Week 9 - Factors affecting performance Flashcards

1
Q

What are some factors that can effect performance

A

Diet
CNS function
Strength/skill
Environment
Aerboic sources
Energy production sources

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2
Q

Define fatigue

A

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

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3
Q

What is the site of central fatigue

A

Central nervous system

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4
Q

What are the possible sites of peripheral fatigue

A

Neural factors
Mechanical factors
Energetics of contraction

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5
Q

What are the advantages of using muscle in vivo study muscle fatigue

A

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

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6
Q

What are the disadvantages of using muscle in vivo as a study of muscle fatigue

A

Mixture of fiber types
Complex activation forms
Produces correlative data; hard to identify mechanisms
Experimental interventions very limited

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7
Q

Whats some advantages of using isolated muscle as a way to study muscle fatigue

A

Central fatigue eliminated
Dissection simple

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8
Q

Whats the disadvantages of using isolated muscle as a way to measure muscle fatigue

A

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

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9
Q

Whats the advantages of using isolated single fiber as a means of measuring muscle fatigue

A

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

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10
Q

What are the disadvantages of using isolated single fiber as a study of muscle fatigue

A

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

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11
Q

What are the advantages of using skinned fiber to study muscle fatigue

A

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

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12
Q

What are the disadvantages of using skinned fiber to study muscle fatigue

A

Relevance to fatigue can be questionable
may lose important intracellular constituents
Relevant metabolites to study must be identified in other system

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13
Q

Central fatigue is characterised by reductions in

A

Motor units activated
motor unit firing frequency

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14
Q

How can the CNS alter the state of fatigue

A

By facilitating motor unit recruitment which increases motivation and physical or mental diversion

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15
Q

How do neural factors lead to peripheral fatigue

A

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

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16
Q

What does cross-bridge cycling and tension development depend on

A

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

17
Q

How can high H+ concentration contribute to fatigue

A

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

18
Q

Why is end result being longer one sign of fatigue

A

Due to slower cross-bridge cycling, important in fast twitch fibres

19
Q

Whats the effect of accumulation of Pi in the imbalance between ATP requirement and generating capacity

A

Inhibits maximal force
Reduced cross-bridge binding to actin
Inhibits Ca2+ release from SR

20
Q

Whats the effect of ATP utilisation being slowed faster than the rate of ATP generation

A

maintains ATP concentration
The cells don’t run out of ATP

21
Q

How is muscle fiber recruitment impaced in increasing exercise intensity

A

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

22
Q

How does exercise promote muscle free radical production

A

Radicals are molecules an unpaired outer orbital electron
Capable of damaging proteins and lipids in muscles

23
Q

How do radical contribute to fatigue during exercise >30min

A

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

24
Q

How do antioxidant supplements effect fatigue

A

They do not prevent fatigue

25
Q

What are the key aspects of ultra short term performance

A

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

26
Q

What are the key aspects of short term performance

A

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

27
Q

What are the key aspects of moderate duration performance

A

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

28
Q

What are the key aspects of intermediate duration performance

A

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

29
Q

What are the key aspects of long-term performances

A

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

30
Q

What are the factors affecting ultra-endurance performance

A

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