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Orthopaedic Biomechanics > Muscles 2 > Flashcards

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
Q

Factors affecting muscle strength (6)

A 
Muscle stretch
Fibre types
Muscle moment arm
PCSA
Level of fibre recruitment
Contraction velocity
26
Q

Determining muscle strength: describe an isokinetic dynamometer

A

Device that allows evalutation of strength, power, endurance and range of motion at pre-determined CONSTANT velocity

27
Q

What can you measure on EMG

A

Muscle electrical activity
Timing
Magnitude of signal

28
Q

What can you NOT measure on EMG

A

Force

29
Q

What can you measure on surface EMG (2)

A

Summation of action potentials

Activity of small superficial muscles

30
Q

What can you measure on fine needle EMG (2)

A

Activity of smaller motor units

Activity of deeper muscles

31
Q

Factors affecting EMG signal (4)

A

Cross-talk between muscles
External noise
Tissue impedance
Skin changes e.g. sweat

Orthopaedic Biomechanics (15 decks)

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