Muscles 2 Flashcards
What is the pennation angle
the angle at which fibres are attached with respect to the tendon/line of action of force (0 ≤ angle < 90)
What is the benefit of having fibres orientated at angle
This allows more fibres to occupy a unit volume
This means more contractile units in the muscle
Therefore more force can be generated
What type of tasks are carried by muscles with a high pennation angle
Static tasks
High angle means shorter fibres and longer tendons
What type of tasks are carried by muscles with a low pennation angle
Motion tasks
Lower angle means longer fibres which allow for more SHORTENING (shortening = movement)
What is Physiological cross sectional area and how is it calculated?
This is the area perpendicular to fibre direction
Muscle volume/Fibre length
How is PCSA used to calculate Fmax for a muscle
Fmax = PCSA x 20 (muscle stress, N/cm2)
What are the 4 different muscle structures?
Fusiform
Unipennate
Bipennate
Multipennate
Describe fusiform muscles and give an example?
Very small pennation angle (almost parallel with tendon)
Allows quick movement and easily fatigued
e.g. Tibialis anterior, Biceps brachii
Describe unipennate muscles and give an example?
ONE pennation angle for the whole muscle Large pennation angle Slower movement Powerful contraction e.g. Gastrocnemius
Describe Bipennate muscles and give an example?
TWO pennation angles
Static contraction and stability
e.g. erector spinae, rectus femoris
Describe Multipennate muscles and give an example?
Multiple pennation angles
Contains short and long fibres
Offers stability and movement
e.g. rotator cuff, Deltoid
What is muscle excursion?
Change in muscle length
What affects excursion (2)
Length of the muscle fibres
Muscle’s moment arm
What is the formula relating moment arm, excursion and joint angle
Moment arm = Change in length (excursion)/Change in joint angle
How does moment arm affect excursion
To achieve the same change in joint angle, muscles with a larger moment arm require a greater change in length
In what order a fibres recruited
Slow fibres –> Fast fibres 2a –> Fast fibres 2b
Force capability and fatiguability for slow fibres (Type I)
Type I fibres can produce low forces
They are slow to contract
These are not easily fatiguable (good blood supply)
Force capability and fatiguability for fast fibres (Type IIa)
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
Force capability and fatiguability for fast fibres (Type IIb)
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)
Rank fibre size in descending order for the different fibre types
Fast Type IIb > Fast Type IIa > Slow
What happens to muscles in strength training
Hypertrophy –> Increased PCSA
Improved innervation
What happens to muscle in endurance training
Increased energy supply to muscle:
Increased mitochondria
Increased capillary density
What happens in sore muscles
Tensile overloading leads to structural injury (tear)
Cell contents diffuse into interstitial fluid
Macrophages come to clear extra content -> inflammation
Elevated intramuscular pressure
What happens with muscle disuse
Decreased length and contractility: fewer sarcomeres in series
Decreased PCSA: Fewer sarcomeres in parallel
Change in ratio of type I and type II
Factors affecting muscle strength (6)
Muscle stretch Fibre types Muscle moment arm PCSA Level of fibre recruitment Contraction velocity
Determining muscle strength: describe an isokinetic dynamometer
Device that allows evalutation of strength, power, endurance and range of motion at pre-determined CONSTANT velocity
What can you measure on EMG
Muscle electrical activity
Timing
Magnitude of signal
What can you NOT measure on EMG
Force
What can you measure on surface EMG (2)
Summation of action potentials
Activity of small superficial muscles
What can you measure on fine needle EMG (2)
Activity of smaller motor units
Activity of deeper muscles
Factors affecting EMG signal (4)
Cross-talk between muscles
External noise
Tissue impedance
Skin changes e.g. sweat
