Energy Metabolism in Nutrition for Sport & Exercise

Energy Metabolism

Introduction to Energy Metabolism

  • Course: NUSC 4250 - Nutrition for Sport & Exercise

  • Instructor: Dr. Fields

Agenda

  • Fuel sources and storage

  • Energy systems

ATP Structure and Function

  • Adenosine Tri-phosphate (ATP): Key energy molecule in cells.

    • Components:

    • Adenine

    • Ribose

    • Triphosphate groups (3 phosphate groups: P-P-P)

  • Energy Absorption and Release:

    • ATP is synthesized from food and provides energy for cellular functions.

    • ATP converts to ADP (Adenosine diphosphate) by releasing one phosphate group, resulting in energy release for cellular work.

    • ATP-ADP Cycle:

    • Energy is absorbed when ADP is phosphorylated back to ATP.

Fuel Sources for Energy

  • Major fuel sources include:

    • Carbohydrates

    • Fat

    • Protein

    • Phosphate (as in creatine phosphate)

Storage of Fuel Sources

  • Liver:

    • Glycogen: Approximately 80-100 grams stored.

  • Adipose Tissue:

    • Triglycerides (TGs): More than 11,000 grams stored.

  • Muscle:

    • Stores include glycogen, ATP, creatine phosphate (CP), and intramuscular triglycerides (IMTGs).

Energy Availability and Exercise Duration

  • Sources of Energy Available and Estimated Duration:

    • Liver glycogen: 380 kcal for ~20 minutes

    • Muscle glycogen: ~1500 kcal for ~80 minutes

    • Blood glucose: ~40 kcal for ~2 minutes

    • Fat stores: ~94,000 kcal available for ~4900 minutes

    • Protein availability: ~34,000 kcal for ~1800 minutes

  • Energy Requirement for Marathon:

    • Approximately ~60,000 grams of ATP needed to complete a marathon.

Types of Energy Systems

  • Depend on the intensity and duration of the exercise.

  • Major systems include:

    • Anaerobic Systems: High intensity

    • Creatine Phosphate System

    • Anaerobic Glycolysis

    • Aerobic Systems: Low intensity

    • Oxidative phosphorylation

ATP Resynthesis and Characteristics

  • Speed of Action, Amount of ATP Replenished, Duration of Action:

    • Creatine Phosphate:

    • Speed: Very fast

    • Amount: Very small

    • Duration: Very short

    • Anaerobic Glycolysis:

    • Speed: Fast

    • Amount: Small

    • Duration: Short

    • Oxidative Phosphorylation:

    • Speed: Very slow

    • Amount: Large

    • Duration: Very long

  • Max Rate of ATP Resynthesis (from anaerobic and aerobic metabolism):

    • PCr breakdown: 2.25 mmol ATP/kg w.w./s

    • Glycolysis: 1.10 mmol ATP/kg w.w./s

    • Glycogen oxidation: 0.70 mmol ATP/kg w.w./s

    • Glucose oxidation: 0.35 mmol ATP/kg w.w./s

    • Fat oxidation: 0.25 mmol ATP/kg w.w./s

  • Delay Time:

    • Instantaneous for PCr

    • 5-10 seconds for Glycolysis

    • 1-3 minutes for Glycogen oxidation

    • Approximately ~90 minutes for Blood glucose oxidation

    • Over 2 hours for Fat oxidation

Enzyme Regulation in Energy Release

  • Enzymes control energy release by

    • Speeding up reactions and lowering activation energy, facilitating the process of ATP resynthesis.

Creatine Phosphate System

  • Overview:

    • Duration: 0-10 seconds at 90-100% intensity.

    • Active at the start of all exercise.

    • Occurs in the cytosol.

  • Central Components:

    • ATP, creatine phosphate (CP), ATPase, and creatine kinase (CK).

  • Regulation:

    • Increased levels of ADP lead to increased rate of CK, while decreased levels of ADP lead to decreased rate of CK.

  • Depletion and Repletion:

    • CP can drop ~70% within 6 seconds of exhaustive exercise.

    • ATP repletion can occur with rest (1-2 minutes rest for ~70% CP replenishment; 30 seconds of rest for 50-70% ATP replenishment).

Adenylate Kinase System: The Bridge System

  • Equation:

    • ATP ⇌ ADP + Pi + energy

    • ATP ⇌ ADP + Pi + energy

    • ADP + ADP ⇌ ATP + AMP

  • Role in Glycolysis:

    • Stimulant of glycolysis mediated by ATPase.

Anaerobic Glycolysis

  • Overview:

    • Duration: 30-90 seconds at 75-90% intensity.

    • Involves 9 chemical reactions occurring in the cytosol.

  • Central Component:

    • Primarily utilizes carbohydrates (glycogen and glucose).

  • Pathways Involved:

    • Conversion of glycogen to glucose to pyruvate.

Lactate and Muscle Fatigue

  • Common Misconception: Lactate DOES NOT cause fatigue; it is a by-product of anaerobic glycolysis.

  • Lactic acid does NOT cause muscle soreness; the by-product is associated with muscle recovery and not soreness.

Glycogen Cycle During High-Intensity Exercise

  • Depletion: Glycogen can be fully depleted during intense exercise.

  • Repletion: Replenishment occurs by consuming carbohydrates ("CARB LOAD HARDER").

Oxidative Phosphorylation

  • Overview:

    • Duration: More than 2-3 minutes using oxygen to generate ATP.

    • Occurs in the mitochondria.

  • Pathways Utilized:

    • Includes carbohydrates, fats, and proteins.

Carbohydrate and Fat Oxidation

  • Carbohydrate Oxidation Pathway:

    • Krebs Cycle → Glycolysis → Electron Transport Chain (ETC)

  • Fat Oxidation Pathway:

    • Lipolysis → Beta-Oxidation → Krebs Cycle → ETC

Protein Oxidation

  • Overview:

    • Involves proteolysis and subsequent entry into Krebs cycle and ETC for energy production.

Summary of Energy Systems and ATP Production

  • End Products of Energy Systems:

    • Creatine Phosphate: 1 ATP/mol

    • Glycolysis: 2-3 ATP/mol of glucose

    • Carbohydrate oxidation: ~38-39 ATP/mol of glucose

    • Fat oxidation: 100+ ATP/mol of fatty acid

    • Protein oxidation: 25-30 ATP/mol of amino acid

  • Interactive Contributions of Energy Systems:

    • All energy systems are active, but the contribution varies based on exercise intensity and duration.

Study Questions

  • Discuss common fuel sources utilized for energy, including storage locations and amounts.

  • Identify anaerobic vs. aerobic energy systems and their characteristics.

  • For each energy system, discuss duration, intensity, metabolic events, involved components, important enzymes, depletion, repletion, and ATP production results.