answer 1

A result of the activation signal produced by the nervous system and the force produced by the muscle-tendon unit. This leads to joint action

Question 2

Innovation Ratio

Answer 2

The ratio between the number of fibres that are innovated by a single neuron.

Question 3

What is a motor unit comprised of?

Answer 3

Alpha motoneurone
Spinal cord
Axons
Fibres

Question 4

Why is the size of the motor neuron and motor unit important?

Answer 4

The activation signal from the motor unit needs to be transformed into contractile activity. Done in an orderly fashion (size principle)

Question 5

How do neurotransmitters depolarise cells?

Answer 5

Through the post-synaptic membrane

Question 6

Muscle spindles

Answer 6

receptors in the muscle that are sensitive to changes in the muscle length

Question 7

Muscle contraction

Answer 7

Muscles contract to shorten the muscle and reduce the stimulus. This happens quickly and allows us to regulate where we are in space

Question 8

Golgi-tendon organs

Answer 8

Receptor that controls tension in the muscle
They send an inhibitory signal into the alpha motoneurone - protective mechanism against excessive tension of the muscle.

Question 9

The size principle

Answer 9

Smaller motor units are recruited first. As a greater force is produced, bigger motor units are recruited.
As motor units are recruited, a twitch occurs (basic contractile response to an action potential).
Lot of twitches are produced at the same time

Question 10

Producing very high forces

Answer 10

We have to discharge motor units at very high frequency and this leads to a summation of the twitches (tetinus).

Question 11

Max contraction

Answer 11

Max contraction for a few seconds (jumping before a sprint) the twitch amplitude of a motor unit will increase and force production will increase acutely.

Question 12

What does a warm up do?

Answer 12

Primes the nervous system to drive the muscles at a higher capacity than it would do with no warm up.

Question 13

How to increase the force producing

Answer 13

You need to recruit more motor units to increase twitch size or discharge motor units at a higher frequency (rate coding)

Question 14

What happens when you recruit new motor units?

Answer 14

the twitches summate and the force production is bigger

Question 15

Fine motor control muscle (muscles of the finger)

Answer 15

Muscles will recruit units at 50% of max force so any further increase will come from discharging at a higher frequency. This is to maintain the resolution of the action, son it remains accurate with low errors.

Question 16

High force muscles

Answer 16

Recruit more motor units to increase the output

Question 17

Rate coding

Answer 17

The first recruited units (smallest units) will reach higher discharge rates that those units recruited later - has more time to develop the discharge rate.

Question 18

What dictates how fast you can produce force?

Answer 18

How high the rate coding is at the beginning and how quickly you are able to recruit all motor units.

Question 19

Fatigue and max force production

Answer 19

When we fatigue our max production capacity decreases. New units are recruited and the rate coding is adjusted. The discharge frequency is increased in the motor units.

Question 20

The change point of fatigue and force production

Answer 20

The later the direction of change point the longer the task (using this you can predict how long a person can perform that action). The later that point the longer the task.

Question 21

Contractile element of the muscle fibre

Answer 21

Active portion of the muscle
Characterised by force length

Question 22

Sarioelastic element of the muscle fibre

Answer 22

can be divided into active (elasticity of the myofibril and the sliding filament/cross bridges) and passive components (tendons and connective tissues)

Question 23

Paraelastic element of the muscle fibre

Answer 23

modulator that transmits the force from the fibres onto the skeleton

Question 24

Tendons

Answer 24

Passive component of force production through recall of the tendon.
At longer length muscles the recall has a greater contribution
Can train the force-length relationship

Question 25

Force - Velocity relationship

Answer 25

Muscles can adapt for lots of different loads, by modulating the velocity at which the muscle contracts. High loads = slower contraction to reach the force needed Can modulate by increasing the temperature of a muscle, all values will increase

Question 26

When is max power produced?

Answer 26

About 1/3 velocity is when you produced the max power

Question 27

How are fibres are arranged in the muscle?

Answer 27

Series Parallel

Question 28

Series

Answer 28

range of motion of muscle is maximised because length at which muscle can operate increases, maximises velocity in the force production

Question 29

Parallel

Answer 29

maximises force, increases strength

Question 30

Maximising muscle mechanical properties

Answer 30

To maximise force, operate at about 1/2 length of the muscle. Sacrifice speed To max power, sacrifice force production

Question 31

Stretch-shortening cycle

Answer 31

Series of actions makes the movement more economical. Allows tendon to store elastic energy, can invoke some reflex into that muscle - produce higher forces.

Question 32

How to increase muscle performance?

Answer 32

Improve neural activation and muscle-tendon force. There is a skill element as well - training in a specific way helps you to be strong in the way you need for sport

Question 33

Training adaptations in first few weeks of resistance training

Answer 33

An untrained person starting resistance training will increase strength rapidly. First few week = no increase in muscle mass, increase is due to skill adaptations and neural adaptations

Question 34

Training adaptations after training for a few year

Answer 34

Increases in strength are largely a result of an increase in muscle size and increase in contractile proteins that are in muscle tissue. Other adaptations are relevant but they are smaller contributors to strength increase.

Question 35

Neural adaptations

Answer 35

Adaptations in the cortical centre (motor cortex) due to strength training result in an decreasing inhibitory input in the motor cortex. Alpha motoneurone is the main transducer of activation signals to muscle contractions

Question 36

Where do inputs from the nervous system converge?

