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Biomechanics > 8 - Muscle Mechanics > Flashcards

8 - Muscle Mechanics Flashcards

1
Q

What is muscle force production?

A

amount of force developed in a sarcomere is directly proportional to the number of cross bridges formed

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2
Q

What does the number of cross bridges formed depend upon?

A
  • length of the muscle
  • contraction velocity
  • level of activation
  • time since onset of activation
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3
Q

What does the force-length relationship of a sarcomere show?

A

how the force a sarcomere can produce changes with the length of the sarcomere

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4
Q

How was the force-length relationship calculated?

A

In vitro:

  • single muscle fibre
  • fibre held at different lengths
  • stimulated to contract
  • force measured with a load cell
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5
Q

Describe the force-length relationship of a sarcomere

A

as the force increases so does the sarcomere length up till an optimum point before it rapidly declines in length

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6
Q

Describe passive tension in elastic tissues

A
  • connective tissue of fascia within muscle is made of an elastic material called collagen
  • collagen provides resistance to stretch like an elastic band
  • the amount of resistance is proportional to the force applied once the structure is stretched beyond its resting length
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7
Q

When does the maximum force in the active component occur in the MTU?

A

when the maximum number of cross bridges are attached

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8
Q

What does a decrease or increase in length of the sarcomere in the MTU mean?

A

that fewer cross bridges are attached and less force in developed

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9
Q

What happens if a muscle is stretched while actively contracting?

A

it is able to generate more force due to the passive components of the muscle

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10
Q

What is the activity and type of contraction related to the quads?

A
  • countermovement phase of countermovement jump (eccentric)

- propulsive phase (concentric)

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11
Q

What is the activity and type of contraction related to the hamstrings?

A
  • stance phase of running (concentric)

- swing phase of running (eccentric)

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12
Q

What is the activity and type of contraction related to the gastrocnemius?

A
  • moving from flat foot to top toe (concentric)

- standing on tip toe (isometric)

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13
Q

What does the force generated by a muscle depend upon?

A

its contraction velocity

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14
Q

Describe the force velocity relationship of a muscle

A
  • fibre bundle attached to a load
  • fibres stimulated to contract and allowed to shorten, moving the load
  • velocity of the shortening cycle measured
  • repeated for a number of different loads
  • the larger the load, the slower the muscle will shorten
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15
Q

What does the force velocity diagram describe?

A

how the force a muscle can produce changes according to the velocity with which it is changing length

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16
Q

When does maximal contraction velocity occur in a muscle?

A

when the muscle generates zero force

17
Q

What happens if the load exceeds the force generated by a muscle?

A

it will lengthen and more force will be produced

18
Q

What happens if force continues beyond maximum force that the muscle can produce?

A

it will continue to increase and will eventually tear

19
Q

Why does muscle produce less force when shortening and more force when lengthening?

A
  • isometric = a constant number of cross bridges are formed
  • concentric = cross bridges are cycling as the muscle shortens
  • eccentric = passive elastic structures in the muscle are stretched
20
Q

Explain the relationship between concentric contraction and cross bridges

A

the faster a muscle shortens the less time there is for the cross bridges to form and uniform, therefore there are fewer cross bridges attached

21
Q

What needs to be considered if the muscle is not under isometric contraction?

A

force length + force velocity relationship

22
Q

What does the force length relationship of a muscle describe?

A

how the force of a muscle can produce changes according to the length of the contractile and elastic components of the muscle

23
Q

What does the force activation relationship of a muscle fibre show?

A

as activation increases the level of force generated for a given length and velocity increases

24
Q

What does the force time relationship diagram show?

A

when muscle is activated the force increases over a period of time until it reaches the peak force for that level of activation

25
Q

What is the mechanical response of a muscle fibre to a single action potential known as?

A

a twitch

26
Q

What are the three major phases of a twitch?

A

1 - latent period
2 - contraction period
3 - relaxation period

27
Q

What is the latent period?

A

the period of time from the action potential to the onset of contraction

28
Q

What is the contraction phase?

A

the time that tension is developing due to the cross bridge cycling

29
Q

What is the relaxation phase?

A

the time that the tension is decreasing and is longer than the contraction phase due to the amount of time it takes to get all the calcium sequestered

30
Q

What are the three types of muscle fibres and giver their characteristics

A

type 1:

  • slow
  • small
  • oxidative
  • aerobic
  • fatigue resistant

type 2a:

  • fast
  • larger
  • oxidative
  • aerobic
  • fatigue quicker due to size

type 2b:

  • fast
  • rapid response
  • anaerobic
  • fatigue easily
31
Q

What does fibre type influence?

A

the amount of force produced and the velocity of the contraction

32
Q

What is contraction velocity determined by?

A
  • calcium release and uptake

- cross bridge kinetics which are dependant on the type of myosin in the fibre

33
Q

Does ramping up the peak force happen quicker in fast or slow twitch muscle fibres?

A

fast

34
Q

How can we determine muscle fibre type and their distribution?

A

muscle biopsies, fibre type distribution from EMG signal

35
Q

Which type of muscle would you expect to be predominantly slow twitch muscle fibres?

A

those related to endurance and continuous force production

36
Q

Which type of muscle would you expect to have a high proportion of fast twitch muscle fibres?

A

those related to power production and fast but transient force development

37
Q

What is the order of fibres recruited for the motor unit?

A

slow

Biomechanics (11 decks)

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