Topic 9: Fatigue (HL) Flashcards
9.1.1. Define fatigue in sports
A reversible, exercise-induced decline in performance
PERIPHERAL FATIGUE
- Fatigue from factors outside the CNS, distal to the neuromuscular junction, affecting muscle activation
- Develops rapidly and is caused by reduced muscle cell force
CENTRAL FATIGUE
- Develops during prolonged exercise, caused by impaired function of the CNS
- Fatigue from factors within the CNS (brain, spinal cord, motor neurons)
High-Intensity Activity
- Involves vigorous bout of intense activity that last for less than a second, or as long as 1–2 minutes
- The major sources of energy for this are derived from anaerobic processes
Endurance Activity
- Prolonged session of low-intensity activity lasting from minutes to hours
- The major sources of energy for endurance activities are aerobic processes
Causes of peripheral fatigue high-intensity activities
- depletion of energy sources (creatine phosphate and ATP)
- increase in levels of the by-products of exercise e.g. lactate and H+
Causes of peripheral fatigue in endurance activities
- depletion of muscle and liver glycogen reserves
- reduction in Ca2+ release
- depletion of acetylcholine
- dehydration
- overheating
- electrolyte loss
ROLE OF ATP
- most important source of chemical energy in the body
- energy from ATP hydrolysis powers cellular functions like muscle contraction
- food energy is critical to ensure sufficient ATP supply
PHOSPHOCREATINE (PCr)
- Important in resynthesis of ATP during explosive, high-intensity exercise
- Stored in muscles
Accumulation of hydrogen ions
Lactate –> release of H+ –> inhibition of enzymes needed for ATP –> fatigue & pain in muscle
Depletion of glycogen stores
Frequent use of a fiber type during exercise depletes glycogen, reducing its ability to produce force.
Decreased availability of Ca2+
- PCr decreases and lactic acid increases –> Ca2+ accumulate in SR and not release –> no muscle contraction
- H+ ions also compete with the calcium for binding sites on the troponin.
Reduction in acetylcholine
Acetylcholine supply decreases with prolonged exercise, impairing muscle contraction
Dehydration
- affect thermoregulation –> extreme cases can lead to collapse and heat stroke
- thickens blood –> reduce blood circulation –> impact availability of oxygen –> worsen performance
Electrolyte loss
increase muscle cramps
Overheating
- increase rate which body uses glycogen
- impair skeletal muscle contraction & muscle metabolism
9.1.5. Discuss recovery from fatigue after sports
Replacement of muscle and liver glycogen stores
Excess post-exercise oxygen consumption (EPOC):
- restoration of muscle PCr stores
- removal of lactic acid
- replenishment of myoglobin stores
Fast replenishment/ lactic acid component
- Restoration of ATP and PCr
- Takes up to 3 min for full restoration (30s to restore 50%)
- Uses 2–3 litres of oxygen
Slow replenishment/lactacid component
- Removal of lactic acid
- Takes up to 1h
- Uses 5–6 litres of oxygen
