Week 9 - Factors affecting performance Flashcards
What are some factors that can effect performance
Diet
CNS function
Strength/skill
Environment
Aerboic sources
Energy production sources
Define fatigue
Inability to maintain power output or force during repeated muscle
contractions, which is reversible with rest.
What is the site of central fatigue
Central nervous system
What are the possible sites of peripheral fatigue
Neural factors
Mechanical factors
Energetics of contraction
What are the advantages of using muscle in vivo study muscle fatigue
All physiological mechanisms are present
Fatigue can be central or peripheral
All types of fatigue can be studied
Stimulation patterns appropriate for fiber types and stage of fatigue
What are the disadvantages of using muscle in vivo as a study of muscle fatigue
Mixture of fiber types
Complex activation forms
Produces correlative data; hard to identify mechanisms
Experimental interventions very limited
Whats some advantages of using isolated muscle as a way to study muscle fatigue
Central fatigue eliminated
Dissection simple
Whats the disadvantages of using isolated muscle as a way to measure muscle fatigue
Mixture of fiber types
Inevitable extracellular gradients o2, Co2, K+, lactic acid
Mechanisms of fatigue biased by presence of extracellular gradients
Drugs cannot be applied rapidly because of diffusion gradients
Whats the advantages of using isolated single fiber as a means of measuring muscle fatigue
Only one fiber type present
Force and other changes can be unequivocally correlated
Fluorescent measurements of ions, metabolites, membrane potential
Easy and rapid appilcation of extracellular drugs, ions metabolites
What are the disadvantages of using isolated single fiber as a study of muscle fatigue
Environemtn to in vivo
K+ accululation and other in vivo changes absent
Prone to damage at physiological temperatures
Small size makes analysis of metabolites difficult
What are the advantages of using skinned fiber to study muscle fatigue
Precise solutions can be applied
Possible to study myofibrillar properties, SR release and uptake, AP/Ca2+ release coupling
Metabolic and ionic changes associated with fatigue can be studied in isolation
What are the disadvantages of using skinned fiber to study muscle fatigue
Relevance to fatigue can be questionable
may lose important intracellular constituents
Relevant metabolites to study must be identified in other system
Central fatigue is characterised by reductions in
Motor units activated
motor unit firing frequency
How can the CNS alter the state of fatigue
By facilitating motor unit recruitment which increases motivation and physical or mental diversion
How do neural factors lead to peripheral fatigue
Neuromuscular junction - not site of fatigue
Sarcolemma and transverse tubules leads to altered muscle membrane to conduction and action potentials.
Inability of Na/K+ pump to maintain action potential, can be improved by training
An action potential block in the T-tubules leads to redcued sarcoplasmic reticulum Ca2+ release
What does cross-bridge cycling and tension development depend on
Arrangement of actin and myosin
Ca2+ binding to troponin
ATP availability
How can high H+ concentration contribute to fatigue
Reduce the force per cross-bridge
Reduce the force generated at a given Ca2+ concentration
Inhibit Ca2+ release from SR
Why is end result being longer one sign of fatigue
Due to slower cross-bridge cycling, important in fast twitch fibres
Whats the effect of accumulation of Pi in the imbalance between ATP requirement and generating capacity
Inhibits maximal force
Reduced cross-bridge binding to actin
Inhibits Ca2+ release from SR
Whats the effect of ATP utilisation being slowed faster than the rate of ATP generation
maintains ATP concentration
The cells don’t run out of ATP
How is muscle fiber recruitment impaced in increasing exercise intensity
Type 1 -> Type 2a -> Type 2x as intensity increases
Up to 40% VO2 max type 1 fibers recruited
Type 2a fibers recruited at 40 to 75% Vo2 max
Exercise >75% VO2 max requires 2x fibers
Results in increased lactate and H+ production
How does exercise promote muscle free radical production
Radicals are molecules an unpaired outer orbital electron
Capable of damaging proteins and lipids in muscles
How do radical contribute to fatigue during exercise >30min
Damage contractile proteins (myosin and troponin)
Limits number of cross-bridges in strong binding state
Depress sodium/potassium pump activity
Disruption of potassium homeostasis
How do antioxidant supplements effect fatigue
They do not prevent fatigue
What are the key aspects of ultra short term performance
Events <10 seconds (high power)
Dependent on recruitment of Type 2 muscle fibers
Generate great forces that are needed
Motivation, skill and arousal are important
Primary energy source is anaerobic
ATP-PC system and glycolysis
Creatine supplements may improve performance
What are the key aspects of short term performance
Events lasting 10 to 180 seconds.
* Shift from anaerobic to aerobic metabolism.
* 70% energy supplied anaerobically at 10 seconds.
* 60% supplied aerobically at 180 seconds.
* Fueled primarily by anaerobic glycolysis.
* Results in elevated lactate and H+ levels.
* Interferes with Ca2+ binding with troponin.
* Interferes with glycolytic ATP production.
* Ingestion of buffers may improve performance
What are the key aspects of moderate duration performance
Events lasting 3 to 20 minutes.
* 60% ATP generated aerobically at 3 minutes.
* 90% ATP supplied aerobically at 20 minutes.
* A high VO2 max is advantageous.
* High maximal stroke volume.
* High arterial oxygen content.
* Hemoglobin content.
* Inspired oxygen.
* Requires energy expenditure near VO2 max.
* Type 2x fibers recruited.
* High levels of lactate and H+ accumulation
What are the key aspects of intermediate duration performance
Events lasting 21 to 60 minutes.
* Predominantly aerobic.
* Usually conducted at <90% VO2 max.
* High VO2 max is important.
Other important factors.
* Running economy or exercise efficiency.
* High percentage of type 1 muscle fibers.
* Environmental factors.
- Heat and humidity.
* State of hydration.
* Lactate threshold
What are the key aspects of long-term performances
Events lasting 1 to 4 hours.
- Clearly aerobic (VO2 max & economy key)
* Environmental factors more important.
* Maintaining rate of carbohydrate utilization.
* Muscle and liver glycogen stores decline.
* Ingestion of carbohydrate.
- Maintain carbohydrate oxidation by the muscle.
* Consumption of fluids and electrolytes.
* Diet also influences performance
Vo2 max sets the upper limit for ATP production in endurance events
What are the factors affecting ultra-endurance performance
ut important factors include:
* VO2 max.
* %VO2 max that can be sustained.
* Metabolic responses.
* Marked increases in fat oxidation
- Consistent with exercise at <60% VO2 max.
* ~50% reduction in muscle glycogen stores.
* Potential for hyponatremia.
* Only affects 4% athletes.
* Non-physiological factors can end performance too
* Foot management
