Week 9 - Factors effecting Performance - Fatigue

Question 1

What are factors that affect performance?

Answer 1

• Diet (carb, water intake)
• CNS function (arousal + motivation)
• Strength/Skill (practice, muscle fiber type)
• Environment (heat, altitude, humidity)
• Energy production (anaerobic sources and aerobic sources)

Question 2

Fatigue

Answer 2

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

Question 3

What are the 3 factors of peripheral fatigue?

Answer 3

• Neural factors.
• Mechanical factors.
• Energetics of contraction.

Question 4

What are some approaches to studying muscle fatigue?

Answer 4

• Muscle in vivo
• Isolated muscle
• Isolated single fiber
• Skinned fiber

Question 5

What is central fatigue characterized by reductions in?

Answer 5

• Motor units activated.
• Motor unit firing frequency

Question 6

How can CNS arousal alter the state of fatigue?

Answer 6

• By facilitating motor unit recruitment.
• Increasing motivation.
• Physical or mental diversion.

Question 7

Describe the Psycho-biological model of fatigue.

Answer 7

Fatigue is a conscious process and exercise will persist if the motivation is greater than the perceived exertion

Question 8

Describe the “Central Governor” model of fatigue.

Answer 8

fatigue is caused by the conscious and subconscious brain, not the spinal cord or motor unit

Question 9

Peripheral Fatigue: What are the sites of fatigue? Describe the neural factors.

Answer 9

Sarcolemma and transverse tubules.

Altered muscle membrane to conduction and action potentials.
* Inability of Na+/K+ pump to maintain action potential amplitude and frequency (can be improved by training)

An action potential block in the T-tubules.
* Reduced sarcoplasmic reticulum Ca2+ release

Question 10

Peripheral Fatigue: Mechanical factors.

What does cross-bridge cycling and tension development depend on?

Answer 10

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

Question 11

Peripheral Fatigue: Mechanical factors.

How may high H+ concentration contribute to fatigue? What does this result in?

Answer 11

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

Results in a longer “relaxation time” (sign of fatigue) due to a slower cross-bridge cycling.

Question 12

Peripheral Fatigue: Describe the energetics of contraction factors causing fatigue.

Answer 12

1) Imbalance between ATP requirements and ATP generating capacity.
Therefore, we get an accumulation of Pi. This inhibits maximal force, reduces cross-bridge binding to actin and inhibits Ca2+ release from SR.

2) Higher exercise intensities (>75% VO2max) lead to recruitment of 2x fibers which results in increased lactate and H+ production.

Question 13

How does radical production during exercise contribute to muscle fatigue during prolonged exercise (>30min)?

Answer 13

They damage contractile proteins (myosin and troponin) which limits the number of cross-bridges bound to actin.

They also depress sodium/potassium pump activity which disrupts potassium homeostasis.

Question 14

Do antioxidant supplements prevent fatigue?

Answer 14

NO - high doses can impair performance and depress training-induced adaptations in skeletal muscle

Question 15

Describe the characteristics associated with “Ultra Short-term performance”.

Answer 15

• Events >10seconds (high power).
• Dependent on recruitment of type 2 muscle fibers to generate high forces.
• Motivation, skill and arousal are important.
• Primary energy sources are anaerobic (ATP-PC system and glycolysis)
• Creatine supplementation may be beneficial.

Question 16

Describe the characteristics associated with “Short-term performance”.

Answer 16

• Events lasting 10-180secs
• Shift from anaerobic to aerobic metabolism: 70% anaerobic at 10 seconds but 60% aerobic by 180secs.
• Fueled primarily be anaerobic glycolysis.
• Buffers may improve performance.

Question 17

Short-term performance is primarily fueled by anaerobic glycolysis. How may this lead to fatigue?

Answer 17

Increased production of lactate and H+. This interferes with Calcium ions binding with troponin and glycolytic ATP production.

Question 18

Describe the characteristics associated with “Moderate-Duration performances”.

Answer 18

• Events last 3-20mins.
• 60% ATP generated aerobically at 3mins and 90% aerobic at 20mins.
• A high V02max is important. As well as high maximal SV, high arterial oxygen content, and high hemoglobin content.
• Requires energy expenditure near V02max.

High levels of lactate and H+ accumulation.

Question 19

Describe the characteristics associated with “Intermediate-Duration Performances”.

Answer 19

• Events lasting 21-60mins.
• Predominantly aerobic and usually conducted at <90% V02max (high V02max important).
• Other important factors include running economy, state of hydration, lactate threshold and environmental factors (heat and humidity).
• High % of type 1 muscle fibers.

Question 20

List some factors that affect fatigue in aerobic performance.

Answer 20

• CHO depletion
• Heat and humidity
• Dehydration
• Lactate threshold
• Running economy + % of type I muscle fibers

Question 21

Describe the characteristics associated with “Long-term performances”.

Answer 21

• Events last 1-4 hours.
• Aerobic so V02max and economy are key.
• Environmental factors more important.
• Maintaining rate of carb utilization: muscle and liver glycogen stores decline so we must ingest carbs to maintain carb oxidation.
• Consumption of fluids and electrolytes prevent hydration.
• Diet influences performance (carb-loading).

Question 22

Describe the factors affecting performance in ultra-endurance events.

Answer 22

• V02max
• % V02max that can be sustained (fractional utilization)
• Metabolic responses: ability to use fat oxidation as well as carb oxidation.
• Hyponatremia can occur (low blood sodium)
• Non-physiological factors: injuries, foot management.