Architectural & Structural Factors Affecting Strength & Power

Question 1

Muscle Architecture (the physical arrangement of muscle fibers) is made up of what three things?

Answer 1

1. Cross-sectional Area (CSA)
2. Pennation Angle
3. Fibre Length

Question 2

Muscle strength depends largely on what? and what is maximum muscle force proportional to?

Answer 2

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

Question 3

Why doesn’t Cross-sectional Area explain everything?

Answer 3

1. Inability to activate entire muscle
2. Co-activation of antagonist muscles
3. Limitations with measurement of strength and muscle size

• Measure size of one muscle instead of muscle group
• Use of ACSA instead of PCSA

4. 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

Question 4

Body Size

Answer 4

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).

Question 5

Type II motor units

Answer 5

Fast contraction velocity (up to 6 fl.s-1) fatiguable, increased motoneuron size, fibre diameter and innervation ratio

Question 6

Type I motor units

Answer 6

Slow contraction velocity (up to 2 fl.s-1) fatigue resistant

Question 7

Motor Unit Types - Contractile Properties

Answer 7

Determined via direct & indirect methods

Examination of Motor Unit twitch or combination of twitches (tetanus)

Examination if histochemical, biochemical & molecular properties

Question 8

Motor Unit key Properties

Answer 8

Contractile Speed: time to peak force

Motor Unit Force: amplitude of twitch/tetanus

Fatigability: decline in peak force with successive tetani

Question 9

What are Pennate muscles?

Answer 9

Muscles that have their fibres arranged around one or more central tendons like the barbs of a feather.

Comes from Greek word for “fan”

Question 10

What are fusiform/Non-Pennate muscles?

Answer 10

Non-pennate muscles have their fibres arranged parallel to the muscles line of pull– often termed ‘fusiform

Question 11

What does a high Pinnation muscle result in?

Answer 11

Increased strength - pennation allows the packing of
more muscle fibres per cross-sectional area thus generating
greater force.

Question 12

What does a low Pennation muscle result in?

Answer 12

Increased range and velocity

Question 13

Influence of high pennation on thickness?

Answer 13

Decreased thickness

Question 14

Influence of low pennation on thickness?

Answer 14

Increased thickness

Question 15

Three training effects on pennation?

Answer 15

1. Increased pennation angle
2. More fibres in set muscle volume
3. Reduction in force transmitted to central tendon

Question 16

Fibre Length (Fact Card)

Answer 16

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

Question 17

Greater fascicle length such as those of a sumo wresler appears to limit what?

Answer 17

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.

Question 18

Eccentric exercises increase what?

Answer 18

Increases fascicle lengths via sarcomerogenesis

players with shorter VF fascicles were at a fourfold greater risk of hamstring strain

Question 19

Injured legs often show what three components?

Answer 19

1. Shorter fascicles
2. Greater pennation angles
3. Lower eccentric strength

Question 20

What does larger PCSA and smaller pennation angles of the posterior compartments indicate?

Answer 20

A muscle design more geared towards high force production

Question 21

The smaller PCSA and pennation angles of the anterior compartment may indicate what?

Answer 21

A role more geared towards establishing muscle excursion, rather than force production

Question 22

What are fusiform muscles?

Answer 22

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)

Question 23

What should be the primary hip extensors during powerful movements like sprinting?

Answer 23

The glutes

Question 24

What happens during isokinetic muscle actions?

Answer 24

The peak torque exerted during concentric actions decreases as the angular velocity increases

Question 25

How Critical are Structural &; Architectural Factors?

Answer 25

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

Question 26

What is Rate of Force Development?

Answer 26

Derived from force- or torque-time curves recorded during explosive/ballistic voluntary contractions

Increasingly evaluated to characterise an individuals explosive strength

Question 27

What are thw two ways in which muscle Cross-sectional Area can be measured?

Answer 27

1. Physiological Cross-sectional Area (PCSA)
2. Anatomical Cross-sectional Area (ACSA)
   A measurement performed perpendicularly to the long axis of the segment

Question 28

Specific tension relates to what?

Answer 28

The intrinsic force-generating capacity of a muscle

Question 29

The force-velocity and length-tension properties of muscles also depends on what three things?

Answer 29

1. Fibre /motor unit composition (structural factors)
2. Fibre arrangement within a muscle
3. The arrange ment of a muscle around a joint (mechanical factors)

Question 30

Fibre arrangement in a muscle is generally classified as one of what two things?

Answer 30

Pennate Muscles
or
Non-Pennate Muscles

Question 31

Describe Pennate Muscles

Answer 31

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

Question 32

Describe Non-Pennate Muscles

Answer 32

Have their fibres arranged parallel to the muscles line of pull, have increased range of
motion and velocity producing capabilities

Question 33

Larger Cross-sectional Area =

Answer 33

Shorter fibre length

Question 34

Longer fibre length =

Answer 34

Greater ROM and velocity of contraction