Architectural & Structural Factors Affecting Strength & Power

Question 1

Why is Cross-sectional area a factor towards strength?

Answer 1

Muscle strength depends (to a large extent) on muscle size
Max muscle force is proportional to number of fibres placed parallel to one another
Measurement of size = PCSA and ACSA

Question 2

What are the techniques for measureing changes in CSA?

Answer 2

1. Girth measurements
2. Ultrasound
3. MRI
4. DEXA
5. Computed temography

Question 3

In terms of strength studies, wh might a study be poorly designed?

Answer 3

1. Poor muscle size measurements
2. Strength measurements taken on one occasion - subjective day-to-day effort?
3. Small participant numbers - invalid correlations

Question 4

Why doesn’t CSA explain everything?

Answer 4

1. Inability to activate each motor unit/fibre
2. Co-activation of antagonist muscles
3. Limitations with measurement of strength and muscle size
4. Different specific tension = the force that a single fibre can exert per unit of cross-sectional areas

Question 5

What is the classic formula of working strength out in relation to body size?

Answer 5

Load lifted / body weight to the power of two thirds

Question 6

How can contractile properties be determined?

Answer 6

• Examination of MU twitch or combination of twtiches (tetanus)
• Examination of histochemical, biochemical & molecular properties

Question 7

What are the key properties of Motor unit types which influence strength?

Answer 7

• Contractile speed: time to peak force
• MU Force: amplitude of twitch/tetanus
• Fatigability: decline in peak force with successive tetani

Question 8

What are the characteristics of Type II motor units?

Answer 8

• Fast contraction velocity (up to 6fl.s-1)
• Fatiguable
• Increased motorneuron size
• Fibre diameter
• Innervation ratio

Question 9

What are the characteristics of Type I motor units?

Answer 9

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

- Fatigue Resistant

Question 10

What influence does High Pennation have on strength?

Answer 10

Incresed strength
Pennation = packing of more muscle fibres per cross-sectional area thus generating greater force
Reduction in force transmitted to central tendon

Question 11

What influence does Low Pennation have on strength?

Answer 11

Increased range and velocity

Question 12

How does Fibre length influence strength?

Answer 12

Larger CSA = shorter fibre length

Fascicles elongation = increase in maximal velocity of muscle shortening

Muscle force is higher with shorter muscle lengths

Muscle velocity is higher with long fibres

Question 13

What does greater fascicle length limit?

Answer 13

Greater fascicle length appears to limit 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 14

What does Eccentric exercise do in terms of injury prevention?

Answer 14

Eccentric exercise increases fascicle lengths via sarcomerogensis.
Players with shorter BF fascicles were at a fourfold greater risk of hamstring strain

Question 15

What are the Archictectural differences between hamstrings and quads?

Answer 15

-Hamstrings are a fusiform musce group = fast contraction, absolute force of contraction is small compared to pennate
-Quadriceps are a pennate muscle group
Quadriceps are often dominant

Question 16

What happens during isokinetic muscle actions?

Answer 16

Peak torque exerted during concentric actions decreases as the angular velocity increases.

Question 17

Which factors are the greatest influence on force production?

Answer 17

Muscle Size
Fascicle Angle
Muscle Activation

Question 18

Does muscle Archictecture influence RFD?

Answer 18

• Max strength correlated with RFD - strength of this relationship increases with the time from contraction onset
• Fibre type considered major factor for RFD