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PHYSIO > Control of muscle mechanical output > Flashcards

Control of muscle mechanical output Flashcards

1
Q

What happens during single muscle fibre isometric contraction?

A

No change in muscle length (but produces force) - when holding something.
Myosin heads trying to push actin but not moving = produce isometric force.

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2
Q

What happens during single muscle fibre concentric contraction?

A

Muscle fibre is actively shortening (performing mechanical work)

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3
Q

What are the different types of contraction?

A

1) Isometric
2) Concentric
3) Eccentric

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4
Q

What is isometric contraction used for?

A

In everyday life to hold positions

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5
Q

What does force depend on?

A

1) Number of sarcomeres in parallel
2) Length of sarcomere (and number of cross-bridges)
= force-length relationship important for isometric contraction

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6
Q

Which muscle fibre can generate the most force?

A

THICK - more sarcomeres which are parallel

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7
Q

What is the force-velocity relationship?

A

?

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8
Q

What does velocity depend on?

A

The number of sarcomeres in series (arrangement of sarcomeres)

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9
Q

What makes a muscle fibre stronger than others?

A

More sarcomeres parallel (stacked) - but has a low velocity

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10
Q

What makes a muscle fibre faster than others?

A

More sarcomeres in series (next to each other) - but has a high velocity

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11
Q

What does it mean if sarcomeres are in parallel?

A
  • Forces add up
  • Each element feels only part of the whole force
  • Movements do not add up
  • Each element experiences the whole movement
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12
Q

What does it mean if sarcomeres are in series?

A
  • Forces do not add up
  • Each element feels the whole force
  • Movements do add up
  • Movement is shared between the elements
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13
Q

Single muscle fibre power?

A
  • Power is not a synonym of force
  • Power = force x velocity
  • Power can be measured during concentric contractions, not isometric conditions
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14
Q

What is the influence of fibre types?

A

Fibre type is defined by the myosin heavy chain isoform composition.

Different isoforms e.g.

  • (S) Type I
  • (F) Type IIa or Type IIx
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15
Q

What happens during single muscle fibre eccentric contraction?

A

Muscle is being actively lengthened (performing negative work or absorbing energy)

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16
Q

What is the maximum voluntary contraction (MVC) dependent on?

A

The type of single muscle fibre.

  • Different apparatus is used to measure different muscle groups.
17
Q

Type II fibres

A

Strong but can’t sustain contraction

18
Q

Type I fibres

A

Sustain contractions for longer

19
Q

What is the peak power order for the 3 types of fibres?

A

type IIx > type IIa > type I

20
Q

Usain Bolt and type IIx fibres

A
  • 99% type IIx fibres

- High power, force + velocity

21
Q

Mo Farah and type I fibres

A
  • type I fibres only as he doesn’t need to produce a lot of force or velocity
  • just need fibres w/ a lot of mitochondria which are able to sustain contractions for longer
22
Q

How can muscle force be determined?

A

1) Physiological cross-sectional area
- Anatomical CSA
- Angle of Pennation
2) Antagonist co-contraction
3) Neural activation
- Recruitment
- Firing rate
- Motor unit synchronisation
4) Fibre type

23
Q

What needs to be considered when looking at the whole force of a muscle?

A

Need to consider CSA (or detection of fibre)

24
Q

How can co-contraction be measured?

A
  • Vastus Lateris EMG

- Biceps Femoris EMG

25
Q

What does co-contraction of antagonists do?

A

Reduces measured external force of agonists (slows down movement - a break)

Force = agonist
Break = antagonist
26
Q

What does the force-velocity relationship in-vivo show?

A

At high velocities, a high force cannot be produced

27
Q

What does neural activation of muscles consist of?

A
  • brain used to make movements
  • to use a muscle to push > activate brain > signal to synaptic cleft > muscle fibres
  • every time you activate muscle, you have neural activation (which differs - many activate different motor units + recruitment may be different; spatial or temporal)
28
Q

What happens to neural activation as a person ages?

A

Weaker - cannot activate muscles as all motor units can’t be recruited

PHYSIO (12 decks)

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