Fatigue - Factors affecting human performance Flashcards

1
Q

What are the 5 factors affecting performance?

A
  • Diet (carb, water intake)
  • CNS function (arousal, motivation)
  • Strength/skill (practise, natural endowment)
  • Environment (altitude, heat, humidity)
  • Energy production (anaerobic/aerobic sources)
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2
Q

What is fatigue?

A

Inability to maintain power output or force during repeated muscle contractions, which is reversible with rest.

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3
Q

Where does central fatigue occur?

A

Central nervous system

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4
Q

What contributes to peripheral fatigue?

A
  • Neural factors.
  • Mechanical factors.
  • Energetics of contraction
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5
Q

What are the 4 different way of study muscle fatigue?

A
  • Muscle in vivo
  • Isolated muscle
  • Isolated single fibre
  • Skinned fibre
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6
Q

What is central fatigue characterised by?

A

Reductions in:
* Motor units activated.
* Motor unit firing frequency.

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7
Q

How can CNS arousal alter the state of fatigue?

A
  • By facilitating motor unit recruitment.
    • Increasing motivation.
    • Physical or mental diversion.
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8
Q

What can excessive endurance training (overtraining) cause?

A
  • Reduced performance, prolonged fatigue, etc.
  • Related to brain serotonin activity
  • and its ratio to Dopamine
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9
Q

What does the “Central Governor” model (Noakes) mention?

A

Conscious and subconscious brain, not spinal cord or motor unit.

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10
Q

What is the psycho-biological model?

A

Fatigue is a conscious process and exercise will persist if the motivation is greater than the perceived exertion.

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11
Q

Are NMJ the sites of fatigue?

A

No

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12
Q

How are sarcolemma and transverse tubules the site of fatigue?

A
  • Altered muscle membrane to conduction and action potentials.
    • Inability of Na+/K+ pump to maintain action potential amplitude and frequency.
      • Can be improved by training.
  • An action potential block in the T-tubules.
    • Reduced sarcoplasmic reticulum Ca2+ release.
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13
Q

Peripheral fatigue, mechanical factors - what does cross-bridge cycling and tension development depend on?

A
  • Arrangement of actin and myosin.
  • Ca2+ binding to troponin.
  • ATP availability.
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14
Q

Peripheral fatigue, mechanical factors - how may high H+ conc contribute to fatigue?

A
  • Reduce the force per cross-bridge.
  • Reduce the force generated at a given Ca2+ concentration.
  • Inhibit Ca2+ release from SR.
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15
Q

How does the imbalance between ATP requirements/generating capacity cause fatigue?

A
  • Accumulation of Pi.
    • Inhibits maximal force.
    • Reduces cross-bridge binding to actin.
    • Inhibits Ca2+ release from SR.
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16
Q

The rate of ATP utilization is slowed faster than rate of ATP generation - what does this cause?

A

Maintains ATP concentration = cell does not run out of ATP

17
Q

In what order are muscle fibres recruited as exercise intensity increases?

A

Type 1 → Type 2a → Type 2x.
* Up to 40% VO2 max type 1 fibres recruited.

18
Q

At what %VO2 max are type 2a AND 2x fibres recruited?

A
  • Type 2a fibres recruited at 40 to 75% VO2 max.
  • Exercise >75% VO2 max requires 2x fibres.
    • Results in increased lactate and H+ production.
19
Q

Exercise promotes muscle free radical production. What are radicals?

A
  • Radicals are molecules with an unpaired outer orbital electron.
  • Capable of damaging proteins and lipids in muscle.
20
Q

How can radicals contribute to fatigue during exercise >30 mins?

A
  • Damage contractile proteins (myosin and troponin).
    • Limits the number of cross-bridges in strong binding state.
  • Depress sodium/potassium pump activity.
    • Disruption of potassium homeostasis.
21
Q

Do antioxidant supplements prevent fatigue?

A

No - High antioxidant doses can impair muscle performance.

22
Q

Would ingesting buffers improve short-term (10-180 seconds) performance?

A

It could do -
Fuelled primarily by anaerobic glycolysis.
* Results in elevated lactate and H+ levels.
* Interferes with Ca2+ binding with
troponin.
* Interferes with glycolytic ATP
production.

23
Q

Is having a high Vo2 max important for moderate-duration (3-20 mins) performance?

A

Yes -
* High maximal stroke volume.
* High arterial oxygen content.
* Haemoglobin content.
* Inspired oxygen.

Required energy expenditure near VO2 max.

24
Q

Other than high VO2 max, what are other important factors for intermediate-duration performances (21-60 mins)?

A
  • Running economy or exercise efficiency.
  • High percentage of type 1 muscle fibres.
  • Environmental factors (Heat and humidity)
  • State of hydration.
  • Lactate threshold.
25
Q

What are the key factors affecting long-term (1-4 hrs) performances?

A
  • Environmental factors (important)
  • Maintaining rate of carb utilization (muscle + liver glycogen stores decline = ingestion of carbs)
  • Consumption of fluids and electrolytes
  • Diet also influences performance
26
Q

Limit of endurance is context speciric but what important factors affect ultra-endurance events?

A
  • VO2 max (and % that can be sustained)
  • Metabolic responses (marked increases in fat oxidation (consistent with exercise as <60% VO2 max)). + (50% reduction in muscle glycogen stores).
  • Potential for hyponatremia (affects only 4% athletes)
  • Non physiological factors (foot management)