Central and peripheral fatigue and pacing Flashcards
What is fatigue?
Failure Limit Catastrophe Reduction Prevention
What are the causes of fatigue?
Failure to supply enough oxygen Failure to keep lactate levels down Failure to keep phosphate or H+ ions down Depletion of glycogen Failure to lose heat
Describe central fatigue
A failure of the CNS to adequately drive the muscle
Describe peripheral fatigue
An impairment located in the muscle and characterised by a metabolic end point
What are the causes of central fatigue?
Disturbances in brain neurotransmitters - increase serotonin, decrease dopamine and high ratio of serotonin to dopamine = fatigue
Depletion of brain glycogen
Increases in core and brain temperature - CNS drive towards exercise work output reduced by elevated core temperature
What are the causes of peripheral fatigue?
Depletion of substrates
Accumulation of metabolites - H+ ions and inorganic phosphates
Feedback from fatigue-sensitive muscle afferents - group III/IV muscle afferents relay exercise induced metabolic disturbances to the CNS
Describe the results of the first investigation by Aman
Pre-existing locomotor muscle fatigue
CMD decreased
PO decreased
Level of peripheral fatigue was the same for all trials despite pre-existing fatigue
Is a critical limit
Role of muscle fatigue - peripheral fatigue as a regulator of exercise
Describe the results of the second investigation by Aman
Blocked sensory feedback from the fatiguing locomotor muscles - prevents feedback from going to CNS
CMD stronger and HR, VE and BP increases, PO decreases = greater cardiovascular and respiratory response despite lower PO = greater CMD
Increased EMG so a stronger drive to perform when not receiving peripheral feedback
Without peripheral afferent feedback still have central drive
Describe the results of the third investigation by Aman
Analgesic to block sensory pathways to muscle
CNS did not limit the development of excessive peripheral fatigue beyond the individuals critical threshold
Still asking muscles to perform - no pain
Even higher PO about critical limit but after 2km decrease in performance due to fatigue
Critical limit is present and there is a crucial role of the combination of central and peripheral fatigue feedback to regulate exercise intensity
What is pacing?
Distribution of work rate throughout an exercise bout and largely influences the success or failure of the performance
Describe the role of feedback
Throughout exercise the integration of physiological afferent feedback and external performance feedback determines what strategic pacing decisions are made to achieve the fastest performance outcome
Describe how pacing is controlled
1) initial pacing strategy is controlled by an anticipatory feedforward algorithm (teleoanticipation)
2) alterations in pace are then a result of feedback control mechanisms using information from peripheral sensors, homeostatic responses and in reaction to a changing external environment
What are the determinants of pacing strategies?
Pacing strategy is in fact merely the output component of a very complex, very interesting physiological system. But there is also psychological and external environmental inputs
What factors were important for breaking 2?
Optimal temperature Optimal terrain Optimal shoe Series of pacers Incentive
What runner characteristics were important for breaking 2?
VO2max Running economy Stature Early 20s Team of pacers - who share prize money
