Factors affecting strength, Neural and CSA. Flashcards
Define strength?
The maximal force that a muscle or muscle group can generate at a specified velocity.
What is the relationship between strength and injury?
Strength influences absorption mechanics for example ACL injuries via glute complex and quad:hamstring ratio.
Asymmetry also increases injury risk.
Bodybuilder, Powerlifter and Strong man - who is strongest?
The powerlifter.
How much strength does CSA of muscle account for and why?
Cross-sectional area accounts for 50% of strength differences between individuals.
Why
-Neural
-Fibre type
What are the different fibre types?
- Type 1 = slow twitch
- Type 11a = fast twitch, fatigue resistant
- Type 11x = fast twitch, potential hybridisation?
What are the factors affecting muscle strength and power?
> Joint position
Joint velocity
Muscle Structure = fibre type breakdown, innervation ratio, Architecture - CSA and angle of pennation.
What are the main factors which influence the conduction velocity of the nerve?
- Cell diameter
- Cell surface area
- Axon conduction velocity
- Voltage threshold
Key points - Muscle unit and Innervation number
> 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
Relationship between Motor Pool, Innervation ratio and cumulative sum (% total).
As the motor neuron pool increases there is a correlative increase with innervation number and cumulative sum.
What is an Interneuron?
Found in the spinal cord. Relays signals between Afferent sensory nerves and efferent motor neurons.
What’s the difference between Afferent and Efferent neurons?
Afferent neurons - provides feedback
Efferent neurons - activates muscle fibres
What is an intrafusal muscle fibres?
Intrafusal muscle fibres monitor the homeostasis of the contractual muscle fibres. They send electrical feedback via the Gamma Motor Neurons
What are the characteristics of a Muscle spindle primary?
Detects the rate of muscle stretch
Neuron type - Afferent Ia
Conduction velocity - 40to90
What are the characteristics of a Tendon Organ?
Detects amount of muscle force
Afferent Ib
Conduction velocity 30to75
What are the characteristics of a Muscle spindle secondary?
Detects the stretch of muscle, amount?
Afferent II
Conduction velocity 20to45
What are the characteristics of a Joint receptor?
Detect the force around a joint
Afferent II to III
Conduction Velocity 4to45
What are the characteristics of a haptic receptor?
Detects skin movement
Afferent ItoIII
Conduction velocity 4 to 80
What is the renshaw cell?
Renshaw cells are inhibitory interneurons which control the activation and feedback thresholds.
What factors influence a reduction of co-contraction?
> Development of skills
Strength training adaptations
Fatigue
Performance enhancements reduces co-contractions
Impaired co-contractions increases risk of injury
Why is PNF stretching effective - how does it work?
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.
What is Post Activation Potentiation (PAP)?
“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).
Physiology behind PAP?
- First contraction, activates large motor units
- Leads to reduced inhabitation by the renshaw cell
- Second contraction recruits more larger motor units - different muscle action
What are the methodological factors which are important to PAP studies?
- 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
PQ 1. Physiological & Mechanical factors affectng strength and power, which factor is associated with joint position?
Moment Arm
PQ 2. What % of force produced by a muscle can be attributed to CSA?
50%
What is the maximal conduction velocity of a large alpha motor neuron?
Up to 101m/s
