Factors affecting strength, Neural and CSA.

Question 1

Define strength?

Answer 1

The maximal force that a muscle or muscle group can generate at a specified velocity.

Question 2

What is the relationship between strength and injury?

Answer 2

Strength influences absorption mechanics for example ACL injuries via glute complex and quad:hamstring ratio.
Asymmetry also increases injury risk.

Question 3

Bodybuilder, Powerlifter and Strong man - who is strongest?

Answer 3

The powerlifter.

Question 4

How much strength does CSA of muscle account for and why?

Answer 4

Cross-sectional area accounts for 50% of strength differences between individuals.
Why
-Neural
-Fibre type

Question 5

What are the different fibre types?

Answer 5

• Type 1 = slow twitch
• Type 11a = fast twitch, fatigue resistant
• Type 11x = fast twitch, potential hybridisation?

Question 6

What are the factors affecting muscle strength and power?

Answer 6

> Joint position
Joint velocity
Muscle Structure = fibre type breakdown, innervation ratio, Architecture - CSA and angle of pennation.

Question 7

What are the main factors which influence the conduction velocity of the nerve?

Answer 7

• Cell diameter
• Cell surface area
• Axon conduction velocity
• Voltage threshold

Question 8

Key points - Muscle unit and Innervation number

Answer 8

> Muscle fibres are recruited by single neurons - motor unit
Motor units activate between 10-1000
Innervation number is the ratio between fibres and axons
High innervation number relates to a higher force production

Question 9

Relationship between Motor Pool, Innervation ratio and cumulative sum (% total).

Answer 9

As the motor neuron pool increases there is a correlative increase with innervation number and cumulative sum.

Question 10

What is an Interneuron?

Answer 10

Found in the spinal cord. Relays signals between Afferent sensory nerves and efferent motor neurons.

Question 11

What’s the difference between Afferent and Efferent neurons?

Answer 11

Afferent neurons - provides feedback

Efferent neurons - activates muscle fibres

Question 12

What is an intrafusal muscle fibres?

Answer 12

Intrafusal muscle fibres monitor the homeostasis of the contractual muscle fibres. They send electrical feedback via the Gamma Motor Neurons

Question 13

What are the characteristics of a Muscle spindle primary?

Answer 13

Detects the rate of muscle stretch
Neuron type - Afferent Ia
Conduction velocity - 40to90

Question 14

What are the characteristics of a Tendon Organ?

Answer 14

Detects amount of muscle force
Afferent Ib
Conduction velocity 30to75

Question 15

What are the characteristics of a Muscle spindle secondary?

Answer 15

Detects the stretch of muscle, amount?
Afferent II
Conduction velocity 20to45

Question 16

What are the characteristics of a Joint receptor?

Answer 16

Detect the force around a joint
Afferent II to III
Conduction Velocity 4to45

Question 17

What are the characteristics of a haptic receptor?

Answer 17

Detects skin movement
Afferent ItoIII
Conduction velocity 4 to 80

Question 18

What is the renshaw cell?

Answer 18

Renshaw cells are inhibitory interneurons which control the activation and feedback thresholds.

Question 19

What factors influence a reduction of co-contraction?

Answer 19

> Development of skills
Strength training adaptations
Fatigue
Performance enhancements reduces co-contractions
Impaired co-contractions increases risk of injury

Question 20

Why is PNF stretching effective - how does it work?

Answer 20

Initial stretch - stimulates efferent type 2 stretch receptors
Contraction stimulates the alpha motor neuron which innervates extrafusol muscle fibres of skeletal muscle
Feedback is achieved via Gamma neuron
Renshaw cell confused = overrides sensory feedback.

Question 21

What is Post Activation Potentiation (PAP)?

Answer 21

“Implementing a resistance exercise prior to an explosive movement has improved subsequent performance above the athletes percieved best” (Yetter & More, 2008; Kilduff et al., 2008).

Question 22

Physiology behind PAP?

Answer 22

• First contraction, activates large motor units
• Leads to reduced inhabitation by the renshaw cell
• Second contraction recruits more larger motor units - different muscle action

Question 23

What are the methodological factors which are important to PAP studies?

Answer 23

• Participant characteristics (training)
• Similarity of activation method to performance measure
• Activation method volume + intensity
• Recovery duration
• Reproducibility of the performance measure
• Study design
• Inital warm up-component

Question 24

PQ 1. Physiological & Mechanical factors affectng strength and power, which factor is associated with joint position?

Answer 24

Moment Arm

Question 25

PQ 2. What % of force produced by a muscle can be attributed to CSA?

Answer 25

50%

Question 26

What is the maximal conduction velocity of a large alpha motor neuron?

Answer 26

Up to 101m/s