Architectural & Structural Factors Affecting Strength & Power Flashcards
Muscle Architecture (the physical arrangement of muscle fibers) is made up of what three things?
- Cross-sectional Area (CSA)
- Pennation Angle
- Fibre Length
Muscle strength depends largely on what? and what is maximum muscle force proportional to?
Muscle strength depends (to a large extent) on muscle size
Maximum muscle force is proportional to the number of fibres placed parallel to
one another
Why doesn’t Cross-sectional Area explain everything?
- Inability to activate entire muscle
- Co-activation of antagonist muscles
- Limitations with measurement of strength and muscle size
- Measure size of one muscle instead of muscle group
- Use of ACSA instead of PCSA
- Different specific tension = the force that a single fibre can exert per unit of cross-sectional areas – this is the main reason why force cannot be attributed to Cross-sectional Area
Body Size
Body size has a profound effect on force production.
In general larger people are stronger than smaller people.
Normalisation techniques for muscle force and torque can improve the external validity of muscle strength tests
Classic Formula = load lifted / body weight to the power of to thirds (0.67)
However, when normalised (weight lifted / body weight) smaller people tend to be
stronger than larger lifters
Scaling = load lifted / body weight to the power of two thirds (0.67).
Type II motor units
Fast contraction velocity (up to 6 fl.s-1) fatiguable, increased motoneuron size, fibre diameter and innervation ratio
Type I motor units
Slow contraction velocity (up to 2 fl.s-1) fatigue resistant
Motor Unit Types - Contractile Properties
Determined via direct & indirect methods
Examination of Motor Unit twitch or combination of twitches (tetanus)
Examination if histochemical, biochemical & molecular properties
Motor Unit key Properties
Contractile Speed: time to peak force
Motor Unit Force: amplitude of twitch/tetanus
Fatigability: decline in peak force with successive tetani
What are Pennate muscles?
Muscles that have their fibres arranged around one or more central tendons like the barbs of a feather.
Comes from Greek word for “fan”
What are fusiform/Non-Pennate muscles?
Non-pennate muscles have their fibres arranged parallel to the muscles line of pull– often termed ‘fusiform
What does a high Pinnation muscle result in?
Increased strength - pennation allows the packing of
more muscle fibres per cross-sectional area thus generating
greater force.
What does a low Pennation muscle result in?
Increased range and velocity
Influence of high pennation on thickness?
Decreased thickness
Influence of low pennation on thickness?
Increased thickness
Three training effects on pennation?
- Increased pennation angle
- More fibres in set muscle volume
- Reduction in force transmitted to central tendon
Fibre Length (Fact Card)
Muscles fibres are generally shorter than muscle length
Muscles that tend to have large Cross-sectional Areas have short muscle fibres
Larger Cross-sectional Area (anti-gravity muscles) = shorter fibre length
A consequence of fascicle elongation is increase in the maximal velocity of muscle shortening
Longer fibre length = greater ROM & velocity of contraction
Greater fascicle length such as those of a sumo wresler appears to limit what?
The degree of change in pennation angle associated with the extreme muscle enlargement seen in sumo wrestlers.
This may improve the expression of the force/CSA relationship with extreme muscle enlargement.
Eccentric exercises increase what?
Increases fascicle lengths via sarcomerogenesis
players with shorter VF fascicles were at a fourfold greater risk of hamstring strain
Injured legs often show what three components?
- Shorter fascicles
- Greater pennation angles
- Lower eccentric strength
What does larger PCSA and smaller pennation angles of the posterior compartments indicate?
A muscle design more geared towards high force production
The smaller PCSA and pennation angles of the anterior compartment may indicate what?
A role more geared towards establishing muscle excursion, rather than force production
What are fusiform muscles?
Muscles are great for fast contractions
Their absolute force of contraction is small compared to pennate muscle groups
(Hamstrings)
(The quadriceps are a pennate muscle group
and are already dominant in many athletes)
What should be the primary hip extensors during powerful movements like sprinting?
The glutes
What happens during isokinetic muscle actions?
The peak torque exerted during concentric actions decreases as the angular velocity increases
How Critical are Structural &; Architectural Factors?
Muscle size ,fascicle angle and muscle activation exerted the greatest influence on force production (R2 = 0.72)
Fibre type did not significantly impact on the torque: Cross-sectional Area relationship
Fascicle angle was not a factor that discriminated between strong and weak individuals unless it was combined with Cross-sectional Area – strong influence of PSCA
The inclusion of fascicle length did not improve the predictive model – more important for force production in high-velocity contractions (slow-speed testing was conducted)
EMG &; VM had big effect on isometric force production
What is Rate of Force Development?
Derived from force- or torque-time curves recorded during explosive/ballistic voluntary contractions
Increasingly evaluated to characterise an individuals explosive strength
What are thw two ways in which muscle Cross-sectional Area can be measured?
- Physiological Cross-sectional Area (PCSA)
- Anatomical Cross-sectional Area (ACSA)
A measurement performed perpendicularly to the long axis of the segment
Specific tension relates to what?
The intrinsic force-generating capacity of a muscle
The force-velocity and length-tension properties of muscles also depends on what three things?
- Fibre /motor unit composition (structural factors)
- Fibre arrangement within a muscle
- The arrange ment of a muscle around a joint (mechanical factors)
Fibre arrangement in a muscle is generally classified as one of what two things?
Pennate Muscles
or
Non-Pennate Muscles
Describe Pennate Muscles
Have their fibres arranged at an angle to the muscles line of pull
Are thicker, have more sarcomeres packed in to a set volume of muscle and have higher
strength capabilities
Describe Non-Pennate Muscles
Have their fibres arranged parallel to the muscles line of pull, have increased range of
motion and velocity producing capabilities
Larger Cross-sectional Area =
Shorter fibre length
Longer fibre length =
Greater ROM and velocity of contraction
