ASIN 500 Introduction to Nutrition Lecture 10 Energy Systems & Exercise Metabolism

Revision - Alcohol

• Chronic alcohol consumption impairs the absorption of certain nutrients.
• Recent evidence links alcohol to specific diseases, leading some countries to implement stricter alcohol guidelines.
• Chronic alcohol consumption can lead to various health issues.

Lecture Objectives

• Identify the fuels used by the body to generate ATP.
• Outline the anaerobic and aerobic pathways that supply energy for muscular work.
  • Anaerobic: without oxygen.
  • Aerobic: with oxygen.
• Discuss how exercise intensity and duration affect the use of metabolic fuels.

Energy

• The body requires energy to:
  • Maintain body temperature.
  • Repair damaged cells.
  • Digest food.
  • Perform mechanical work (movement).
• ATP (adenosine triphosphate) is the primary energy currency used by the body to perform daily tasks.

ATP - The Body’s Energy Currency

• ATP is the energy source muscles use for movement, growth, and repair.
• The body produces ATP through different pathways depending on the intensity and duration of the activity.
• Two main energy systems:
  • Anaerobic (without oxygen).
  • Aerobic (with oxygen).

Anaerobic (Without Oxygen) - Short/Fast Activity

• Used in high-intensity, short bursts of activity (e.g., sprinting, lifting).
• Two pathways:
  • ATP-PC System:
    • Duration: 0–10 seconds.
    • Fuel source: Stored creatine phosphate.
  • Glycolysis:
    • Breaks down glucose.
    • Produces lactic acid.
• Provides quick energy but fatigues rapidly.

Aerobic - Needs Oxygen - Endurance Activity

• Kicks in after approximately 2 minutes of sustained activity (e.g., jogging, swimming).
• Uses oxygen to break down carbohydrates, fats, and a small amount of protein.
• Produces a large amount of ATP, but at a slower rate.
• Sustainable for long durations.

How is Energy Released?

• ATP Formation (Phosphorylation):
  • ADP + Pi + Energy \rightarrow ATP
  • Enzyme: ATP synthase
• ATP Breakdown (Hydrolysis):
  • ATP \rightarrow ADP + Pi + Energy
  • Enzyme: ATPase

Sources of Energy

• ATP comes from the chemical breakdown of fuel sources:
  1. Blood Glucose
  2. Muscle Glycogen
  3. Fats (Adipose Tissue)
  4. Proteins (Amino Acids)
• The breakdown of glucose, fats, and proteins contribute to ATP-ADP cycle:
  • ATP \rightarrow ADP + Pi + Energy
• Metabolic pathways include:
  • Glucose to Pyruvate.
  • Pyruvate to Acetyl CoA.
  • Glycerol and Fatty acids.
  • Lactate.
  • Glucogenic and Ketogenic Amino acids.

ATP Production - 3 Ways

• Anaerobically:
  • Phosphagen system.
  • Lactic acid system.
• Aerobically:
  • From carbohydrate, fats, and protein.

Anaerobic Pathways

• Do not require oxygen.
  1. Phosphocreatine system:
     • Anaerobic ATP production from stored phosphocreatine.
     • Immediate energy system.
  2. Lactic acid system:
     • Anaerobic glycolysis producing ATP from stored glycogen.
     • Glucose breakdown (glycolysis).
     • Build-up of lactic acid.
     • Short-term system.

Aerobic Pathways

• Require oxygen.
  3. Aerobic glycolysis:
     • Aerobic production of large amounts of ATP from stored glycogen.
     • Moderate to high intensity.
     • Carbohydrate stores are limited.
  4. Oxygen system:
     • Aerobic production of ATP from stored fat and carbohydrate.
     • Prolonged low-intensity exercise.

Activity Intensities - 4 Categories

• Extreme intensity: 5–10 seconds.
• Very High intensity: 20 seconds – 2 minutes.
• High intensity: 2 minutes – 20 minutes.
• Moderate intensity: >20 minutes.

Energy Systems and Activities

• Examples of activities with corresponding energy systems:
  1. Extreme (sprint): ATP-CP system (phosphocreatine).
  2. Very High (400-meter run): Lactic acid system (anaerobic glycolysis).
  3. High (run): Aerobic system (glucose).
  4. Moderate (hike): Aerobic system (fatty acids).

Sources of CHO & Lipid for Aerobic Metabolism During Exercise

• Glycogen supplies approximately 8,000 kJ of energy, sufficient for about 40 km of running.
• Fat supplies more than 300,000 kJ of energy.

Exercise Intensity and Fuel Selection

• Low-intensity exercise (<30% VO2max): Fats are the primary fuel.
• High-intensity exercise (>70% VO2max): Glucose is the primary fuel.
• Crossover concept: Describes the shift from fat to glucose metabolism as exercise intensity increases.

The “Crossover” Concept

• Shift from fat to glucose metabolism as exercise intensity increases.

Effects of Exercise Intensity

• Graphical representation of energy expenditure vs. relative exercise intensity (% of VO2max) for:
  • Plasma glucose.
  • Plasma FFA (free fatty acids).
  • IMTG (intramuscular triglycerides).
  • Muscle glycogen.

Summary

• Fuels for energy in the body include:
  • Stored carbohydrate (glycogen).
  • Blood glucose.
  • Stored fat.
  • Amino acids.
• ATP is produced from any of these sources.
• Some methods of ATP production need oxygen (aerobic), and some do not (anaerobic).
• Fat can only be broken down in an aerobic system, so fat stores are used more for long, slow activity.