Limits to human performance Flashcards
What is fatigue?
failure of the working musculature to maintain force or power output during a series of contractions. it is caused by a complex mix of central and peripheral mechanisms
What is central fatigue?
Reduction in the function of motor units that are involved in contraction or a reduction in motor unit firing frequency
What causes central fatigue?
- CNS takes signals from around the body and integrates them to affect the rate of motor recruitment
- possibly based on serotonin and dopamine levels
- Muscles themselves are also likely to signal the CNS
- peripheral factors send signals via afferents which will inhibit the CNS, limit the output of spinal motor neurons and limit the exercise
What is peripheral fatigue?
- Most common form of fatigue
- Caused by changes in the working musculature
What causes peripheral fatigue?
- Neural: anywhere in the excitation-coupling process
- Muscular: mechanics of muscle function - cross bridging cycle - accumulation in H+ and decrease pH
- Energetics: increased rate of ATP demand = build up of phosphate and H+
What factors limit VO2max?
- Pulmonary system: possible large Q with reduced transit time in endurance athletes
- Cardiovascular sytstem: cardiac output cannot deliver O2 fast enough
- Oxygen carrying capacity of blood: amount of Hb to deliver oxygen
- Peripheral: possibly the uptake of O2 into the muscle
- Functional threshold: Efficiency and Lactate threshold -> fatigue
What factors limit short and long endurance?
- VO2 max and lactate threshold (velocity at VO2 for shorter distances)
- glycogen depletion (less likely for shorter duration)
- hyperthermia due to increased metabolism (hydrolysis), increased heat production and environmental heat. Core temp limit 40 deg.
- dehydration: sweating decreases plasma volume
- accumulation of metabolites: H+ increase = pH decrease in shorter sprints
What factors limit short duration high-intensity efforts?
- Muscular: CSA, number of type 2 fibres
- Central factors: ability to maximally activate the muscle; training, motivation and arousal, skill and technique
- Energy systems: PCr store depletion, decrease in pH due to increase in H+, affects PFK, PHOS, Ca2+ peripherally, accumulation of Pi and K+.
Explain how H+ accumulation and decreased pH may cause fatigue
Anaerobic glycoloysis causes an accumulation of H+ and a decrease in pH. This peripherally affects PFK, PHOS and Ca2+. The decrease in pH makes the body acidic and causes fatigue. PFK and PHOS affect glycolysis and require the aerobic system. Ca2+ affects the muscle cross bridging cycle and slow muscle relaxation rates.
What are the common movement patterns observed during match play in team-sports
Typically bouts of 4-7 x 2-3s sprints with short active recovery between.
Describe the timeline for PCr recovery?
PCr stores are almost fully recovered after 3 mins rest following a single sprint. After a bout of sprints only 84% is recovered.
Initially there is a fast recovery of PCr controlled by the rate of oxidative ATP resynthesis then the rate slows following pH recovery (3-5 mins)
What affects PCr recovery?
Low pH and low ATP possibly affect PCr recovery. O2 is required for rapid repletion of PCr stores
Why is aerobic fitness important to team-sport players?
Team sports use repeated single sprints with minimal recovery.
- not enough time for PCr to recover
- VO2 max could be reached during final sprints of a bout of repeated sprints
How is energy supplied for a single short sprint?
ATP + PCr
How is energy supplied for repeated sprints with only short recovery?
Anaerobic glyoclysis and aerobic glycolysis
