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BPK 306 > Muscle Fatigue And Plasticity > Flashcards

Muscle Fatigue And Plasticity Flashcards

1
Q

Colloquial definition of fatigue

A

Reduction in physical or mental performance

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2
Q

Physiological definition of fatigue

A

1 failure to maintain the required or expected force
- definition appropriate for isometric contraction)
2 failure to maintain force, power, velocity
- definition for dynamic contraction

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3
Q

What is submaximal fatigue

A

Some fibres become fatigued and less able to generate force (power) so additional motor units recruited in order to achieve the same task
- increased effort required to maintain submaximal task

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4
Q

How is skeletal muscle controlled by the nervous system

A

Controlled by CNS via alpha-motor neuron efferents

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5
Q

Where are alpha-motor neurons cell bodies

A

Cell bodies localized to ventral horn

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6
Q

How does one muscle fibres get innervated

A

ONLY ONE FIBRE INNERVATED BY ONE ALPHA MOTOR NEURON

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7
Q

What determines exercise duration

A

Ability of muscle to meet energy needs for exercise

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8
Q

What factors impact fatigue and what factors do not impact fatigue

A

Do- metabolic byproducts, mental fatigue, pain, rapid failure of fast motor units, accumulation of Pi and lactic acid
Don’t- depleted energy stores = ATP always present

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9
Q

Where does fatigue occur neurally

A

Any point between CNS or PNS

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10
Q

Central vs peripheral fatigue

A

Central- associated with CNS (pre motor cortex, motor cortex, descending pathways, motor neuron activation/inhibition)
Peripheral- associated with function of motor units (NMJ, sarcolemma, T-tubules, voltage sensors, RYR1, Cav1.1, Ca availability, actin myosin interaction)

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11
Q

Causes of central fatigue

A
  • reduced excitatory drive from the motor cortex
  • presynaptic inhibition may be increased via increased firing of III-IV afferents
  • neural factors: 5-HT, DA, NA, play an important role during exercise- heat
  • exercise induced increases in neurotransmitters?
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12
Q

How is central fatigue measured

A

Using twitch interpolation

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13
Q

What is central fatigue hypothesis

A

Exercise induced increases in these neurotransmitters lead to CNS fatigue

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14
Q

What is the twitch interpolation technique

A
  • subject performs maximum voluntary contraction
  • partway through maximal electrical stimulation elicits a twitch
  • if force increases during interpolated twitch- shows that muscle was capable of generating extra force
  • so poor force during MVC was due to reduced motor drive from CNS
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15
Q

How does peripheral fatigue occur and why

A

Two phases- rapid fall and slower decline
Rapid- due to fatigue of type II fibres (type I fatigue resistant)

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16
Q

All factors of peripheral fatigue

A
  • type II fibre fatigue (limited tetanic ability)
  • depletion of glycogen and CrP
  • increased intracellular H+ and lactic acid
  • decreased pH alters Ca binding to TnC and actin myosin interactions
  • increased Pi exerts effects via Ca release, Ca sensitivity and actin myosin binding
17
Q

During high impulse activity what ion pools in T-tubules and what does this mean for the muscle

A

K+
High concentrations of K+ cause a decrease in muscle cell efficiency

18
Q

What T-tubule events can cause fatigue

A
  • High concentration of K+ causes decrease in muscle cell efficiency (K+ pools)
  • sustained depolarization of T-tubule membrane blocks local action potentials (causes decrease in release of Ca from SR- leads to decreased contractility)
19
Q

What SR event can cause fatigue, explain possible mechanisms

A

Impaired Ca release from the SR
- high K+ concentration extra cellular reduces voltage sensor activation and AP amplitude reducing RYR1 activity
- use of ATP increases free Mg2+ therefore decreasing RYR1 activity
- increased myoplasmic Pi levels can reduce Ca release by entering SR and chelating Ca

20
Q

What kind of motor units do fibres innervated with type II motor neurons become

A

Fast MU

21
Q

What kind of motor units do fibres innervated with type I motor neurons become

A

Slow oxidative MU

22
Q

How do muscles lengthen

A

Formation of additional sarcomeres (during growth)

23
Q

What happens to muscles if you become immobile

A

Shortening of muscle can occur- remove sarcomeres

24
Q

How do changes in sarcomere length effect force and velocity of shortening

A

DO NOT effect FORCE
Change velocity of shortening

25
Q

What changes does hypertrophy cause

A

Increases in strength and diameter of myofibril
(Strength training- no change velocity)

26
Q

What does a muscle need to maintain normal growth, what happens if it doesn’t

A

Muscle must be used and experience a load
Otherwise muscle atrophy- inhibition of protein synthesis, stimulation of protein degradation

27
Q

What can anabolic steroids abuse cause

A

Hormone disturbances
Impaired testosterone production

BPK 306 (18 decks)

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