Week 9 - Factors affecting performance

Question 1

What are some factors that can effect performance

Answer 1

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

Question 2

Define fatigue

Answer 2

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

Question 3

What is the site of central fatigue

Answer 3

Central nervous system

Question 4

What are the possible sites of peripheral fatigue

Answer 4

Neural factors
Mechanical factors
Energetics of contraction

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Central fatigue eliminated
Dissection simple

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Central fatigue is characterised by reductions in

Answer 13

Motor units activated
motor unit firing frequency

Question 14

How can the CNS alter the state of fatigue

Answer 14

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

Question 15

How do neural factors lead to peripheral fatigue

Answer 15

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

Question 16

What does cross-bridge cycling and tension development depend on

Answer 16

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

Question 17

How can high H+ concentration contribute to fatigue

Answer 17

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

Question 18

Why is end result being longer one sign of fatigue

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

How is muscle fiber recruitment impaced in increasing exercise intensity

Answer 21

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

Question 22

How does exercise promote muscle free radical production

Answer 22

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

Question 23

How do radical contribute to fatigue during exercise >30min

Answer 23

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

Question 24

How do antioxidant supplements effect fatigue

Answer 24

They do not prevent fatigue

Question 25

What are the key aspects of ultra short term performance

Answer 25

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

Question 26

What are the key aspects of short term performance

Answer 26

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

Question 27

What are the key aspects of moderate duration performance

Answer 27

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

Question 28

What are the key aspects of intermediate duration performance

Answer 28

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

Question 29

What are the key aspects of long-term performances

Answer 29

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

Question 30

What are the factors affecting ultra-endurance performance

Answer 30

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