Central and peripheral fatigue

Question 1

What are the causes of fatigue?

Answer 1

• Failure to supply o2
• Failure to keep lactate down
• Failure to keep h + ions and phosphates down
• Depletion glycogen
• Failure to lose heat

Question 2

Define central and peripheral fatigue?

Answer 2

• Central fatigue is a failure of the central nervous system to adequately drive the muscle
• Peripheral fatigue is an impairment located in the muscle characterized by a metabolic end point

Question 3

What causes central fatigue?

Answer 3

• Disturbances in brain neurotransmitters – increased serotonin and reduced dopamine. High ratio of serotonin to dopamine causes fatigue
• Depletion of brain glycogen
• Increases in core and brain temperature resulting in a reduced drive of the CNS to work output

Question 4

What causes peripheral fatigue?

Answer 4

• Depletion of substrates
• Accumulation of metabolites such as hydrogens and inorganic phosphates
• Feedback from fatigue-sensitive muscle afferents. Group III / IV muscle afferents relay exercise induced metabolic disturbances to the CNS.

Question 5

What did the first investigation by Amann show about peripheral fatigue?

Answer 5

• Pre existing locomotor muscle fatigue had a substantial dose dependent inverse effects on CMD and power output during 5ktt
• Higher pre existing fatigue the lower the average CMD and power output on subsequent time trials
• Levels of peripheral fatigue were identical at the end of the trials with no further peripheral fatigue suggesting the CMD regulated exercise power output so no further peripheral fatigue was accumulated

Question 6

What was shown when peripheral afferent feedback was blocked?

Answer 6

• Still have a central drive
• Stronger drive to perform suggested by increase EMG when not receiving peripheral feedback
• Greater cardiovascular and respiratory response suggest a greater CMD despite a lower power output and metabolic rate

Question 7

What was shown when sensory pathways were blocked?

Answer 7

• Peripheral fatigue increased when there was less CMD activity
• The cns tolerated the exercise induced peripheral locomotor fatigue
• Much different pacing strategies displayed without afferent feedback
• There is a critical role of afferent feedback to the central drive in pacing during an event.

Question 8

Is there a critical limit?

Answer 8

• Yes, there is and there is a crucial role of the combination of central and peripheral fatigue feedback to regulate exercise intensity
• When we have reduced feedback from periphery CMD still present and when we prevent CNS from receiving feedback muscles were able to produce fatiguing levels

Question 9

What is pacing and what determines pacing strategies?

Answer 9

• The distribution of work rate throughout an exercise bout and largely influences the success or failure of the performance
• Initial pacing strategy is controlled by an anticipatory feedforward algorithm
• Throughout exercise the integration of physiological afferent feedback and external performance feedback determines what strategic pacing decisions are made to achieve a faster performance outcome