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PDEP > W1 - Central Fatigue > Flashcards

W1 - Central Fatigue Flashcards

1
Q

Define fatigue

A

Reduction in the ability of muscle to generate force.

Reversible with rest.

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2
Q

How can fatigue be measured?

A

By the MVC using the biodex.

MVC = Max voluntary contraction

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3
Q

Define central fatigue

A

A subset of fatigue associated w/ specific alterations in the CNS function that can’t reasonably be explained by dysfunction within the muscle itself.

(Davis & Bailey 1997)

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4
Q

How might central fatigue come about?

A

As a result of conscious or unconscious mechanisms, subject may decide that the sensations are unacceptable and deliberately red level of activity. - Motivation?

Alternatively….

Afferent information from working muscles, joints or tendons may inhibit motor activity at spinal or supra spinal levels, leading to an obligatory loss of performance that no amount of voluntary effort can overcome.

(James et al, 1995)

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5
Q

What is reflective of central motor drive (CMD)?

A

Minute ventilation

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6
Q

What is CMD

A

Neural drive to the muscles from the motor cortex in the brain.

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7
Q

What did Chen et al, 2016 study show?

A

That yelling at participants activates the muscle to a greater extent despite no changes in HR compared to not being yelled at.

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8
Q

Using diagram in notes, what sections come under Central fatigue?

A

Motor cortex

Cortical spinal tract

Motor neurones/efferent nerves

NMJ

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9
Q

What happens at the cortical spinal tract

A

Transmission from the motor cortex to the motor and interneurones

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10
Q

Where is peripheral fatigue found on the diagram in notes?

A

Anything distal from the NMJ.

So where there’s

  • Excitability of the postsynaptic terminal
  • Ca2+ handling
  • Substrate availability
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11
Q

Compare central and peripheral fatigue

A

C = Progressive, exercise-induced reduction in the neural drive to the muscle, resulting in a decline in force prod.

P = Less force/power prod for a given neural input.

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12
Q

What technique can be used to stimulate the motor Cortex of the brain?

A

TMS

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13
Q

What happens in TMS

A

Electricity running through a coil of copper wire generates a rapidly changing magnetic field to excited the underlying tissue.

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14
Q

What would happen to the neurones if fatigue was present in the motor Cortex of the brain, shown by use of TMS

A

Neurones would be less excitable.

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15
Q

What is motor-evoked potential (MEP)?

A

It’s the electrical activity experienced at the muscle tissue after the brain has been stimulated.

The difference in MEP before + after an intervention indicates whether central fatigue has occurred.

Doesn’t tell you where in the chain of events the fatigue is taking place - you’d have to use it alongside a different technique to find that out.

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16
Q

A reduced MEP at the muscle tells us there is a reduction in which of the possible parts of central fatigue?

A

Cortical

Corticospinal

Motor neurone excitability

OR a combination of all the above.

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17
Q

What would cervicomedullary and spinal activation cause if used following TMS?

A

CMEP which is the medullary stimulation.

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18
Q

What does it mean if the MEP is greater following cervicomedullary and spinal activation compared to TMS alone?

A

Means the motor cortex is less excitable so would make it the predominant cause of central fatigue.

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19
Q

How would you further isolate where central fatigue induced impairment is occurring after TMS and cervicomedullary and spinal activation?

A

Could stimulate motor neurones directly via PNS.

20
Q

How can the electrical activity of the muscle be measured when carrying out PNS?

A

Using EMG to observe the changes in MEP.

21
Q

How can changes of force be measured?

A

Using a biodex.

22
Q

What does the twitch interpolation technique allow us to measure?

A

Maximum voluntary contraction

23
Q

What does the twitch interpolation technique measure?

A

Max possible force that can be voluntarily produced w/ muscle alone

Then stimulate peripheral nerve to cause muscle to produce the MVC.

Seen on a graph as the “extra” force produced.

24
Q

How do you get a % of the voluntary activation?

A

Voluntary force / Max force after stimulation.

25
Q

Possible results of doing the twitch interpolation technique after vigorous exercise

A

If central fatigue is present, results after would show a larger increase in force after the peripheral nerve stimulation than before the test.

Voluntary activation % would have decreased to indicate central fatigue.

26
Q

How would peripheral fatigue be shown following stimulation?

A

Peripheral fatigue would be a lower MVC prior to any stimulation.

27
Q

Would high or lower % voluntary activation be associated more with central fatigue?

A

Lower

28
Q

Severe domain for steady state exercise.

Central or peripheral fatigue

A

Associated more to peripheral fatigue.

29
Q

Heavy domain for steady state exercise

Central or peripheral fatigue

A

Both

30
Q

Moderate domain for steady state exercise

Central of peripheral fatigue

A

Both

31
Q

What did a study show that happened after 2 days following repeated prolonged exercise?

A

There was still central fatigue present but not peripheral fatigue.

32
Q

In what direction does afferent transmission occur?

A

Muscle to brain

33
Q

What does the Critical Peripheral Threshold Hypothesis (CPTH) promote?

A

The idea that a feedback loop informed by the conditions in the muscle restricts the excessive development of fatiguing metabolites.

34
Q

CPTH

What happens as conditions in the muscle become more extreme due to peripheral fatigue?

A

Group 3 + 4 muscle afferents ramp up their discharge interpreted by the CNS.

35
Q

What does the CPTH suggest happens as a result of the group 3 +4 muscle afferents ramping up their discharge due to conditions in the muscle becoming more extreme?

A

That it would down regulate CMD by way of a protection mechanism to prevent us from doing excessive exercise with that muscle group.

36
Q

What has had a substantial dose-dependent inverse effect on CMD + performance?

A

Pre-existing muscle fatigue.

37
Q

How could CMD never be impaired?

A

By using pharmacological blockade + prevent afferent feedback

38
Q

What has been used in a study to knock out afferent feedback?

A

Lidocaine

39
Q

Negative to blocking the afferent feedback

A

Decreases power output due to the epidural used to block the afferent fb also blocking the efferent feedback to the muscle – inhibiting perf.

40
Q

What is fentanyl?

A

An opioid analgesic

41
Q

What happens when fentanyl is delivered into the spine?

A

Selectively blocks the ascending sensory pathways (afferent)

Doesn’t affect motor efferent

42
Q

What happens to CMD following fentanyl?

A

Less inhibited

43
Q

Impact of fentanyl on TT time

A

No difference

44
Q

Central Governor Model

What does Noakes suggest?

A

Fatigue can’t solely be explained by changes in peripheral conditions, even if these conditions influence CMD via afferent feedback.

Perhaps the brain integrates information + subconsciously forecasts the exercise duration that can be maintained…

45
Q

Central Governor Model

Teleoanticipation

A

Idea that theres an area of the predicting + planning the level of effort an athlete must put in to complete a task.

Then controls the muscle power accordingly.

That its also related to prior experience

46
Q

The Psychobiological Model

A

Focuses more on the conscious regulation of pace by looking at:

  • Perception of effort
  • Potential motivation
  • Knowledge of distance/time to cover
  • Knowledge of distance/time remaining
  • Previous experience/memory of perception of effort
47
Q

List the strategies that can be used to protect against central fatigue

A

Blunting afferent fb

⬆️ efferent fb via TDCS to ⬆️ cortical excitability.

Drugs i.e paracetemol

Caffeine

Mental imagery/motivation

Pain training

Mental fatigue training (Brain Endurance training)

PDEP (7 decks)

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