Muscles 2 Flashcards

1
Q

What is the pennation angle

A

the angle at which fibres are attached with respect to the tendon/line of action of force (0 ≤ angle < 90)

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2
Q

What is the benefit of having fibres orientated at angle

A

This allows more fibres to occupy a unit volume
This means more contractile units in the muscle
Therefore more force can be generated

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3
Q

What type of tasks are carried by muscles with a high pennation angle

A

Static tasks

High angle means shorter fibres and longer tendons

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4
Q

What type of tasks are carried by muscles with a low pennation angle

A

Motion tasks

Lower angle means longer fibres which allow for more SHORTENING (shortening = movement)

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5
Q

What is Physiological cross sectional area and how is it calculated?

A

This is the area perpendicular to fibre direction

Muscle volume/Fibre length

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6
Q

How is PCSA used to calculate Fmax for a muscle

A

Fmax = PCSA x 20 (muscle stress, N/cm2)

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7
Q

What are the 4 different muscle structures?

A

Fusiform
Unipennate
Bipennate
Multipennate

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8
Q

Describe fusiform muscles and give an example?

A

Very small pennation angle (almost parallel with tendon)
Allows quick movement and easily fatigued
e.g. Tibialis anterior, Biceps brachii

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9
Q

Describe unipennate muscles and give an example?

A
ONE pennation angle for the whole muscle
Large pennation angle
Slower movement 
Powerful contraction
e.g. Gastrocnemius
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10
Q

Describe Bipennate muscles and give an example?

A

TWO pennation angles
Static contraction and stability
e.g. erector spinae, rectus femoris

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11
Q

Describe Multipennate muscles and give an example?

A

Multiple pennation angles
Contains short and long fibres
Offers stability and movement
e.g. rotator cuff, Deltoid

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12
Q

What is muscle excursion?

A

Change in muscle length

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13
Q

What affects excursion (2)

A

Length of the muscle fibres

Muscle’s moment arm

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14
Q

What is the formula relating moment arm, excursion and joint angle

A

Moment arm = Change in length (excursion)/Change in joint angle

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15
Q

How does moment arm affect excursion

A

To achieve the same change in joint angle, muscles with a larger moment arm require a greater change in length

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16
Q

In what order a fibres recruited

A

Slow fibres –> Fast fibres 2a –> Fast fibres 2b

17
Q

Force capability and fatiguability for slow fibres (Type I)

A

Type I fibres can produce low forces
They are slow to contract
These are not easily fatiguable (good blood supply)

18
Q

Force capability and fatiguability for fast fibres (Type IIa)

A

Type IIa can produce more force than Ia but less than IIa
They contract quickly
These are not easily fatiguable (moderate blood supply)
more fatguable than I but less than IIb

19
Q

Force capability and fatiguability for fast fibres (Type IIb)

A

These can produce the largest force VERY quickly
Easily fatiguable - Think of this like a large burst of force
They have poor blood supply (anaerobic actibity)

20
Q

Rank fibre size in descending order for the different fibre types

A

Fast Type IIb > Fast Type IIa > Slow

21
Q

What happens to muscles in strength training

A

Hypertrophy –> Increased PCSA

Improved innervation

22
Q

What happens to muscle in endurance training

A

Increased energy supply to muscle:
Increased mitochondria
Increased capillary density

23
Q

What happens in sore muscles

A

Tensile overloading leads to structural injury (tear)
Cell contents diffuse into interstitial fluid
Macrophages come to clear extra content -> inflammation
Elevated intramuscular pressure

24
Q

What happens with muscle disuse

A

Decreased length and contractility: fewer sarcomeres in series
Decreased PCSA: Fewer sarcomeres in parallel
Change in ratio of type I and type II

25
Factors affecting muscle strength (6)
``` Muscle stretch Fibre types Muscle moment arm PCSA Level of fibre recruitment Contraction velocity ```
26
Determining muscle strength: describe an isokinetic dynamometer
Device that allows evalutation of strength, power, endurance and range of motion at pre-determined CONSTANT velocity
27
What can you measure on EMG
Muscle electrical activity Timing Magnitude of signal
28
What can you NOT measure on EMG
Force
29
What can you measure on surface EMG (2)
Summation of action potentials | Activity of small superficial muscles
30
What can you measure on fine needle EMG (2)
Activity of smaller motor units | Activity of deeper muscles
31
Factors affecting EMG signal (4)
Cross-talk between muscles External noise Tissue impedance Skin changes e.g. sweat