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How many muscle fibers are fired
Varies considerably among muscles
innervation ratio
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What is released in order to generate movement?
Calcium
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Controlled by the CNS
Peripheral nervous system
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Innervation ratio for delicate movements
Low ratio (5-10)
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Innervation ratio for gross movements
High ratio (several thousands)
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Feed Back Loop:
Motor and sensory cortex -> _________ _>motor cortex with indication of movement, intensity and length of muscle movement
Cerebellum
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Activation:
Action potential (AP)generated when several sub-threshold impulses arrive in succession
Temporal summation (time component)
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Activation:
AP generated when several presynaptic terminals on the same motor neuron are stimulated simultaneously
Spatial summation (from all different directions signal comes)
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Which principle?
In normal muscle, once the neuron is activated and the impulse reaches the NMJ,AcH is released and all the muscle fibers in that motor unit contract simultaneously
All or None Principle
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Where can fatigue occur in the motor unit pathway?
Anywhere. the brain, brain to spinal cord or from motor neuron to muscle
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Serves to smooth out muscle contraction
Neural inhibition
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Protective function; excessive force is not produced
Minimizes musculoskeletal injury
Neural inhibition
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Can occur for supramaximal performance
-Verbal encouragement
-Hypnosis
Disinhibition
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Classification of Motor Units:
Technique of classifying fibersby staining the muscle tissue for various enzymes
Histochemical Analysis
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What are the 3 factors considered for classification of motor units?
- Morphological characteristics
- Contractile properties
- Metabolic characteristics
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Classification of Motor Units:
Physical characteristics
Morphological
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Classification of Motor Units:
Velocity of contraction
Contractile
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Classification of Motor Units:
Enzyme characteristics
Biochemical
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Light: Slow contractile speed
Light: Low glycolytic capacity
Dark: High oxidative capacity
Slow Oxidative, Type I
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Dark: Fast contractile speed
Dark: High glycolytic capacity
Light: Low oxidative capacity
Fast Glycolytic, Type II
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Contractile Properties of Motor Units:
Slow twitch
Low tension
Fatigue resistant
Type I
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Contractile Properties of Motor Units:
Fast twitch
Moderate force
Fatigue resistant (intermediate)
Type IIa
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Contractile Properties of Motor Units:
Fast twitch
High force
High fatigue
Type IIb
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True or false:
Slow twitch = low tension = fatigue resistant
True
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True or false:
High twitch = High tension = High fatigue
True
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Would you want Type I or Type II as a sprint athlete?
Type II - High glycolytic, low oxidative
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Would you want Type I or Type II as an endurance athlete?
Type I - High oxidative, low glycolytic
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Is fiber type genetic?
Yes - twin studies
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Is the fibre type distributed fairly consistent among major muscle groups?
yes
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True or false:
Some muscle groups are predominantly ST or FT.
- True.
- ST - soleus & gastroc.
- FT - ocular (eye)
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True or false:
You cannot modify musle fibers through training
False. You can modify 20-30% (metabolic and contractile properties)
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Fibre Type: Are there significant gender differences?
No
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Fibre type true or false:
Variation is quite large, especially in men
True
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If you do endurance training for extended time the fast twitch motor units will increase _____ ______ and become more like slow twitch.
oxygen capacity
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Based on contractile speed, can FT convert to ST?
No.
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Why are muscle fibers lost from spinal cord injury?
- Atrophy
- Loss of capillaries
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After a spinal cord injury do fast twitch become slow twitch?
- No. Slow twitch (metabolic) become more like fast twitch.
- Lose oxidative capacity because of loss of capillaries
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No visible change in muscle length
Cross bridges link to generatemuscle tension
Muscular tension insufficient toovercome resistance
Energy metabolised from anaerobic sources
ATP is broken down
Isometric (Static) Contraction
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Constant tension throughoutthe ROM
-Misnomer – tension variesthroughout ROM
-Muscle is only as strong as itsweakest point (sticky point)
Isotonic (Dynamic) Contraction
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Constant velocity throughout the ROM
Muscle stressed throughout the ROM
Isokinetic (Dynamic) Contraction
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Types of Muscle Contractions:
Muscle shortens while overcomingresistance
Muscle tension varies throughout ROM
Length – tension relationship differs among muscle groups
Concentric
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Types of Muscle Contractions:
Muscle lengthens againstresistance
Peak muscle tension exceeds thatattained during concentriccontractions
-Optimal linkage of cross bridges?
Eccentric
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Soreness/stiffness in muscles and joints which is onset a few hoursafter exercise and lasts for 2 to 4 days
Usually occurs after unaccustomed physical activity
Delayed Onset of Muscle Soreness (DOMS)
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Not due to the accumulation of lactic acid
Possible causes include:
Connective tissue damage: hydroxproline in urine
Cellular damage: can detect CK and myoglobin in serum
Metabolite accumulation: osmotic changes cause edema
Muscle spasm: due to transient ischemia
Delayed Onset of Muscle Soreness (DOMS)
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-small alpha motor neuron
-ST (slow twitch)
-Low force output
Endurance Type Activities
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-large alpha motor neuron
-ST/FT (slow twitch then includes fast twitch as velocity of contraction increases and force output continues)
-High force output
-with fatigue recruit more slow twitch
Power Type activity
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recruit motor units in specific patterns (can be learned)
Voluntary Modulation
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True or false:
Motor units are not plastic and their biochemical properties cannot be altered by the amount of physical activity/inactivity
False. They are plastic and biochemical properties can be altered by physical activity/inactivity
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True or false:
Motor unit recruitment patterns may be altered in diseased/disabilitystates which can adversely affect the energy cost of physical activity inindividuals with neuromuscular disorders
True
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