Cardiopulmonary Module 6

What are the three main energy systems?

ATP-PC (phosphagen), Anaerobic glycolysis, and Aerobic metabolism.

How is energy from food stored and used?

Carbohydrates, fats, and proteins are broken down to produce ATP for cellular work.

What is ATP and why is it important?

Adenosine triphosphate; main energy currency that fuels muscle contraction and all cellular functions.

What happens when ATP is broken down?

ATP → ADP + Pi + energy; this energy powers cellular work.

How is ATP resynthesized?

ADP + Pi + energy → ATP (via phosphagen, glycolytic, or oxidative pathways).

Where is ATP stored?

In muscle cytosol, but only in small amounts (enough for ~2-3 seconds of contraction).

Describe the ATP-PC system.

Uses creatine phosphate to rapidly regenerate ATP; no O₂ needed; supports ~10 seconds of maximal effort.

Which enzyme catalyzes ATP-PC reactions?

Creatine kinase.

What are advantages of the ATP-PC system?

Immediate energy, no O₂ required, rapid ATP resynthesis.

What are disadvantages of the ATP-PC system?

Limited storage of phosphagen; short duration.

Describe the anaerobic glycolysis system.

Uses glucose/glycogen without O₂ to produce ATP and lactate; supports ~30-90 seconds of activity.

What are advantages of anaerobic glycolysis?

Produces ATP quickly; can work when O₂ is limited.

What are disadvantages of anaerobic glycolysis?

Produces lactic acid → fatigue; inefficient ATP yield.

What is the net ATP yield of glycolysis?

2 ATP (from glucose) or 3 ATP (from glycogen).

What are end products of glycolysis?

Pyruvate (aerobic) or lactate (anaerobic).

When does the body shift from anaerobic to aerobic metabolism?

Around 1-2 minutes into moderate exercise as O₂ availability increases.

Describe the aerobic metabolism system.

Uses O₂ to oxidize carbohydrates, fats, and proteins for ATP in mitochondria.

What is the main site of aerobic metabolism?

Mitochondria.

Advantages of aerobic metabolism?

High ATP yield, sustainable for long duration.

Disadvantages of aerobic metabolism?

Slower to start, requires oxygen.

How many ATP are produced from aerobic metabolism of one glucose molecule?

~36-38 ATP.

What are the three stages of aerobic metabolism?

Glycolysis → Krebs cycle → Electron Transport Chain (ETC).

What happens in the Krebs cycle?

Pyruvate → acetyl-CoA → CO₂ + H⁺ + electrons; generates NADH and FADH₂ for ETC.

What happens in the Electron Transport Chain?

Electrons from NADH/FADH₂ pass through complexes to form ATP and water.

How many ATP are generated in the Krebs cycle and ETC combined?

~34 ATP per glucose.

How do fats enter aerobic metabolism?

Triglycerides → glycerol + free fatty acids → β-oxidation → acetyl-CoA → Krebs cycle.

How much ATP comes from fat metabolism?

~460 ATP per molecule of triglyceride.

When are proteins used for energy?

During long-duration or starvation states when glycogen is depleted.

What is the crossover concept?

As intensity increases, fuel source shifts from fat → carbohydrate.

What is the respiratory exchange ratio (RER)?

CO₂ produced ÷ O₂ consumed; estimates substrate use (fat vs carbohydrate).

What does an RER of 0.7, 0.85, and 1.0 indicate?

0.7 = 100% fat; 0.85 = mix; 1.0 = 100% carbohydrate.

What is oxygen deficit?

Difference between O₂ required and O₂ actually consumed at exercise onset.

What is steady-state oxygen consumption?

O₂ uptake plateaus and energy demand = supply aerobically.

What is EPOC (Excess Post-Exercise Oxygen Consumption)?

Elevated O₂ use after exercise to restore ATP-PC stores, remove lactate, and normalize physiology.

What is the lactate threshold?

Point where lactate production exceeds clearance; indicates shift toward anaerobic metabolism.

How does endurance training affect lactate threshold?

Increases threshold → higher intensity before fatigue.

What is VO₂ max?

Maximal oxygen consumption; reflects aerobic fitness and endurance capacity.

What determines VO₂ max?

Cardiac output (HR × SV), O₂ extraction by muscles, and muscle oxidative capacity.

How is VO₂ max measured?

Graded exercise test to volitional fatigue with gas analysis.

Typical VO₂ max values?

Sedentary: 25-35 mL/kg/min; Trained: 50-70; Elite: 70-90.

What is the Fick equation for VO₂?

VO₂ = CO × (a-vO₂ difference).

What is oxygen drift?

Gradual increase in VO₂ during prolonged submaximal exercise due to heat and catecholamines.

What is the energy cost of walking vs running?

Nonlinear; walking more economical at low speeds, running more efficient at high speeds.

What is the concept of mechanical efficiency?

Ratio of work output to energy input; higher = more efficient.

What is MET (Metabolic Equivalent)?

1 MET = resting O₂ consumption = 3.5 mL O₂/kg/min.

What are examples of MET values?

Sitting = 1 MET; Walking = 3-4; Jogging = 7; Running = 10+.

How does training affect energy systems?

↑mitochondria, ↑capillaries, ↑enzymes, ↑fat utilization, ↓lactate production.

What energy system dominates during sprinting?

ATP-PC.

What energy system dominates during a 400m run?

Anaerobic glycolysis.

What energy system dominates during a marathon?

Aerobic metabolism.

What is the major determinant of energy system use?

Exercise intensity and duration.