Answer 36

Alpha motoneurone

Question 37

Performing resistance training on an untrained person will cause:

Answer 37

Recruitment of more motor units Discharging motor units at a higher frequency

Question 39

The effect of strength training on the threshold of recruitment

Answer 39

The threshold at which recruitment will occur will decrease with strength training - more effective at producing force.

Question 40

Derecruitment

Answer 40

time at which the muscle relaxes (motor unit is not active). Unaffected by training. Happens in certain situations (stroke)

Question 41

What happens when we are performing an action?

Answer 41

We don't just use the agonist, there are also lots of synergists involved as well as the antagonist. These protect the joints and the bones, but are counterproductive to force production

Question 42

H reflex

Answer 42

The electrophysiological equivalent to a tendon-tap reflex

Question 43

Muscle spindles

Answer 43

Muscle receptor that detects length and rate of change of length in the muscle Project via the interneuron (transmits information from one side of the body to the other) Have an inhibitory effect - when they are excited they inhibit the antagonist muscle, so we can move freely not stiffly.

Question 44

Electromyography (EMG)

Answer 44

Not the best way to measure muscle activation - has limitations It is a very simplistic view of the role of the antagonist

Question 45

Antagonist coactivation

Answer 45

After 8 weeks of training, strong evidence that by using complex simulation procedures on nerves you can reduce the activation of the antagonist. Increase the activation of the agonist and decrease the activation of the antagonist - a combo of these increase force

Question 46

Why is muscle size important?

Answer 46

there is a close linear relationship (high correlation) between cross sectional area of the muscle and the force they can produce

Question 47

What is strength also influenced by

Answer 47

Genetic components Muscle mechanical properties (how tendons attach) Environmental factors - can't control these

Question 48

Estimated force =

Answer 48

cross sectional area x tension a fibre can produce

Question 49

How to increase muscle size

Answer 49

By increasing the amount of contractile proteins you have in the muscle tissue and connective tissue (hypertrophy)

Question 50

Specific Tension

Answer 50

how much tension a specific fibre can theoretically produce. Bigger fibres have greater tension

Question 51

Myonuclei

Answer 51

Fills up with contractile proteins when you put stimulus on the muscle. Limits you very quickly on building up muscle. Can only take on so many proteins

Question 52

Satellite cells

Answer 52

Single nuclei cells Activated by protein synthesis Signalling pathways to trigger protein synthesis involve gene expression Progress into myonuclei so can be filled with contractile proteins as well

Question 53

Ratio of protein synthesis and breakdown

Answer 53

Each training session you do causes protein breakdown If ratio between breakdown and synthesis is positive = growing muscle If ratio is negative no muscle growth = overtraining

Question 54

What happens when there is a muscle stimulus?

Answer 54

You will trigger the signalling pathway which activates mTOR (enzyme)

Question 55

Signalling protein goal

Answer 55

activate mTOR which leads to protein synthesis and hypertrophy. Proteins are stacked in parallel (maximises force production) - increases force producing capacity of the muscle Proteins in series would maximise length of the muscle and the velocity with which it would contract

Question 56

Why is mechanical tension needed?

Answer 56

to maintain the muscle mass you have for normal daily function

Question 57

Exercising individuals at different intensities

Answer 57

protein synthesis will be maximised by using higher loads - high loads not necessary for hypertrophy As long as you reach a given threshold of a muscle you will increase the muscle mass. Need to go into failure and need to do a lot of sets

Question 58

H-zone

Answer 58

where the thick and thin filaments overlap during contractions

Question 59

Why aren't sarcomeres aligned perfectly?

Answer 59

They are at a slight angle. When there's enough tension and the thin filaments are being pulled it causes a rupture in the Z-disk and that causes the repair of the muscle (protein synthesis) Mechanical tension has to be high or the Z-disk won't rupture

Question 60

Muscle damage

Answer 60

Occurs when you perform certain actions (something new) Causes a disruption in the extracellular matrix of the muscle which leads to a cascade of processes that are linked to information that excites receptors in the muscle and you feel soreness Soreness typically delayed - after 2 days, slowly disappears

Question 61

Why is muscle damage more prevalent in eccentric contractions

Answer 61

forces are high and doing contractions at longer muscle lengths You are putting your muscle in a position where it will produce higher forces and it will cause a greater disruption in the sarcomere

Question 62

Muscle damage and mechanical tension

Answer 62

Difficult to separate Difficult to introduce muscle damage without mechanical tension and it's difficult to induce hypertrophy without mechanical tension

Question 63

Blood flow restriction training

Answer 63

Reducing blood flow causes the accumulation of metabolites during exercise in the muscle. Blood can't get in to remove the metabolites Done at fairly light loads At a given percentage of max it induces hypertrophy

Question 64

Hypertrophy

Answer 64

accumulation of proteins within a given muscle fibre

Question 65

Specificity of strength

Answer 65

The way we express and how we express the neural activation and power is important. More typical resistance training causes increase of strength in concentric contractions, not as much eccentric

Question 66

Hyperplasia

Answer 66

the splitting of a muscle into two cells. The daughter eventually becomes an adult muscle cell. Increases cell count in the body and size in a more effective way