Week 8 - Muscle Mechanics 2

Question 1

Explain how morphology and neural factors can affect strength.

Answer 1

• Morphological:
  
  • muscle strength is related to cross-sectional area/size
  • Human skeletal muscle can generate approx 3-8kg of force per cm^2 (regardless of gender)
• Neural:
  
  • Rate coding = frequency of signal travelling to motor unit (influences the force and tension in mm)
  • Inter-muscular coordination = correct sequencing of muscular contractions (eg. switching muscles on/off at the right time)
  • Intra-muscular coordination = ability to activate motor units in same muscle at appropriate time

Question 2

Define Muscular strength.

Answer 2

• Defined by peak force or torque developed during a maximal voluntary contraction

Question 3

Strength is also influenced by other factors. List and explain several of these.

Answer 3

• The no. of motor units activated
  
  • The size of such motor units (no. of mm fibres)
  • The size of individual mm fibres
  • The % of fast twitch fibres
  • Frequency of motor unit stimulation
  • The length of mm fibres
  • The type of mm contraction
  • The angle of mm pull

Question 4

Define muscle power

Answer 4

speed x strength
force x velocity

Question 5

How do you increase muscle power?

Answer 5

increasing speed, increasing strength and/or increasing coordination of speed and strength interaction

Question 6

Describe the relationship between muscle contraction velocity and power.

Answer 6

• There is an optimal speed of muscle shortening at which the most powerful contraction is produced (because force-velocity relationship of decreasing force as velocity of application increases, and power equals force applied times the velocity at which the force is applied)

Question 7

How are strength and Power related?

Answer 7

• An increase in strength may not necessarily result in an increase in power
• Power involves ability to ‘mobilise’ force quickly but is not guaranteed by strength
• the production of maximum power is dependent upon the production of optimum force and optimum velocity

Question 8

Discuss how Strength / Power changes can occur neurologically.

Answer 8

• Disinhibition: reduction of golgi tendon organ inhibitory mechanism
• Motor unit synchrony: ability of motor units to fire in a synchronised, coordinated fashion
• Learning: ability of stabiliser muscles (antagonists) to switch off results in greater prime mover force / power

Question 9

Discuss how Strength / Power changes can occur due to morphology changes.

Answer 9

• Hypertrophy: increase diameter of muscle fiber through cell size increase
• Fast twitch hypertrophy is greater than slow twitch
• Hyperplasia: splitting of muscle fibers
• Other adaptations to strength / power training
  
  • increased bone density
  • increased stiffness of tendinous structures through organised deposition of non-elastic materials

Question 10

List several ways that strength / power adaptation can improve the SSC.

Answer 10

• Neural improvements: GTO kicks in later, therefore stretch reflex augmentation to SSC can be improved
• Combined with learning effects, greater stretch reflex results in greater inhibition of antagonist muscles
• Together, these adaptations allow a muscle to be stretched at a faster rate therefore increasing the amount of energy that will be stored by elastic components
• Synchronisation of motor units result in greater force development in concentric phase
• Increased bone density and tendon stiffness allows more energy to be tolerated by these structures before failure results
• Greater tendon stiffness results in greater recovery and utilisation of energy from eccentric loading phase
• Morphological changes: hypertrophy and hyperplasia allows greater force development
• Greater cross-sectional area results in greater strength. However, force-output capacity varies depending on skeletal levers and muscle architecture

Question 11

What is plyometrics?

Answer 11

• a form of exercise that involves rapid and repeated stretching and contracting of the muscles, designed to increase power/speed.
• Purpose is to improve velocity of performance
• Mm is put on rapid stretch

Question 12

List and explain 4 principles of resistance training.

Answer 12

• Specificity (for strength, power, muscle groups, etc)
  
  • Overload / intensity
  • Variation (e.g. utilising other muscle groups)
  • Recovery / Rest

Question 13

Can resistance training be disadvantageous for an athlete? Explain your answer.

Answer 13

• During some exercises (isometric) the blood flow to the muscle stops, blood pressure rises, and less blood flows back to the heart (it could be dangerous if you have heart problems)
• Isometric training is not sufficient on its own, You need to combine it with isotonic training

Question 14

Define flexibility.

Answer 14

• Defined as terminal ROM of a segment

Question 15

List and explain several factors that influence flexibility.

Answer 15

• Joint structure
• Soft tissue
• Ligaments
• Actual physical length of the antagonistic mms & the level of neurological innervations as mm is stretch

Question 16

Increased flexibility can generate a shift in the length-tension relationship for that muscle. Explain this shift and how it occurs.

Answer 16

• Increase in sarcomeres in series

Question 17

How might increased flexibility provide protection from muscle injury?

Answer 17

• Due to sarcomeres in series, therefore each sarcomere is not stretched as much –> less muscle damage
• Muscle exerts more force at longer positions (can be stretched further with less damage) eg. football kick