Fatigue - Factors affecting human performance

Question 1

What are the 5 factors affecting performance?

Answer 1

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

Question 2

What is fatigue?

Answer 2

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

Question 3

Where does central fatigue occur?

Answer 3

Central nervous system

Question 4

What contributes to peripheral fatigue?

Answer 4

• Neural factors.
• Mechanical factors.
• Energetics of contraction

Question 5

What are the 4 different way of study muscle fatigue?

Answer 5

• Muscle in vivo
• Isolated muscle
• Isolated single fibre
• Skinned fibre

Question 6

What is central fatigue characterised by?

Answer 6

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

Question 7

How can CNS arousal alter the state of fatigue?

Answer 7

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

Question 8

What can excessive endurance training (overtraining) cause?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

What is the psycho-biological model?

Answer 10

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

Question 11

Are NMJ the sites of fatigue?

Answer 11

No

Question 12

How are sarcolemma and transverse tubules the site of fatigue?

Answer 12

• 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.

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

Maintains ATP concentration = cell does not run out of ATP

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Exercise promotes muscle free radical production. What are radicals?

Answer 19

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

Question 20

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

Answer 20

• 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.

Question 21

Do antioxidant supplements prevent fatigue?

Answer 21

No - High antioxidant doses can impair muscle performance.

Question 22

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

Answer 22

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.

Question 23

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

Answer 23

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

Required energy expenditure near VO2 max.

Question 24

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

Answer 24

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

Question 25

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

Answer 25

- 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

Question 26

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

Answer 26

- 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)