Exercise Physiology: Cardiorespiratory, Fatigue, and Hydration Concepts

What is fatigue?

Decline in performance (force, power, efficiency, effort); fatigue does not equal limitation.

What is the cardiac output equation?

Q = Stroke Volume × Heart Rate

How does heart rate change with exercise intensity?

Increases

How does stroke volume change with exercise intensity?

Increases initially then plateaus or decreases.

How do we know VO₂max is achieved?

VO₂ plateaus despite increased workload.

What is the oxygen transport sequence from high to low PO₂?

Atmosphere → lungs → blood → tissues → mitochondria.

Where is PO₂ highest?

Atmosphere.

Where is PO₂ lowest?

Mitochondria.

What carries oxygen in blood?

Hemoglobin.

What are the three weak links of cardiorespiratory limitation?

Ventilation/diffusion, oxygen transport, oxygen extraction.

Where does ventilation/diffusion limitation occur?

Lungs.

Where does oxygen transport limitation occur?

Heart.

Where does oxygen extraction limitation occur?

Tissues.

What is the Frank-Starling principle?

Increased EDV → increased stroke volume.

What happens to heart rate during cardiovascular drift?

Increases.

What happens to stroke volume during cardiovascular drift?

Decreases.

How does increased skin blood flow influence cardiovascular drift?

Decreases EDV and stroke volume.

How do catecholamines influence cardiovascular drift?

Increase HR and contractility to maintain cardiac output.

How does dehydration influence cardiovascular drift?

Decreases blood volume → decreases stroke volume.

What is central fatigue?

Fatigue originating in the brain and neural drive.

What is peripheral fatigue?

Fatigue occurring at or beyond the sarcolemma.

What is the effect of PCr depletion?

Loss of rapid ATP regeneration (15-30 seconds).

What is the effect of glycogen depletion?

Reduced endurance after ~60 minutes.

What is the effect of dehydration on the brain?

Reduced volume and cognitive function.

What is the effect of temperature above 40°C?

Severe cognitive decline.

What is the effect of low fuel on the CNS?

Reduced neural drive.

What is the effect of ammonia accumulation?

Increased cerebral blood flow and pressure → possible hypoxia.

What is the role of serotonin?

Promotes lethargy and reduced arousal.

What is the role of dopamine?

Energy, motivation, mindfulness.

What is the role of adenosine?

Inhibits dopamine; caffeine blocks adenosine receptors.

When does fluid loss occur?

Prolonged exercise or exercise in heat.

What is the impact of fluid loss on aerobic performance?

Decreased endurance.

What is the hydration guideline?

16 oz per 1 lb lost.

What hormones counteract fluid loss?

ADH and Aldosterone.

What is the normal serum sodium range?

135-145 mmol/L.

What are early symptoms of hyponatremia?

Bloating, nausea, headache.

What are late symptoms of hyponatremia?

Confusion, seizures, coma, death.

What does the Central Governor Model propose?

The brain limits performance to prevent physiological damage.

What is the evidence supporting the Central Governor Model?

End-race sprint, incomplete motor unit recruitment.

What are exercise-associated muscle cramps?

Altered neuromuscular control; relieved by stretching.

What are heat cramps?

Electrolyte loss (Na⁺, Cl⁻); treated with rehydration.

What is the difference between cramp types?

Neuromuscular excitation vs electrolyte/fluid loss.