Kin 4100 Exam 1 Lactate Threshold

Is any exercise 100% aerobic or anaerobic?

No, all exercise uses both systems

What are the two main ways anaerobic effort is estimated?

Lactate threshold and EPOC

What is lactate threshold (LT)?

Point where blood lactate accumulation increases rapidly

What is the physiological cause of lactate threshold?

Lactate production rate exceeds lactate clearance rate

What systems interact at lactate threshold?

Aerobic and anaerobic systems

How is lactate threshold usually expressed?

% of VO2max

Why is lactate threshold a good endurance indicator?

Higher LT allows sustained higher intensities

If two athletes have the same VO₂max, who performs better?

The one with the higher lactate threshold

What causes oxygen deficit during early exercise?

ATP demand exceeds oxygen consumption

Why does oxygen consumption remain elevated post-exercise?

Excess postexercise oxygen consumption (EPOC)

What is the primary purpose of EPOC?

Restore the body to pre-exercise state

What does EPOC help replenish?

ATP and PCr stores

What happens to lactate during EPOC?

Converted to glycogen or oxidized

What other processes occur during EPOC?

Replenish hemo/myoglobin O2, clear CO2

What hormones are elevated during EPOC?

Epinephrine and norepinephrine

What are two common definitions of fatigue?

Performance decrement with effort OR inability to maintain required power

What distinguishes fatigue from muscle damage?

Fatigue is reversible with rest

What are the four major causes of fatigue?

↓ energy delivery, ↑ metabolic by-products, contractile failure, altered neural control

Why does PCr depletion cause fatigue?

Limits ability to rapidly resynthesize ATP

Which depletes faster: ATP or PCr?

PCr

How does pacing affect PCr depletion?

Slows depletion and delays fatigue

Is glycogen depletion linked to fatigue?

Yes, strongly correlated

Is fatigue related to rate or total glycogen depletion?

Total depletion, not rate

When does glycogen deplete fastest?

High-intensity exercise and early in exercise

What is the fiber recruitment order related to glycogen depletion?

Type I → Type IIa → Type IIx

What is the role of liver glycogen during prolonged exercise?

Maintains blood glucose

What causes fatigue during long exercise?

Muscle glycogen depletion + hypoglycemia

What are key fatigue-related metabolic by-products?

Pi, lactate, H+

Why is H⁺ accumulation problematic?

Causes acidosis and ↓ muscle pH

How do buffers help during exercise?

Limit pH drop (7.1 → 6.5)

What happens if pH <6.9?

Inhibits glycolytic enzymes and ATP synthesis

What happens at pH ~6.4?

Prevents further glycogen breakdown

How does heat affect metabolism?

Increases carbohydrate use and glycogen depletion

At what temperature is time to exhaustion longest?

~11 °C

At what temperature is time to exhaustion shortest?

~31 °C

How does muscle precooling affect fatigue?

Prolongs exercise time

Where can neural fatigue occur?

Neuromuscular junction or CNS

What are possible NMJ causes of fatigue?

↓ ACh release, altered membrane potential, ↓ Ca2+ release from SR

How does the CNS contribute to fatigue?

Conscious or subconscious reduction in motor drive

Why do elite athletes fatigue differently?

Better pacing and tolerance of discomfort

Summarize fatigue in one sentence.

Fatigue is a reversible decline in performance caused by interacting metabolic, neural, and energetic factors